Effects of Attachment Sites and Joint Angle at the Time of Lateral Suture Fixation by Salah EL MOUSTAGHFIR

Effects of Attachment Sites and Joint Angle at the Time of Lateral Suture Fixation on Tension in the Suture for Stabilization of the Cranial Cruciate Ligament Deficient Stifle in Dogs Christof Fischer1, DVM, Mitzi Cherres1, DVM, Vera Grevel1, Prof. Dr. med. vet., Diplomate ECVS, Gerhard 1 Oechtering1, Prof. Dr. med. vet., Diplomate ECVAA, and Peter Bottcher , Dr. med. vet., Diplomate ECVS ¨ 1

Department of Small Animal Medicine, University of Leipzig, Leipzig, Germany

Corresponding Author Peter Bottcher, Dr. med. vet., Diplomate ¨ ECVS, Klinik fur ¨ Kleintiere, An den Tierkliniken 23, D-04103 Leipzig, Germany E-mail: boettcher@kleintierklinik. uni-leipzig.de Submitted March 2009 Accepted January 2010 DOI:10.1111/j.1532-950X.2010.00659.x

Objective: To investigate the influence of different sites of lateral suture fixation for stabilization of the cranial cruciate ligament (CCL) deficient stifle and different joint angles at time of tightening on suture tension. Study Design: Controlled laboratory study. Sample Population: Stifle joints (n = 9) of dogs Z20 kg. Methods: After CCL transection, each stifle was stabilized using 12 combinations of 4 different methods of lateral suture stabilization (LSS) and 3 different joint angles at time of suture tightening. Load within the suture throughout a full range of passive motion (ROM) was measured for each combination using a custom made load cell. Results: All 4 LSS methods had an increase in suture tension on stifle flexion. LSS with the suture looped around the lateral fabella and secured to the proximal aspect of the tibia through 2 parallel drill holes at the tibial crest had the least change in suture tension during ROM. Tightening the suture at 701 joint angle resulted in a significant loss of suture tension on extension. Conclusions: None of the LSS resulted in constant suture tension, questioning current recommendations regarding ‘‘isometric’’ points for lateral suture fixation. Tightening the suture with the stifle held in flexion may result in joint instability on extension. Clinical Relevance: LSS as commonly performed is associated with a significant increase in suture tension on flexion of the stifle, potentially over-constraining the joint. Tightening should be performed with the stifle in slight extension rather than in flexion.

Rupture of the cranial cruciate ligament (CCL) is the most common cause for lameness in dogs,1 resulting in stifle instability and degenerative joint disease.2–4 Surgical techniques for correction have focused on intraarticular repair,5,6 extraarticular stabilization,7–9 or osteotomy of the proximal tibia.10,11 None of the techniques have superiority for clinical efficacy12,13 making technique selection the surgeon’s preference.14 Technical modifications of the lateral suture stabilization (LSS) technique reflect changes in suture material, knotting, and attachment sites.15–23 Placing the suture caudal to the lateral fabella and curving distally to a drill hole in the proximal tibial crest has been the established technique16 but recently, attachment points craniodistal to the fabella and caudoproximal to the tibial tuberosity at the proximal aspect of the tibial plateau have been reported.24,25 These modifications are thought to improve

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suture isometry and thus overall impact on functional outcome after LSS.20,22 ´ ego ´ et al24 had good functional outEven though Guen come using bone anchors on the lateral femoral condyle in 48 stiﬂes, a high percentage of bone anchors pulled out when the anchor was not positioned in an isometric location.24 This outcome could be attributed to anisometric placement of the lateral suture, resulting in over-tensioning of the implant during range of motion with resultant suture breakage or bone anchor loosening. When investigating isometry of various attachment points on the distal aspect of the femur and proximal aspect of the tibia, Roe et al20 used a 2-dimensional radiographic technique, which they considered to be a major limitation in study design because it does not account for the suture not taking a direct path from the fabella to the tibial crest.20 Hyman et al22 measured the change in strain

