Management of concurrent patellar luxation and cranial cruciate ligament rupture using modified tibi by Salah EL MOUSTAGHFIR

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PAPER

Management of concurrent patellar luxation and cranial cruciate ligament rupture using modified tibial plateau levelling OBJECTIVES: To evaluate a novel surgery aimed at managing concurrent medial patellar luxation (MPL) and cranial cruciate ligament (CCL) ruptures in dogs weighing more than 30 kg. METHODS: Tibial plateau levelling osteotomy (TPLO) and femoral trochleopasty were performed. The principal tibial fragment was laterally translated by 3 to 6 mm and was externally and abaxially rotated to create a wedge measuring 1·5 to 2·5 mm at the medial and cranial aspect and 1 to 3 mm at the medial and distal aspect of the tibial plateau fragment. The fragments were stabilised with a narrow TPLO plate. RESULTS: Thirteen surgeries were performed in 12 dogs with a mean weight of 39·8 kg. The mean postoperative tibial plateau slope was 8·1°. Additional surgery was required in two cases, one due to failure of fixation and another due to screw breakage. The mean lameness score was 3·5 (out of 5) before surgery, 0·7 after 8 to 12 weeks, and 0·3 at final follow-up. Median follow-up was 1115 days (range, 270 to 2040 days). No patella luxated after surgery. CLINICAL SIGNIFICANCE: MPL and CCL ruptures may be successfully managed by performing a TPLO and simultaneously altering the relationship of the principal and tibial plateau fragments during surgery. ANKE LANGENBACH AND DENIS J. MARCELLINLITTLE* Journal of Small Animal Practice (2010) 51, 97–103 DOI: 10.1111/j.1748-5827.2009.00854.x Accepted: 1 September 2009; Published online: 11 January 2010

Veterinary Surgical Center, Vienna, VA 22180, USA *Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA Presented in part at the ACVS Symposium, Chicago, IL (October 2007) and the ECVS Annual Scientific meeting, Basel, Switzerland (July 2008).

INTRODUCTION Cranial cruciate ligament (CCL) ruptures and medial patellar luxations (MPL) are common causes of hind limb lameness in dogs and may occur concurrently (DeAngelis and Hohn 1970, Hayes and others 1994, Aragon and Budsberg 2005, Powers and others 2005). MPL is considered a predisposing factor for CCL rupture (Willauer and Vasseur 1987). MPL is primarily found in small and toy breeds (dogs weighing <20 kg) but large breeds (weighing >20 kg) represent 9% to 35% of all MPL patients (Prister 1972, Remedios and others 1992, Johnson and others 2002, Arthurs

and Langley-Hobbs 2006). Surgical management options for dogs with clinical MPL disease include soft tissue procedures, including lateral imbrication of the fascia lata, stifle joint derotational sutures, cranial sartorius muscle release and hard tissue procedures, such as wedge or block trochleoplasty, and tibial crest transposition (Roy and others 1992, Johnson and others 2001, Johnson and others 2002, Arthurs and Langley-Hobbs, 2006). Several of these procedures are routinely combined to address MPL in dogs. Trochleoplasty and tibial crest transposition have been recommended in large breed dogs to reduce the likelihood of recurrence of MPL (Gibbons and others 2006). However, complication rates of 18% to 29% have been reported in large breed dogs (Arthurs and LangleyHobbs 2006, Gibbons and others 2006). Osteotomies of the femur or tibia have been advocated to manage angular and rotational deformities of the femur and tibia, including varus deformities of the femur and internal rotation of the tibia (Swiderski and Palmer 2007, Roch and Gemmill 2008). CCL ruptures occur in dogs of all sizes. They are managed with intracapsular or extracapsular stabilization techniques. Surgical alterations of the tibial plateau, such as tibial plateau levelling osteotomy (TPLO), are now popular when addressing CCL ruptures in large and giant dog breeds (Slocum and Slocum 1993, Kim and others 2008). When MPL and CCL ruptures occur concurrently, both conditions must be addressed to regain normal stifle joint function. This may be achieved using staged surgical procedures (that is, TPLO followed by MPL management several weeks later) or by combining several surgical procedures in a single event. During the TPLO procedure, the curved cut of the tibial plateau preserves the tibial crest. If a tibial crest transposition is required, an additional osteotomy is necessary which requires additional fixation and may decrease 97

