Luxating patella is essentially a displacement or dislocation of the patella (also known as the knee cap) from its normal position in the groove at the end of the femur (the trochlea). The patella is at the lower end of the quadriceps group of muscles and is attached to the tibia by means of the patellar tendon. The patella normally moves up and down in this groove but should not move out of the groove to either side. When it does move out of the groove, it is called a luxating patella. Movement out of the groove to the inside of the groove is called a medial luxation and movement out of the groove to the outside is called a lateral luxation. The underside of the patella and the femoral trochlea are each covered with a smooth thin articular cartilage which protects the joint.

Causes

The vast majority of dogs with luxating patella have musculoskeletal malformations. These malformations include bowing of the femur and tibia, inward rotation of the tibia, shallow or absent femoral trochlea and displacement of the quadriceps muscle group. Genetics appears to play a role in the problem. Occasionally the patella luxates because of trauma or injury.

Symptoms

Dogs of all ages may be affected and exhibit signs of either persistent lameness or an intermittent lameness whereby a skipping gait may be seen. Signs may be more difficult to detect when the problem affects both rear legs. Some dogs may manage with the luxated patella or patellas with little in the way of lameness until the secondary arthritis becomes significant. Dogs with intermittent lameness may appear completely normal on the leg except for brief episodes of lameness when the patella luxates. Some dogs can extend their leg enabling the patella to go back into the trochlea and carry on with no sign of lameness until the patella re-luxates.

Long-Term Effects

The effects of an untreated luxating patella can be significant with the progression of arthritis and poor mobility.

Treatment

Most cases of luxating patellas causing lameness require surgery. Each case must be carefully evaluated by the surgeon. Techniques generally involve transposition of the tibial tubercle with one or more of the following:

• Making the trochlea or groove deeper
• Releasing the tissue on the inner side of the joint
• Tightening the tissue on the lateral side of the joint
• Placing a permanent suture from the patella to the lateral fabella

Cases with severe boney deformity may involve straightening the bones. Fortunately these cases are few and far between.Most cases of luxating patella with surgical correction do extremely well and live a life free from discomfort.

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