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of a suture attached to different femoral and tibial fixation sites without mimicking the suture loop around the caudal aspect of the fabella.22 Therefore, the sites of suture attachment proposed by these studies might not result in a significant improvement in suture tension pattern, when applied to dogs with a torn CCL. Furthermore, when assuming some degree of anisometry regardless of the exact type of LSS performed, loop tension pattern during range of motion might be related to the angle of stifle flexion at the time the suture is tied. To our knowledge this has not been investigated in dogs, but some veterinary surgeons secure the suture with the stifle flexed, even though most prefer an angle close to full extension.16 Accordingly, our purpose in this in vitro study was 2-fold: (1) to compare suture tension pattern with 4 different types of LSS while moving the stabilized stifle through a full range of passive motion (ROM); and (2) to determine whether the angle at which the suture is tied affects recorded suture tension patterns.

MATERIAL AND METHODS Dogs Randomly chosen right or left pelvic limbs were obtained by coxofemoral disarticulation from 9 adult orthopedically sound dogs (mean weight, 36 kg; range, 20–55 kg) euthanatized for reasons unrelated to this study. For inclusion, stifles had to be free of any gross morphologic abnormality on lateral radiographs as well as visually on joint inspection at the end of the study. Limbs were double sealed in plastic bags and immediately frozen at 181C and then thawed at room temperature for 24 hours before testing. Limbs were prepared for testing by complete skin removal and removal of most of the thigh musculature, leaving the quadriceps muscle attached. The periarticular tissues of the stifle and the muscles surrounding the tibia were preserved. Experimental Setup The femur was fixed in a vertical position with a custom made holder using 2 pipe clamps (1 distal and 1 proximal to the femoral diaphysis), allowing for unconstrained manipulation of the stifle, tibia, and tarsus. Each clamp was fixed with a screw to a vertical table (Fig 1). A plastic goniometer was attached lateral to the stifle for measurement of joint angle. The arms of the goniometer were aligned at the greater trochanter, the lateral epicondyle of the distal femur, and the longitudinal axis of the tibia.26 After mid body transection of the CCL through a medial mini-arthrotomy, the joint was stabilized using a combination of 4 different LSS techniques (LSS1–LSS4) and 3 different joint angles at the time of suture tightening (1301, 1001, 701). This resulted in 12 repetitions/stifle, for which the order had been randomized using a random list generator (http:// www.random.org). During testing, the soft tissues were kept moist with isotonic saline (0.9% NaCl) solution. Test-

Figure 1 Schematic representation of the special holder used to fix the femur in a vertical position, allowing for unconstrained manipulation of the stifle, tibia, and tarsus. The diagram shows the 3 different angles at which the suture was tightened (1301, 1001, 701).

ing of each stifle took 7 hours, so each stifle was studied on a separate day. LSS were performed by 1 investigator (C.F.) assuring consistency between the different trials. An 80 lb monofilament nylon leader (Securos Europe, Neuhausen ob Eck, Germany) was passed through a hole in the proximal tibia and attached to the distal femur either using a bone anchor or looping the suture around the lateral fabella. Method 1: (LSS1; Fig 2A). Traditional form of LSS according to Flo.7 The nylon suture was passed through the femorofabellar ligament in a proximal to distal direction, around the lateral fabella. The distal strand of the suture was passed from lateral to medial through a hole in the tibial crest, 1 cm caudal to the attachment of the patellar ligament, and advanced medially beneath the patellar ligament. Method 2: (LSS2; Fig 2B). A slight modification of ´ ego ´ LSS1 described by Guen et al.24 The distal fixation at the tibial crest was performed by drilling 2 parallel 2.0 mm diameter bone tunnels in the proximal part of the tibial crest just cranial to the bony groove of the long digital extensor tendon. Thus the suture crossed the tibial crest from lateral to medial then medial to lateral.’’ Method 3 (LSS3; Fig 2C). The nylon suture was looped around the lateral fabella. For the distal attachment, two 2 mm diverging bone tunnels were drilled both starting at the same point at the Gerdy’s tubercle emerging at the medial aspect of the proximal tibia, resulting in a bony bridge of 5–8 mm in between the 2 openings of the proximomedial cortex of the tibia. The distal end of nylon was passed through 1 tunnel from lateral to medial and than back through the other tunnel emerging at the Gerdy’s tubercle.

