Tibial Plateau Leveling Osteotomy or Tibial Tuberosity

Veterinary Surgery 38:1–22, 2009

INVITED REVIEW

Tibial Plateau Leveling Osteotomy or Tibial Tuberosity Advancement?

RANDY J. BOUDRIEAU,

DVM, Diplomate ACVS & ECVS

Objective—To review the proposed biomechanical basis of the tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA) and recommendations for these techniques.

Study Design—Literature review.

Methods—Literature search through Ovid Medline Plus, Pub Med, CAB Abstracts, and conference proceedings abstracts (August 1983 to March 2008).

Results—TPLO and TTA stabilize the cranial cruciate ligament (CrCL) deficient stifle joint neutralizing tibiofemoral shear forces by altering the geometry of the proximal aspect of the tibia.

Stability is attained by placing the joint in a functionally greater flexion angle so that the patellar tendon angle (PTA) remains 901. Both procedures target slightly differing endpoints, the significance of which is unknown. Many of the biomechanical variables investigated appear to favor the TTA; however, TPLO appears to have more clinical versatility. The clinical ramifications of these differences remain to be determined but the reported results for both procedures are comparable. Only the early results of these techniques have been reported, which is reflected in the relatively high number of complications associated with the early learning curve for both procedures.

Conclusions—There are many similarities between TPLO and TTA although it remains to be fully elucidated if either procedure is superior and under what conditions.

Clinical Relevance—TPLO and TTA are effective at returning dogs with a CrCL-deficient stifle joint to good limb function. Surgeon discretion and case selection drive selection of TPLO or TTA based mostly on anecdotal evidence and personal experience. r Copyright 2009 by The American College of Veterinary Surgeons

has been reported to functionally stabilize the stifle joint during weight bearing, neutralizing the cranial tibiofemoral shear force (cranial tibial thrust [CrTT]) by reduction of tibial plateau angle (TPA). This is accomplished by radial osteotomy of the proximal aspect of the tibia and rotation of the proximal fragment.5,6 The mechanics of TPLO have been validated in 2 experimental models.7,8 Another popular surgical technique used to achieve stifle joint stability that neutralizes the tibiofemoral shear forces dynamically in a CrCL-deficient knee is tibial tuberosity advancement (TTA).9–11 TTA has been

INTRODUCTION

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RANIAL CRUCIATE ligament (CrCL) deficiency results in both translational and rotational instability of the stifle joint that leads to the development of osteoarthritis.1–3 Surgical techniques to restabilize the joint, with either static or dynamic repairs, are performed to neutralize the tibiofemoral shear forces in a CrCLdeficient knee. One popular surgical technique used to achieve stifle joint stability that neutralizes the tibiofemoral shear forces dynamically in a CrCL-deficient knee is tibial plateau leveling osteotomy (TPLO).4,5 TPLO

From the Department of Clinical Sciences, Cummings School of Veterinary Medicine at Tufts University, North Grafton, MA. Address reprint requests to Dr. Randy J. Boudrieau, Department of Clinical Sciences, Cummings School of Veterinary Medicine at Tufts University, 200 Westboro Road, North Grafton, MA 01536. E-mail: randy.boudrieau@tufts.edu.

Submitted March 2008; Accepted June 2008 r Copyright 2009 by The American College of Veterinary Surgeons 0161-3499/08 doi:10.1111/j.1532-950X.2008.00439.x

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TPLO OR TTA?

reported to functionally stabilize the stifle joint during weight bearing by neutralizing the cranial tibiofemoral shear force (CrTT) by advancing the tibial tuberosity.

This is accomplished by an osteotomy of the tuberosity in the frontal plane with advancement of this bone fragment.9 The mechanics of TTA have also been validated in 2 experimental models.12,13 Success rates with CrCL repair are reported to be 490% regardless of the surgical technique used.14 Historically, selection of a surgical technique has been based primarily on surgeon preference rather than definitive evidence that one technique might be better than another.15 Unfortunately, there is no study that demonstrates that TPLO is a better procedure than, for example, the extra-capsular stabilization16—this despite much anecdotal opinion that the TPLO is a superior technique, especially for active, athletic dogs. Likewise, there are no data for functional evaluation of TTA other than similar anecdotal evidence that it is an effective technique in similar types of affected dogs. There are no peer-reviewed reports comparing the outcome of TPLO to TTA; however, anecdotal comments have been presented.17 Therefore, one selection criteria for TPLO versus TTA may simply continue to be surgeon preference, where perhaps one can admit to be captivated with the latest and greatest newest technique(s).

The questions posed regarding these 2 techniques are many and include what we definitely know, what we assume to be true, and what we definitely do not know.

Many questions have been raised by proponents of one or the other of these procedures for which a number of ongoing and future studies may help provide answers.

The purpose of this review is to address the available data, discuss the pressing questions to be answered, and suggest possible areas that should be investigated.

the CrCL).4,6 Slocum proposed that the CrTT in the normal stifle joint was primarily controlled by the caudally directed forces of the hamstring muscles.5,6 In this theory, the compressive forces across stifle joint were proposed to be parallel to the tibial axis, but because of the caudally directed TPS, compression between the joint surfaces resulted in cranial tibial translation.5,6 This theory was developed as the ‘‘active model of the stifle’’5; CrTT is created by compression between the femur and tibia, which acts through the functional axis of the tibia, and is dependent upon the amount of compression and the TPS.5 Axial compression of the limb is thought to generate a compressive force across the joint, and this resultant force can be reduced to 2 orthogonal components, one perpendicular and one parallel to the tibial plateau, the latter representing the CrTT (Fig 1).4 The CrTT is a result of the tibial plateau oriented at an angle to the axial compressive force. If the angle of the tibial plateau is reduced to zero, the joint compressive force and resultant force become the same, as the CrTT becomes zero, as this force vector is eliminated (Fig 1).4 Clinically, however, the

PROPOSED MECHANISM OF ACTION A number of biomechanical studies in humans have demonstrated an increase in translational knee joint instability by variation with tibial plateau slope (TPS),18 axial loading,19 and flexion knee angle.20,21 It has been reasonably assumed that these findings are similar in the dog.

Evaluation of this resultant translational stifle joint instability because of a CrCL rupture in the dog can be clinically detected by the tibial compression test.20 Axial compressive forces are thought to cause a cranial subluxation of the tibia relative to the femur because of unopposed CrTT. TPLO Slocum proposed that the tibiofemoral shear force, or CrTT was an internally generated force that caused the tibia to translate cranially (and is opposed by

Fig 1. Schematic representation of the tibiofemoral forces in the stifle joint, according to Slocum,5 before (A) and after (B) tibial plateau leveling osteotomy (TPLO). The resultant compressive force (large white arrow) across stifle joint is parallel to the tibial axis. Using the tibial plateau slope (TPS) as the baseline, whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient, the resultant force can be broken down into its 2 orthogonal components (small shaded arrows), one perpendicular and one parallel to the tibial plateau. The latter represents the tibiofemoral shear force (resulting in cranial tibial thrust [CrTT]). If the angle of the tibial plateau is reduced to zero, the tibiofemoral shear force vector becomes zero, and the joint compressive force and resultant force become one and the same.

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plateau is not returned to 01, but has 51 of remaining slope.5,6,22 This concept relies on the hamstring muscles, which contribute to neutralizing this small remaining force.5,6,22 The CrTT, therefore, can be eliminated by changing the angle of the TPS, thereby enhancing the effectiveness of the flexors of the stifle joint.5,6,22 The technique performed to accomplish this was standardized as a radial osteotomy of proximal aspect of the tibia and rotation of proximal fragment, and was called TPLO (Fig 1; Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc., Eugene, OR).5,6 TTA The premise of TTA was based on a biomechanical model analysis of joint forces in the human knee.23 This model demonstrated that the tibiofemoral compressive force was approximately of the same magnitude, and oriented in the same direction, as the patellar tendon force, which resulted in a variable tibiofemoral shear force.23 This force was either anteriorly or posteriorly directed dependent upon the angle of knee joint extension or flexion, respectively.23 The point of neutral tibiofemoral shear force was termed the crossover point in this human mechanical model, which occurred at a patellar tendon angle (angle between the tibial plateau and the patellar tendon; PTA) of 1001.23 Therefore, it was proposed that the direction and magnitude of the tibiofemoral shear force was determined by the PTA.23 The assumption was made that this same reasoning could be applied to the dog’s stifle joint, where the total joint forces were also believed to be approximately parallel to the patellar tendon, although in the dog the crossover point was suggested to be at 901 PTA.9–11 Similarly, it was proposed that there is a cranially directed tibiofemoral shear force at a PTA4901 and a caudally directed tibiofemoral shear force at a PTA o901.9–11 With the crossover point at 901 it was proposed to move the tibial tuberosity cranially so that at full stifle joint extension, and any joint flexion during weight bearing ( 1351), the PTA was always 901, and therefore only a neutral or caudally directed tibiofemoral shear force would remain, thus stabilizing the joint.9–11 The CrTT, thus, is neutralized by advancement of the tibial tuberosity.

The technique performed to accomplish the advancement of the tibial tuberosity was standardized by performing an osteotomy of the tibial tuberosity in the frontal plane and moving it far enough cranially such that the PTA is 901 in full extension (during weight bearing, 1351), and called the TTA.9 In this model, the total joint force is parallel to the patellar tendon; therefore, if the compressive joint forces are oriented as such, the resulting components can be

Fig 2. Schematic representation in the stifle joint of the tibiofemoral forces, according to Tepic et al,10,11 before (A) and after (B) tibial tuberosity advancement (TTA). The resultant compressive force (large white arrow) across stifle joint is parallel to the patellar tendon. Using the tibial plateau slope (TPS) as the baseline, whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient, the resultant force can be broken down into its 2 orthogonal components (small shaded arrows), one perpendicular and one parallel to the tibial plateau. The latter represents the tibiofemoral shear force (resulting in cranial tibial thrust [CrTT]). If the angle of the tibial tuberosity is advanced cranially until the patellar tendon angle (PTA, angle between the tibial plateau and the patellar tendon) is reduced to 901, the tibiofemoral shear force vector becomes zero, and the joint compressive force and resultant force become one and the same.

viewed as parallel and orthogonal to this force along the tibial plateau (Fig 2).10 The CrTT is a result of the tibial plateau oriented at an angle to the axial compressive force.

If the tibial tuberosity is moved cranially, thus changing the PTA to 901, the joint compressive force becomes a single component, parallel to the axial compressive force, and the CrTT force vector is eliminated (Fig 2).10 The proof of concept for both TPLO and TTA have been demonstrated in experimental cadaver studies.7,8,12,13 Two of these studies used the same experimental limb-press model.7,12 In 3 studies, it was shown that the caudal cruciate ligament (CaCL) becomes the primary stabilizer to the joint as CrTT is converted to caudal tibial thrust.7,8,12 The primary difference between the 2 proposed mechanisms is the direction of the tibiofemoral compressive force. With TPLO, the force is proposed to be parallel with the tibial long axis (Fig 1), whereas with TTA it is proposed to be parallel to the patellar tendon (Fig 2).

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TPLO OR TTA?

