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.

Anatomy

The patella normally moves up and down in a groove in the lower femur bone called the trochlear groove. In patella luxation the groove is often shallow. This shallow groove prevents the patella from seating deeply and predisposes it to dislocation. This results in the luxation of the patella as the leg is used. The quadriceps or extensor muscles of the leg are associated with the patella. In patellar luxation, the extensor muscles are often maligned to the inside or outside of the leg, The degree of patella luxation is graded from I to IV depending on the relative ease with which the patella luxates. Grade I is the mildest and grade IV the most severe. Grade I and II patellar luxations may be completely asymptomatic and may be incidental findings is mature dogs and cats who have never been lame. Grade III and IV MLP patients are usually lame. Severe cases may develop abnormal growth of the long bones of the leg or a non functional knee.

Medially Luxating Patellas

In medial patella luxation, the patella (knee-cap) dislocates to the inside of the knee. This is the most common form of patella luxation and it is often congenital and affects both knees. one knee may be more severely affected than the other. MLP generally affects smaller breeds of dogs and cats.

Laterally Luxating Patellas

Lateral patellar luxation can be congenital or the result of trauma to the knee. This condition often affects larger breeds of dogs and can cause problems similar to MLP. In some cases the patella can luxate both medially and laterally. Grading and recommendations for surgery follow the same guidelines as for MLP.

Surgical Correction

The decision to perform surgery on animals with patellar luxations is based on many factors including the degree of lameness, the grade of patellar luxation, the age of the animal, and the presence of concurrent problems with the knee. As previously discussed, some animals with lameness. often low grade MLP, which has been present all of the animal's life, is noted on routine physical examination without any history of lameness. in these cases, surgery is not indicated. Arthritis will develop, whether or not surgery is performed. Additionally, there is no increased incidence of ligament injuries in these knees, contrary to what was previously believed. Surgery is performed to improve function of the leg, therefore, if the animal is not lame, surgery is not indicated. Grade of patellar luxation may dictate the need for surgery. In growing animals, severe patellar luxation may result in crippling deformity of the leg. if the grade of patellar luxation is high (some II and all of fit and IV), your veterinarian will likely suggest surgery as soon as your pet can tolerate the procedure. In older animals with higher grade patellar luxations, lameness if often present and surgery should improve function of the leg. Patellar luxation may also be found in conjunction with other injuries to the knee which require surgery, most commonly, rupture of the cranial cruciate ligament. Often the surgeon will discuss correction of the patellar luxation at the same time the other injury is repaired.

Surgical Techniques

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 (see diagram 2). 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.

Postoperative Care

Following surgery, the affected leg may be placed in a soft padded bandage. This is to reduce discomfort and discourage excessive use of the leg in the early post-operative period. The pet.is usually hospitalized for one night after surgery. The bandage and sutures are removed approximately 10 to 14 days after discharge. Additional rechecks will be scheduled as needed and usually include reassessment at 4 to 6 weeks post-operatively. Most animals begin using the leg soon after bandage removal, but may not reach full function for several weeks. Physical therapy may be suggested to facilitate early use of the leg. Exercise restriction should be enforced for 10 to 12 weeks after surgery. As previously mentioned, some arthritis is expected even after surgical correction of the patellar luxation. The arthritis generally does not result in lameness. Prognosis is favorable in cases without excessive arthritis or growth deformities. After surgery in small breeds of dogs and cats, use of the leg is often normal or close to it. The prognosis for your pet will be discussed prior to surgery. If your pet requires surgical correction of both knees, they will generally be operated approximately 6 weeks apart. This is allow the one leg to recover from surgery and strengthen prior to performing surgery on the second side. In some cases, on small dogs and cats, both knees may be operated at the same time. Patellar luxations (dislocation of the knee-cap) occur frequently in dogs and rarely in cats. Patellar luxations can be 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 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.