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cell (19 mm 11 mm 21 mm), equipped with 2 unidirectional strain gauges (7 mm 5 mm; Type 0.6/120LY41, HBM Germany, Darmstadt, Germany) to reduce the influence of temperature changes during testing to a negligible amount (Fig 3A).27 To prevent humidity effects, the fully instrumented load cell was covered with silicon. After application of the nylon suture to the stifle at the points of suture attachment (Fig 3B), the 2 ends of the nylon suture loop were passed through the arms of the load cell, tightened and subsequently secured with 2 screws. This type of suture fixation had been shown to allow secure fixation without any evidence for slippage of the suture up to 180 N. The design of the load cell was such that pull of the 2 suture ends on the arms of the load cell resulted in a change in strain at the connecting element. This change in strain was recorded by the 2 strain gauges glued to both sides of the connecting element.

Figure 2 Lateral suture stabilization (LSS) techniques performed in 9 stifles using an 80 lb nylon leader line and a custom made crimp. (A) Traditional technique according to Flo (LSS1); (B) modification of LSS1 with 2 parallel drill holes at the tibial crest (LSS2); (C) distal attachment of the suture through 2 divergent drill tunnels at the Gerdy’s tubercle (LSS3); and (D) distal attachment at the Gerdy’s tubercle. Proximal attachment with a bone anchor placed into the caudolateral cortex of the lateral femoral condyle, at the level of the distal pole of the lateral fabella (LSS4).

Method 4 (LSS4; Fig 2D). The femoral anchorage site was a 3.5 mm bone anchor (Securos Europe) attached to the caudolateral cortex of the lateral femoral condyle, at the level of the distal pole of the lateral fabella.25 The exact point of anchor placement was based on palpation of the lateral fabella and the joint space between the fabella and the lateral condyle after dissection through the skin and fascia. Radiographic confirmation was not performed. After completion of all 12 measurements, anchor position was confirmed in all stifles by gross inspection. Distal point of attachment was the same as in LSS3, with 2 divergent bone tunnels in the Gerdy’s tubercle. Load Cell Measurement of tension within the nylon suture loop used to stabilize the stifles was performed using a custom load

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Figure 3 (A) Custom made load cell used to measure the tension within the suture loop (bar indicating 10 mm). At the same time the load cell was used for crimping the suture ends similar to commercially available crimps. To prevent humidity effects the fully instrumented load cell was covered with silicon (not shown). Both ends of the nylon suture were passed through the arms of the load cell and secured with 2 screws under a preload of 100 N (each end with 50 N). The pull exerted on the arms of the load cell though the nylon suture loop throughout a full range of motion was recorded by 2 strain gauges glued to both sides of the connecting element of the load cell. (B) Mounting of the load cell lateral onto the cadaveric stifle.

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The 2 strain gauges were arranged forming a Wheatstone half-bridge, which was completed by 2 precision resistors forming a full Wheatstone bridge circuit.27 The Wheatstone bridge was connected to a strain amplifier (ADS1232REF, Texas Instruments, Dallas, TX) which was connected to a computer. Data recording as well as configuration of the strain amplifier was done using software provided with the strain amplifier (ADS1232REF Evaluation System, Texas Instruments). Before the measurements, the strain gauges and signal conditioner were statically calibrated with different weights to correlate change in voltage with change in tension, establishing a linear relationship with a Pearson’s correlation coefficient of r = 0.986 (R2 = 0.973) over the force range of interest (5–140 N). The slope of this calibration line was used as a constant factor for the conversion of change in output volt-

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age, measured in millivolt (mV) to change in applied force/ pull at both arms of the load cell, expressed in N. Data Recording For the 4 LSS methods and 3 variations in joint angle, the suture was secured to the load cell while applying even tension of 50 N to both ends of the suture using 2 spring scales (Macro-Line Spring Scale, Pesola, Baar, Switzerland). Independent of the joint angle at which the suture was tightened, the stiﬂe was passively moved through 2 complete ranges of motion to allow for preconditioning of the reconstruction. Passive range of motion started at maximal extension (1601) moving to complete ﬂexion (401). After these 2 cycles of preconditioning, data recording was started and tension within the suture line was measured

Figure 4 Median change in tension within the suture over a full passive range of motion for 4 methods of lateral suture stabilization (LSS1–LSS4) and 3 joint angles at time of suture tightening (1301, 1001, 701), expressed in Newtons (N) with associated interquartile range. Values are normalized for the value measured at the angle at which the suture was tightened (1301, 1001, 701).