Both theories are credible; however, in the proposal by Slocum (compressive forces through the joint parallel to the long axis of the tibia), regardless of the assumptions made for this mechanical model of the knee, there are no studies that document that the direction of the proposed force is valid. Furthermore, the contribution to joint stability because of the quadriceps muscle group is not factored into the model.20,24 Without a functional quadriceps, there is no ability to bear weight. Despite this apparent deficiency, the idea of leveling the plateau remains as a reputably plausible explanation with an analogy often used of a wagon parked on a hill (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.),6 demonstrating that if there is a slope the weight of the wagon will generate a force that will pull it down the slope, which is counteracted by the rope, or CrCL, securing it. This argument illustrates that once the slope becomes level, the weight of the wagon no longer generates a force in either direction, and therefore the wagon no longer needs to be secured.

One problem with this theory is that it remains a static model that does not consider the contribution of the quadriceps muscle, the major muscular force generator about the stifle joint. Secondly, irrespective of the joint flexion angle, the TPS remains constant and joint position is not accounted for. Finally, regardless of the TPS being level, there is a considerably low coefficient of friction between the 2 joint surfaces (lower than standing on ice), and this surface is not flat, but convex, both of which would indicate that other factors must play a role in maintaining joint stability.

As noted, the TTA theory proposes that the compressive forces at the joint are approximately parallel to the patellar tendon. This theory does account for the quadriceps muscle. Furthermore, there are studies that document that the direction of this proposed force is valid.20,23,25 Despite the differences in proposed mechanisms of action, clinical results appear comparable between TPLO and TTA.26–30 An argument could be made that the proposed mechanism of action for TTA can also explain the mechanism for TPLO (Fig 3). This can be observed after reduction of TPA via radial osteotomy and rotation of the proximal tibial fragment, as this also reorients the patellar tendon to the angle of the patellar tendon, which approaches 901, although these exact measures are yet to be determined. Obviously, different techniques are used to approach this mechanism from 2 different perspectives: (1) a radial cut of the proximal tibial plateau segment for TPLO, and (2) an osteotomy of the tibial crest performed in the frontal plane for TTA. For TPLO, the tibial plateau is moved to meet the force; alternatively, for TTA, the force is moved to meet the tibial

Fig 3. Schematic representation in the stifle joint of the tibiofemoral forces, according to Tepic et al,10,11 before (A) and after (B) tibial plateau leveling osteotomy (TPLO). The resultant compressive force (large white arrow) across stifle joint is parallel to the patellar tendon. Using the tibial plateau slope (TPS) as the baseline, whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient, this resultant force can be broken down into its 2 orthogonal components (small shaded arrows), one perpendicular and one parallel to the tibial plateau, the latter represents the tibiofemoral shear force (resulting in cranial tibial thrust [CrTT]). If the angle of the tibial plateau is reduced to zero, the tibiofemoral shear force vector becomes negative, resulting in a negative force vector (resulting in caudal tibial thrust). Compare with Fig 1 to note that the tibiofemoral shear vector (parallel to the tibial plateau slope [TPS]) is smaller with this proposal, and leveling the tibial plateau results in a correspondingly more negative tibiofemoral shear force for the same amount of rotation.

plateau (Fig 4). In either case, it appears that the end result is the same: the tibial plateau and the patellar tendon become oriented at 901 to each other.

Specific documentation of this endpoint remains to be demonstrated for TPLO; however, it has been demonstrated that at 901 of stifle joint flexion the CrCL-deficient joint does become stable, which again corroborates the proposed theory that the flexion angle affects the direction of the joint reaction forces and subsequent stability.31 Additionally, it can be argued that the quadriceps mechanism plays a primary role in stability of the stifle joint, as without it there no longer remains a possibility to weight-bear or extend this joint; therefore, the quadriceps, and more specifically the direction of the quadriceps muscle force,32,33 needs to be considered in

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Fig 4. Schematic representation of the stifle joint of the tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA) with respect to patellar tendon angle (PTA). With the TPLO, the tibial plateau is moved to meet the force (parallel to the patellar tendon). With the TTA, the force is moved to meet the tibial plateau. In both cases, the end-point sought is for the PTA to become oriented at approximately 901 or less.

any mechanical analysis of the stifle joint. Reduction of the PTA, whereby the effect of the cranial pull of the quadriceps muscle is limited during extension may be the key to the success of both these procedures. In humans, it has been demonstrated that the angle of the patellar tendon insertion onto the tibia is a key determinant as to whether there is an effect of quadriceps contraction aggravating anterior tibial translation in an anterior cruciate deficient knee.33 This would suggest that any technique that reduces the PTA would protect the joint from CrTT. Nonetheless, it must also be realized that any biomedical modeling of the stifle joint is a crude approximation, or simplification, of that which exists in vivo. In both models, there is no consideration of magnitude of the many redundant forces attributed to the hamstring muscle group, which certainly must play a role. The role of the hamstring muscle group can be demonstrated with the many surgical techniques used in humans to advance these muscles, and the significant role of aggressive physical therapy in strengthening these muscles.34–36 The impact of these muscles, and the concept of co-contraction, may be recognized in a theoretical 3-dimensional, 3-segment mathematical model of the

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stifle joint that demonstrated an elimination of the cranial tibiofemoral shear forces at an angle of 01 after TPLO, but not at 51.37 Subsequently, it was concluded that 51 might be insufficient to neutralize the cranial tibiofemoral shear forces.37 Alternatively, one in vitro experimental study showed a neutralization of the cranial tibiofemoral shear force at an angle of 6.5 0.91 after TPLO.7 The latter appears to support the results seen clinically where the target angle has been 51 (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.).6 Furthermore, there are reports that postoperative TPS angles can be as high as 141 after TPLO with good results.38–42 Therefore, it is reasonable to assume that other factors appear to be acting at the stifle joint not accounted for in the modeling, such as proximal tibial conformation, articular surface geometry, meniscal integrity, and weight-bearing angle.

For these reasons, any model’s assumptions may be questioned. As a prerequisite, any biomedical modeling approach must meet certain criteria: (1) any unknown parameter may be calculated using reasonable approximations, mechanical laws, and experimental measurements; (2) it must be realistic and its validity studied by comparing experimental measurements with results from the model.25 The model of the human knee as put forward by Nisell and colleagues,21,23,25 in which the tibiofemoral shear forces were proposed to be either anterior or posterior depending upon the knee joint flexion angle, and where the compressive forces were approximately parallel to the patellar tendon, can be shown to meet these criteria. It is not an exaggeration to then apply this reasoning to the stifle joint of the dog, as proposed by Tepic et al.10 Furthermore, there is experimental support for this model in the dog, as has been demonstrated in an in vitro cadaver model.12 Based upon the absence of a similar reasonable proposal supported by some published scientific literature that the direction of the proposed force for the mechanism of the TPLO is parallel to the tibial axis, it can be argued that the mechanism of action is identical, i.e., that the forces around the canine stifle joint may be approximated to being parallel to the patellar tendon (Fig 3).

Furthermore, in both TPLO and TTA, the neutralization of the tibiofemoral shear forces occurs as a result of moving the cross-over point such that the cranial tibiofemoral shear force is eliminated during weight bearing (the point at which the patellar tendon force is perpendicular to the tibiofemoral shear force, defined along the TPS), and becomes negative (caudal tibiofemoral shear force) once the stifle joint flexes. The aforementioned in vitro studies certainly support this concept as an elimination of cranial tibiofemoral shear force was observed with either technique; additionally, it was observed that

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TPLO OR TTA?

this force became caudally directed with either increased rotation (TPLO)7 or increased advancement (TTA).12 The latter correspond to the PTA obtained, similar to additional stifle joint flexion, and in both cases then rely upon the CaCL becoming the primary stabilizer of the joint.7,8,12 THEORETICAL ADVANTAGES OF TPLO VERSUS TTA The question that is raised is whether one or the other of these techniques (TPLO or TTA) might be a better choice for repair of the CrCL-deficient stifle joint, and if so, under what conditions would one choice perhaps be better than the other.

Total Joint Force The first issue may have to do with the proposed mechanism. If one accepts that with either technique, tibiofemoral shear force is dependent upon PTA, then altering the direction of the patellar tendon force is the mechanism for obtaining dynamic joint stability. Then, based upon the proposed directions of the total joint force, either parallel to the patellar tendon (TTA) or to the functional axis of the tibia (TPLO), the difference could account for as much as 10–151 difference in endpoint after surgery (compare Figs 1 and 2, redirection of the resultant vector forces, a 10–151 difference). Based on this argument, it would appear that the TPLO overcorrects for the cross-over point compared with TTA, as can be observed with the caudally directed component of the tibiofemoral shear force with similar postoperative rotation of the proximal aspect of the tibia in TPLO (compare Figs 1 and 3). It is worth considering, however, that this proposed difference between the 2 techniques might be o10–151 because of the anatomic configuration of the joint, i.e., the craniocaudal translation of the femoral condyles and the contact point with the tibia during flexion/extension (Fig 5). During extension, the femorotibial contact point moves cranially; similarly, during flexion, it moves caudally; whereas the TPS remains constant. The effect of this varied positioning is yet to be evaluated, but a suggestion has been made that it should be considered when assessing the joint forces.43 The issue has been raised as to the determination of the best method for calculating the amount of tuberosity advancement to perform with TTA (Boudrieau RJ. Tibial Tuberosity Advancement [TTA]: Tibial plateau slope or common tangent? KYON 2007 Symposium: Innovations in Veterinary Orthopedics and Trauma. Boston, MA; April 21, 2007).44 If, instead of determining the amount of advancement necessary with the TPS, it is performed with the common tangent between the tibial and femoral

Fig 5. Schematic representation of stifle joint flexion with respect to patellar tendon angle (PTA). In full extension, the PTA is 4901 and in full flexion the PTA is o901. There is a point such that the PTA is 901, which is termed the ‘‘crossover’’ point. At this point, there is neither cranial nor caudal tibiofemoral shear force present. The premise with respect to the tibiofemoral force, according to Tepic et al,10,11 is that with any geometric alteration of the proximal tibia with either the tibial plateau leveling osteotomy (TPLO) or tibial tuberosity advancement (TTA) (see Fig 4) the cranially directed shear force as the stifle joint in fully extended during weightbearing position is eliminated. The PTA is thus maintained 901 throughout the stifle joint range of motion during weight bearing.

surfaces at the contact point (Fig 6), then although a smaller amount of advancement is performed with TTA (Fig 7), the same method results in a smaller change of the TPA with a TPLO (the TPLO does not permit the same degree of stifle joint extension because the joint is placed into greater flexion by rotation of the tibial plateau). These anatomic changes further minimize the difference between the calculated endpoints between the 2 techniques, perhaps only 5–101. This issue, considering the common tangent, is discussed further below.

The difference in endpoints after surgery raises the question as to whether it has any potential adverse effects. Because the primary stabilizer of the joint becomes the CaCL after either TPLO or TTA,7,8,12 could this difference put the CaCL at greater risk for subsequent injury with TPLO? Does this 5–151 difference make a measurable difference in the strain experienced by

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stabilizer to the joint. No clinical studies have been performed that evaluate the stifle joint after either TPLO or TTA, much less clinical function, long-term.

