Tibial Plateau Leveling Osteotomy and Cranial Closing Wedge Ostectomy in a Cat With Cranial Cruciate Ligament Rupture

Introduction

Treatment of cranial cruciate ligament (CCL) rupture in the cat has been previously described and includes conservative nonsurgical management and various extracapsular stabilization techniques.^1,2 The cat in this report had a complete CCL rupture with concurrent deformity of the proximal tibia. The cause of the tibial deformity was unknown but was presumed to be secondary to trauma to the caudal aspect of the proximal tibial growth plate. This deformity resulted in an exaggerated tibial plateau angle, which may have predisposed the cat to CCL rupture.³ This report describes the combination of tibial plateau leveling osteotomy (TPLO) and cranial closing wedge ostectomy for treatment of CCL rupture associated with a tibial deformity. To the authors’ knowledge, the combination of these surgical techniques for the treatment of CCL rupture in the cat has not been described.

Case Report

A 5-year-old, spayed female, domestic shorthair cat developed an acute, nonweight-bearing lameness in the left pelvic limb. The cat was housed exclusively indoors, and the owner was not aware of recent or past trauma to the limb; however, a mild, intermittent lameness had been noted for approximately 1 year. Other features of the medical history were unremarkable. Initial orthopedic and radiographic evaluation by the referring veterinarian revealed a probable CCL rupture and undefined abnormalities of the proximal tibia.

At presentation, the cat was nonweight bearing on the left pelvic limb. Orthopedic examination revealed a complete left CCL rupture, cranial subluxation of the proximal tibia with cranial stress, and a grade 1/4 medial patellar luxation.⁴ Range of motion of the left stifle was limited, with only 160° of extension possible. Flexion range of motion in the stifle was normal. A grade 1/4 medial patellar luxation was also present in the right stifle with no associated lameness. The rest of the physical examination was normal.

Radiographs of the affected limb were obtained with the cat anesthetized; they revealed moderate effusion of the stifle joint, cranial displacement of the proximal tibia, and malformation of the proximal tibial metaphysis [Figure 1]. The tibial plateau angle was measured for the limb as previously described.⁵ The tibial plateau angle of the affected stifle measured approximately 75°. Information regarding tibial plateau angle in normal cats is limited, so radiographs of the contralateral stifle were obtained to document the tibial plateau angle of the unaffected limb, which measured 28° [Figure 2].

The operative goal was to reduce the existing tibial plateau angle by approximately 55° to obtain a postoperative tibial plateau angle of 20°. To obtain the desired reduction in tibial plateau angle, a combination of TPLO and cranial closing wedge ostectomy was planned [Figure 3]. Based on standardized TPLO rotation chart criteria, creating a curved osteotomy with a 12-mm bi-radial saw blade and rotating the tibial plateau caudally 5 mm would reduce the existing tibial plateau angle by approximately 25°. Additionally, the creation of a 10-mm cranial wedge at the area of greatest curvature on the cranial proximal tibia would further reduce the tibial plateau angle by approximately 30°.

Hydromorphone^a (0.1 mg/kg) and atropine^b (0.04 mg/kg) were administered subcutaneously as preanesthetic medications. General anesthesia was induced with intravenous diazepam^c (0.25 mg/kg) and propofol^d (3 mg/kg) and maintained with isoflurane^e following tracheal intubation. Epidural anesthesia with preservative-free morphine^f (0.1 mg/kg) and bupivacaine^g (0.3 mg/kg) was administered following anesthetic induction.

The left pelvic limb was clipped and prepared for aseptic surgery. A standard medial approach to the left stifle and proximal tibia was performed. A medial parapatellar arthrotomy allowed exposure of the stifle joint. The articular surface of the tibia was positioned in an extreme caudal slope. Only the distal, cranial aspect of the femoral condyles articulated with the malformed tibia. The CCL was completely ruptured. The caudal cruciate ligament was normal. The medial and lateral menisci were normal and left intact. Articular cartilage of both the tibial plateau and femoral condyles appeared grossly normal. The arthrotomy was closed in a routine manner.

The proximal medial tibial metaphysis was exposed as previously described for a TPLO.⁶ A 12-mm bi-radial Slocum TPLO saw blade^h was then used to make three osteotomies in the proximal tibia. The most proximal osteotomy was made as described for a standard TPLO.⁶ The second and third osteotomies were performed distal to the first osteotomy at the point of greatest curvature of the proximal tibia [Figure 3]. With the concave surface of the saw blade directed distally, these cuts were directed to intersect on the caudal cortex while leaving a 10-mm gap between the two saw cuts on the cranial cortex. The wedge of bone created by the second and third cuts was then removed to allow closure of the cranial defect and further reduction of the tibial plateau angle.⁷ A middiaphyseal fibular osteotomy was performed via a small lateral approach to allow rotation of the tibial plateau. The tibial plateau was then rotated caudally 5 mm prior to fixation. The free tibial plateau segment and tibial tuberosity segment were secured to the proximal tibial diaphysis using a 2.0-mm TPLO plateⁱ and 2.0-mm bone screws. A double tension band was placed between the tibial tuberosity and tibial diaphysis to further stabilize the three tibial segments. The proximal segment of the fibula was then secured to the tibia using cerclage wire. Closure of muscle, subcutaneous tissue, and skin was routine.