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the stability of the proximal portion of the tibia and lead to tibial crest avulsion (Priddy and others 2003, Kergosien and others 2004). To reduce patient morbidity and accelerate postoperative recuperation, it would be advantageous to combine the management of MPL and CCL ruptures without increasing the invasiveness of the surgical procedure. We proposed that we could manage CCL ruptures and MPL by displacing the osteotomised tibial plateau in relation to the principal tibial fragment during TPLO, mimicking a tibial crest transposition and realigning the quadriceps mechanism. The purpose of this study was to prospectively evaluate the combined MPL and CCL stabilisation in large breed dogs.

MATERIAL AND METHODS Dogs were included in this study if they were presented for hind leg lameness, had cranial cruciate ligament ruptures and MPL, weighed more than 30 kg, and were seen at the Veterinary Surgical Center in Vienna, Virginia (USA) between January 2001 and December 2006. Twenty-five dogs undergoing TPLO in our hospital were randomly selected as case controls to compare the age of patients at the time of surgery in both groups. Clinical evaluation All dogs had a physical, orthopaedic, and radiographic evaluation. Preoperative complete blood count and chemistry were performed on all dogs. Lameness was graded subjectively as described by Impellizeri (2000). A numerical rating scale (NRS) with 5 levels of lameness severity was utilized per the following: 0 = no detectable lameness at a walk or trot, no detectable lateral weight shift at a stance; 1 = no detectable lameness at a walk or trot and minor lateral weight shift at a stance; 2 = lameness at a walk or trot without hip hike; 3 = lameness at a walk or trot with hip hike; 4 = non-weight bearing at a trot; 5 = non-weight bearing at stance or walk. MPL was graded by Putman’s grading system with grades 1 to 4 (Singleton 1969). Written consent was obtained from all clients. 98

Radiographic evaluation Mediolateral stifle radiographs were produced with the stifle and hock held at 90° allowing for both joints in the radiographic projection. The radiographic beam was centred on the stifle. A craniocaudal projection was produced also, including hock and stifle in the exposure. The beam was centred on the stifle. Preoperative radiographs were produced immediately before surgery, postoperative radiographs immediately following. These radiographs were produced with the patients anaesthetised. Radiographs were produced in the same manner at four and eight weeks post surgery and at other reevaluations, but under sedation. The tibial plateau slope (TPS) was measured on preoperative and postoperative radiographs using the method proposed by Slocum (Baroni and others 2003). The orientation of the femoral trochlea in relation to the distal portion of the femoral shaft as seen on craniocaudal radiographs was measured. Surgery Inhalation anaesthesia was performed after endotracheal intubation using isoflurane as an anaesthetic agent. Epidural analgesia was administered preoperatively in four patients at L7/S1 using a combination of bupivicaine (Marcaine (5 mg/ml), Hospira, Inc., Lake Forest, IL) (1 ml/4·5 kg) and morphine (Morphine Sulfate (15 mg/ml), Baxter Healthcare Corporation, Deerfield, IL) (0·11 mg/kg) delivered through a 0·9-mm diameter, 6-cm long diamond point spinal needle. The remaining nine procedures the patients received a 3-ml intra-articular injection of bupivicaine (5 mg/ml) with epinephrine (Marcaine with epinephrine (5 mg/ml and 0·0091 mg/ml), Hospira, Inc., Lake Forest, IL) (0·0091 mg/ml). All patients received an intravenous dose of cefazolin (Cefazolin (reconstituted to 100 mg/ml), Watson Laboratories, Inc., Corona, CA) (22 mg/kg IV) that was repeated at 90minute intervals when necessary. The durations of surgery and anaesthesia were recorded. A craniomedial approach to the stifle was performed, followed by complete stifle joint exploratory arthrotomy. A ruptured CCL and MPL were confirmed in all cases

