The knee cap is a frequent source of pain. While treatments for other parts of the knee have evolved, the knee cap — or patella — remains in the old school of frustratingly vague treatment options. Here are some of the lowlights:

The patella is a sesamoid bone, meaning that it sits in the middle of a tendon and is not attached to anything else. Its best function is to act as a lever arm, permitting the thigh quadriceps muscle contractions to elevate the lower leg. When it is injured and painful, the thigh muscle weakens, the patella moves abnormally and the cycle worsens.

The undersurfaces of the patella are covered by articular cartilage: the smooth bearing material that permits the knee to glide with five times the slickness of ice on ice. If an injury to the patella damages or roughens that surface, small bits of cartilage break off into the knee. This irritates the joint lining, called the synovium. This process produces joint fluid and swells the knee. The rough cartilage causes the familiar grinding sensation, and the swollen knee forms scar tissue.

This cycle can be interrupted, at least partially. Injuries to the knee cap that don’t damage the bearing surface can often be successfully treated with physical therapy, soft tissue massage, muscle strengthening, ice and anti-inflammatories. Injections are also used. Today, the irritated tissues around the patella are more commonly treated with growth factors combined with lubrication injections rather than cortisone, since steroids have been shown to weaken tissues.

When the cartilage is damaged enough to warrant repair, though, our techniques have not improved very much over the years. The damaged cartilage can be smoothed down with shavers or heating devices, but neither of these actually repairs the tissue. And if the wear increases, the bone of the patella is exposed and pain can be become chronic.

All of the true cartilage repair techniques that we use on the femur and tibia fail at the patella. The causes are many, but they are generally related to the bone’s poor blood supply, and the strong forces applied to the patella when the quadriceps contracts. Once damaged, the cartilage of the patella never heals normally. Even the addition of stem cells and growth factors has not yet changed this outcome.

When the patella truly wears out, patella replacement techniques—using robotic surgery — have advanced to the point where there is no reason to live in pain. These replacements are highly successful at removing the anterior knee pain. But even artificial replacements may eventually fail and thus are reserved for the worst bone-on-bone cases.

Where to from here?

The future lies in better cartilage replacement. Our team and others are dedicated to the advancing this science. Stopping the arthritis before it progresses is the first step, with biologic surface replacement being the ultimate solution.

In the meantime, protect your knee caps, treat minor injuries immediately, smooth down the more serious ones before they grind away the surfaces, and employ the best lessons of physical therapy and muscle development on a daily basis. And if you kneel to pray, pray to be able kneel forever.

Dr. Kevin R. Stone is an orthopedic surgeon at The Stone Clinic and chairman of the Stone Research Foundation in San Francisco.

Dr. Kevin R. Stone
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Dr. Kevin R. Stone

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