Isolated Posterior Medial Ankle Dislocation with Associated Os Trigonum Dislocation after Low-Energy Mechanism.

We describe a case of an isolated posteromedial ankle dislocation, without malleolar fracture, with associated dislocation of an os trigonal process after a low-energy tennis injury. We demonstrate that nonoperative treatment results in excellent functional outcome scores with minimal arthritic progression at 2 years of follow-up. We discuss pathoanatomic risk factors of pure dislocations and propose that an os trigonum is a risk factor for isolated dislocations of the ankle.