An os trigonum is a small extra bone attached by fibrocartilage to the back of the ankle (near the heel bone). It can be round, oval or triangular. Some people are born with it, says physical therapist Alyson Filipa, PT, DPT, who treats dancers at Cincinnati Children’s Hospital. “As you grow, it develops into a harder, bone-like material,” she says. Os trigonum can occur on one or both feet.

When this extra bone causes pain, it’s called os trigonum syndrome. Read on to learn why it’s so difficult for ballet dancers in particular and what you can do about it.

Why is os trigonum syndrome so common in ballet dancers?

According to Dr. Donald Rose, an orthopedic surgeon who specializes in dance injuries, about 12 to 23 percent of all people have this extra bone in their foot, and many live their entire lives without being affected by it. However, dancers can struggle with the os trigonum because they spend so much time relevé.

Filipa says that some dancers can dance for years without any problems. Then an increase in training, a change in choreography, or more time in pointe shoes (or switching to a different pair) can suddenly cause pain. That’s because each of these changes can cause you to spend more time in a fully extended position, where the os trigonum can irritate the connective tissue at the back of the heel. In addition, pointe shoes that don’t provide enough support can put extra pressure on the area.

How can you tell if you have it?

If an os trigonum is causing pain, you’ll feel it when you go on pointe or relevé, or even do a tendu. The pain goes away when you stand on the flat side again or flex your foot, Filipa says. “Most people think there’s something wrong with their Achilles tendon,” she adds. “But it goes deeper than that.”

If you see a doctor and they identify a possible posterior ankle injury, they will likely use their hand to passively extend your foot to test whether it reproduces the pain you are feeling. “This actually relaxes the Achilles tendon and compresses the os trigonum, which causes pain,” Rose explains. While an X-ray can show an os trigonum, Rose usually orders an MRI to clearly see the extent and rule out a soft tissue injury, such as a ganglion cyst.

What options do you have if you have an os trigonum?

Here’s the good news: Just because you have that extra bone doesn’t necessarily mean it needs to be removed. “Surprisingly, many people do very well with conservative treatment,” says Filipa. A physical therapist might have you rest the area more when you’re not dancing (i.e., wear boots outside of dance time) — or immobilize it completely for about three weeks, so you don’t dance at all. “Usually a period of immobilization is very effective at calming down the tissue around the extra bone,” says Filipa. Rose says he’s also had experience with restrictive taping and anti-inflammatory medications helping.

“You don’t have to go straight to surgery,” says Filipa, adding that conservative measures may be enough to relieve the irritation, especially if it’s a new problem that has arisen after years of being pain-free.

However, these measures are not always enough. Ross, for example, says he tried anti-inflammatories, had two cortisone shots and took a break from dancing for a few months, but the pain kept coming back. In cases like his, doctors usually suggest surgical removal to provide relief.

Surgeons can take different approaches, but Rose says the procedure usually takes just half an hour. Afterward, he says, patients typically walk in boots or on crutches for up to two weeks, then begin physical therapy. (Ross cautions that the pain in the first week after surgery was “excruciating” for him, though of course not all recoveries or surgeries are the same.)

Filipa says she often works with her patients for about four months after surgery to help them get back to full pointe dancing (the time frame may be shorter if they’re not dancing on pointe). “We work to restore their full range of motion, get rid of any post-operative swelling in that area, and do a lot of work on balance and proprioception—and then get their strength back,” she says. She notes that it’s especially helpful to work with a dance medicine professional who’s knowledgeable about ballet so they can recommend exactly how to adjust barre work and core work during recovery.

Back to dancing

After os trigonum surgery, dancers are sometimes surprised to find they suddenly have a greater range of motion than usual. “You have to get used to a new balance point,” says Filipa, explaining that some basic skills such as pirouettes may need to be relearned due to possible shifts in balance points on half or full pointe.

Ross says that was the hardest part for him. “They removed something and the mechanics changed,” he explains. He had to relearn the basic technique with a completely new body part. In his case, it took almost two years for him to fully heal and feel completely confident in his body again.

Yet most dancers eventually make it through. Rose says about 95 percent of patients who undergo the surgery can expect to return to their pre-surgery dancing level in about six to seven weeks, although sometimes the road back can take longer. “I danced the rest of my career with no pain in that part of my body,” Ross says. “I just had to learn to use the ankle and foot that I have now and trust my body again.”