The patella normally runs in a groove on the anterior surface of the distal femur. (front of the lower part of the bone running from the hip to the knee) The patella is attached by the patella ligament to a raised area of bone on the tibia (bone from the knee to the hock) called the tibial crest.

Most dogs with patella luxation have a conformation with either bowing of the legs or inward rotation of the lower leg (pigeon toed). Both of these conformations lead to an inwardly directed force on the patella which can eventually lead to luxation. Some dogs may also have an inherently shallow groove however more commonly the inside (medial) ridge is gradually worn away by the patella.

Lameness may be quite marked with the leg held up on full flexion (bent up) when the patella first luxates, however this may only last a very short time until it falls back into the groove. Gradually as the episodes become more frequent the degree of lameness is reduced which is often mistaken by owners for an improvement in the condition. Eventually the patella remains permanently luxated. If both knees are effected the may be no apparent lameness as the gait (action) of both legs will be the same. Arthritis is the long term outcome for these dogs.

Surgery is the only effective long term treatment of patella luxation. A number of techniques have been developed which involve a combination of tightening the lateral (outside) support structures of the patella, repositioning the tibial crest more laterally, and deepening the patella groove.