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continuously at a frequency of 80 Hz, moving the stifle from full extension to complete flexion at constant intervals of 301. For each of the resulting 5 joint angles (1601, 1301, 1001, 701, and 401) the stifle was held constant for 5 seconds, resulting in about 400 measurements per data point. After completing the measurements for 1 type of LSS at 1 of the 3 joint angles, the lateral suture was removed and the stifle reconstructed according to the randomized testing protocol. This was repeated 12 times until the 4 variations of LSS at the 3 different joint angles had been investigated. Data Analysis The continuously recorded measurements from the load cell for each of the measurement cycles were smoothed using a low-pass Butterworth filter and subsequently averaged calculating the mean voltage output at the 5 data points (1601, 1301, 1001, 701, 401) over a time period of 4 seconds each. Subsequently, the voltage output data were normalized to the value measured at the angle at which the suture was tightened (1301, 1001, 701). This transformed the data into change in voltage output in relation to the measurement when the suture was tied. Using the established linear relationship and calibration constant derived from the calibration of the load cell, the change in voltage output was finally transformed into Newtons (N). Descriptive statistics were performed with statistical software (SPPS 13.0 for Windows, SPSS Inc., Chicago, IL and confidence interval analysis [CIA], v.2.1.2, University of Southampton, Southampton, UK). All data were tested for normal distribution using the Kolmogorov–Smirnov

Test. As the assumption of normality was rejected, median and associated interquartile range (IQR) were calculated for each of the 5 data points pooling the data once for the 4 LSS methods and once for the 3 joint angles. Other variables derived from the data were peak-topeak load (PPL), maximal positive load (MPL), and maximal negative load (MNL). PPL was defined as the difference between MPL and MNL. The latter expresses loss of tension within the suture (negative values) when compared with the tension applied at time of suture tightening, whereas MPL indicates an increase in tension in addition to that applied at time of suture tightening. PPL, MPL, and MNL were expressed as median and associated IQR. Differences between methods and joint angles at the time of suture fixation for these 3 variables were determined from calculation of the 95% CI of the median difference (CI Diff), being considered significantly different if the CI Diff did not include 0.28

RESULTS Median change in tension within the lateral suture along a full range of motion of the stifle for the 4 LSS methods and 3 joint angles is shown in Fig. 4. Associated median values for PPL, MPL, and MNL are given in Figs 5, 6 and Tables 1, 2. Overall, the 4 methods resulted in a uniform tension pattern along a full ROM of the stifle, with the minimum change in tension at 1301, a slight increase in tension at full extension of the stifle and a high increase in tension at maximal flexion.

Figure 5 Median peak-to-peak load (PPL), maximal positive load (MPL) and maximal negative load (MNL) measured in the lateral suture loop pooled for 4 methods of lateral suture stabilization (LSS1–LSS4) expressed in Newtons (N) with associated interquartile range. Values are normalized for the value measured at the angle at which the suture was tightened (1301, 1001, 701).

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Figure 6 Median peak-to-peak load (PPL), maximal positive load (MPL) and maximal negative load (MNL) measured in the lateral suture loop pooled for the 3 joint angles at time of suture tightening (1301, 1001, 701), expressed in Newtons (N) with associated interquartile range. Values are normalized for the value measured at the angle at which the suture was tightened (1301, 1001, 701).

