Introduction

The cranial cruciate ligament is one of the primary stabilizing structures of the canine knee. Rupture of the cranial cruciate ligament is one of the most common canine orthopedic problems leading to patient morbidity, reduced activity and progressive osteoarthritis. Many techniques to stabilize the stifle after rupture of the cranial cruciate ligament have been attempted. Until recently no single technique has been shown superior to others and the veterinary surgeon's selection of repair technique is largely based on training and personal experience.

Tibial Plateau Leveling Osteotomy (TPLO) has attracted increased attention and great acceptance within the veterinary surgical community in recent years. Recent investigations suggest that tibial plateau leveling may hold the answer for surgeons and patients alike in our quest for the best solution to canine cranial cruciate rupture.

Biomechanics

In 1983, a model of the stifle was proposed which hypothesized that analysis of the canine stifle must include active forces generated by weight bearing and muscle/tendon action as well as passive forces produced by ligamentous structures. In this model the role of the muscles of the caudal thigh which limit cranial translation of the tibia as well as other contributors to stifle function are accounted for such that the algebraic sum of the active and passive forces acting on the normal stifle is zero. See Figure 1.Compression between the tibia and the femur, as occurs in weight bearing, produces a force defined as cranial tibial thrust. This unchecked cranial tibial thrust is proposed to be the underlying source of patient discomfort, meniscal damage, lameness and ultimately, degenerative joint disease. Accordingly, a surgical technique was developed to neutralize this force even in the event of a cranial cruciate ligament rupture. Tibial plateau leveling osteotomy ("TPLO") neutralizes the forces that produce abnormal or uncontrolled cranial tibial thrust. This technique changes the angle of the tibial plateau which provides the stifle flexors with a mechanical advantage, shifts responsibility to the caudal cruciate ligament and permits stifle stabilization by active forces. In addition, the change in tibial plateau slope produces a flatter surface on which the tibial forces of weight bearing may be transferred to the femur.

Diagnosis

Diagnosis is made based on history, physical examination findings and radiographic examination. Lameness of varying degree or decreased willingness to work in performance dogs is the primary presenting complaints with CrCL rupture. Duration of clinical signs is highly variable. Physical examination of the stifle may be divided into standing, locomotive and recumbent elements.

Standing examination from a distance includes assessment of weight bearing, muscle atrophy, pain, angulation, rotation and symmetry. Palpation while standing provides information about joint distention, medial buttress, patella position, atrophy, meniscal damage, swellings and masses. See Figure 2.

Examination of the patient in lateral recumbancy can be performed with manual or chemical restraint. The cranial drawer test and tibial compression tests are the standard for diagnosis CrCL rupture.Other parameters assessed include patella luxation, range of motion, excessive internal rotation, collateral ligament stability, crepitus, clicking and hyperextension.

Locomotive assessment may be made with the patient on a short lead. Walking and trotting may be performed to assess lameness and weight redistribution. A patient may be asked to jump to an elevated platform or ascend a flight of stairs to demonstrate discomfort or subtle lameness. Finally, the patient is asked to sit in an attentive fashion and is examined for complete stifle and hock flexion and symmetry of rear leg placement well beneath the pelvis. Patients with ruptured CrCL tend to extend the effected leg. See Figure 3.

Radiographic Examination

Initial radiographic assessment includes two views of the knee (front and side). See Figure 4.Measurements and calculations of the degree of surgical correction are based on these radiographs making quality and positioning is extremely important. Radiographic evidence of cruciate rupture is evaluated on these projections as well, including joint distention, osteoarthritis and cranial translation of the tibia.

Radiographs are also used to assess rotational and angular abnormalities and to develop a surgical plan to treat these problems.

Surgical Procedure

The tibial plateau leveling osteotomy is a patented technique for treatment of cranial cruciate rupture with licenses available through Slocum Enterprises, Eugene, OR. Initially, the technique was reserved for patients greater than approximately 50 lbs.. Recently the instrumentation has been developed to extend the benefit of the procedure to patients as small as 12-18 lbs depending upon bone size. The technique does not address the reconstruction of the passive constraints of cranial tibial thrust but rather seeks to enhance the active forces and provide a flatter surface for transfer of weight bearing forces from the tibia to the femur by leveling the tibial plateau. This leveling has been shown to convert cranial tibial thrust to caudal tibial thrust thus utilizing the intact caudal cruciate ligament to stabilize the joint. See Figure 5.

Rehabilitation

Strict exercise restriction is maintained until radiographic healing of the osteotomy is demonstrated, usually 6 to 8 weeks. Passive range of motion therapy is performed twice daily during this period. The patient's activities are then gradually increased to improve range of motion and increase muscle mass. The amount of activity should not create patient discomfort. Explosive activities such as running, jumping and rough play are avoided. If at any time during the rehabilitation process the patient becomes uncomfortable activity is reduced to the previously comfortable level.

After bone healing is confirmed generally the recommended regime involves progressively longer leash controlled walks during the first three weeks. Multiple walks to gain aggregate distance are superior to a single long outing. During the fourth through sixth week the walks are continued on a long lead allowing the dog the freedom to trot short distances. Beginning at week seven controlled off lead activity is initiated. Small enclosures without distractions are ideal for this phase of the program. Following a final re-evaluation at approximately 10 weeks (4 months post-operative) the patient is normally able to return to full function. See Figure 6.

Conclusion

Tibial Plateau Leveling Osteotomy offers an attractive alternative to traditional stifle stabilization techniques. Our experience with TPLO over 6 years of exclusive use is excellent. In our practice we routinely operate stifles with failed extra-capsular repairs. TPLO appears to be an excellent salvage procedure for these patients in addition to providing the best clinical results of any technique we have performed for cranial cruciate rupture.