Anatomic Configuration

Fig 6. Lateral radiographs of the stifle joint before (A) and after (B) the common tangents are drawn to outline its position in the joint. The anatomic shape of the femoral condyles in the stifle joint changes the position of femoral–tibial joint contact during stifle joint flexion and extension (see Fig 5). Therefore, an alternate orientation of the tibiofemoral contact point is used as the baseline to define the tibiofemoral shear force, whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient. This line is determined by circumscribing a circle over both the articular surfaces of the femoral condyle and the tibial plateau (defined by the limits of the menisci). The tibiofemoral shear force is then defined by a line perpendicular to a line drawn through the center of these 2 circles at their contact point.

the CaCL? Furthermore, if there is a difference, is it enough to show a measurable effect on the ligament? It has been reported that the CaCL undergoes marked morphologic changes in CrCL-deficient joints, which may result in compromised material properties.45 Regardless of it, there is no clinical evidence that the CaCL is at risk for failure after either TPLO or TTA. There is only anecdotal information as to the risk to the CaCL with over-rotation of the tibial plateau with TPLO.5 From a theoretical standpoint, TTA would be correcting the tibiofemoral shear force closer to a neutral tibiofemoral shear force at full extension ( 1351) during weight bearing, thus there may be less stress placed on the CaCL. A well-designed biomechanical study could determine if such a difference in endpoints exists between the 2 surgical techniques. Similarly, there is no documentation as to the ideal point at which tibiofemoral shear is neutralized with either TPLO or TTA, and which of these techniques comes closer to this theoretical point. More information is needed about the possible risks to the CaCL over time, especially in its new role as the primary

Another point to consider is whether or not an anatomic alteration of the tibial plateau (i.e. changing the TPS with a TPLO) makes a functional difference. The tibial plateau remains unaltered with TTA, whereas with TPLO, the tibial plateau is effectively placing the joint in 15–201 of increased flexion. This raises 2 immediate questions. (1) Is the gait altered with perhaps a diminished range of motion in full flexion? (2) Is there any additional stress placed upon the menisci because of this change in joint orientation?

Gait. Based upon kinematic gait analysis, stifle and hock mechanics remain unaltered with TPLO during weight bearing; however, some changes can be seen in the swing phase of the gait.46 Therefore, gait seems to be unaltered with TPLO, assuming that the alterations observed in the swing phase have no functional or clinical ramifications. This assumption appears to be reasonable based upon the absence of weight bearing during this time frame. It has been theorized that because TTA does not alter the orientation of the articular surfaces, there would be no effect on gait; however, to date there has been no similar evaluation of gait with kinematics. Any alteration of the point of insertion of the patellar tendon into the tibia and any effect on gait mechanics remain to be investigated.

Femorotibial Pressure Distribution. After TPLO, the femoral and tibial articular surfaces are placed in a relatively increased flexed position (although the stifle joint flexion angle remains unchanged). Altered flexion of these surfaces, or change in geometry, during weight bearing results in changes in the pressure distribution to the caudal compartments of the joint (medial greater than lateral),31 possibly affecting the menisci (especially the medial meniscus); this altered positioning may also reduce the space for the meniscus. Both factors may place the meniscus at a greater risk for injury. The abnormal pressure distribution may either place the meniscus at risk (potential increased risk of tear) and/or contribute to articular cartilage changes (degeneration caused by abnormal loading).31 The original description for TPLO recommended that a medial meniscal release be performed to spare the immobile caudal pole of this structure from subsequent injury in a cruciate-deficient stifle.5,6,47 However, the rationale presented was some remaining functional laxity with the anatomic alteration of the tibial plateau, and the lack of compensation by the active muscular forces around the joint (hamstring muscles), which could subsequently damage the immobile

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TPLO OR TTA?

Fig 7. Schematic representation of the tibiofemoral forces in the stifle joint, according to Tepic et al,10,11 before (A) and after (B) tibial tuberosity advancement (TTA). The resultant compressive force (large white arrow) across the stifle joint is parallel to the patellar tendon. Using the common tangent at the tibiofemoral contact point (see Fig 6) as the baseline (solid line), whereby the femur can move along this surface if the cranial cruciate ligament (CrCL) is deficient, the resultant force can be broken down into its 2 orthogonal components (small shaded arrows), one perpendicular and one parallel to the tibial plateau. The latter represents the tibiofemoral shear force. If the angle of the tibial tuberosity is advanced cranially until the patellar tendon angle (PTA) is reduced to 901, the tibiofemoral shear force vector becomes zero, and the joint compressive force and resultant force become one and the same. Notice that the cranial tibiofemoral shear force is smaller than that depicted with the PTA using the tibial plateau slope (TPS), which is indicated by the dotted line (compare with Fig 2). Notice that the common tangent and TPS are similar in stifle joint flexion (C). Insets clarify the force vectors depicted on the schematic bone models.

caudal pole of the medial meniscus with tibiofemoral subluxation.5 This was the rationale to perform a medial meniscal release in these cases, and was taught at the TPLO courses (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.).5 More recently, it also has been shown that performing the meniscal release, or caudal pole hemimeniscectomy, in a CrCL-deficient stifle joint with a TPLO further changes and increases the pressure distribution in the medial compartment of the joint, an argument that would perhaps favor leaving the meniscus intact.31 There are no similar evaluations reported of medial meniscectomy after TTA. Although there is no evidence that the increased stifle joint flexion predisposes the menisci to damage, it was proposed that TTA might provide less risk for such damage because of the unaltered joint position.48 This led to the original recommendation to leave the intact menisci in situ when performing TTA.9 Femorotibial contact pressure and location have been evaluated in vitro with both TPLO and TTA.49 In a CrCL-deficient stifle joint, there is a 40% decrease in contact area with an associated 100% increase in peak pressure; furthermore, the positioning of the peak

pressure is found to shift caudally.49 TTA appears to restore the normal femorotibial contact and pressure distributions, whereas TPLO results in a continued decrease (12%) of contact area and caudal positioning of peak pressure distribution.49 These latter effects may predispose the caudal pole of the intact medial meniscus to trauma after TPLO, and apparently spare the meniscus after TTA. These studies seem to suggest that the caudal pole of the medial meniscus is at risk for trauma after TPLO, whereas not after TTA. This study also suggests that TPLO radically changes the biomechanics of the stifle and potentially predisposes to further progression of osteoarthritis; because TTA does not change the geometry of the joint and the pressure distributions essentially remain unchanged, there may be less development of osteoarthritis. This issue may be more relevant that the potential risk of meniscal injury increases after TPLO. It has been proposed that after TTA there could continue to be the possibility of meniscal damage29,30; thus, the varying recommendations as to whether or not to perform a meniscal release clinically (Instructional Course for Tibial Tuberosity Advancement [TTA] for Cranial Cruciate Ligament Deficient Stifle Joints in Dogs;

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Kyon Veterinary Surgical Products, Denver, CO). The speculation is that despite the results of the experimental studies, a continued passive laxity not adequately balanced by muscular forces around the joint potentially remains after TTA (similar to that postulated after TPLO). This instability and the resultant remaining tibiofemoral shear forces cause a tibiofemoral subluxation injuring the menisci. Passive laxity has been demonstrated in vitro with both TPLO and TTA in a CrCL-deficient stifle joint.50 It has been suggested that there is a difference in degree of passive laxity in the joint between TPLO (less laxity) compared with TTA, although the impact of this laxity in clinical cases has not been determined.50 This concept suggesting a possible mechanism for subsequent meniscal damage remains to be investigated.

Meniscus. Whatever the opposing mechanisms proposed regarding the meniscus, debate remains as to whether or not to perform a medial meniscal release in both TPLO and TTA. It appears there are 2 opposing opinions regarding the necessity of meniscal release at this time with TPLO.51 Similar anecdotal information has been presented for TTA.52 One argument to preserve the menisci has to do with the important biomechanical functions of the meniscus and the role of this structure to stabilize the joint. The opposing argument to perform a meniscal release relates to the costs, both in terms of surgery to the patient and economic impact to the owner, for additional surgery should the preserved meniscus subsequently be damaged versus the clinical ramifications of a joint with a meniscal release performed, which essentially is a meniscectomy.

The meniscus functions as a load-bearing structure to distribute the femoral condyle forces more uniformly over the tibial plateau. Meniscal release eliminates this function and results in increased areas of localized stress to the articular cartilage.53,54 As previously noted, there is experimental evidence that preserving the meniscus with either TPLO or TTA better preserves joint mechanics in the CrCL-deficient stifle joint, and perhaps there is a more normal distribution after TTA.49,53 These studies suggest leaving the meniscus intact if it is uninjured.

Alternatively, as the meniscus acts as a secondary joint stabilizer in the CrCL-deficient joint, with any persistent passive laxity the caudal pole of the meniscus may be more easily injured with a failure to fully neutralize the tibiofemoral shear forces.53,54 Sparing this structure from injury by performing a meniscal release has been suggested.55 However, it has also been noted that performing a meniscal release does not completely eliminate the possibility of subsequent meniscal tears.56 It has been reported that after TPLO with meniscal release, there is cartilage damage present on the tibial plateau and medial femoral condyle, confirming that

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subsequent articular cartilage damage does occur.51,57,58 However, it has also been stated that there is little outward evidence of clinical dysfunction as a result of these changes,51,56 which is consistent with most clinical impressions. Despite the progressive effects of osteoarthritis in these dogs, clinical dysfunction is considered minor as opposed to that occurring with an injured meniscus; therefore, this argument supports the meniscal release in favor of possible future meniscal impingement.51 The question is the unknown frequency of meniscal injury at initial surgery, and the number of undetected tears at that time as opposed to tears occurring after surgery.56 These meniscal injuries have been defined as either latent (undetected) or postliminary (subsequent) tears.59 Failure to detect a medial meniscal tear is thought to be a result of incomplete inspection and probing of the posterior horn.59,60 Patellar Tendon. There is the question as to whether the altered anatomy created by either of the procedures could result in other anatomic or functional changes within the joint. For example, there have been a number of reports of patellar tendon thickening, or even patellar tendinitis after TPLO.27,28,61 It has been proposed that by rotating the tibial plateau, greater stress is placed on the patellar tendon compared with decreased stress to this structure after performing a TTA (Instructional Course for Tibial Tuberosity Advancement (TTA) for Cranial Cruciate Ligament Deficient Stifle Joints in Dogs; Kyon Veterinary Surgical Products).61,62 The proposed increased stress (TPLO) versus decreased stress (TTA) on the patellar tendon can theoretically be explained by the change in lever-arm lengths to the patellar tendon after the osteotomies. If one considers that the CaCL becomes the primary stabilizer to the joint after either TPLO or TTA, the lever arm to the patellar tendon is the distance between the femorotibial contact point to the point of attachment of the patellar tendon to the tibial tuberosity (Figs 8 and 9). For TPLO (Fig 8), it is thought that this lever arm can shorten by as much as 10% compared with the intact joint, whereas, with TTA (Fig 9) this lever arm can lengthen by as much as 10% (Instructional Course for Tibial Tuberosity Advancement (TTA) for Cranial Cruciate Ligament Deficient Stifle Joints in Dogs; Kyon Veterinary Surgical Products).