LSS2 appeared to result in the least change in tension among the 4 LSS methods (PPL 39.8 N; IQR: 34.9–52), whereas LSS4 consistently had the highest change in tension (PPL 85.6 N; IQR: 79.0–98.5). With a PPL of 69.3 N (IQR: 54.5–88.8) and 59.5 N (IQR: 47.8–69.7) for LSS1 and LSS3, respectively, these 2 methods scored in-between LSS2 and LSS4. Analysis of CI Diff among the 4 methods of LSS revealed that PPL was significantly different for each method, whereas MNL did not appear to be different among methods, in the range of 2.0 N (IQR: 14.8 to 0.6) for LSS4 to 12.0 N (IQR: 22.0 to 1.9) for LSS1. For MPL, LSS2 scored significantly better having the smallest increase in suture tension (34.7 N; IQR: 23.1–38.9), followed by LSS3 (53.0 N; IQR: 37.9–62.4) and LSS1 (54.9 N; IQR: 45.6–78.6), which were not significantly different from each other (95% CI Diff = 5.4, 19.9 N). LSS4 was associated with the highest increase in tension (79.1 N; IQR: 64.8–87.5), being significantly higher than the 3 other methods. Analyzing suture tension and joint angle at time of tightening of the lateral suture revealed that 1301 and 1001 resulted in significantly higher PPL and MPL, and less

MNL than when tightening the lateral suture at 701. Whether the suture was tightened at 1301 or 1001 made no signiﬁcant difference in PPL and MPL. However, MNL for 1301 was 1.1 N (IQR: 2.1 to 0.4), which was a signiﬁcantly smaller drop in tension than observed when tightening the suture at 1001 (95% CI Diff = 2.5, 7.7 N).

DISCUSSION Our results show that irrespective of the precise point of lateral suture attachment, substantial changes in suture tension occur during a full range of stifle motion. This change in tension increases significantly with joint flexion and may be 4 100 N, depending on the LSS technique. This finding is similar to a previous study on suture tension with different LSS technqiues.22 Our findings are in disagreement with the reported shortening in distance between the femoral and tibial attachment points on flexion of the stifle.20 That study used 2-dimensional radiographic measurements which likely contributed to this discrepancy. We also found that tightening the suture with the stifle in

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Table 1 Median and Associated Interquartile Range (IQR) of Peak-toPeak Load (PPL), Maximal Positive Load (MPL), and Maximal Negative Load (MNL) for the 4 Lateral Suture Stabilization (LSS) Methods (LSS1–LSS4), as well as the Comparison of the Methods to Each Other Using 95% Confidence Interval Analysis of the Median Difference (95% CI Diff) Median Difference in Change in Suture Tension (N; 95% CI Diff)

Median Change in Suture Tension (IQR) (N) PPL LSS 1 LSS 2 LSS 3 LSS 4 MPL LSS 1 LSS 2 LSS 3 LSS 4

69.3 (54.5–88.8) 39.8 (34.9–52.0) 59.5 (47.8–69.7) 85.6 (79.0–98.5) 54.9 (45.6–78.6) 34.7 (23.1–38.9) 53.0 (37.9–62.4) 79.1 (64.8–87.5)

MNL LSS 1

12.0 ( 22.0 to LSS 2 5.2 ( 13.4 to LSS 3 4.5 ( 10.3 to LSS 4 2.0 ( 14.8 to

LSS 1

LSS 2

/ /

29.1w (18.7, 39.7) /

24.2w (14.5,36.4) /

7.0 19.7w ( 5.4,19.9) ( 32.1, 7.1) 19.0w 44.9w ( 28.0, 7.8) ( 54.4, 33.9) / 26.8w ( 37.3, 14.3) / /

( /

2.1)

(

1.1)

3.8 11.4,0.7) 1.9 ( 5.8 to 1.9) 0.5 ( 3.9,2.7) /

Data expressed in Newtons (N). Any CI Diff excluding 0 indicates a significant difference between the two groups evaluated. w Significant difference based on the calculation of CI Diff. 95% CI Diff, 95% confidence interval of the mean difference.

701 flexion results in the most even tension pattern within the lateral suture loop, but stabilizing the stifle using LSS at flexed angle would probably allow persistent joint instability, as the suture loop tends to loosen at joint angles between 701 and 1601 (Fig 4). When interpreting tension within a lateral suture used to stabilize the CCL deficient stifle, 2 aspects should be considered. First, any disproportionate increase in suture tension would increase the risk of premature suture failure, or if the suture does not fail, stretching of the suture loop might occur. Secondly, very high tension within the suture will probably over-constrain the joint,29 whereas a substantial loss of tension within the suture will certainly result in some degree of joint instability.30 Recently, attaching the lateral suture at a point close to the laterally projected origin of the CCL has been claimed to improved suture isometry.20,22 For optimal tibial fixation, these studies sug-

