Abstract

Clinical treatment of canine patellar luxation mainly involves trochlear wedge or rectangular resection, quadriceps release, joint capsule release, supporting ligament relaxation, and tibial tubercle transposition. , joint capsule overlap surgery, corrective osteotomy, pulley replacement and other methods for treatment. However, due to the different incidence and complexity of different dogs, various treatment methods have certain limitations. This article reports a case of a Teddy dog ​​with bilateral hindlimb lameness. Bilateral patellar lateral dislocation was diagnosed by Basically recovered.

Background

The patella, also called the kneecap, is an extensor of the quadriceps muscle of the thigh. A small bone underneath the muscle. Clinically, patellar luxation often occurs in small dogs and sometimes in large dogs. Patellar luxation has an incidence rate of 7.2% among all genetic diseases, and the incidence rate is higher in purebred dogs. Most causes of patellar dislocation are skeletal muscle abnormalities, such as medial shift of the quadriceps muscle group, lateral rotation of the distal femur, lateral bending of the distal 1/3 of the femur, hypoplasia of the femoral shaft, rotational instability of the knee joint, and tibial deformation. Patellar dislocation is generally divided into 4 clinical levels: Grade I - intermittent patellar dislocation, spontaneous dislocation rarely occurs during normal movement. Artificial patellar dislocation can occur when the knee is bent during a physical examination, but when the pressure is relieved, the patella is reset and joint flexion and extension return to normal. Grade II - The femur is twisted and slightly deformed, and the patella is dislocated under the action of artificial external force, such as squeezing or flexing the knee joint. It can only be restored by applying the opposite force and counter-rotating the tibia of the sick dog. Grade III - The patella is dislocated in most cases and can only be manually reduced when the knee is extended. However, when the reduction is successful, as the knee joint flexes, extends, and moves, it will be dislocated again. Grade IV - The proximal tibial plateau rotates 80° to 90°, and the patella cannot be manually reduced. The trochlear groove of the distal femur becomes shallow or disappears, the quadriceps muscle group is displaced, the soft tissue structure supporting the knee joint is abnormal, the femur and tibia are significantly deformed, and clinical symptoms include lameness, difficulty in weight-bearing, and bending of the affected limb.

Case information

A male Teddy dog, 2 years old, weighing 6.2kg, has not undergone castration surgery, is fully immunized, and is raised indoors. The dog suffered from bilateral hind limb lameness for up to half a year, and had a "bunny hop" posture when running.

Clinical examination

The body temperature was 39°C, the pulse was 115 beats/min, and the diet and bowel movements were normal. Place the sick dog on a soft blanket with the abdomen facing up. Hold the distal femur of the left affected limb with your left hand and the distal tibia with your right hand. It is found that the affected limb cannot bend the knee and extend. The thumb and index finger of the left hand supported the knee joint, flexed the knee joint, palpated the patella and found that the patella was not within the pulley. After careful inspection, a free hard mass was found on the outside of the pulley. The hard block can be reset by pushing the hard block inward with force, and it will prolapse when the leg is bent at the knee. The trochlear groove is smooth on palpation, and there is a "clicking" sound when the knee is bent, and there is obvious pain. The right affected limb was examined using the same method, and the results were the same, indicating high suspicion of lateral patellar dislocation.

Imaging examination

X-ray examination showed that the dog’s bilateral trochlear grooves became shallower and the bilateral patellas were third-grade dislocation of the lateral patella (Figure 1).

Surgery

1) The surgical access is opened. An anterolateral skin incision was made starting 4 cm proximal to the patella and extending to 2 cm below the tibial tubercle. Cut the subcutaneous tissue along the same line, cut the lateral supporting ligament and joint capsule, and expose the joint.

2) Rectangular trochlear resection. Cut into the articular cartilage of the trochlea, which has a rectangular appearance. Make sure the width of the incision is enough to accommodate the width of the patella, but retain the trochlear ridge. For small and medium-sized dogs, use a hand-held saw to cut 2~6mm into the bone, using the same width as the osteotomy. Use the osteotome to lift up the osteochondral block (Figure 2). Insert osteotome proximal and distal to the osteotomy, meeting in the middle. Care is taken to remove the appropriate thickness of bone and avoid splitting the osteochondral mass. Remove excess bone from the base of the sulcus and deepen the pulley. Reposition the free osteochondral block when it is deep enough to accommodate 50% of the patellar height. Rinse away the blood clots and epiphysis with normal saline, and then re-cover the osteochondral block in the trochlear groove to form a new cartilage glenoid. Due to the compression force of the patella and the friction of the cancellous bone surface of the cross-section, the osteochondral block can be maintained in situ.

3) Tibial tubercle transposition. An incision is made lateral through the fascia lata parallel to the patella and extended distally to the tibial tubercle below the joint line. Lift the tibialis anterior muscle away from the lateral aspect of the tibial tubercle and tibial plateau. Sharp dissection is performed to obtain deep access to the patellar tendon for easy resection using an osteotome. The width of the nodule resection should be as wide as possible, from the caudal side to the muscle groove, and the bone should be kept intact at the distal osteotomy. At this time, the surgeon must select a suitable attachment point for the tibial tubercle, and usually use 2 Kirschner wires to refix the tibial tubercle. The first K-wire is perpendicular to the osteotomy plane, and the second K-wire is perpendicular to the straight knee ligament. When the tibial tubercle transposition is completed, use a large amount of sterile saline to flush the blood clots from the surgical site, and flex the knee joint to check its stability.

4) Close the surgical wound. The excess joint capsule is removed, and absorbable sutures are used to sew the joint capsule and the fascia of the knee joint in the first layer, and then the fascia lata of the proximal patella is continuously sutured, the muscle layer is continuously sutured layer by layer, and the skin is sutured in nodes. . Rinse the wound with saline or chlorhexidine, clean up the blood near the wound, and finally wipe the wound with iodophor.

Discussion

Because the patella is in a dislocated state for a long time, the supporting ligament on the opposite side of the dislocation will be stretched. Removing the excess supporting ligament and joint capsule will cause the closed joint to be incised. parts are closer together. When the trochlear groove is rectangular and deepens, cutting too close to the edge will cause trochlear crest fracture; when the tibial tuberosity is displaced, the cutting point should be in front of the muscle groove. If the tibial tuberosity is accidentally completely cut off, an "8" steel wire should be used to cut the tibia. Nodule fixation.

Patellar luxation in dogs has many physiological and pathological factors. Appropriate surgical options should be selected for different cases. Under normal circumstances, grade I patellar luxation does not require surgical treatment. Most dogs can be well controlled through conservative treatment, limited activities and long-term oral administration of Provicon. Grade II to III patellar dislocation requires the application of trochlear deepening and tibial tuberosity translation. Combined use of positioning surgery to correct, simple trochlear deepening surgery will lead to rapid postoperative recurrence and cannot achieve good therapeutic effects; grade IV patellar dislocation requires trochlear deepening, tibial tuberosity displacement and osteotomy correction according to the situation. Or trochlear ridge thickening surgery for treatment. In addition, pain caused by arthritis caused by patellar dislocation itself and damage to articular cartilage caused by surgery requires long-term oral administration of shark chondroitin or regular oral administration of non-steroidal anti-inflammatory drugs for pain management.