Postoperative radiographs documented proper placement of implants with a tibial plateau angle of 23° [Figure 4]. A modified Robert-Jones bandage was placed on the limb, and the cat recovered from anesthesia uneventfully. Twenty-four hours after surgery, the bandage was removed, and the cat had a limited range of motion of the stifle joint and was willing to bear weight on the limb. The cat was discharged with instructions for strict cage rest. Ten days postoperatively, the cat was evaluated and had a consistent, moderate, weight-bearing lameness on the operated limb. Range of motion had improved significantly with nearly 180° of extension and normal flexion.

One month postoperatively, the cat was ambulatory with a mild, consistent lameness and normal range of motion of the left stifle joint. Radiographs obtained at the 1-month recheck revealed early healing of the osteotomy sites and normal positioning of the implants. Three months after surgery, the cat had only a mild, intermittent lameness and normal range of motion. Radiographs taken at this time revealed healed osteotomy sites and normal positioning of implants, and the cat was released to full activity. At a final recheck 4.5 months postoperatively, the cat was fully weight bearing with no reported problems.

Discussion

A caudally sloping tibial plateau angle, resulting in cranial tibial thrust, has been postulated as a stressor of the CCL in the dog.^3,8,9 Continual tibial thrusting is hypothesized to weaken the CCL and contribute to complete or partial CCL rupture.^3,8 Retrospective studies have evaluated surgical techniques designed to abolish cranial tibial thrust by modifying the tibial plateau angle. This treatment technique for CCL rupture has resulted in favorable clinical outcomes in many dogs.^6,10 Previous reports have also shown an association between proximal tibial deformity and CCL rupture in the dog.^3,11,12 To the authors’ knowledge, no such association has been described in the cat. In the cat of this report, a 75° tibial plateau angle was found concurrently in a stifle with CCL rupture. Because of persistent cranial subluxation of the tibia and persistent, nonweight-bearing lameness, surgical therapy was pursued rather than conservative medical therapy.² The abnormal femorotibial articulation created by the malformed proximal tibia made extracapsular stabilization of this joint unfeasible. Therefore, modification of the tibial plateau angle was performed as treatment for CCL rupture.¹³

A previous in vitro study indicated that a tibial plateau angle of 6.5±0.9° is ideal to minimize cranial tibial thrust in the CCL-deficient canine stifle model.¹⁴ Similarly, a postoperative tibial plateau angle of approximately 5° is considered desirable with a standard TPLO procedure in the dog.^6,15 However, evidence from a clinical case series documenting CCL rupture with concurrent proximal tibial deformity in dogs with excessive tibial plateau angles suggests that rotation of the tibial plateau to 6.5±0.9° may not be necessary to obtain a good clinical outcome.^11,12

Preoperative planning in this cat, including diagram manipulation by the authors, revealed that a cranial closing wedge ostectomy of 1 cm of the cranial tibial cortex would produce a 25° inclination change in the tibial plateau angle. This was determined to be the largest ostectomy possible that would not create significant tibial shortening and deformation. The TPLO procedure allows a maximal correction of the tibial plateau angle of 30°.¹⁶ Given these conditions, a postoperative tibial plateau angle of 20° was planned in order to mimic the unaffected stifle and provide anatomical articulation of the affected stifle joint. The surgical procedure resulted in a postoperative tibial plateau angle of approximately 23°. This was an excellent outcome and coincided with previously reported results in dogs with extreme tibial plateau angles and concurrent CCL rupture, in which a good or excellent outcome was achieved via correction of the tibial plateau angle to mimic a functional angle rather than 5°.^11,12

A medial meniscal release has been recommended by some authors as part of a routine TPLO.^15,16 Meniscal release is performed to allow the caudal horn of the medial meniscus to move from beneath the medial femoral condyle during cranial tibial translation and escape potential crushing injury.^15,16 Recent reports support leaving an undamaged medial meniscus intact, as subsequent injuries in a TPLO-stabilized stifle are unlikely.^17,18 In this cat, the medial meniscus was undamaged and left intact, and subsequent medial meniscal damage did not occur during follow-up.

The degree of tibial plateau rotation required in this cat would have been difficult using either the TPLO or cranial closing wedge ostectomy alone. The combination of the two procedures easily allowed rotation of the tibial plateau to the desired tibial plateau angle. Middiaphyseal fibular osteotomy was also performed to prevent potential constraint on rotation of the tibial plateau by the fibular head.

Conclusion

A young domestic shorthair cat was diagnosed with CCL rupture and concurrent deformity of the left proximal tibia. A combination of TPLO and cranial closing wedge ostectomy was performed and provided an excellent clinical outcome. The menisci were undamaged, and a medial meniscal release was not performed. The results of this case concurred with previous results in which animals with exaggerated tibial plateau angles and concurrent CCL rupture achieved excellent clinical outcomes with surgical modification of the tibial plateau angle. Further study is warranted to evaluate the degree of tibial plateau angle modification necessary to achieve acceptable clinical results and the necessity of medial meniscal release in cases with this presentation.