Posterior Impingement of the Ankle Caused by Anomalous Muscles

Abstract

P osterior impingement of the ankle results from the compression of the talus and surrounding soft tissue between the tibia and the calcaneus and has been likened to a “nut in a nutcracker.”1 It is produced by repetitive or forced plantar flexion of the foot and has been described in female ballet dancers, athletes, and in nonathletes after an ankle sprain1-4. Patients have pain in the posterolateral or posteromedial aspect of the ankle with activity, particularly plantar flexion. Often there is tenderness medial or lateral to the Achilles tendon, and soft-tissue thickening may be palpated. A positive posterior impingement test consists of reproduction of the symptoms with forced plantar flexion of the ankle2. The diagnosis is made on the basis of the history and physical examination of the patient and the clinical judgment of the surgeon and is supported if the symptoms are temporarily relieved by an injection of a local anesthetic and steroid into the region of the posterior process of the talus through a posterolateral approach2. Structures implicated in the etiology of posterior impingement of the ankle include an os trigonum5, an enlarged lateral process of the talus2, an enlarged posterior process of the calcaneus1, the posterior intermalleolar ligament6, soft-tissue impingement7, a gouty os trigonum8, loose bodies, ganglia, calcified inflammatory tissue, and a low-lying flexor hallucis longus muscle belly1,2. The surgical resection of symptomatic structures can be a successful treatment even in the high-level athlete2. Anomalous muscles about the ankle have been documented since the nineteenth century9-11. The peroneus quartus has been reported most frequently, and studies involving anatomical dissection of cadavera have shown that the prevalence …