By DR. FRED SELF / Veterinarian

Does your four-legged friend hop across the backyard? Do you see a skip going across the kitchen? Maybe you noticed an unexpected jump running to the mailbox.

If you have seen these things or similar scenarios, your furry friend may have a luxating patella.

The patella, or knee cap, is a remarkable little bone. The main job the patella performs is acting as a pulley. For those of us not used to dealing with pulleys on a regular basis, a pulley takes force or work done in one direction and redirects it in a new direction.

That is why, when you want to raise the blinds on your windows, you pull down on the string. When you pull down, the blind goes up thanks to a pulley. The patella redirects the work being done by the thigh muscles so that the lower leg can move.

In a normal pet, the patella attaches to a muscle and tendon that run between the pelvis and a bone in the lower leg. The normal patella is designed to work in a groove with high sides. In the case of a pet with a luxating patella, there are two things wrong. First, the muscle involved is attached to the pelvis in the wrong position. This causes the patella to be pulled out of the groove. Second, the sides of the groove are too low to keep the patella in place.

There are four types of luxating patella. The first stays in place most of the time but can be forced out. The second slides in and out of position on its own but is in place most of the time. The third type is out of position most of the time but can slide in and out on its own. Type number four is usually out of place and may or may not slide into normal position. The repair for this condition is to surgically deepen the groove and change the location of attachment on the bone of the lower leg.

The first two types of luxation may not need repair. However, all forms increase the chance of having early arthritic change in the joint and a bowlegged appearance to the leg. If your pet finds it necessary to hop, skip or jump on three legs from time to time, let your veterinarian know. They can help you determine if a luxating patella is to blame.

Dr. Fred Self is a veterinarian at Shelbiana Animal Clinic in Columbiana, along with Dr. Charles Thornburg. You can reach them at 669-7717.