The patellar bone doesn’t come fully developed at birth — it is either two or three peices that eventually ossify (harden into bone). By age six, most children have the pieces necessary to form a single, hard patellar bone. Between ages six and 12, all the pieces join together and fuse into one bone that forms the adult patella.
But in about two to six per cent of children (boys more often than girls), fusion doesn’t take place. The patella may remain in two pieces called bipartite patella or three pieces called tripartite patella. The patella remains that way into adulthood. Most of the time, the person isn’t even aware that there’s a problem.
It’s only if the knee is injured and an X-ray is taken or (more rarely) the knee becomes painful slowly over time that the diagnosis is made. It sounds like the skiing injury brought this to your attention. There’s still some debate whether the bipartite condition is really just a failure of the growing bone fragments to form solid bone or if injury somewhere along the line caused a fracture that hasn’t healed.
Either way, the question of what can be done is important. Current guidelines for the management of this problem begin with a recommendation for conservative care first (for at least six months). Treatment begins with rest, the use of nonsteroidal antiinflammatory drugs (NSAIDs), and physical therapy. The therapist prescribes stretching exercises, a dynamic patellar brace, and possibly low-intensity pulsed ultrasound to stimulate a healing response. Steroid injections administered by the physician may also be helpful.
If there’s no response to treatment or an inadequate response (i.e., patient still can’t participate in sports or tolerate daily activities), then surgery is the next step. There is a wide range of surgical options to choose from.
If the surface of the patella is scarred and irregular and the bone is in pieces that move, the surgeon removes the moveable fragments. This can be done with arthroscopic surgery but in some cases, an open-incision procedure may be needed.
Anyone with this condition who has a healthy surface and the patellar pieces are stable (not moving) may be treated differently. Small fragments can be removed. Or instead of taking the extra bone out, the soft tissues still attached to the fragment can be cut to release the pull on the patellar piece. There are different ways to do this — each one has some disadvantages (e.g., muscle weakness, muscle imbalance, abnormal patellar tracking up and down).
Larger pieces can be wired back in place but there’s always the risk of stiffness from the long period of immobilization needed to foster healing. Fortunately, not very many people end up needing surgery for this problem. When they do, the results are usually pretty good.
The key to a successful outcome is to choose the right treatment for each patient individually. The goal of treatment is to provide pain relief, return to full activity (including sports participation for athletes), and protection of the remaining knee cap.