Patellar luxation

Medial patellar luxation (MPL) is a condition in which the kneecap (patella) pops out of its groove. It luxates (dislocates) to the inside of the knee, making the knee unstable. This condition is usually seen in small breed dogs, but can also occur in large breeds. It frequently affects both rear legs, and can be either traumatic or congenital (congenital being common). The severity of the luxating patella (or ease with which it luxates) is graded on a scale of 1-4, with a grade 4 being a patella that is chronically luxated. Lateral luxation (in which the patella luxates to the outside of the knee) is far less common, and is seen mostly in large breeds.

With lower grades of patellar luxation, dogs display an intermittent lameness and are seen as occasionally “skipping” on the affected limb. As the condition progresses, the dysfunction in the limb becomes more consistent and pronounced, to a point of minimal use and constant abnormal carriage and position of the limb.

Surgical repair may consist of several steps: the kneecap is put back in to the groove, the groove is deepened and the surrounding soft tissues and bone are altered to secure the patella within the groove. Sometime the tibial tuberosity (front section of the shin bone) is transposed to a slightly different location and secured with small pins. If surgery is successful, most dogs return to good use of the limb. Less commonly, in cases where a deformity of the femur (thigh bone) causes the luxation, corrective osteotomy (re-alignment surgery) of this bone is needed.

Strict rest is required following surgery to prevent the patella from re-luxating during the healing process. Initially, there should be no running, jumping, or playing. After a gradual increase in activity, full function is allowed by 2 months in most cases.

Although uncommon, re-luxation may occur, and often requires an additional surgery. This is of most concern during the first 2 months following surgery, especially in cases with a high grade luxation. If pins were used to transpose the tibial crest, these can sometimes cause irritation and may need to be removed in 3-12 months.