Izzy is an 11 month old miniature Daschund owned by Debra Robinson. Recently, Izzy was examined by Dr. Schaeffer after Debra noticed she was favoring her left hind leg the night before. At times, Izzy was not putting any weight on the leg at all and seemed painful. The lameness seemed to improve overnight with rest, but she was still not walking normally.
On examination, Izzy was found to have a condition that affects many toy or small breed dogs called medial luxating patella (MPL). The kneecap (patella) is normally located in a groove (the trochlear groove) at the far end of the femur.
The patella sits on the underside of the patellar ligament, which is attached to muscle at the thigh and to the front of the tibia, just below the knee joint. In a normal knee, the patella slides up and down the trochlear groove when the thigh muscles contract, keeping the patellar ligament in place. A luxating patella is a kneecap that moves out of its normal location. In most cases, the luxation is brief and the patella moves back into place.
Patellar luxation is caused by a congenital malformation of the trochlear groove, making it more shallow than normal. In some dogs, the point of attachment of the patellar ligament on the tibia is not in the center of the bone as it should be. When these abnormalities are present and the thigh muscles contract, the patella is pulled toward the inside of the knee (medially).
When the patella luxates, a dog has a difficult time bearing weight on the affected leg, as Izzy did. Many dogs learn how to stretch or “kick” their legs into a position that helps put their patella back in place. One or both knees can be affected and to differing degrees. It turns out that Izzy has bilateral MPL (both knees affected), with her left knee affected more severely.
Dr. Schaeffer recommended monitoring Izzy for recurrent or persistent lameness on either leg. Since Izzy was sore at her exam, a short course of an anti-inflammatory medication was prescribed and activity restriction advised.
Long term, Izzy could tolerate this condition for years, but it may predispose her to other injuries of the knee and arthritis. She may need to be evaluated for surgical repair of her MPL in the future, but for now, Debra will monitor Izzy closely.
For more information on MPL, please ask for a helpful informational handout we have available in the office or visit www.veterinarypartner.com.