and remnants of the CCL were removed. In cases where a meniscal tear was present the torn portions were removed, while in cases where the meniscus was intact a meniscal release was performed. A wedge resection trochleoplasty and a cranial sartorius muscle release were performed. The TPLO procedure followed (Slocum and Slocum 1993). The jig was removed after completion of the curved cut. The surgeon and an assistant levelled the tibial plateau to the desired level and aligned the quadriceps mechanism by performing three alignment alterations beyond plateau levelling. With the patella reduced and facing cranially, the principal tibial fragment was externally rotated along its long axis until torsion between the patella and the tibial tubercle was eliminated (first alteration). This created a 1·5- to 2·5-mm gap between the medial and cranial aspect of the osteotomised tibial plateau fragment and the tibial crest on the principal tibial fragment (Fig 1). Gaps were measured intraoperatively using a sterile ruler. The bow-legged appearance (genu varum) was addressed by aligning the femoral shaft, patella, tibial tubercle, tibial shaft and hock. This was done by laterally translating the tibial crest in relation to the osteotomised tibial plateau fragment by 3 to 6 mm (second alteration) and by abaxially rotating the distal portion of the tibia to create a 1- to 3-mm wide gap between the medial and distal aspect of the osteotomised tibial plateau fragment and the principal tibial fragment (third alteration). There was no gap between the cranial or distal aspect of the osteotomised tibial plateau fragment and the principal tibia fragment on the lateral aspect of the tibia. The displacement of the principal tibial fragment in relation to the tibial plateau fragment resulted in a lateral transposition of the tibial crest (Fig 2) and realigned the mechanical axis of the pelvic limb. A stainless steel bar was used to confirm the alignment of the femur and tibia. The tibial plateau was secured with a 1·55-mm-diameter Kirschner wire passed from the proximo-lateral tibial crest to the caudal central tibial plateau. The patella was checked for stability. Plate contouring for this procedure differed from typical TPLO procedures. Bending irons were used to create an approximately 30° angle between the third and fourth screws and

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tablet), Novartis Animal Health US, Inc., Greensboro, NC) (1 to 2 mg/kg PO q 24 hours), two patients were administered tramadol hydrochloride (Tramadol Hydrochloride (50 mg tablet), Caraco Pharmaceutical Laboratories, Ltd., Detroit, MI) (2 mg/kg PO q 12 hours) in addition to deracoxib, and two separate patients were administered Acepromazine Maleate (25 mg tablet, Boehringer Ingelheim Vetmedica, Inc., St. Joseph, MO) (1 to 2 mg/kg PO q 12 hours) for sedation. Patients were discharged to owners the day after surgery.

FIG 1. Front view of the stifle joint of a dog with MPL and CCL rupture before (A) and after realignment (B). Genu varum is initially present. The tibial plateau fragment is tilted forward to decrease the TPS (arrow). The alignment of the quadriceps is improved by rotating the principal tibial fragment externally (in relation to the osteotomised tibial plateau fragment), by laterally translating the principal tibial fragment and by displacing its distal portion abaxially (arrow). This displacement creates an open wedge on the medial aspect of the tibia between the cranial aspect of the osteotomised tibial plateau and the tibial crest and between the distal aspect of the osteotomised tibial plateau and the tibial shaft

medially twisting the cranial aspect of the proximal portion of the plate (Fig 3). The contoured TPLO plate was applied and secured with six screws: three distal cortical and three proximal cancellous screws. The Kirschner wire was removed. The stifle was checked for patella stability, quadriceps alignment and absence of cranial tibial thrust. The area was lavaged followed by a multi-layer closure using monofilament absorbable (PDS, Ethicon, Inc., Somerville, NJ) and non-absorbable (Ethilon, Ethicon, Inc., Somerville, NJ) sutures. The stifle joint was iced following surgery and then bandaged with a modified Robert Jones bandage. The bandage was removed the following morning and the stifle was iced again. Analgesia was provided in eight patients with morphine (0·44 mg/kg) combined with acepromazine (Acepromazine Maleate (10 mg/ml),

