The patella or knee cap should normally run smoothly in a bone groove in the femur above the knee joint. In some dogs, the patella luxates or slips out of the groove, which may cause discomfort, pain and lameness. It is a condition most commonly seen in small breed dogs but any dog may be affected.
Why does this happen?
The big muscle above the patella called the quadriceps muscle, the patella itself and the ligament attaching the patella to the bone below the knee, all need to run in a straight line to function correctly. If a component of this mechanism is not aligned, then the patella can luxate out of the groove, most commonly to the inside of the knee (medial) but sometimes to the outside of the knee (lateral).
Many smaller dogs will appear to be skipping when they walk as they compensate for the patella popping in and out of the groove. The patella may sometimes be felt clicking as it slides over the ridge of bone on the side of the groove. Some dogs are not very lame but have an unusual gait, others can be painful and non-weight bearing on the affected leg.
Deciding on Surgery
The decision to operate depends on the severity of the luxation and also the symptoms experienced by an affected animal. Veterinary surgeons grade the severity of luxation from I to IV with IV being the worst. Most dogs grade II and above will benefit from surgery.
A thorough presurgical workup is required to establish the severity of the condition in each individual. If the bones of the femur or tibia are severely affected, a computed tomography (CT) examination may be recommended.
Most cases can be surgically corrected with a combination of the following:
- Deepening the groove the patella runs in
- Shifting the attachment of the patellar ligament below the knee
- Tightening or loosening the tissue on either side of the patella
More severe and complicated cases may require procedures to straighten out the femur, tibia or both.
All orthopaedic surgeries require careful postoperative care. The body needs time to recover and if the bone has been repositioned as part of the surgery, time is needed for it to heal in the new position. For some animals the exercise restrictions may necessitate cage confinement.
There is a small risk of infection in any orthopaedic procedure. We do take extensive precautions to limit this risk. Sometimes the implants used to reattach the bone below the knee can cause irritation and need to be removed. A low percentage of cases may reluxate and require further surgery.