Medial patellar luxation (MPL) is a condition where the patella (kneecap) does not stay in the groove of the knee. It can occur in both dogs and cats. Medial patellar luxations can be caused by a variety of factors including joint anatomy, muscle weakness, gait mechanics, or trauma. With a medial patellar luxation, the patella glides towards the inside of the knee joint leading to tightened muscles. These taut muscles can continue to make the luxation worse as they pull the patella out of place.
Medial patellar luxations can be graded based on their severity as outlined below. The luxations can progress from a lower grade to a higher grade as time goes on.
- Grade 1: The patella can be manually luxated but will pop back in place.
- Grade 2: For the most part the patella is in place. However, the patella can be manually luxated, but will need to be manually placed back in place.
- Grade 3: The patella is out of place most of the time, but can be manually placed back in.
- Grade 4: The patella is out of place and can not be manually placed back in.
The most common symptom of a medial patellar luxation is a skipping gait. A dog will occasionally hold the leg up for a few steps when the patella pops out of place, and then start using it again once it goes back in. This may happen every few steps or just occasionally. Other symptoms may include limping on the back leg, holding the leg in abnormal positions, sitting down often, or stiffness. Higher grade luxations can develop into a bowed leg stance that looks like a cowboy stance. They often rotate their knee outward and bow when walking.
Medial patellar luxations can be diagnosed with a physical exam to feel for laxity or luxation of the patella. Radiographs can be helpful to see if there are degenerative changes in the joint or anatomical abnormalities that are contributing to the luxation. Radiographs can also show the position of the knee cap.
Consultation with an orthopedic specialist is usually recommended. They will likely go through and discuss possible surgical options. The type of surgery recommended will depend on the cause of the luxation. Whether you choose to pursue surgery or not we still go forth and create a treatment plan to delay progression and assist the pet in decreasing a grade in their medial patellar luxation. First we will focus on decreasing pain and swelling around the patella. Then we focus on relaxing the sartorius, adductors, and vastus medialis to allow the patella to sit closer or more frequently in place. Lastly we focus on building up the hamstrings and eccentric control of quads/sartorius to provide stability to the patella.