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1301 PPL 1301 1001 701 MPL 1301 1001 701 MNL 1301

69.9 (54.0–88.0) 68.7 (49.4–82.7) 54.4 (38.0–68.1)

67.5 (52.5–87.2) 59.1 (40.5–77.0) 36.6 (25.6–50.4)

1.1 2.1 to 0.4) 1001 6.0 ( 11.3 to 1.6) 701 16.6 ( 23.3 to 12.1)

1001

( / /

3.3 8.3,15.7) / /

(

10.2 1.1, 23.3) /

/ /

4.8w (2.5,7.7) /

(

0.6)

Median Difference in Change in Suture Tension (N; 95% CI Diff)

Median Change in Suture Tension (IQR) (N)

LSS 4

12.9w 15.2w (2.7, 24.1) ( 26.6, 3.1) 17.3w 45.0w ( 25.1, 8.0) ( 53.2, 35.1) / 28.2w ( 37.9, 18.2) / /

4.6 11.4,0.2) 1.2 ( 5.2,2.1) /

1.9)

3.1 9.9, 2.1) /

LSS 3

Table 2. Median and Associated Interquartile Range (IQR) of Peak-toPeak Load (PPL), Maximal Positive Load (MPL), and Maximal Negative Load (MNL) in Respect to the 3 Joint Angles (1301, 1001, 701) at Time of Suture Tightening, as well as the Comparison of the 3 Joint Angles to Each Other Using 95% Confidence Interval Analysis of the Median Difference ( 95% CI Diff)

701 16.1w (4.2, 27.3) 12.1w (1.4, 23.1) /

31.3w (20.9, 42.3) 21.1w (10.8,31.6) /

15.7w (12.9, 19.7) 10.2w (5.5,14.4) /

Data expressed in Newtons (N).

Any CI Diff excluding 0 indicates a significant difference between the 2

groups evaluated. Significant difference based on the calculation of CI Diff. 95% CI Diff, 95% confidence interval of the mean difference. w

gest attaching the suture at a point just caudal or cranial to the digital extensor groove, at the most proximal aspect of the tibial plateau.20,22 However, using a bone anchor on the lateral condyle and a divergent drill tunnel at Gerdy’s tubercle, just cranial to the digital extensor groove (LSS4) resulted in the highest PPL and MPL among the 4 techniques we investigated. Passing the suture around the lateral fabella instead of using a bone anchor at the lateral femoral condyle might allow for some soft tissue movement, potentially reducing high strains within the suture, but relaxation of the fabellofemoral ligament might occur in the long term, resulting in loosening of the LSS and recurrent joint instability. Based on our in vitro data, LSS2 might be the preferred method when attempting to stabilize the stifle with a lateral suture, as this method consistently resulted in the least change in suture tension. Even though LSS2 is only a slight modification of the traditional technique popularized by Flo,7 omitting the lateral branch of the suture loop may improve isometry. None of the 4 methods we studied reached isometry in terms of maintaining a constant tension throughout passive stifle motion, potentially resulting in loss of suture tension at some joint angles with consequent joint instability. Whereas the tension within the

