Randon Hall, MD
Os Trigonum Syndrome
Updated: Mar 31, 2020
Os Trigonum Syndrome (Posterior Impingement), most commonly seen in ballet dancers, can be a frustrating condition to get a handle on. Basically an overuse injury related to repetitive pointing of the foot downward. In sports this is typically seen in soccer when a player kicks the ball or ballet when dancing en pointe. As always, if you understand the anatomy it helps explain the injury and how to treat it.
The primary bone that connects the foot to the lower leg to create the ankle joint is called the talus bone. The joint acts as a hinge to allows the foot to be pushed upward or downward as needed throughout everyday activities. When the foot is pushed downward as a result the heel moves toward the back of the lower leg. The issue arrises when this is done in a repetitive manner, it will continuously cause compression or pinching of the structures between the heel and lower leg. The compression is referred to as posterior ankle impingement.
The condition can be further aggravated when the athlete has the presence of an Os Trigonum. The os trigonum is simply a bony structure off the posterior part of the talus that failed to fuse during young childhood. The presence of the os trigonum itself is considered a normal variant, however when there is symptomatic posterior impingement associated, it is referred to as os trigonum syndrome.
The classic presentation is a ballet dancer or kicking sport athlete that presents with ankle pain on the posterior aspect of the ankle. Many times it is believed to be an Achilles tendon issue. I use two specific exam techniques to evaluate for this condition when suspected. The first is simply pushing the foot downward in a rapid fashion to replicate the compression to see if this elicits similar pain. I like this maneuver because it should not be painful when there is an Achilles tendon injury or with pain coming from the growth plate of the heel. The second test is to apply direct pressure to the area just lateral to the Achilles tendon. While pressing firmly and deeply this should also replicate the pain.
If the diagnosis of posterior impingement with an os trigonum is suspected, an x-ray is not always necessary if the patient is willing to rest. However, in most cases I will obtain an ankle x-ray to look for this anatomic variant, especially in dancers, to be able to give some indication as to the likelihood of recurrence. In some cases, I will proceed with an MRI to confirm the diagnosis.
The first and most obvious step is to rest the ankle. If the athlete is weight-bearing without pain then modified activity should be enough. However, with moderate to severe pain even with everyday activities outside of their sport, I recommend a boot for 4 weeks. I ensure that physical therapy is started at the same time to prevent loss of strength while in the boot. Typically the combination of rest and boot is enough, but on occasion, an injection could be considered. Lastly, if the issue is chronic on rare occasions the os trigonum can be removed.