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Luxating Patella Surgery

Dislocation of the kneecap (patella), medically referred to as medial luxation of the patella, is a very common developmental abnormality of small toy breed dogs especially Pomeranians and Chiuahua's. In the normal situation the kneecap should track smoothly up and down a groove in the femur bone when the knee joint bends and flexes. In luxating patella the kneecap slips out of this groove causing pain and lameness. In many situations the kneecap slips in and out of position causing the lameness and pain to be intermittent. We grade luxating patella based on the following rules:-
  • Grade 1 - The kneecap can be manually luxated but when released retruns to a normal position
  • Grade 2 - The kneecap can be manually luxated but only returns to the normal position after manipulation of the leg or manual replacement.
  • Grade 3 - The kneecap is constantly luxated. It can be physically returned to its correct position but then spontaneously luxates once released.
  • Grade 4 - The kneecap is permanently luxated and cannot be returned to its normal position.

This anatomical problem can be corrected surgically and the need for surgery increases with the grade of luxation. With grade 1 luxations surgery is only needed if there is regular lameness. With grade 2 luxations arthritis of the knee joint is likely to develop if surgery is not performed. With grade 3-4 luxations the knee cap is constantly out of position and this causes mal-alignment of the muscles and tendons operating the knee join. This causes tension and strain on all the tissues involved with the knee joint including the cruciate ligament. If grade 3-4 luxating patella's are left untreated rupture of the cruciate ligament and permanent twisting and bowing of the leg bones is likely to occur as well as arthritis. It is best to perform the surgery whilst the dog is still young to minimise the degree of twisting of the leg bones that slowly occurs if left untreated.

Surgery involves several corrective procedures including:-
  • Deepening of the groove in the femur that the knee cap runs in.
  • Translocation of the tibial tuberosity. This involves cutting the bone that the tendon of the kneecap is attached to and moving it towards the outside of the knee. Doing this encourages the kneecap to sit in the middle of the groove making luxation less likely.
  • Anti-rotational suture to help prevent rotation of the tibia
  • Lateral imbrication - to tighten the tissues to one side of the kneecap
  • In severe cases the leg bones may need to be cut and plated to correct any bowing present.

Surgery is very successful with few complications.