IVX Animal Health, Inc., St. Joseph, MO) (0·02 mg/kg) given ½ intramuscularly and ½ intravenously and in four, a constant rate infusion of morphine (3 ml/kg/hour IV for 8 hours) was administered. The CRIs were reduced sequentially by 50% at each of 8, 12 and 16 hours. Oral antibiotics and analgesics were provided the morning following surgery. Nine patients were administered cephalexin (Cephalexin (250 mg and 500 mg capsules), Ranbaxy Pharmaceuticals, Inc., Jacksonville, FL) (22 mg/kg PO q 12 hours) and four patients were administered cefpodoxime proxetil (Simplicef (200 mg tablet), Pharmacia & Upjohn Company division of Pfizer, Inc., New York, NY) (5 mg/kg PO q 24 hours) for a seven-day antibiotic course. Ten patients were administered the non-steroidal anti-inflammatory drug (NSAID) deracoxib (Deramaxx (100 mg

Follow-up evaluation Patients’ follow-up included a 7- to 10-day reevaluation and suture removal, 4- and 8- to 12-week reevaluation with radiography of the stifle. An additional reevaluation with radiographs was performed in 12 of 13 patients more than six months after surgery and a phone interview was conducted with the owner and referring veterinarian of the remaining patient. Outcome was considered excellent if no lameness was present, good if grade 1 or 2, fair if grade 3 and poor if grade 4 or 5 lameness was present at final reevaluation.

RESULTS Twelve consecutive client-owned dogs: three Labrador retrievers, three Labrador retriever mixed, two golden retrievers, two greater Swiss mountain dogs, one Dalmatian and one husky mixed were included in this study. One dog was operated bilaterally with staged procedures. These procedures were considered as independent procedures in this report. The mean age at surgery was 3·6 years (median age, 2 years; range, 1 to 10 years). By comparison, the mean age of control dogs undergoing TPLO in our hospital was 5·5 years. There were nine male neutered dogs and three female spayed dogs in the study. The mean weight was 39·8 kg (range, 30·3 to 49 kg). The mean preoperative lameness grade was 3·5 out of 5 (range, 2 to 5). The mean preoperative TPS was 26° (range, 20 to 34°). The mean orientation of the femoral trochlea in relation to the distal portion of the femoral shaft was 9° of varus (range, 5 to 12° of varus). 99

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FIG 2. Craniocaudal radiograph of the stifle joint of a 1·5-year-old neutered male Labrador Retriever with a grade 3 MPL and CCL injury before (A) and immediately after simultaneous management of the stifle joint instability and patellar luxation (B) using a modified tibial plateau levelling procedure. The patella is luxated and the tibial crest is on the medial aspect of the tibia on the preoperative radiograph. The patella is reduced and the tibial crest is centred on the postoperative radiograph

