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Patella Luxation (Knee Cap Dislocation) in Pets

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Patella Luxation is when the patella (knee cap) luxates (dislocates) out of its normal position in a groove in the femur (upper leg). 

INTRODUCTION

Patella Luxation is when the patella (knee cap) luxates (dislocates) out of its normal position in a groove in the femur (upper leg). It is a common cause for limb lameness in dogs. The stifle (knee) is essentially a hinge joint, allowing the major muscles of the upper leg to cause the normal swinging movement of the lower leg with walking or running. The patella (knee cap) is a small bone in the patellar tendon of the quadriceps muscle that rides in a groove in the femur (upper leg) at the stifle joint, stabilizing the stifle. The patellar tendon attaches to the tibial crest below the stifle. These structures make up the quadriceps mechanism.

Occasionally the quadriceps mechanism is not well aligned during development, generally due to bowing of the femurs. The end result is that the bones and stifle joint do not develop properly allowing the patella to luxate or dislocate, flipping in and out of the groove. The result is excessive wear on the cartilage, which may lead to osteoarthrosis (degenerative arthritic changes). Dislocation of the kneecap also causes the shin bone to turn inward which may cause the cranial cruciate ligament (CCL) to tear. In fact, about 20 to 25% of the dogs that have a patellar luxation sustain an injury to this main stabilizing ligament of the knee.

Luxations occur most commonly in small breed dogs, although cats and larger dogs can also be affected. In mild cases, the abnormality may have gone unnoticed until the pet is much older. In moderate to severe cases the diagnosis can be made as early as 3 months of age. In these cases, the earlier that corrective surgery can be performed, the less likely future problems will develop or that future surgeries will be necessary.

SIGNS AND DIAGNOSIS

Signs of a dislocating kneecap include lameness, intermittent skipping gait, intermittent crying out or unwillingness to jump on elevated surfaces. The diagnosis is made on physical examination, in which the surgeon can feel the kneecap dislocate out of place. X-rays of the knee and thigh bone will be made to evaluate for twisting of the femur bone.

Whenever your pet is showing signs of a health issue your first step is to contact your primary care veterinarian. If it is indicated that your pet may suffer from patella luxation or another serious condition, a veterinary specialist is available at an ExpertVet certified hospital.

TREATMENT

Surgery is the only method to correct a luxating patella. A board-certified surgeon has the most expertise and experience correcting this condition and will ensure a more predictable outcome.

The primary goal of surgery is to realign the quadriceps mechanism and thus prevent luxation/dislocation of the patella. Mild to moderate patella luxation (grade II-III), may be surgically treated by deepening the groove that the patella slides in and realignment of the attachment of the quadriceps muscle (the patellar tendon) on the crest of the tibia (lower leg) or the attachment of the quadriceps muscle at the top on the pelvis. Often other procedures to tighten the soft tissue support structures and loosen others are performed in conjunction with these orthopedic procedures.

If the condition is severe (grade III-IV) and not treated early enough, in addition to repairing the groove, major corrective osteotomies are usually necessary. Corrective osteotomies involve cutting the femur and/or the tibia and realigning them with pins and clamps (external skeletal fixation device) or bone plates and screws. This is a major surgery and may require multiple surgeries over the course of a few months. Thus, it is very important that surgery be done in these patients as soon as possible.

POST-OPERATIVE HOME CARE

After surgery, your pet will be prescribed pain reliever medication to minimize discomfort. anti-inflammatory medications and medications to improve the quality of the healing joint cartilage may also be started immediately after surgery. Strict control of activity is required after surgery. No off leash activity, no running, no jumping, no rough housing, no playing can be allowed during the rehabilitation period. Slow leash walks and range-of-motion physical therapy exercises can begin as early as 2 days after surgery. Although fibrosis (scarring) is required for joint stability, early controlled use of the operated leg will improve joint mobility. The development of good muscle tone and strength is critical to the overall recovery. If patients are too active, too soon, they can tear or damage recovering tissues. It is IMPERATIVE that your pet’s activity is control during the healing period! Rehabilitation exercises can be done at your home or if you choose, by professionally trained therapists at an animal rehabilitation center. Rehabilitation therapy should be continued until your dog is using the limb well (typically 2 – 4 weeks after surgery).

About 90% of dogs that undergo this surgery will make a full recovery. Dogs that have a severe case of patellar luxation may have a recurrence of patellar luxation, necessitating a second operation.

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