Comparison of Two Surgical Techniques to Remove Os Trigonum in Ankle

Some people are born with an extra little bone in the ankle called the os trigonum. Studies show that up to 50 per cent of all people have this anatomic anomaly. Without an X-ray or other imaging study, they might never know about it. It doesn't cause any problems until and unless the person is involved in activities that require full and repeated foot and ankle plantarflexion (toe pointed downward). Ballet dancers and soccer players fall into this category most often.

When the foot and ankle are plantarflexed, the os trigonum (and soft tissues attached to it) get pinched between the tibia (lower leg bone) and the calcaneus (heel bone). Ankle pain can develop that is so severe, the athlete must stop all activities and motions that aggravate the problem. Running and jumping are out of the question until the inflammation has subsided. Physical therapy may be needed to address postural and alignment issues that could be contributing.

If conservative (nonoperative) care is not successful in treating the problem, then surgery to remove the bone may be needed. In the past, surgeons used an open incision technique to cut the bone out but problems developed. Permanent nerve damage occurred in some patients and the large, visible scar was a problem for professional dancers.

As smaller surgical instruments became available and more precise surgical techniques were developed, it became possible for this procedure to be done using an arthroscope. Then in 2000, a new technique called posterior endoscopy was introduced. Since that time, a group of surgeons from the College of Medicine at the Catholic University of Korea have been using both the arthroscopic and endoscopic techniques to excise (take out or remove) the os trigonum.

In this study, they report the results comparing these two surgical techniques. It is the first study published making direct comparisons. Their goal was to "clarify the efficacy and safety of each surgical procedure." Patients between the ages of 17 and 55 who had this surgery (os trigonum excision) were followed for three years. Results were measured using a variety of outcomes including pain, motion, function, length of time in surgery, time to return to sports participation, and patient satisfaction.

Patients in both groups improved significantly and were pleased with the results. Both techniques were considered "safe and effective." Certainly, the length of time for the surgery and recovery were much shorter when compared with the open incision technique.

The differences really lie with the surgical technique and level of surgeon expertise. Large os trigonums are more difficult to remove using the arthroscopic approach. There is very little room inside the subtalar joint where the scope enters. It's also difficult to see inside this area. Using the endoscopic approach from the back side of the ankle requires cutting the flexor hallucis longus tendon but gives the surgeon more room to work in and greater visibility.

The authors advise surgeons to consider using the endoscopic technique for patients with large-sized os bones (more than 135 mm²) or in cases that are more demanding. Open surgery may be needed if arthroscopic and/or endoscopic techniques are not successful in eliminating the problem. As this study showed, all patients benefitted from either method (arthroscopic or endoscopic). Everyone returned to their previous level of sports participation. Even the ballet dancers were able to dance up on pointe with full motion and without pain.

Reference: 

Jae Hoon Ahn, MD, et al. Arthroscopic Versus Posterior Endoscopic Excision of a Symptomatic Os Trigonum. A Retrospective Cohort Study. In The American Journal of Sports Medicine. May 2013. Vol. 41. No. 5. Pp. 1082-1089.

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