A 21-year-old professional football player presented with a two-month history of increasing posterior ankle pain. This was initially only present when striking a ball from his ‘laces’. It is now present when sprinting and jumping.
On examination there was pain with normal ankle plantar-flexion. This was made worse by forced plantar-flexion (a posterior thrust test). His ankle and sub-talar range of motion was otherwise normal. He had good power of all ankle movements and no evidence of past instability. The ankle examination was otherwise quite unremarkable.
X-ray images, including one taken in a plantar flexed position, show a large os trigonum. An MRI has demonstrated that there is bone oedema within the os trigonum. There is a small amount of subchondral cyst formation and reactive change in the posterior process of the talus adjacent to the synchondrosis. The appearance suggests an unstable os trigonum. The os is also quite large measuring approximately 12 x 12 x 7 mm.
This player was initially managed with time, physiotherapy and taping to limit ankle plantar-flexion. This was followed by a transient improvement with a corticosteroid injection into the posterior ankle. Unfortunately, the athlete’s symptoms returned and surgery was eventually required to excise the os trigonum. This was done at the end of their competitive season. They were able to return to all normal activity a little after three months post-surgery.
Ankle impingement can involve either the anterior or posterior ankle and may be due to bony or soft tissue causes (or both). Posterior impingement can have a variety of causes. A prominent posterior process of the talus or os trigonum (as in this case) may predispose a player to developing this condition. Soft tissue causes of impingement include synovial hypertrophy, capsular injury, ligament injury and flexor hallucis longus (FHL) tenosynovitis or tendinitis.
In very general terms impingement often resolves with avoidance of aggravating activity. Taping or bracing to prevent terminal plantar-flexion (or dorsiflexion when there is anterior impingement) can allow an athlete to remain active. Oral NSAIDs can also be helpful. Steroid injections can provide very dramatic relief of symptoms if these other interventions fail but unfortunately often only give short-term relief. When the symptoms are refractory to treatment, arthroscopic debridement can give a good result.
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