These measurements have not been demonstrated experimentally other than to note that both saw blade kerf and osteotomy position will influence the femorotibial contact point position, as both will induce a cranial tibial long axis shift shortening the lever arm (Fig 8).62,63 A shorter lever arm requires more force to move an object the same distance; conversely, a longer lever arm requires less force to similarly move an object. In this case, the object is the tibial tuberosity and the force is the

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TPLO OR TTA?

Fig 8. Schematic representation of the lever arm in the stifle joint before (A) and after (B and C) tibial plateau leveling osteotomy (TPLO). (A) Patellar tendon lever arm (bending moment) in the stifle joint extends from the patellar tendon to the femorotibial contact point (heavy dotted line). (B) After TPLO, the patellar tendon lever arm (heavy dotted line) shortens marginally provided that the osteotomy is centered on the intercondylar tubercles (because of the loss of bone removed by the kerf of the saw blade). (C) Positioning of the osteotomy more often is centered just below the joint surface and caudal to the medial collateral ligament; furthermore, any additional placement of the osteotomy more distal of the tibia results in further shortening of the patellar tendon lever arm with rotation of the tibial plateau (heavy dotted line; compare with part [B]).

quadriceps muscle pull on the patellar tendon. In other words, more force is required to extend the joint with a TPLO, and less force is required with a TTA. Patellar

Fig 9. Schematic representation of the lever arm in the stifle joint before (A) and after (B) tibial tuberosity advancement (TTA). (A) Patellar tendon lever arm (bending moment) in the stifle joint extends from the patellar tendon to the femorotibial contact point (heavy dotted line). (B) After TTA, the patellar tendon lever arm (heavy dotted line) lengthens.

tendon thickening after TPLO has been reported in 1–5% of cases.27,28 Anecdotally, this change is a much more common finding in stifle joints after TPLO, and is found in 450% of cases, despite this low reported occurrence.

In fact, this percentage of stifle joints with patellar tendon thickening is consistent with one study that specifically evaluated the radiographic changes of the patellar tendon after TPLO, and which reported moderate to severe patellar tendon thickening at 2 months postoperatively in 79.8% of dogs.61 The proposed increased forces required to extend the stifle joint may be responsible for this inflammation. There are no published reports of patellar tendinitis with TTA at this time. Again, the decreased forces proposed as a result of this lengthened lever arm may be the explanation. This proposed cause remains to be investigated, both clinically and experimentally.

Regardless, there are no known clinical ramifications in dogs with mild to moderate patellar tendon thickening after TPLO, although a small percentage of dogs with severe patellar thickening have clinical signs consistent with patellar tendinitis.61 It remains to be determined if TTA has fewer of such problems and if the proposed theory can be validated clinically. Regardless, there are no specific studies that have investigated this issue, clinically or experimentally, much less comparing the different techniques and their potential ramifications.

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Retropatellar Pressure. Another result of the altered patellar tendon position has been the proposed alteration (decrease) of retropatellar force with TTA. Theoretically, this diminished force can protect the articular cartilage of both the patella and the femur from subsequent damage (P.M Montavon; personal communication, 2008). This claim needs to be substantiated. As previously noted, there are isolated reports of articular cartilage damage to the tibial plateau and femoral condyle after TPLO with second look arthroscopy.51,57 Decreased retropatellar pressure was the stimulus to perform TTA in humans to treat cases of severe patellofemoral arthritis.64 Recently, a 3-dimensional nonlinear joint finite element model reconstruction based on a human cadaver knee joint confirmed not only this procedure’s effectiveness in decreasing patellofemoral contact forces, but also femorotibial contact forces with stifle joint extension.65 This same model, however, showed an increase in these forces at larger flexion angles.65 The question remains as to whether or not this same effect occurs in the dog, and if it has any significant effect.

SURGICAL TECHNIQUE Both the TPLO and TTA are complex procedures, requiring appropriate preplanning and accurate execution of the details of the procedure.

Preoperative Planning TPLO. Preoperative planning must include a proper assessment of the angle of the TPS, such that precise surgical execution results in the desired postoperative TPA of 51 (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.).6 The measurement technique for TPLO uses the TPS, and for ease of positioning, the convention is to place the stifle joint at 901 to the tibia.

These measurements are obtained from a true lateral radiographic projection of the stifle joint, centered on the stifle joint (perfect positioning confirmed by superimposition of both femoral and tibial condyles).66 It has been demonstrated that accurate preoperative radiographic positioning is important to obtain precise and reproducible measurements.66,67 In addition, there is some inter- and intraobserver variability when making these measurements.67–69 Despite these attempts at obtaining precise preoperative measurements, there have been a wide variety of postoperative TPAs reported, from 0–141.38–42 Regardless of this postoperative variation, excellent clinical outcomes have been reported.38–42 Force plate analysis appears to indicate a wide range of acceptable postoperative TPAs (0–141).42 This variation

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indicates that the ideal clinical postoperative TPA is unknown, despite the recommendation for a postoperative TPA of 51. One in vitro experimental study shows neutralization of the cranial tibiofemoral shear force at an angle of 6.5 0.91.7 TTA. Preoperative planning must also include a proper assessment to ensure that advancement of the tibial tuberosity results in a PTA of 901.29,30 A standard lateral radiographic projection of the affected stifle joint is obtained preoperatively to assess the joint. The lateral projection is centered on the stifle joint (perfect positioning confirmed by superimposition of both femoral condyles) at a stifle joint angle of 1351 using the long axes of the femur and tibia (the entire femur is included to determine the appropriate femoral long axis). This reference point is made based upon some clinical and experimental observations of the canine stifle joint during weight bearing. The choice of this angle for assessment of PTA in the preplanning for the surgical technique reflects the midstance phase angle of the gait cycle as determined by kinematic analysis.70–72 Because the patellar tendon is part of this measurement, the PTA also is dependent upon the position of the femur (angle of stifle joint flexion/extension; Fig 7). In addition, the joint must be positioned so that there is no cranial tibial translocation. A standardized TTA transparency (Kyon; Zu¨rich, Switzerland) is used to determine the amount of TTA required to position the patellar tendon perpendicular to the tibial plateau in a standing position (1351 stifle joint extension) and the size of plate to cover the entire extent of the tibial crest.30 No reported studies have investigated inter- and intraobserver variabilities when making these measurements.

Similarly, it is unknown if any postoperative variation in the amount of advancement actually obtained has an effect on the outcome, and the degree to which such errors might affect postoperative results.

Despite these recommended measurement guidelines for the amount of TTA distance, the evaluation method based upon the TPS recently has been questioned (Boudrieau RJ. Tibial Tuberosity Advancement [TTA]: Tibial plateau slope or common tangent? KYON 2007 Symposium: Innovations in Veterinary Orthopedics and Trauma. Boston, MA; April 21, 2007). In some cases, the proposed advancement appears to be excessive for the size of the dog, which indicates that there is some difference among dogs related to stifle joint anatomy. An alternative procedure has been recommended to obtain these measurements with the tangent method, i.e., a line perpendicular to the contact point between the femoral and tibial joint surfaces, again at 1351 of stifle joint extension at the point of contact between the femur and tibia (2007 Veterinary Symposium—The Surgical Summit; Pre-Symposium Laboratories: TTA Laboratory;

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TPLO OR TTA?

Chicago, IL; Fig 6). It has been suggested that this measurement is a more anatomically representative reference point as identified by the desired crossover point to obtain a neutral tibiofemoral shear force (Fig 7).43 The results of this study also suggest that the angle between the patellar ligament and the tibial plateau decreases linearly with increasing stifle joint flexion in dogs, which is similar to the findings in knee joints of humans.43 Furthermore, both inter- and intraobserver variabilities appear to be minimal with this technique.43 In clinical usage, both measurement techniques result in similar amounts of calculated TTA in most cases, although the tangent method consistently is a slightly lower angle compared with the TPS. The assumption is that this small difference is inconsequential in these cases, but this has not been documented (Fig 10). Of greater potential concern, however, is that the anatomic configuration in some cases shows a large difference between these measurements (Fig 10), as previously noted.

It is suggested that there is some variability in the postoperative outcomes with the TTA despite an attempt to obtain precise preoperative measurements.29 No objective studies, such as force plate analysis, have been published to date to assess the results of the TTA, much less the effect of any such variability. Similar to TPLO, there probably is some amount of postoperative variability that will be tolerated, but the ideal clinical

postoperative PTA is unknown, despite the recommendation for a postoperative PTA of 901, using either the TPS or common tangent as the origin for the angle of the patellar tendon.

There has been no validation for the newer proposal to measure PTA using the common tangent with TTA; however, the same could be said of the measurement technique for TPLO using the TPS. Despite the recommendations to rotate the TPA to 51, there is no evidence which supports this as the ideal target angle other than a single in vitro cadaver study where 6.51 is suggested,7 as previously noted. The only presently published work with TTA is based upon the TPS similar to the method of the TPLO, and the data support the desired outcome of a PTA (oriented along the TPS and PT) of 90.3 9.01.12 We are currently evaluating the tangential method in an in vitro experimental study. Regardless, in our current clinical cases, the measurements being performed use the tangent method. This method is also being taught in the Kyon TTA courses (2007 Veterinary Symposium— The Surgical Summit; Pre-Symposium Laboratories: TTA Laboratory) Another question to be raised is whether the common tangent should be used instead of the TPS for determination of the amount of planned rotation and postoperative evaluation of rotation with the TPLO. The suggestion is that using the common tangent would demonstrate less postoperative variability in the final joint position obtained, and perhaps be closer to the 901 PTA proposed endpoint. If true, the apparent differences between the techniques may not be so different after all. This concept is yet to be evaluated.

Surgical Considerations

Fig 10. Lateral stifle joint radiographs demonstrating differences in the anatomic shape of the femoral condyles resulting in a difference in the tibial plateau slope (TPS) (solid line) and the common tangent (dotted line) at the femorotibial contact point.

(A) A difference of approximately 101 between these measurements in this example; the TPS is consistently observed at a higher tibial plateau angle (TPA). (B) Essentially no difference is observed between these measurements in this example. Compare TPS (solid line) and the common tangent (dotted line) at the femorotibial contact point and femoral condylar anatomy between parts (A) and (B). Notice the different anatomic conformations between the femoral condyles.

TPLO. As originally described, TPLO is a relatively invasive procedure where there is abundant circumferential dissection of the entire proximal aspect of the tibia, and a greater potential for injuring some vital structures around the joint. The substantial soft tissue dissection and limited coverage in the area of the proximal tibia may contribute to dead space and may predispose dogs to incisional complications. In a retrospective evaluation of 281 dogs at the Tufts Cummings School of Veterinary Medicine, there was an infection rate of 1.8% for dogs that had a lateral fabellotibial suture compared with 6.1% with TPLO.73 More recently, however, a more conservative approach has been recommended with the TPLO whereby there is an absence of lateral dissection and limited caudal dissection. Even so, the location of the saw cut with the TPLO has greater potential for iatrogenic damage to vital structures compared with TTA. Nonetheless, there do not appear to be significant clinical ramifications as a result of such iatrogenic damage.

