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A 57 year old retired male truck driver and known sufferer from myaesthenia gravis presented to the accident and emergency department with severe pain in his left ankle. The pain had begun suddenly while standing on tiptoe. His myaesthenia gravis had been treated with oral prednisolone and azathioprine for three years. Physical examination revealed a palpable gap over the posterior ankle. As Symmonds test was negative, a clinical diagnosis of partial rupture of the Achilles tendon was made and the limb was placed in an equinous plaster of Paris.
Seven days later in clinic, it was noted that the presumed defect in the Achilles tendon was unusually low and appeared to be demarcated by bone both above and below. Plain radiographs confirmed an avulsion fracture of the calcaneum (fig 1). This was successfully treated by open reduction with internal fixation. Subsequently, dual x ray absorptiometry showed that the patient's bone was well into the osteopenic range.
Ruptured Achilles tendon is a common presentation in the casualty department and is usually diagnosed on clinical grounds alone. One of the most striking features is the presence of a palpable gap on the affected side. In this case, the gap caused by an unusual fracture was mistaken for a gap in the tendon. Only when more senior staff examined the patient was the discrepancy noted. Radiographs then revealed the fracture.
Avulsion fractures of the calcaneum can be attributable to direct trauma1, 2 but have also been regarded as neuropathic fractures3 with diabetes being the usual pathology. However, this injury is most common seen in elderly and osteoporotic women. While it is unreasonable to suggest that all Achilles tendon ruptures should be radiographed, Banerjee et al4 have pointed out that apparent rupture of the Achilles tendon in the elderly should be regarded as an indication for radiography. We would suggest that these criteria should be expanded. If the patient is at increased risk of fracture for reasons other than advancing age (in our case long term corticosteroids for myaesthenia gravis) then an avulsion fracture should be considered. If the gap is close to the calcaneum and Symmonds test is negative then radiographs are indicated.
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