Medial Patellar Luxation

What is medial patellar luxation?

•  The patella (kneecap) normally rides in a groove called the trochlea at the end of the femur bone (Figure 1). When the patella luxates or moves out of the groove, the knee joint cannot flex properly (Figure 2).
•  Patellar luxation is usually caused by a conformational abnormality at the level of the hip joint and results in abnormal forces that act on the kneecap causing it to ride outside the groove. In young animals, the groove becomes very shallow and the attachment of the patellar ligament is often malpositioned on the tibia (shin bone). The kneecap most often luxates to the inner aspect of the knee joint and is called medial patellar luxation.

Clinical Signs:

•  Lameness/Pain
•  Intermittent skipping
•  Stiffness of the affected leg
•  Combination of the above

Surgery:

•  In most cases, a series of three to four surgical steps are taken to properly align the patella.

1.  If the groove is shallow or misshapen, it is surgically deepened to allow the patella to sit deeper within the femur. Replacement cartilage (fiibrocartilage) will gradually fill in the recontoured portion of bone (Figure 3).
2.  The attachment of the patellar ligament to the tibial crest is often surgically repositioned to the side opposite the luxation. It is then secured in place with one or two metal pins (Figure 4).
3.  The joint capsule and surrounding muscle along the side of the patella are often stretched during a luxation. These tissues are sutured or tightened on the opposite the side of the luxation to provide additional support and prevent abnormal movement of the patella.
4.  Occasionally, the joint capsule on the side of the luxation is ‘released’ to reduce tension.

Recovery:

•  Pets are often beginning to touch the toes to the ground by 10-14 days. Some take a bit longer depending upon the severity of the luxation.
•  Most pets are using the operated limb well by 6-8 weeks.

Prognosis:

•  Approximately 90% of our patients will return to normal function of the limb.
•  Surgery is designed to address the luxating patella, but cannot reverse arthritic changes that are already present in the knee joint. Patients with arthritic knees may have some stiffness after rest or may become lame after heavy exercise.
•  Some patients with a severe luxation are at risk for reluxating after surgery. Fortunately, this is not common for most pets.

Potential Complications:

•  Anesthetic related complications can occur with any procedure. Close monitoring of our patients throughout the surgery and recovery period minimizes these complications.
•  As with any surgical procedure, infection is always a concern. Keeping the surgical site clean and preventing pets from licking the incision is of paramount importance.
•  Occasionally, the pin(s) used to secure the transposed portion of the shin bone can shift or back out. Once the bone is healed (at approximately 8 weeks), the pin(s) is no longer needed and are removed if they migrate.
•  A fluid swelling (seroma) may occur over the pins.
•  Excessive activity during the first 6-8 weeks can result in a breakdown of the repair requiring additional surgery.