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There are a number of surgical technical errors that can occur with TPLO. Placing the osteotomy too far cranial and/or distal will result in a higher than expected TPA postoperatively, and inadequate neutralization of the CrTT.62,63 Such malposition of the osteotomy also results in a small tibial tuberosity fragment, creating the possibility of a tibial tuberosity fracture. Similarly, placing the temporary holding pins (after initial rotation of the tibial plateau) too far distally into the tibial tuberosity results in a possible stress-riser in this fragment, again predisposing this bone to fracture. Fibular fractures can result in excessive stresses placed on this structure during the rotation, or may occur as a result of stress-risers from drill holes into this structure. Other issues may include fractured drill bits, intra-articular screw placement, and medial tibial cortical damage when placing osteotomy marks for the rotation. Additional miscellaneous items may include excessive osteotomy gaps, sponges left at the surgery site, intra-articular placement of jig pins, long digital extensor tendon damage, CaCL injury, broken holding pins, and screws placed within the osteotomy site. It can also be argued that the TPLO is a fairly complex procedure with perhaps some potentially unrecognized pitfalls where iatrogenic errors can result in a change in limb angulation and rotation.74 These errors can be readily demonstrated in a carpentry analogy where an angled cut results in a translation with rotation (Fig 11). Therefore, it is not unreasonable to consider the TPLO as a procedure with a steep learning curve.

TTA. Anecdotally, TTA is considered by many to be a much simpler procedure than the TPLO. Similar comments regarding soft tissue dissection and limited coverage in the area of the proximal tibia may be made for TTA; however, the surgical dissection is confined to cranial portion of the bone. There is very limited possibility for iatrogenic surgical injury with TTA, but damage to the long digital extensor tendon is one potential pitfall.29 There are a number of surgical technical errors that can occur with TTA. These issues include too small of an osteotomy fragment, shifting the patella distally, or predisposing to a patellar luxation with improper tibial tuberosity repositioning. A small osteotomy fragment does not allow adequate fork purchase as there is insufficient bone available. Another potential error is patellar malposition. Patella baja results if the tibial tuberosity is not allowed to shift proximally to maintain the patellar position, i.e., a distal tibial crest centered rotation rather than the desired patella-centered rotation.30 Patellar luxation can result if attention is not paid to the plate contouring, ensuring that the tibial tuberosity is advanced cranially without changing the orientation within the sagittal plane. Any shift either medially or laterally could result in a malalignment of

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Fig 11. Schematic representation of the differences in axial positioning after a perpendicular cut to the axis (top) of a straight beam versus an angled cut (middle) with rotation (bottom); curved (circular) arrows indicate axis of rotation. An angled cut results in a translation of the end of the beam after rotation (single curved arrow). Similar malalignment of the tibial osteotomy in a tibial plateau leveling osteotomy (TPLO) will result in iatrogenic rotational and angular deformities after rotation of the tibial plateau.

the quadriceps mechanism, and thus the resultant patellar luxation.

Other issues may include poor plate position, either rostrally along the tibial crest or distally along the tibial diaphysis. Additional miscellaneous items may include cage malposition and also intra-articular screw placement. There appear to be fewer technical issues with TTA compared with TPLO, but there are no published reports to document this. Finally, the difference in implants could be considered: commercially pure titanium (cpTi) is the norm with TTA versus stainless steel with TPLO. Pure titanium is touted as a more biocompatible implant with tissues as compared with stainless steel.75–77 Furthermore, the plate profile with TTA is very thin and provides less overall bulk in a position on the limb where soft tissue covering is limited to a thin muscle layer and skin. This may play a role in limiting soft tissue complications. It may be argued that despite TTA also being a relatively complex procedure, there are fewer unrecognized pitfalls that may result in postoperative problems.

Therefore, it is not unreasonable to consider TTA as a procedure with a short learning curve. Regardless, much of this is supposition as there are no reports of objective comparisons of the 2 surgical techniques comparing these factors and their possible effects.

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TPLO OR TTA?

OUTCOME AND COMPLICATIONS TPLO In general use for at least 9–10 years, TPLO has a ‘‘track record,’’ even if much of it is regarded as mostly anecdotal. Various published reports on outcome are the early experiences of a number of surgeons.26–28 These reports, therefore, are biased with the respective learning curves for these individuals.

In the 3 studies reporting complications in CrCLdeficient stifle joints with a TPLO, the overall complication rate was 18.8–28%.26–28 A similar overall rate of complications (31.1%) of another initial case series has been reported recently.73 Averaging the complication rate in these 4 reports (1772 cases) results in an overall complication rate of 26.3%. A reoperation rate was reported in 5%27 to 9%73 of the cases. These complications, presented in order of frequency, were as follows: incisional complications, infection, bone-related complications, intraoperative problems, and implantrelated problems. Incisional complications (edema, swelling, seroma, dehiscence) were most commonly reported and occurred in 2–16% (mean 9.3%).26–28,73 Infection was next most commonly reported in 5.9–7.1% (mean 6.0%),26,27,73 followed closely by bone-related problems (tibial tuberosity, fibular, or tibial fracture) in 4.9–7.1% (mean 5.4%).26–28,73 Intraoperative problems (hemorrhage, broken drill bit, damage to medial tibial cortex, intra-articular screw placement, etc.) were reported in 0.9–6.7% (mean 2.8%).26–28,73 Implant-related problems (screw loosening, breakage) occurred in 1.1– 5.2% (mean 2.4%).26–28,73 A number of these complications can be considered technical failures associated with the learning curve in performing this surgical procedure.

Other complications related to anatomic changes after TPLO include pivot shift, patellar tendon thickening, and patellar tendinitis. The pivot shift, as described in common usage with this technique, is a sudden internal rotation of the tibia with lateralization of the hock, and a sudden lateral change in direction of the stifle joint during weight bearing (in humans it is characterized by anterior subluxation of the tibial plateau from beneath the lateral femoral condyle).78 Although there are anecdotal comments from a number of surgeons regarding this phenomenon in the dog after TPLO, the actual frequency is unknown. Furthermore, the reason for its occurrence is also unknown, but is thought to be a result of insufficient correction of tibial torsion or angular deformity. Patellar tendon thickening has been reported in 1–80% of cases after TPLO27,28,61; this issue was previously discussed.

Healing of the osteotomy was not evaluated in these reports, and in only 1 report was the overall outcome reported (owner satisfaction in 93% of the cases).26

TTA A relatively new procedure, TTA has been in general use for o5 years. Similar to TPLO, there are anecdotal reports of good to excellent results, and some early clinical results published.29,30 The latter again are the early experiences of a number of surgeons, which also remain biased with the respective learning curves for these individuals. The 2 studies (179 cases) reporting complications in CrCL-deficient stifle joints repaired using TTA, report an overall complication rate of 31.6–59%.29,30 A number of minor complications were reported in both studies, including postoperative swelling and bruising accounting for 19.3–21% of these complications.29,30 The major complications accounted for 12.3–38%.29,30 A reoperation rate of 11.3% was reported.30 Combining the data, these complications, in order of frequency, were as follows: meniscal tears (7.2%), infection (3.9%), medial patellar luxation (1.1%), tibial fractures (1.1%), and catastrophic implant failure (1.1%).29,30 The primary discrepancies between these reports were the frequency of meniscal tears in one (21.7%)30 and technical failures in the other (22%).29 Radiographic healing was reported to be ‘‘partially complete by 7–8 weeks postoperatively and fully complete as early as 8–10 weeks postoperatively’’ in one report,29 and at a mean of 9.4 weeks postoperatively in the other report.30 Overall function (outcome and lameness) of the dogs postoperatively reported to be good to excellent in 490% of the dogs.29,30 In both studies, 2 major points are discussed: early technical errors with the procedure and meniscal injury.29,30 It is important to note that with the elimination of technical errors, also associated with the learning curve in performing this surgical procedure, as with the TPLO, would significantly reduce the number of major complications. The issue with the meniscus is more confounding, as there is much controversy as to the best method of approach: meniscal release or no meniscal release. TTA was originally performed without a meniscal release, in contrast to the recommendation for TPLO; therefore, the disparity between reports (TPLO versus TTA) most likely reflects this bias. It appears that most complications occurring postoperatively in one TTA study were because of meniscal tears, either those that may have been missed at the time of the original surgery or those that subsequently occurred.30 A suggestion was made that meniscal release may eliminate this issue.30 Comparison of TPLO and TTA The study designs with these reports, both TPLO and TTA, cannot be directly compared because of the many

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differences in study variables that are reported. The only unifying similarity in all studies is that they represent early experience with both techniques. Although there are no published reports of a comparison between these 2 techniques, some initial data has been presented.17,79 In one retrospective evaluation, the first 85 cases using each technique were compared (the 2 series of cases were performed by the same surgeon 6 years apart).17 Similar age, weight, and breeds were seen in both groups; few short-term (o2 months) and long-term (46 months) complications were reported.17 Outcomes were not presented, other than noting that both techniques were clinically effective in restoring good function and both had a similar frequency of postoperative complications.17 In the other report,79 TPLO and TTA outcomes were compared over a 6-month time frame after surgery. No obvious limb-loading differences, as determined by force plate analysis, were observed between the techniques, although some minor early differences were noted (slightly quicker loading and clinical function seen with TTA, and greater patellar tendon thickening observed with the TPLO).79 At this time, review of the early results and complications of both the TPLO and TTA indicate that their outcomes are very similar. There are no published clinical reports that compare the techniques, much less the complications and outcomes with experienced surgeons that might allow a direct comparison of the techniques and their outcome. Based upon anecdotal comments, it is assumed that with both procedures the results currently obtained are better than that reported, but this is only a supposition.

CASE SELECTION Some factors specific to the anatomic configuration of the limbs being operated need to be considered, from the standpoint of conformational issues that would make one procedure perhaps the better choice than the other. These include angular and torsional limb deformities, patellar luxation, and excessive TPS. Furthermore, the size of the dog may also play a factor.

Low Versus High Insertion Point When performing a TPLO, rotation of the tibial plateau segment only to the level of the patellar tendon insertion on the tibial tuberosity has been suggested to ensure its role as a buttress support for the tibial tuberosity segment.80 Therefore, dogs with high patellar tendon insertion point would run the risk of the rotation of the tibial plateau segment to a point below the patellar tendon insertion, thus potentially leaving the tibial tuberosity more prone to fracture because of an absence of buttress support (Fig 12). Alternatively, in dogs with a

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Fig 12. Lateral stifle joint radiographs demonstrating differences in the anatomic shape of the proximal tibia and tibial tuberosity with a low (A) versus high (B) insertion point of the patellar tendon (PT; arrows). The dotted and solid lines represent the positions of the tibial plateau leveling osteotomy (TPLO) and tibial tuberosity advancement (TTA) osteotomies, respectively. Rotation of the tibial plateau (TPLO) maintains continued buttress support behind the tibial tuberosity for a larger distance of rotation with a low PT insertion point (compare part [A] versus part [B]). Similarly, enhanced plate placement (larger area that enables a plate with additional points of contact/larger number of fork tines) and buttress support of the tibial tuberosity after a frontal plane osteotomy with advancement (TTA) is observed with a high PT insertion point (compare part [A] versus part [B]).

low patellar tendon insertion point, much greater rotation could be obtained while continuing to preserve the caudal buttress behind the tibial tuberosity. In contrast, the tibial tuberosity may be at more risk for possible fracture with TTA in cases with a low patellar tendon insertion point, as a smaller plate is applied to the tibial crest and the usual position of the interspersed cage is above the most proximal position of the plate with little bone present for support. In dogs with a high insertion point, a larger TTA plate can be applied to the tibial crest, and the interspersed cage is placed within the gap, which remains buttressed with adequate bone and a larger plate that disperses all the forces to the tibial crest (Fig 12).