MPL was present in all dogs with six grade 2 and seven grade 3 MPL. All stifles had complete CCL ruptures as determined by physical examination and confirmed during stifle surgery. One surgeon (AL) performed all surgeries. The mean (±sd) durations of surgery and anaesthesia were 69 ± 17 minutes and 122 ± 34 minutes, respectively. All dogs received a single narrow 3·5 mm plate from one of three sources: nine Slocum plates (3·5 mm TPLO plate 224TL3.5-R/L or 225TL3.5-R/L, Slocum Enterprises, Eugene, OR), three Veterinary Orthopedic Implants plates (3·5 mm TPLO plate, Veterinary Orthopedic Implants, South Burlington, VT), and one Securos plate (3·5 mm TPLO plate 9107401010R or 91077401011L, Securos, Fiskdale, MA) were used. The mean postoperative TPS was 8·1° (range, 2 to 14°). The median time to follow-up was 1115 days (range, 270 to 2040 days). The mean TPS at the time of reevaluation was 9·8° (range, 2 to 15°). Although all dogs had bilateral stifle disease, 11 dogs had MPL/TPLO surgery 100

on one stifle but one dog had MPL/TPLO surgery on both stifles, nine months apart. Eight dogs had only MPL on the contralateral leg. Five of these eight patients had standard MPL surgery on the opposite leg. Three had no surgery on the opposite leg, despite existing MPL during the study period. Three dogs had CCL on the other side and two received a TPLO surgery and one a standard extracapsular repair. Eleven of 12 dogs were alive at the end of the study period. The mean postoperative lameness score was 0·7 out of 5 (range, 0 to 2) 8 to 12 weeks after surgery and was 0·3 out of 5 (range, 0 to 2) at long-term reevaluation. There was no recurrence of MPL. One dog weighing 49 kg fell down a flight of stairs chasing a cat two weeks after surgery. He broke all proximal screws, fractured his fibular head and reluxated his patella. A second procedure with stabilisation of the tibial plateau using a TPLO plate and bilateral external fixation device was necessary. He developed a postoperative wound infection that was treated with enrofloxacin (136 mg Enrofloxacin tablets,

FIG 3. Artist rendering based on left plates used to perform a standard TPLO procedure (A) and for the combined management of patellar luxation and CCL rupture described in this report (B). The plate used for conventional TPLO is contoured to the surface of the medial aspect of the proximal portion of the tibia, forming approximately a 20° angle. The plate used to stabilize the tibia of the dogs in this study has an increased concavity in its proximal portion, forming approximately a 30° angle. The cranial aspect of its proximal portion is medially twisted

Bayer HealthCare LLC, Shawnee Mission, KS) (5 mg/kg PO q 12 hours) and amoxicillin trihydrate/clavulanate postassium (Clavamox (375 mg tablet), GlaxoSmithKline, Research Triangle Park, NC) (12·5 mg/kg PO q 12 hours), as well as septic arthritis that was treated with amikacin (Amikacin sulfate (50 mg/ml), Phoenix Pharmaceutical, Inc., St. Joseph, MO) (10 mg/kg IV q 24 hours), ampicillin (Ampicillin (reconstituted to 250 mg/ml), American Pharmaceutical Partners, East Schaumburg, IL) (10 mg/kg IVq 8 hours) and ceftriaxone (Ceftriaxone sodium (reconstituted to 350 mg/ml), Roche Laboratories, Inc., Nutley, NJ) (25 mg/kg IM q 24 hours). He recovered and improved his grade 5 lameness to grade 3 at eight weeks and grade 2 at three months post surgery. The external fixator was removed 56 days later and plate and screws were removed at 251 days post the initial TPLO with MPL surgery. He was reevaluated for a right forelimb lameness and elbow pain at

Modified tibial plateau levelling

suture removal, 261 days post surgery. No pelvic limb lameness was present at that time. He was euthanatised 605 days post surgery after acute onset tetraparesis, neck pain, and anorexia. Another dog had plate and screws removed at day 293 because of a mild pain response to palpation. All but a portion of the broken most proximal screw were removed. That screw fragment was removed 591 days after surgery because of potential interference with the lateral collateral ligament. Two patients had incisional complications and healing occurred uneventfully.

