Patellar luxations (dislocation of the knee-cap) occur frequently in dogs and rarely in cats. Patellar luxations can he grouped into two main categories. First, and most commonly, is medially luxating patellas (MLP) which are congenital (existing from birth) and commonly affect cats and smaller breed of dogs. The second type is laterally luxating patellas which are often the result of trauma and can affect any pet. Lameness occurs as the patella luxates and often resolves when it spontaneously reduces. Lameness is often intern-intermittent and animals will learn to reduce the patella themselves by extending the hip and the knee together behind them. Diagnosis is made on physical examination and may be confirmed with radiographs. Radiographs will demonstrate the patella luxation if the patella is dislocated -at the time the radiographs are taken. All animals with patellar luxation can develop some degree of arthritis.
Most surgical corrections of patellar luxations consist of deepening the groove in which the patella rides, removal of redundant (excess) tissues and possibly, movement of the bone on which the patellar ligament inserts. Deepening the groove (trochleoplasty) can be accomplished in several ways, depending on the age and size of the patient. By deepening the groove, the patella is less likely to move into an abnormal position. This is usually combined with other techniques to maximize stability of the knee.
When the patella is returned to its normal position, the soft tissues around it will be loose on one side and tight on the other. The surgeon will therefore tighten the soft tissues on the one side to hold the patella in place and release or loosen the tissues on the opposite side.
The insertion of the patellar ligament on the tibia or shin bone may require repositioning. Because bone heals better than ligament, the bone is cut, with the ligament attached, and move to a more normal location. It is secured with two small pins. This is usually necessary for grade III and IV MLP.
Not all cases require use of all these techniques. Each case is individually assessed and the appropriate combination of techniques utilized. Often, the final decision is made at the time of surgery.
Because of the strong genetic relationships, animals with this disorder should not be used for breeding. They can still be excellent pets - and those that do require surgery will usually lead perfectly normal lives without any restrictions on activity