It is suggested that cases with a high patellar tendon insertion point are more conducive to a TTA, whereas cases with a low patellar tendon insertion point are better suited for a TPLO. In any case, there are no experimental or clinical studies reported that support these assumptions.

Excessive TPS Cases where there is excessive TPS are not conducive to TTA, because the procedure requires that the advancement produce a PTA of 901, which likely would

16

TPLO OR TTA?

result in a required amount of advancement beyond that obtained with the currently available implants (maximal cage width for the osteotomy gap of 12 mm). Additionally, there is a conformational deformity of the joint with excessive TPS that places it in a relative angle of hyperextension despite the limb itself not being in the extended position (Fig 13). TTA does not address this malformation, whereas the TPLO can correct it. Even with the TPLO, however, a straightforward correction by rotation of the TPS only may not provide sufficient correction of the TPA; it has been recommended that a postoperative TPA of 141 be performed.81 It has also been recommended that the TPLO be combined with a closing wedge osteotomy (CCWO) to obtain more uniform postoperative corrections of TPA to 51.80 It has been suggested that the tibial tuberosity is at risk of fracture if the tibial tuberosity is rotated beyond the ‘‘safe point’’ where it remains buttressed by the rotated proximal tibial fragment.80,81 Regardless, it has also been suggested that additional implants be used to secure the osteotomy with large amounts of rotation with or without an additional osteotomy.80,81 The question remains, however, as to the maximal angle of the TPS (or common tangent) that should be used as a guideline to consider whether to perform a TTA. In one presentation,17 it was reported that in a single case in which a dog had a TPS of 271 with a TTA, the dog continued to have a positive tibial compression test postoperatively, and subsequently was successfully reoperated at a later date with a TPLO. No TTAs were performed in dogs with a TPS 4271.17 Although no data has been published regarding the range of TPS in dogs with TTA, it has been presented that

successful procedures have been performed in dogs with a TPS of 301 and anecdotally proposed that angles 4301 probably are not well suited for a TTA (2007 Veterinary Symposium—The Surgical Summit; Pre-Symposium Laboratories: TTA Laboratory).

Similarly, despite the recommendation with a TPLO to maintain the rotation of the tibial plateau such that the tibial tuberosity remains buttressed caudally, there is evidence that this may not be necessary in all cases.81 Limits to the amount of rotation with a TPLO and the amount of advancement with a TTA to adequately neutralize the tibiofemoral shear forces in the clinical patient remain to be definitively defined.

Angular and Torsional Limb Deformities Angular and torsional limb deformities may be treated with either TPLO or TTA; however, TPLO may be better suited to make these corrections simultaneous with the rotational osteotomy, either alone or combined with a closing wedge osteotomy, the latter procedure enhancing the stability of the fixation. With minor angulation or rotation, these deformities can be addressed after rotation of the proximal tibial fragment, after it has been temporarily secured with a pin or K-wire, and before plate fixation. At this point in the procedure, an angular correction (stifle varus or valgus) can be performed by shifting the jig position along either the proximal or distal jig pin (a translation of the jig along the pin) so as to obtain limb realignment (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.).82 Similarly, a rotational

Fig 13. Lateral stifle joint radiographs demonstrating differences in the anatomic shape of the proximal tibia such that the tibial plateau angle (TPA) is either considered excessive (A) at 431, or within normal limits (B) at 251. This conformational deformity of the stifle joint angle in part (A) places the joint in a relatively hyperextended position (compare with part [B]). Advancing the tibial tuberosity does not correct this hyperextension as the TPA remains unaltered. A tibial plateau leveling osteotomy (TPLO) corrects this joint position by altering the TPA (either alone or combined with a cranial closing wedge osteotomy).

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correction can be performed by bending one of the jig pins (usually the distal pin) while the jig is securely fixed to these pins (Seminars entitled Tibial Plateau Leveling Osteotomy for Cranial Cruciate Ligament Repair; Slocum Enterprises Inc.).82 The osteotomy position, however, changes such that the opposing bone surfaces no longer remain in full contact. Instead, they tip respective to one another, while maintaining cortical contact on the side opposite the distraction (Fig 14). The final plate fixation spanning the osteotomy site, and gap, is then applied.

Rotational and stifle varus deformities are amenable to repair by this technique as the gap is directly under the plate and cortical contact is obtained on the trans cortex.

A cancellous graft may be applied to the gap. Small corrections can be performed in this manner, generally o5–101, although no specific guidelines have been published. Larger corrections could be performed, but these result in large gaps at the osteotomy site, which decreases the rigidity of the fixation and potentially slows healing, the latter despite application of a cancellous graft. Additionally, larger corrections require an osteotomy of the fibula to allow the desired shift in the tibia, further decreasing the stability of the repair. Stifle valgus deformities result in the gap occurring in the trans cortex opposite the plate, which also is a more unstable situation. The latter problem may be better handled with a TPLO combined with a lateral closing wedge osteotomy.

Treatment for larger deformities include a TPLO combined with a single transverse osteotomy (rotational deformity) or medially or laterally based closing wedge osteotomy (valgus/varus deformity), or a cuneiform wedge osteotomy (valgus/varus deformity with excessive TPS; Fig 15). Regardless of a TPLO performed alone or as in combination as indicated, all osteotomies are spanned with plate fixation along the medial tibial surface. If a TTA was performed to correct the CrCL-deficient joint, a separate osteotomy, rotational, closing wedge or cuneiform, would still be required. The disadvantage is that the medial side of the bone already has the plate positioned for TTA in the proximal onethird of the medial tibial surface, which will interfere with subsequent additional medial plate fixation. Although a standard plate could be applied over the thin TTA plate, this is far from ideal and generally not recommended.

Currently, there are no studies that evaluate any of these recommendations.

Patellar Luxation Patellar luxation requiring tibial tuberosity transposition, on the other hand, may be better suited for a TTA, as any desired transposition could be simultaneously

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Fig 14. Craniocaudal preoperative (A) and postoperative (B) radiographs illustrating the torsional correction performed with the tibial plateau leveling osteotomy (TPLO) by rotating the 2 tibial bone fragments relative to each other in the axis parallel to the bone. The distal positioning of the medial side of the calcaneus is seen to move such that it now intersects the center of the talus postoperatively (straight arrows). Notice the slight malalignment of the plated osteotomy in part (B) as a result of this rotational correction. Lateral postoperative radiograph (C) shows a slight gap at the osteotomy as a result of this axial rotation; this gap is open along the medial cortex only and spanned with the TPLO plate. The axial rotation is schematically represented (D) to illustrate the opening of the wedge with the rotation of the distal fragment (curved arrow), and continues to maintain contact on the side opposite the opening wedge (dotted line).

performed with the advancement. In this case, the TTA plate is slightly over-bent to conform to the new laterally (or medially) transposed tibial crest. The alteration in the surgical technique occurs with cage application. For example, in a medial patellar luxation, where the tibial crest is moved laterally, either the caudal ‘‘ear’’ of the cage must be recessed into the proximal tibia, or the

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TPLO OR TTA?

deformity that also needed to be corrected at the same time. In the latter instance, TPLO would again be the better choice. In this instance, if there was a simultaneous rotational deformity this correction could result in appropriate alignment of the tibial tuberosity after the repositioning. Alternatively, a single transverse osteotomy, or combined with a closing wedge or cuneiform osteotomy in the presence of an additional angular deformity would allow the entire tibial tuberosity bone fragment to be translated and then secured as previously described (Fig 15).

Once again, there are no studies that evaluate any of these recommendations. Furthermore, there have been no comparisons performed to suggest whether TPLO or TTA provides a superior result, and no assessment of frequency of the possible complications encountered.

Fig 15. Schematic representation of the proximal tibia with a tibial plateau leveling osteotomy (TPLO) and a second transverse osteotomy coincident with the caudal margin of the TPLO (A and B). Large rotational deformities may be addressed by rotation around the transverse osteotomy (curved arrows), allowing full contact and compression plate fixation to be applied. In addition, this technique allows the tibial tuberosity fragment to be translated medially or laterally (large white arrows) to adjust the position of the patellar tendon insertion (tibial tuberosity transposition of this entire bone segment) in order to realign the quadriceps muscle force in cases of patellar luxation. Full bone contact is maintained between the bone fragments such that compression plate fixation may be applied.

A further correction may be performed to address excessive tibial plateau angle (TPA) or proximal tibial varus or valgus by modifying the transverse osteotomy into a cranial, medial, lateral (not shown), or cuneiform wedge (C) at this position (double-headed arrow).

cranial ‘‘ear’’ of the cage elevated above the surface of the tibial tuberosity by interposing some washers, or both.

No additional fixation is required, although in an unusual case some additional fixation may be required craniocaudally. This fixation may be a K-wire or 2.4 mm screw through the tibial tuberosity, and the spaces within the cage, into the proximal tibia. A figure-of-8 tension band wire could also be applied, but generally is not thought to be necessary. This technique has been briefly described (2007 Veterinary Symposium—The Surgical Summit; Pre-Symposium Laboratories: TTA Laboratory),52 and an abstract presented on a series of cases.83 With a TPLO in the presence of a patellar luxation, the preference is not to isolate the tibial tuberosity in front of the rotational osteotomy, although this could be performed with pin and tension band wire fixation techniques. The limitation with the tibial tuberosity transposition and TTA, however, would be cases of patellar luxation that also had a significant angular/torsional

Patient Size Both TPLO and TTA have been performed in dogs as small as 5 kg and as large as 92 kg.26–30 Size limitation for these techniques is dependent upon the availability of the appropriately sized implants. Both devices are produced in a variety of sizes such that they can accommodate almost any sized dog. In some instances, in very large breed dogs it has been suggested using 2 plates with TPLO; however, this is not a universally accepted opinion. One current limitation of the TTA may be the large distance (412 mm) of TTA that is required for some large breeds of dogs (not necessarily the heavier dogs, but rather the taller dogs, e.g., Great Danes).44 The widest cage currently available to support the osteotomy gap is 12 mm. Whereas the cage can be moved further distally to increase the width of the gap, this must be done judiciously, as the tibial tuberosity above the cage may become prone to fracture because of a large stress-riser created above the cage.44 One alternative would be to buttress the tibial tuberosity above the cage with a cancellous bone block allograft, which has been successfully performed in a few cases; however, adding this graft adds a considerable additional expense to the procedure.44 Costs The wide difference in implants not only encompasses a different plating concept, compression or neutralization plating of the osteotomy with a TPLO versus a tension-band plate with a supported gap (cage) with a TTA, but also a difference in costs. In general, for an average large breed dog, the implant costs for a TTA are $250, whereas for a TPLO they are $150–360 depending upon which implant manufacturer is selected s (Slocum Enterprises; New Generation Devices, Glen

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BOUDRIEAU s

s

Rock, NJ; Securos , Charlton, MA; Synthes , Paoli, PA, etc.). For TPLO, using standard screw fixation, regardless of manufacturer, costs are $150–175. The addition of locked screws can increase the cost to $360 (e.g. Syns thes LC-DCP TPLO plate with 3 locked screws in the head, and 3 standard screws in the body).