DISCUSSION Our results show that MPL and CCL rupture correction using a modified TPLO procedure and trochlear wedge resection may be performed successfully in large dogs with grade 2 or grade 3 MPL. The outcome assessment methods in this study were limited to joint palpation and visual assessment of lameness. Lameness was addressed with a subjective numerical scale. The use of a force plate would have increased the objectivity of our outcome assessments (Waxman and others 2008), but was unavailable in our practice. Subjectively, this procedure is not more technically challenging than either procedure alone and may be performed without major technical difficulty. This procedure appears technically simpler than the combination of a TPLO with a transposition of the tibial crest and it does not require two osteotomies and the creation of a small crest fragment that could avulse in the postoperative period. The procedure requires simultaneous alignment of the quadriceps mechanism and rotation of the tibial plateau. This is achieved by moving the principal tibial fragment laterally and abaxially while rotating it externally. The successful realignment of the tibia leaves an open wedge, medially. As a consequence, the plate used to stabilise the proximal portion of the tibia is used in buttress fashion. The specific mechanical consequences of this form of fixation have not been assessed experimentally. Buttress fixation of bone fragments is less stable than fragment apposition using

interfragmentary compression (Hulse and Hyman 1991, Prayson and others 2001, Marcellin-Little and others 2008). Few reports have compared the complication rate after fixation of bone fragments with buttress or compressive fixation. In one randomised study of unstable trochanteric fractures in 233 people, failure of fixation occurred after 9% of buttress fixations and after 19% of compressive fixations (Buciuto and others 1998). The acute failure of fixation and screw breakage seen in the two cases in this report may have resulted from the fact that buttress fixation was used. However, the low incidence of mechanical failures for the patients and the absence of tibial plateau fragment “roll back” in this report suggest that the stability of buttress fixation is acceptable. Even though all patients in this report received a single narrow plate, a broad plate or second plate could be added to the fixation to lower the likelihood of mechanical failure. Three different narrow plates were used in this report. The first nine cases received original TPLO plates (3·5 mm TPLO plate 224TL3.5-R/L or 225TL3.5-R/L, Slocum Enterprises, Eugene, Oregon). Because of concerns regarding the material properties of these plates (Boudrieau and others 2006), plates from two other manufacturers were used in four cases. While we felt that the overall alignment of the operated limb was improved in all cases, we did not objectively evaluate the impact of the surgical procedure on the shape of the pelvic limb when dogs were standing or using goniometry, radiography or computed tomography. Such assessments would be necessary to assess the impact of this procedure on the mechanical axis of the pelvic limb. Mean postoperative TPS (8°) was slightly larger that the proposed TPS of 5° (Slocum and Slocum 1993). One patient in this report was undercorrected (14°) because of the perceived difficulties and risk of fibular fracture during correction. This patient was free of lameness at reevaluation. In vitro studies demonstrate that cranial tibial thrust is neutralised at 6·5° (Warzee and others 2001, Reif and others 2002). In one report, good outcomes after TPLO were present in dogs with postoperative TPS ranging from 0 to 14° (Robinson and others 2006).

All dogs in this study had mild to moderate varus angulation of their femoral trochlea in relation to the femoral shaft (genu varum), as seen on their craniocaudal radiographs and from their bow-legged stance. Because the mean (±sd) femoral varus angulation of the dogs in this report (9 ± 2°) was similar to the angulation measured in nine mixed breed dogs free of orthopaedic problems in a previous report (9 ± 2°)(Dudley and others 2006), it is not possible to ascertain whether the dogs in this report had true deformities of the distal portion of the femur and whether these potential femoral deformities impacted the development of patellar luxations and CCL ruptures. None of the dogs managed during the study period had grade 4 MPL. While the surgical procedure described in this report could possibly be performed in dogs with grade 4 MPL, the presence of more severe angular and rotational femoral and tibial deformities may require additional corrective procedures, such as a distal femoral osteotomy (Swiderski and Palmer 2007, Roch and Gemmill 2008). The patients in this report had a mean age of 3·6 years. They represented approximately 3% of TPLO patients in our hospital. They were in average two years younger than the control dogs undergoing TPLO. They were also younger than dogs undergoing TPLO in other reports, who had a mean age of 4·7, 5·0 and 6·2 years (Pacchiana and others 2003, Priddy and others 2003, Stauffer and others 2006). The younger age of the dogs in our report may be due to the fact MPL is a developmental condition likely to affect young patients and, if MPL predisposes dogs to CCL rupture, then such rupture is more likely to occur in a younger population of dogs than that suffering from CCL rupture alone. The 12 patients in this report had bilateral stifle disease. Eight patients (67%) had bilateral MPL. The reported rate of bilateral MPL is approximately 50% (Alam and others 2007). Our rate was higher, possibly because of the long-term prospective nature of this study. Four patients (33%) had bilateral CCL rupture. This is in agreement with the reported rate of bilateral CCL rupture (Doverspike and others 1993). A jig is used to prevent malalignment in normal hind legs during TPLO procedure 101

