What is it?
Patellar luxation is the dislocation of the kneecap, a common cause of lameness in dogs. It tends to be a developmental problem of limb misalignment but can also occur secondary to trauma. Toy and small breeds (e.g. terriers, poodles) are most commonly affected but it also occurs in larger breeds, as well as cats. The patella most commonly gets displaced towards the inside (medial patellar luxation) but can also become displaced towards the outside (lateral patellar luxation). The displacement can be partial, complete, continuous or intermittent. It often affects both knee joints.
The patella is a small ovoid sesamoid bone that is an important structural part of the stifle (knee joint). It sits in the patellar tendon which attaches it to the strong thigh muscles and glides within a groove in the femur (thigh bone). If this groove is too shallow or there is misalignment of the bones of the back leg (common in smaller breeds) then this can allow the patella to dislocate.
Clinically dogs may skip when running, a pop may be felt or heard in the stifle and the dog may hold its leg up with the knee bent (patella dislocated) then stretch it behind them (patella relocates); this may be accompanied by vocalisation. Patellar luxations are graded in severity from grade 1 to 4 with the latter being most severe.
Grade 1 and 2 luxations can sometimes be managed without surgery. Grade 3 and 4 usually require surgery to make the dog comfortable. In general, surgery is recommended for dogs that are lame regardless of grading. Surgery usually consists of three procedures:
- Sulcoplasty: deepening of the groove the patella glides in
- Tibial Tuberosity Transposition: moving the insertion point of the quadriceps muscles on the tibial tuberosity on the top of the tibia (shin bone). This is done by cutting the tibial tuberosity and fixing it in its new position with surgical steel pins
- Soft Tissue Reconstruction: releasing or tightening of the soft tissues adjacent to the stifle joint.
After the surgery the patient needs to be strictly rested for six weeks to allow the soft tissues and bones to heal. Physiotherapy and hydrotherapy are recommended to speed recovery. Most patients regain near normal function of their knee joint though this may take up to 3-6 months. Post-operative complications to be aware of include implant failure, implant loosening, and reluxation of the patella. Your vet will be able to discuss these with you and create a tailored rehabilitation plan with you.