TTA also requires a graft for the osteotomy gap. This can be filled either with an autogenous cancellous graft or an allograft using banked bone (corticocancellous chips and demineralized bone matrix; Veterinary Transplant Services, Kent, WA). Adding a cancellous graft adds some operating time and a second surgical site to the procedure, whereas adding the allograft (banked bone) adds a significant cost, $200 for the average large breed dog ( 2 mL). Another alternative to an auto- or allograft is to use an osteoconductive compound such as s an injectable nanoparticle hydroxyapatite (Ostim ; Heraeus Kulzer Inc., Armonk, NY). The latter has recently been recommended by the original manufacturer of the TTA (Kyon); current costs for an average-sized large breed dog ( 2 mL) are $100. This new material has recently been investigated and was found to have mineralization rates that were not significantly lower than those found with autogenous bone in the in vivo animal model investigated.84 This material is yet to be evaluated in the dog, and more specifically, for use with the TTA.

surgeon to select the technique that he/she believes is the most appropriate for the specific task at hand and their own experience/expertise. This is not unlike the concept of selecting from among the many different methodologies, for example, with fracture fixation. Increasing our armamentarium simply allows a greater number of options for a particular procedure, which hopefully addresses the specifics of the case presented more ideally. Lastly, it is recognized that in many cases, personal preference may be the overriding driving force on technique selection.

There are a number of areas outlined where there is a lack of documentation of many of the anecdotes presented with both techniques. These include the proposed mechanisms and their ramifications, and indications for their use, much less any direct comparisons between the 2 surgical techniques. At this time, there are only a few studies that present reasonable scientific support for either procedure. A number of experimental and clinical studies are necessary to attempt to shed more light on these repair methods. It is hoped that this summary has stimulated some thought and will result in additional and continued investigations into these techniques, which may substantiate or contradict the present plethora of anecdotal information that continues to be disseminated.

ACKNOWLEDGMENTS

CONCLUSIONS There are a number of apparent advantages/disadvantages in both TPLO and TTA procedures. TTA may correct the tibiofemoral shear force closer to the neutral point compared with TPLO, which might protect the CaCL from additional stress as the primary joint stabilizer. Another advantage of the TTA is the unchanged joint geometry and superior cartilage pressure distribution compared with TPLO. TTA may also be a less invasive, simpler surgical procedure with fewer potential technical issues with adverse effects. TTA may be more suitable in cases of patellar luxation. On the other hand, TPLO is a more versatile procedure than TTA in cases with excessive TPS, and in cases with a variety of angular and rotational limb deformities, including cases with concurrent patellar luxation. Implant costs are marginally higher with the TTA, especially if a commercial allograft is used. Early clinical results and complications appear to be comparable; however, the TTA may have an advantage as it appears that the technical aspects of the procedure are fewer and it has a shorter learning curve. In addition, most complications appear to involve fewer major issues, which appear to be more easily overcome with adherence to the details of the procedure. As with many surgical procedures, it is at the discretion of the

The author thanks Drs. Michael P. Kowaleski and Leslie L. Williams for their contributions; in addition, Tim Vojt (Medical Illustration and Computer Graphics, Columbus, OH) for the 3-dimensional computer graphics of the stifle joint, and Beth Mellor (Graphic Design/Multimedia Production, Cummings School of Veterinary Medicine at Tufts University) for the line drawings.

REFERENCES 1. Elkins AD: A retrospective study evaluating the degree of degenerative joint disease in stifle of dogs following surgical repair of anterior cruciate ligament rupture. J Am Anim Hosp Assoc 27:533–539, 1991 2. Vasseur PB, Berry CR: Progression of stifle osteoarthritis following reconstruction of the cranial cruciate ligament in 21 dogs. J Am Anim Hosp Assoc 28:129–136, 1992 3. Arnoczky SP, Marshall JL: The cruciate ligaments of the canine stifle: an anatomical and functional analysis. Am J Vet Res 38:1807–1814, 1977 4. Slocum B, Devine T: Cranial tibial thrust: a primary force in the canine stifle. J Am Vet Med Assoc 183:456–459, 1983 5. Slocum B, Slocum TD: Tibial plateau leveling osteotomy for repair of cranial cruciate ligament rupture in the canine.

Vet Clin North Am 23:777–795, 1993 6. Slocum B, Slocum TD: Tibial plateau leveling osteotomy for cranial cruciate ligament, in Bojrab MJ (ed): Current

20

7.

8.

9.

10.

11.

12.

13.

14.

15.

16.

17.

18.

19.

20.

TPLO OR TTA? Techniques in Small Animal Surgery (ed 4).

Baltimore, MD, Williams & Wilkins, 1998, pp 1209–1215 Warzee CC, Dejardin LM, Arnoczky SP, et al: Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate-deficient stifles: an in vitro experimental study. Vet Surg 30:278–286, 2001 Reif U, Hulse DA, Hauptman JG: Effect of tibial plateau leveling on stability of the canine cranial cruciate ligamentdeficient stifle joint: an in vitro study. Vet Surg 31:147–154, 2002 Montavon PM, Damur DM, Tepic S: Advancement of the tibial tuberosity for the treatment of cranial cruciate deficient canine stifle, in Proceedings of the 1st World Orthopaedic Veterinary Congress, Munich, Germany, September 2002, p 152.

Tepic S, Damur DM, Montavon PM: Biomechanics of the stifle joint, in Proceedings of the 1st World Orthopaedic Veterinary Congress, Munich, Germany, September 2002, pp 189–190.

Tepic S, Montavon PM: Is cranial tibial advancement relevant in the cruciate deficient stifle? in Proceedings of the 12th ESVOT Congress, Munich Germany, September 2004, pp 132–133.

Apelt A, Kowaleski MP, Boudrieau RJ: Effect of tibial tuberosity advancement on cranial tibial subluxation in canine cranial cruciate-deficient stifle joints: an in vitro experimental study. Vet Surg 36:170–177, 2007 Miller JM, Shires PK, Lanz OI, et al: Effect of 9 mm tibial tuberosity advancement on cranial tibial translation in the canine cruciate ligament-deficient stifle. Vet Surg 36: 335–340, 2007 Moore KW, Read RA: Cranial cruciate ligament rupture in the dog: a retrospective study comparing surgical techniques. Aust Vet J 72:281–285, 1995 Korvick DL, Johnson AL, Schaeffer DJ: Surgeons’ preferences in treating cranial cruciate ligament ruptures in dogs. J Am Vet Med Assoc 205:1318–1324, 1994 Conzemius MG, Evans RB, Besancon MF, et al: Effect of surgical technique on limb function after surgery for rupture of the cranial cruciate ligament in dogs. J Am Vet Med Assoc 226:232–236, 2005 Vezzoni A: Comparison of tibial plateau leveling osteotomy and tibial tuberosity advancement. Abstracts of the 2nd World Veterinary Orthopaedic Conference, 33rd Annual Conference of the Veterinary Orthopedic Society, February 25-March 4, 2006, pp 47–48.

Giffin JR, Vogrin TM, Zantop T, et al: Effects of increasing tibial slope on the biomechanics of the knee. Am J Sports Med 32:376–382, 2004 Li G, Rudy TW, Allen C, et al: Effect of combined axial compressive and anterior tibial loads on in situ forces in the anterior cruciate ligament: a porcine study. J Orthop Res 16:122–127, 1998 Nisell R, Ericson MO, Ne´meth G, et al: Tibiofemoral joint forces during isokinetic knee extension. Am J Sports Med 17:49–54, 1989

21. Henderson RA, Milton JL: The tibial compression mechanism: a diagnostic aid in stifle injuries. J Am Anim Hosp Assoc 14:474–479, 1978 22. Slocum B, Devine T: Cranial tibial wedge osteotomy: a technique for eliminating cranial tibial thrust in cranial cruciate ligament repair. J Am Vet Med Assoc 184:564–569, 1984 23. Nisell R, Ne´meth G, Ohlse´n H: Joint forces in the extension of the knee: analysis of a mechanical model. Acta Orthop Scand 57:41–46, 1986 24. Li G, Rudy TW, Sakane M, et al: The importance of quadriceps and hamstring muscle loading on knee kinematics and in-situ forces in the ACL. J Biomech 32:395–400, 1999 25. Nisell R: Mechanics of the knee: a study of joint and muscle load with clinical applications. Acta Orthop Suppl 56:1–42, 1985 26. Priddy NH, Tomlinson JL, Dodam JR, et al: Complications with and owner assessment of the outcome of tibial plateau leveling osteotomy for treatment of cranial cruciate ligament rupture in dogs: 193 cases (1997–2001). J Am Vet Med Assoc 222:1726–1732, 2003 27. Pacchiana PD, Morris E, Gillings SL, et al: Surgical and postoperative complications associated with tibial plateau leveling osteotomy in dogs with cranial cruciate ligament rupture: 397 cases (1998–2001). J Am Vet Med Assoc 222:184–193, 2003 28. Stauffer KD, Tuttle TA, Elkins AD, et al: Complications associated with 696 tibial plateau leveling osteotomies (2001–2003). J Am Anim Hosp Assoc 42:44–50, 2006 29. Hoffman DE, Miller JM, Ober CP, et al: Tibial tuberosity advancement in 65 canine stifles. Vet Comp Orthop Traumatol 19:219–227, 2006 30. Lafaver S, Miller NA, Stubbs WP, et al: Tibial Tuberosity Advancement (TTA) for stabilization of the canine cranial cruciate ligament deficient stifle joint: surgical technique, early results and complications in 101 dogs. Vet Surg 36:573–586, 2007 31. Pozzi A, Kim SE, Banks SA, et al: In vitro pathomechanics of the Pond-Nuki model. Abstracts of the 35th Annual Conference of the Veterinary Orthopedic Society, March 8-15, 2008, p 31.

32. Berchuck M, Andriacchi TP, Bach BR, et al: Gait adaptations by patients who have a deficient anterior cruciate ligament. J Bone Jt Surg 72(A): 871–877, 1990 33. Shin CS, Chaudhari AM, Dyrby CO, et al: The patella ligament insertion angle influences quadriceps usage during walking of anterior cruciate ligament deficient patients. J Orthop Res 25:1643–1650, 2007 34. Engebretsen L, Lew WD, Lewis JL, et al: The effect of an iliotibial tenodesis on intraarticular graft forces and knee joint motion. Am J Sports Med 18:169–176, 1990 35. Noyes FR, McGinniss GH, Grood ES: The variable functional disability of the anterior cruciate ligament-deficient knee. Orthop Clin North Am 16:47–67, 1985 36. Wilk KE, Reinold MM, Hooks TR: Recent advances in the rehabilitation of isolated and combined anterior cruciate ligament injuries. Orthop Clin North Am 34:107–137, 2003

BOUDRIEAU 37. Shahar R, Milgram J: Biomechanics of tibial plateau leveling of the canine cruciate-deficient stifle joint: a theoretical model. Vet Surg 35:144–149, 2006 38. Schwarz PD: Tibial plateau leveling osteotomy (TPLO): a prospective clinical comparative study, in Proceedings of the 9th Annual ACVS Symposium, San Francisco, CA, 1999 (abstract), p 379.