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(Slocum and Slocum 1993). It also acts as a guide during TPLO performed on dogs with CCL rupture and internal torsion of the tibia, varus or valgus tibial deformities. In our study, we felt that complete quadriceps alignment was not possible with the jig in place and we decided to perform the correction without the jig. While the absence of a jig could lead to iatrogenic axial or rotational malalignment, the very focus of this procedure was on realigning the tibia. We felt that the good long-term clinical outcome supported our realignment method. Using preoperative CT planning or intraoperative fluoroscopic image intensification could increase the precision of this tibial realignment method. TPLO performed without a jig did not appear to lead to axial or rotational malalignment in two recent reports (Bell and Ness 2007, Schmerbach and others 2007). The reported complication rate of TPLO has ranged from 19% to 28% (Pacchiana and others 2003, Priddy and others 2003, Stauffer and others 2006). The reported complication rate after MPL surgery in large breed dogs has been reported to be 29%, with 10% of patients having major complications such as patellar reluxation or implant failure (Gibbons and others 2006). The heaviest dog in our study had implant failure and patellar reluxation due to a traumatic event. This complication occurred during a fall that resulted in fibular fracture, fracture of the top three screws and reluxation of the patella. An additional surgical procedure was required to stabilise the stifle. The patient recovered and improved to a grade 2 lameness, three months after surgery. Proper client compliance with confinement is important after surgery. The use of a broad plate or the addition of a second plate could lower the likelihood of such mechanical failure in patients placing large loads on their operated legs in the early postoperative period. We now use broad plates on patients weighing more than 41 kg with tibiae that can accommodate the larger plate. One patient was referred for poor progress after extracapsular stabilisation of a CCL-deficient stifle joint. This patient also had an MPL. While MPL was not diagnosed in that patient before the origi102

