Patellar Luxation

patellarThe patella (kneecap) is the flat, movable bone at the front of the knee (stifle). The kneecap is embedded in the lower end of the quadriceps muscle and forms a tendon (patellar tendon) that attaches to the shinbone. The patella usually runs in a groove of the thighbone (femur) when the stifle is flexed. When the patella pops out of this groove to either the inside (medial) or outside (lateral) a patellar luxation is diagnosed. This dislocation occurs when the knee is flexed and the groove in the thighbone isn’t deep enough or the tendon doesn’t properly hold the patella in place. Medial luxation of the kneecap is the more common of the two especially in small dogs. The conditions are classified by a grading system with Grade I being the least severe (mild instability without associated signs) through grade IV (complete, irreducible luxation), which is the most severe.

Signs that your pet has this disorder may vary with the severity of the disease. This condition may cause your dog to carry his/her leg up during physical activity (lameness). Most pets affected with this condition will carry their leg up for a few steps, and then put it back down and be completely normal. This is due to the patella luxating and creating mechanical lameness that resolves once the kneecap goes back into place. Sometimes you can observe that dogs will kick their leg out in order to pop the kneecap back into place. The lameness may become more severe as time goes on. This is usually due to arthritis or worsening of the severity. Dogs with a high grade luxation do not show the typical ‘skipping’ lameness since the kneecap does not pop back into place. Dogs who are born with this disease in both legs may have a “bow legged” appearance.

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