39. Palmer RH: Tibial plateau leveling osteotomy, in Proceedings of the 10th Annual ACVS Symposium, Arlington, VA, 2000 (abstract), pp 271–275.

40. Matis U: Radiographic evaluation of the progression of osteoarthritis after tibial plateau leveling osteotomy in 93 dogs, in Proceedings of the 12th ESVOT Congress, Munich, Germany, 2004 (abstract), p. 250.

41. Petazzoni M: TPLO in the small dog: 18 cases, in Proceedings of the 12th ESVOT Congress, Munich, Germany, 2004 (abstract), p 258.

42. Robinson DA, Mason DR, Evans R, et al: The effect of tibial plateau angle on ground reaction forces 4–17 months after tibial plateau leveling osteotomy in Labrador retrievers.

Vet Surg 35:294–299, 2006 43. Dennler R, Kipfer NM, Tepic S, et al: Inclination of the patellar ligament in relation to flexion angle in stifle joints of dogs without degenerative joint disease. Am J Vet Res 67:1849–1854, 2006 44. Burns CG, Boudrieau RJ: Modified tibial tuberosity advancement procedure with tibial tuberosity advancement in excess of 12 mm in four large breed dogs with cranial cruciate ligament-deficient joints. Vet Comp Orthop Traumatol 21:250–255, 2008 45. Zachos TA, Arnoczky SP, Lavagnino M, et al: The effect of cranial cruciate ligament insufficiency on caudal cruciate ligament morphology: an experimental study in dogs. Vet Surg 31:596–603, 2002 46. Lee JY, Kim G, Kim JH, et al: Kinematic gait analysis of the hind limb after tibial plateau leveling osteotomy and cranial tibial wedge osteotomy in ten dogs. J Vet Med A 54:579–584, 2007 47. Slocum B, Slocum TD: Meniscal release, in Bojrab MJ (ed): Current Techniques in Small Animal Surgery (ed 4).

Baltimore, MD, Williams & Wilkins, 1998, pp 1197–1199 48. Tepic S: Cranial tibial tuberosity advancement (TTA) for the cruciate deficient stifle. Abstracts of the 2nd World Veterinary Orthopaedic Congress/33rd Annual Conference of the Veterinary Orthopedic Society, February 26-March 4, 2006, pp 44–46.

49. Kim SE, Pozzi A, Banks SA, et al: Effect of tibial plateau leveling osteotomy and tibial tuberosity advancement and on femorotibial contact mechanics. Abstracts of the 35th Annual Conference of the Veterinary Orthopedic Society, March 8-15, 2008, p 33.

50. Milgram J: The effect of tibial plateau leveling osteotomy and tibial tuberosity advancement on passive laxity of the cranial cruciate ligament deficient stifle joint in dogs, in Proceedings of the 16th Annual Scientific Meeting of the ECVS, June 28–30, 2007. Vet Surg 36:E10, 2007

21

51. Lozier SM: Meniscal release in TPLO—A necessary evil? in Proceedings of the 2006 ACVS Veterinary Symposium, October 5-7, 2006 (abstract), pp 492–496.

52. Boudrieau RJ: Tibial tuberosity advancement (TTA): clinical results, in Proceedings of the 2005 ACVS Veterinary Symposium, October 27-29, 2005 (abstract), pp 443–445.

53. Pozzi A, Litzky AS, Field J, et al: Pressure distributions on the medial tibial plateau after medial meniscal surgery and tibial plateau levelling osteotomy in dogs. Vet Comp Orthop Traumatol 21:8–14, 2008 54. Pozzi A, Kowaleski MP, Apelt D, et al: Effect of meniscal release on tibial translation after tibial plateau leveling osteotomy. Vet Surg 35:486–494, 2006 55. Kennedy SC, Dunning D, Bischoff MG, et al: The effect of axial and abaxial release on meniscal displacement in the dog. Vet Comp Orthop Traumatol 18:227–234, 2005 56. Beale BS, Hulse DA: Second look arthroscopy—What happens after TPLO? in Proceedings of the 2005 ACVS Veterinary Symposium, October 27-29, 2005 (abstract), pp 474–477.

57. Thieman KM, Tomlinson JL, Fox DB, et al: Effect of meniscal release on rate of subsequent meniscal tears and owner-assessed outcome in dogs with cruciate disease treated with tibial plateau leveling osteotomy. Vet Surg 35:705–710, 2006 58. Luther JK, Cook CR, Cook JL: Meniscal release in cruciate ligament intact stifles causes lameness and medial compartment cartilage pathology in dogs. Abstracts of the 35th Annual Conference of the Veterinary Orthopedic Society, March 8-15, 2008, p 35.

59. Hulse D: Meniscal injury following surgery for the ACL deficient stifle joint, in Proceedings of the 2006 ACVS Veterinary Symposium, October 5-7, 2006 (abstract), pp 447–448.

60. Pozzi A, Hildreth BE III, Rajalla-Schultz PJ: Comparison of arthroscopy and arthrotomy for the diagnosis of medial meniscal pathology: an in vitro study. Abstracts of the 34th Annual Conference of the Veterinary Orthopedic Society, March 3-10, 2007, p 48.

61. Carey K, Aiken SW, DiResta GR, et al: Radiographic and clinical changes of the patellar tendon after tibial plateau leveling osteotomy. Vet Comp Orthop Traumatol 18:235– 242, 2005 62. Kowaleski MP, Apelt D, Mattoon JS, et al: The effect of tibial plateau leveling osteotomy position on cranial tibial subluxation: an in vitro study. Vet Surg 34:332–336, 2005 63. Kowaleski MP, McCarthy RJ: Geometric analysis evaluating the effect of tibial plateau leveling osteotomy position on postoperative tibial plateau slope. Vet Comp Orthop Traumatol 17:30–34, 2004 64. Maquet P: Advancement of the tibial tuberosity. Clin Orthop Rel Res 115:225–230, 1976 65. Shirazi-Adl A, Mesfar W: Effect of tibial tubercle elevation on biomechanics of the knee joint under muscle loads. Clin Biomech 22:344–351, 2007

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TPLO OR TTA?

66. Reif U, Dejardin LM, Probst CW, et al: Influence of limb positioning and measurement method on the magnitude of the tibial plateau angle. Vet Surg 33:368–375, 2004 67. Reif U: Influence of limb positioning and interobserver variation on the measurement of the tibial plateau angle.

Abstracts of the 20th Annual Meeting of the Veterinary Orthopedic Society, Lake Louise, Alberta, Canada, 2001, p 6.

68. Caylor KB, Zumpano CA, Evans LM, et al: Intra- and interobserver measurement variability of tibial plateau slope from lateral radiographs in dogs. J Am Anim Hosp Assoc 37:263–268, 2001 69. Fettig AA, Rand WM, Sato AF, et al: Observer variability of tibial plateau slope measurement in 40 dogs with cranial cruciate ligament deficient stifle joints. Vet Surg 32: 471–478, 2003 70. Hottinger HA, DeCamp CE, Olivier NB, et al: Noninvasive kinematic analysis of the walk in healthy large-breed dogs.

Am J Vet Res 57:381–388, 1996 71. DeCamp CE, Soutas-Little RW, Hauptman J, et al: Kinematic gait analysis of the trot in healthy Greyhounds. Am J Vet Res 54:627–634, 1993 72. Schaefer SL, DeCamp CE, Hauptman JG, et al: Kinematic gait analysis of hind limb symmetry in dogs at the trot. Am J Vet Res 59:680–685, 1998 73. McCarthy RJ: TPLO complications. Proceedings notes, Seminar on Advanced TPLO Problem Solving, 2nd World Veterinary Orthopaedic Conference, 33rd Annual Conference of the Veterinary Orthopedic Society, March 1, 2006 (abstract), pp 10–12.

74. Wheeler JL, Cross AR, Gingrich W: In vitro effects of osteotomy angle and osteotomy reduction on tibial angulation and rotation during the tibial plateau-leveling osteotomy procedure. Vet Surg 32:371–377, 2003 75. Imam MA, Fraker AC: Titanium alloys as implant materials, in Brown SA, Lemons JE (eds): Medical Applications of Titanium and its Alloys: The Material and Biological Issues, ASTM STP 1272. West Conshohocken, PA, American Society of Testing Materials, 1996, pp 3–16

76. Schmidt C, Ignatius AA, Claes LE: Proliferation and differentiation parameters of human osteoblasts on titanium and steel surfaces. J Biomedical Mater Res 54:209–215, 2001 77. Pennekamp PH, Gessmann J, Diedrich O, et al: Shortterm microvascular response of striated muscle to cp-Ti, Ti-6Al-4V, and T-6Al7Nb. J Orthop Res 24:531–540, 2006 78. Galway HR, MacIntosh DL: The lateral pivot shift: a symptom and sign of anterior cruciate ligament insufficiency.

Clin Orthop Rel Res 147:45–50, 1980 79. Shires PK, Lanz O, Martin RA, et al: Early post-operative outcomes in unilateral cranial cruciate ligament deficient dogs treated with tibial tuberosity advancement or tibial plateau leveling osteotomy. Abstracts of the 2007 American College of Veterinary Surgeons Symposium, October 18-21, 2007, p E24.

80. Talaat MB, Kowaleski MP, Boudrieau RJ: Combination tibial plateau leveling osteotomy and cranial closing wedge osteotomy of the tibia for the treatment of cranial cruciate ligament-deficient stifles with excessive tibial plateau angle.

Vet Surg 35:729–739, 2006 81. Duerr FM, Duncan CG, Savicky RS, et al: Comparison of surgical treatment options for cranial cruciate ligament disease in large-breed dogs with excessive tibial plateau angle. Vet Surg 37:49–62, 2008 82. Fitzpatrick N, Johnson J, Hayashi K, et al: TPLO and medial opening wedge via a single osteotomy for cranial cruciate rupture and genu varum. Abstracts of the 35th Annual Conference of the Veterinary Orthopedic Society, March 815, 2008, p 67.

83. Fitzpatrick N, Yeadon R, Kowaleski M: Tibial tuberosity transposition-advancement for treatment of medial patellar luxation and concomitant cranial cruciate ligament disease in the dog. Abstracts of the 34th Annual Conference of the Veterinary Orthopedic Society, March 3-10, 2007, p 67.

84. Thorwarth M, Schultze-Mosgau S, Kessler P, et al: Bone regeneration in osseous defects using a resorbable nanoparticular hydroxyapatite. J Oral Maxillofac Surg 63:1626– 1633, 2005