nal surgery, it is likely that the MPL was developmental and did not result from the extracapsular stabilisation because of the distal portion of the femur had a varus angulation and because the wound closure of the fascia lata was intact when evaluated during the second surgery. It is possible, however, that MPL was secondary to the CCL stabilisation in that dog. MPL has been reported to result from CCL stabilisation (Arthurs and Langley-Hobbs 2007). In that report including 32 patients, MPL after CCL stabilisation was considered challenging and a variety of management methods were used. The reluxation rates ranged from 35% to 100% and were lower with tibial crest transposition, sulcoplasty and tibial realignment. The overall success rate was 79%. We cannot conclude whether the procedure evaluated in this report would be appropriate to manage patients with failed CCL stabilisation and MPL. We conclude from this report that MPL and CCL ruptures may be simultaneously managed in large dogs by externally rotating, by laterally translating and by abaxially displacing the principal portion of the tibia during the TPLO procedure. The geometric and mechanical features of this corrective surgery could be optimised using in vitro experiments. References ALAM, M. R., LEE, J. I., KANG, H. S., KIM, I. S., PARK, S. Y., LEE, K. C. & KIM, N. S. (2007) Frequency and distribution of patellar luxation in dogs. 134 cases (2000 to 2005). Veterinary and Comparative Orthopaedics and Traumatology 20, 59-64 ARAGON, C. L. & BUDSBERG, S. C. (2005) Applications of evidence-based medicine: cranial cruciate ligament injury repair in the dog. Veterinary Surgery 34, 93-98 ARTHURS, G. I. & LANGLEY-HOBBS, S. J. (2006) Complications associated with corrective surgery for patellar luxation in 109 dogs. Veterinary Surgery 35, 559-566 ARTHURS, G. I. & LANGLEY-HOBBS, S. J. (2007) Patellar luxation as a complication of surgical intervention for the management of cranial cruciate ligament rupture in dogs. A retrospective study of 32 cases. Veterinary and Comparative Orthopaedics and Traumatology 20, 204-210 BARONI, E., MATTHIAS, R. R., MARCELLIN-LITTLE, D. J., VEZZONI, A. & STEBBINS, M. E. (2003) Comparison of radiographic assessments of the tibial plateau slope in dogs. American Journal of Veterinary Research 64, 586-589 BELL, J. C. & NESS, M. G. (2007) Does use of a jig influence the precision of tibial plateau leveling osteotomy surgery? Veterinary Surgery 36, 228-233 BOUDRIEAU, R. J., MCCARTHY, R. J., SPRECHER, C. M., KUNZLER, T. P., KEATING, J. H. & MILZ, S. (2006) Material properties of and tissue reaction to the Slocum TPLO plate. American Journal of Veterinary Research 67, 1258-1265

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Modified tibial plateau levelling

PRISTER, W. A. (1972) Sex, size, and breed as risk factors in canine patellar luxation. Journal of the American Veterinary Medical Association 160, 740-742 REIF, U., HULSE, D. A. & HAUPTMAN, J. G. (2002) Effect of tibial plateau leveling on stability of the canine cranial cruciate-deficient stifle joint: an in vitro study. Veterinary Surgery 31, 147-154 REMEDIOS, A. M., BASHER, A. W., RUNYON, C. L. & FRIES, C. L. (1992) Medial patellar luxation in 16 large dogs. A retrospective study. Veterinary Surgery 21, 5-9 ROBINSON, D. A., MASON, D. R., EVANS, R. & CONZEMIUS, M. G. (2006) The effect of tibial plateau angle on ground reaction forces 4–17 months after tibial plateau leveling osteotomy in Labrador Retrievers. Veterinary Surgery 35, 294-299 ROCH, S. P. & GEMMILL, T. J. (2008) Treatment of medial patellar luxation by femoral closing wedge ostectomy using a distal femoral plate in four dogs. Journal of Small Animal Practice 49, 152-158

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(2001–2003). Journal of the American Animal Hospital Association 42, 44-50 SWIDERSKI, J. K. & PALMER, R. H. (2007) Long-term outcome of distal femoral osteotomy for treatment of combined distal femoral varus and medial patellar luxation: 12 cases (1999–2004). Journal of the American Veterinary Medical Association 231, 1070-1075 WARZEE, C. C., DEJARDIN, L. M., ARNOCZKY, S. P. & PERRY, R. L. (2001) Effect of tibial plateau leveling on cranial and caudal tibial thrusts in canine cranial cruciate-deficient stifles: an in vitro experimental study. Veterinary Surgery 30, 278-286 WAXMAN, A. S., ROBINSON, D. A., EVANS, R. B., HULSE, D. A., INNES, J. F. & CONZEMIUS, M. G. (2008) Relationship between objective and subjective assessment of limb function in normal dogs with an experimentally induced lameness. Veterinary Surgery 37, 241-246 WILLAUER, C. C. & VASSEUR, P. B. (1987) Clinical results of surgical correction of medial luxation of the patella in dogs. Veterinary Surgery 16, 31-36

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