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suture reached its minimum at 1301 for all 4 methods, LSS1 permitted the largest decrease in suture tension; however this difference was not significant when compared with the other LSS techniques. There is little information about the precise joint angle at which the suture should be tightened. For any suture fixation that is not isometric, securing the loop at a joint angle when the lateral suture loop is longest will result in the least increase in suture load during range of motion, but may allow some joint laxity during range of motion of the stifle. If the suture is tied at a joint angle when the loop is shortest, tightening will occur during range of motion potentially over-constraining the stifle and promoting early suture break down. Surgical texts mostly recommend tightening the suture ‘‘at slight flexion of the joint’’ or ‘‘at normal standing angle.’’31,32 A survey of veterinary surgeons revealed that 67% positioned the stifle at 1401 when the suture was tied, full joint extension was preferred by 19%, and only 5% had the stifle at 901flexion.16 Although not investigated statistically because of low statistical power, visual interpretation of the load patterns during full range of motion for the 4 LSS methods and 3 joint angles at time of suture tightening (Fig 4) suggests that the effect of joint angle on tightening of the suture may be uniform among the 4 LSS. Analyzing the data for the 3 joint angles at time of suture tightening showed that with the stifle held at 701 flexion on tightening, PPL and MPL were significantly decreased, imposing less constraint to the joint on flexion. At the same time, MNL was significantly increased (largest decrease in suture tension) when compared with 1301 and 1001 joint angle, inducing some degree of joint instability on extension of the stifle. Even though the data did not yield a significant difference between 1001 and 1301, the CI Diffs for MPL and MNL suggest that a joint angle of 1001 might result in the best balance between MPL and MNL. Clinically, this might reduce MPL on joint flexion, potentially limiting stretch of the suture-knot construct and therefore early destabilization of the joint. At the same time an angle of 1001 would preserve most of the tension within the suture when extending the joint. Limitations Using stifles without any evidence of degenerative joint disease while moving the joint passively through a full range motion does not account for any effects of periarticular fibrosis commonly found in stifles with naturally occurring CCL rupture.4,33 The study design also does not consider muscular forces or differences in dog weight. However, reconstructing the stifle with the same material in the same way it would be done in the operating room might be considered a significant improvement in methodology, over previous studies, where neither the 3-dimensionality of the joint nor soft tissue elasticity have been considered.20,22 Measuring tension within the suture loop is not an alternative means of assessing the degree of anisometry. Change in tension within the suture loop is related to the length of the suture loop. An elongation of 1 mm will in-

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duce higher tension in a short suture than in a longer suture. Because suture length was not recorded for the different trials, normalization of suture load for this variable was not possible precluding comparison of the degree of anisometry between the 4 LSS techniques. We concluded that in vitro, altering suture attachment points when performing LSS changes the pattern of tension within the suture throughout a full range of stifle motion. However, regardless of LSS technique, a significant increase in suture tension occurs on flexion of the joint increasing the risk of suture breakage and irreversible stretch. This unwanted peak in tension on flexion of the joint might be reduced when tightening the lateral suture at either 1001 or 701 joint angle. But 701 joint angle at time of suture tightening will probably lead to insufficient stabilization of the stifle on extension and therefore cannot be recommended.

REFERENCES 1. Johnson JA, Austin C, Breur GJ: Incidence of canine appendicular musculoskeletal disorders in 16 veterinary teaching hospitals from 1980 through 1989. Vet Comp Orthop Traumatol 1994;7:56–69 2. Arnoczky SP, Marshall JL: The cruciate ligaments of the canine stifle: an anatomical and functional analysis. Am J Vet Res 1977;38:1807–1814 3. Innes JF, Bacon D, Lynch C, et al: Long-term outcome of surgery for dogs with cranial cruciate ligament deficiency. Vet Rec 2000;147:325–328 4. Marshall JL, Olsson SE: Instability of the knee. A long-term experimental study in dogs. J Bone Joint Surg Am 1971;53: 1561–1570 5. Paatsama S: Ligament injuries of the canine stifle joint: A clinical and experimental study. Doctoral Thesis, Helsinki University, Helsinki, 1952 6. Arnoczky SP, Tarvin GB, Marshall JL, et al: The over-thetop procedure: a technique for anterior cruciate ligament substitution in the dog. J Am Anim Hosp Assoc 1979;15:283–290 7. Flo GL: Modification of the lateral retinacular imbrication technique for stabilizing cruciate ligament injuries. J Am Vet Med Assoc 1975;11:570–576 8. DeAngelis M, Lau RE: A lateral retinacular imbrication technique for the surgical correction of anterior cruciate ligament rupture in the dog. J Am Vet Med Assoc 1970;157: 79–84 9. Smith GK, Torg JS: Fibular head transposition for repair of cruciate-deficient stifle in the dog. J Am Vet Med Assoc 1985; 187:375–383 10. 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 1984;184: 564–569 11. Montavon PM, Damur DM, Tepic S: Advancement of the tibial tuberosity for the treatment of cranial cruciate deficient canine stifle. ESVOT – VOS 1st World Orthopaedic Veterinary Congress, Munich, Germany, p 152

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