Luxating Patella

Dear Dr. Jody:  “Candy”, our six year old Pomeranian, will occasionally be running along and then suddenly skip a few steps on her left hind leg.  She will run on three legs for a few steps, and then eventually put her leg back down and continue running along with all four legs working fine.  It doesn’t seem to bother her.  Why does she do this?

It sounds as if Candy may be experiencing a condition known as a medially luxating patella (MLP).  This condition is surprisingly common in toy breed dogs, but that does not mean that we should accept it as “normal”.

The patella (or kneecap) is a tiny piece of bone that is attached to her tibia (shin bone) and her femur (thigh bone) by a ligament.  This ligament slides smoothly up and down in a trough (known as the trochlear groove) at the end of her femur.  If this groove is too shallow, it allows the patellar ligament to slip sideways out of the groove, taking the patella with it.  When the patella and its ligament are out of their normal position, it prevents the knee from extending correctly, and forces the dog to hold the knee in a flexed position until she is able to wiggle it enough that the patella slips back into place.

Although many dogs do not display obvious signs of pain when this happens, it does not mean that the condition is comfortable.  We know from humans who have experienced the same condition that it does feel quite uncomfortable, even painful, when the patella pops out of place.  Additionally, the repetitive motion of the patella popping in and out of place leads to abnormal bone-on-bone rubbing as it scrapes against the medial condyle of the femur.  This can lead to arthritis and chronic pain in the knee.  The condition can also predispose your pet to other orthopedic diseases such as ruptured cruciate ligaments or a bowed-leg appearance.

If you suspect your pet may have this condition, it is best to have the knee examined by your veterinarian.  Your vet will be able to grade the severity of the condition and decide whether the condition is advanced enough to warrant corrective surgery.  Although none of us like the idea of our dog undergoing any type of surgery, it will be far better for her to have her luxating patella corrected surgically now rather than risk any further damage to the joint.