PATELLA LUXATION (MPL/LPL)
WHAT IS A PATELLA LUXATION?
The patella is a sesamoid bone that is located within the cartilage groove of the lower part of the femur (thigh bone). The patellar tendon, which is a continuation of the quadriceps muscles of the upper leg, extends over the surface of the patella and inserts on the tibial tuberosity at the front of the shin bone. The patella moves within the cartilage groove and protects this tendon while the knee is bending and extending. A medial patella luxation (MPL) is a condition in which the patella dislocates to the inner part of the knee. A lateral patella luxation (LPL) occurs when the patella dislocates to the outer part of the knee. MPLs are much more common and will often occurs in smaller breed dogs and cats; however, larger breed dogs can also be affected.
WHAT ARE THE GRADES OF PATELLA LUXATION?
Patella luxations are graded on a scale of I to IV based on severity.
Grade I: The patella is situated in the groove, but feels loose and rarely luxates.
Grade II: The patella is situated in the groove the majority of the time, but periodically luxates.
Grade III: The patella is luxated out of the groove, but can be reduced into its normal position.
Grade IV: The patella is luxated out of the groove and cannot be reduced into its normal position.
WHAT CAUSES PATELLA LUXATIONS?
A number of breeds including Chihuahuas, Boston Terriers, Yorkshire Terriers, miniature poodles, and Pomeranians are predisposed to patella luxations. Larger breed dogs can also be affected by this condition. There is growing evidence that there is a hereditary component to patella luxations. Patella luxations can also be traumatic, but this is less common. Dogs that have a bow-legged conformation may also be prone to developing patella luxations. This creates an underlying mal-alignment between the extensor mechanism (quadriceps muscles and patellar tendon) and the underlying bone axis.
WHAT ARE THE SIGNS THAT MY DOG MAY HAVE A PATELLA LUXATION?
Limping is the most common sign of a patella luxation. Limping may be sporadic with low grade patella luxations. Limping becomes more consistent and noticeable with higher grade patella luxations. Holding the leg in an awkward position may also be observed. The patella can often be felt moving and can even be manually reduced.
WHAT IS THE SUCCESS RATE OF PATELLA STABILIZATION?
The prognosis for return to full function is excellent following surgery.
IS SURGERY REQUIRED FOR PATELLA LUXATIONS?
The decision on whether to perform surgical stabilization is largely based on the severity of the patella luxation as well as how severely your dog or cat is affected. For grade I patella luxations, surgical stabilization is typically not required. For grade II patella luxations, surgical stabilization is usually recommended if your pet is showing increased frequency and severity of limping. Surgical stabilization is highly recommended for grade III and IV patella luxations as high grade luxations will often cause significant lameness and cartilage degradation.
WHAT IS THE PATELLA STABILIZATION SURGERY?
The standard techniques used for patella stabilization include a trochleoplasty (deepening of the patella groove), re-alignment (transposition) of the tibial tuberosity, release of the joint capsule on one side (desmotomy), and tightening (imbrication) of the joint capsule and supporting tissue of the patella on the other side of the knee. These techniques are used for both medial and lateral patella luxations. If there is significant curvature to the femur (thigh bone), a straightening procedure called a distal femoral osteotomy may need be performed.
WHAT IS THE RECOVERY TIME FOLLOWING PATELLA STABILIZATION?
Recovery time following surgery is typically 6 to 8 weeks but can extend to up to 12 weeks depending on the severity of the luxation and extent of repair.
WHAT ARE THE POTENTIAL COMPLICATIONS ASSOCIATED WITH PATELLA STABILIZATION?
Infection of the surgery site, reluxation of the patella, implant migration, tibial tuberosity avulsion, and chronic osteoarthritis are all complications that may be encountered. The reluxation rate is around 10%, however, the risk of reluxation increases with luxation grade, higher weight, and younger age. If a reluxation of the patella occurs, a revision surgery may be needed to further stabilize the patella.
ARE THERE NON-SURGICAL TREATMENT OPTIONS?
There are not any effective nonsurgical methods to treat patella luxations. Surgical stabilization is the only proven treatment for patella luxations. Since non-traumatic patella luxations are associated with an underlying anatomic conformation abnormality, muscle strengthening exercises are unlikely to reduce luxation of the knee cap.