What is a Luxating Patella?
The “patella” is also known as a knee cap. It is located in the central part of the stifle (knee) joint.
“Luxating” means “dislocated” or “out of joint.”
A “luxating patella” is a knee cap that is out of joint or dislocated. This typically is a painful condition that typically needs surgical repair.
What Causes a Luxating Patella?
First things first, it’s important to understand the structure of the knee and joint. The muscles of the thigh attach to the top of the patella while a tendon—called the patellar tendon—runs from the bottom of the knee cap to just below the knee joint, specifically attaching to the tibia. The contraction of the thigh muscles transmits force through the patella and the patellar tendon, causing the straightening or bending of the knee joint.
The patella is attached to the midline of the tibia and slides in a groove on the lower end of the femur (called the trochlear groove). When a patella luxates, it is most often because the point of attachment is not on the midline where it should be but rather located nearer the center of the body. When thigh muscles contract to move the knee joint, movement is not occurring in a straight line but rather pulling off to the side, creating a weakness and wearing down the groove. Once this groove is worn down, the patella will often luxate (dislocate). It can be snapped back into place, but because of the wear, may dislocate again and again.
What Long-Term Problems Can This Cause for a Dog?
Typically, long term complications may vary depending on the severity of the luxation, the frequency of the luxation, the size of the pet, the activity level of the pet, and the age. We would recommend an examination with a veterinarian to better answer this question because it may vary from pet to pet. It is important to note, though, that a luxating patella can predispose a dog to other knee injuries, especially cruciate ligament ruptures. Arthritis can also affect the joint over time, increasing pain and discomfort.
What Corrective Procedures are Available?
Surgical intervention is the most common corrective procedure used on a luxating patella. It is often necessary if the dog experiences pain or other injuries because of the weakness in the knee. Surgical repair typically involves:
- Changing the “point of attachment” for the patellar tendon
- Improving the groove in the femur to keep the patellar tendon in place
- Tightening of the capsule around joint to prevent dislocation from occurring again
It is better to perform this reparative surgery before arthritis begins in the knee. If arthritis has already occurred, the dog may experience intermittent pain in the joint and may need long term medical management.