Working Diagnosis:
Posterior Ankle Impingement with Os Trigonum syndrome

Treatment:
The athlete used a CAM walking boot for 3 weeks . During this time period, he was told to focus on RICE therapy. Next, he began physical therapy, with emphasis on ROM, strengthening, and proprioceptive/ balance exercises.

Outcome:
The patient was able to begin a gradual return to play, just prior to 1 month after the initial injury. A telephone call to the patient's mother, 2 months after the initial Achilles tendon injury occurred, revealed he was still having symptoms of intermittent numbness in the toes with plantar flexion.
MRI of the ankle was performed, showing signs of inflammation, concerning for os trigonum syndrome. This was discussed with podiatry, who recommended continued conservative management with physical therapy. The patient made a full recovery, without any remaining numbness, and never required a surgical intervention.

Author's Comments:
The os trigonum is an accessory ossicle in the posterolateral ankle, present in 3-15% of the adult population. Os trigonum syndrome is common is ballet dancers, and soccer players, or any athlete who might repeatedly plantar-flex the ankle. It is can be triggered by an acute ankle injury, but can also be chronic, due to repetitive microtrauma known as "the nutcracker phenomenon" where the ossicle and surrounding tissue are wedged between the tibia, talus, and calcaneus.
Typically, signs and symptoms of os trigonum syndrome include pain, and swelling in the posterolateral ankle, usually when the ankle is plantar-flexed.
Diagnosis can be challenging, as the symptoms often mimic other injuries, but plain films will often reveal an os trigonum, less than 1cm in size, and may show scarring along the talus or ossicle. MRI may show soft tissue inflammation and inflammation in the posterior capsule.
Although toe paresthesia, as in our patient, is not a common presentation for os trigonum syndrome, we find this case a helpful reminder for providers to always consider the possibility of an os trigonum causing ankle pain in soccer players. If os trigonum syndrome is suspected, conservative management is first line, followed by referral for surgical consideration if there is no improvement in 1-4 months.

Editor's Comments:
Posterior impingement of the ankle can occur due to an os trigonum. As stated previously, it can occur acutely with a hyper-flexion injury or due to repetitive trauma. It can cause inflammation and scarring of the joint capsule and may also involve the posterior inferior tibiofibular ligament, the posterior deltoid ligament, or the flexor hallucis longus tendon.
Pain may be non-specific, so os trigonum syndrome should be consider in athletes with posterior or posterior lateral ankle pain. It is most common in dancers with dancers represent 61% of patient that underwent surgical intervention in a review.
Treatment is initially conservative with relative rest, possible protected weight-bearing, NSAIDs, and physical therapy. Ultrasound guided corticosteroid injection have both therapeutic and diagnostic value. In patients that fail conservative treatment, surgical intervention with excision of the os trigonum and debridement of surrounding soft tissue can be done using open or endoscopic techniques.

References:
1. Chokkappan, Kabilan, et al. "Os Trigonum - Sheer Incidental or Quite Significant? Single Photon Emission Computed Tomography/Computed Tomography's Role in a Case of Ankle Impingement." World Journal of Nuclear Medicine, Medknow Publications & Media Pvt Ltd, 2015, www.ncbi.nlm.nih.gov/pmc/articles/PMC4564925/. 2. Jones, D M, et al. "The Diagnosis of the Os Trigonum Syndrome with a Fluoroscopically Controlled Injection of Local Anesthetic." The Iowa Orthopaedic Journal, Dept. of Orthopaedics, The University of Iowa, 1999, www.ncbi.nlm.nih.gov/pmc/articles/PMC1888622/#R2.
3.Lavery KP, McHale KJ, Rossy WH, Theodore G. Ankle impingement. J Orthop Surg Res. 2016;11(1):97. Published 2016 Sep 9. doi:10.1186/s13018-016-0430-x.
4. Nault, Marie-Lyne MD, PhD; Kocher, Mininder S. MD, MPH; Micheli, Lyle J. MD Os Trigonum Syndrome, Journal of the American Academy of Orthopaedic Surgeons: September 2014 - Volume 22 - Issue 9 - p 545-553 doi: 10.5435/JAAOS-22-09-545

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