Doctors in Florida have reported an injury rarely seen. A professional basketball player hit his knee on a tray table during an airplane landing. He still played basketball, but he had discomfort on and off that became constant pain. A year later, he was unable to play basketball.
Doctors were puzzled at first. The usual tests in the office didn't show anything. The kneecap (patella) was moving normally and the knee was stable with full motion. X-rays and MRIs showed some dense bone tissue that looked like chronic knee (patellar) tendonitis.
After trying various treatments, the athlete chose to have surgery. Doctors used a device called an arthroscope to look inside the knee. They found a bipartite patella. The kneecap was in two parts that had never fully fused together.
Only about two to six percent of the American population has this condition. At birth, the patella is normally a thick piece of cartilage. By age four to six, it has hardened into bone and has become one piece. If this doesn't happen, a direct force to the kneecap can cause it to separate.
Bipartite patella can be treated with drugs, changes in activity level, and local steroid injections. A cast to keep it immobile may work. In other cases, surgery is needed to remove small pieces of the patella. Since it doesn't happen very happen, doctors haven't been able to study this condition enough to know if there's a "best" treatment for everyone.
George H. Canizares, MD, and F. Harlan Selesnick, MD. Case Report: Bipartite Patella Fracture. In Arthroscopy. February 2003. Vol. 19. No. 2. Pp. 215-217.'