As an adult, you’ve probably never known that your patella (knee cap) wasn’t always a single, round bone. But, in fact, we are born with a knee cap that starts out as a piece of cartilage. Eventually, it hardens and forms the bone that glides up and down over the knee.
The patellar bone doesn’t develop into one unit right from the start — 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. What should be done about this? What can be done? Current guidelines for the management of this problem are the topic of this article from the United Kingdom. The authors present an algorithm for the conservative and surgical treatment when the condition is painful.
An algorithm is a very useful way to solve a problem using a specific set of instructions. The algorithm for bipartite patella begins with a patient who is having knee pain that started after trauma to the knee, from overuse (e.g., cycling or hill climbing) or more gradually with no known cause. Bending the knee is the main aggravating factor.
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. But it’s not that simple. There are many more decisions to be made regarding the most appropriate surgery. The algorithm continues.
In the algorithm, patients who are surgical candidates are divided into two separate groups. The first group is made up of those with test results that show the surface of the patella is scarred and irregular and the bone is in pieces that move. The second group has a healthy surface and the patellar pieces are stable (not moving).
In the surgical treatment of the first group, the surgeon removes the moveable fragments. This can be done with arthroscopic surgery but in some cases, an open-incision procedure may be needed.
For patients with the healthy, immobile bone fragments, 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 algorithm helps guide this decision-making process. 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.
Even with this nicely laid out algorithm, there are many unknowns about the best way to treat bipartite patella. If the larger fragments are wired in place, will the knee develop arthritis later? What size fragment responds well to this type of fixation? Where does the surgeon draw the line on what size fragments can be removed versus which ones can be preserved? These are just some of the many questions that remain to be answered in future studies on this condition.