June 2001

By James R. Roberts, MD

A healthy 60-year-old woman standing at a curb felt a "pop" in her ankle as she stepped back quickly to avoid being struck by a passing car. Afterward, she had difficulty walking and noted some relatively minor pain and swelling. Although the discomfort caused her to limp, she had no major disability. When she presented to the emergency department, the staff recorded the complaint as a "sprained ankle." An x-ray film of the foot and ankle did not indicate fracture. A cursory examination performed while the patient was seated in a wheelchair revealed minor bruising and swelling of the foot, which suggested a benign ligamentous injury. Movement of the foot was intact but decreased. While seated, the patient was able to demonstrate weak plantar flexion and dorsiflexion of the foot. Why is this not a case of simple sprain, and how do you make the correct diagnosis?

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ANSWER

The Achilles tendon is completely ruptured, a significant injury that usually necessitates surgical repair. A delayed diagnosis is the most frequent mistake, rendering surgical repair and rehabilitation more difficult. Physicians often commit the error of diagnosing a patient's injury as an ankle sprain and discharge him or her with a splint, crutches, and instructions for follow-up "as needed." Achilles tendon rupture often occurs after seemingly minor trauma, especially among the elderly or those receiving steroids, but it can also occur relatively easily in completely healthy persons.

Curiously, fluoroquinolone therapy has also been associated with this disorder. Often, the patient notices a popping sensation at the time of injury, but this phenomenon can occur with minor ligamentous injuries as well. The mechanism responsible for this type of injury is sudden plantar flexion, as occurs when someone takes a quick step backward. The injury also occurs when heavy objects, such as a stalled car, are pushed or during activities that involve jumping, such as basketball.

The diagnosis simply cannot be made while a patient sits in a wheelchair, because other tendons can induce plantar flexion of the foot, thereby giving the impression of normal function. Similarly, although posterior swelling may often be noted through palpation, that technique will not necessarily reveal a diagnostic defect in the tendon. An ultrasound study can often confirm the tissue defect, but the diagnosis is also easily made with the Thompson test (depicted above).

To rule out rupture of the Achilles tendon, physicians should perform the Thompson test on all patients believed to have a "sprained ankle": As a patient lies face down on a stretcher with the feet hanging over the end, the examiner briskly squeezes the calf to isolate the Achilles tendon function. If passive plantar flexion is absent, the tendon is ruptured. Although partial tears are theoretically possible, they are actually quite rare. Patients who have this injury should seek prompt orthopedic consultation, but an office visit the next day will suffice. Selected cases can be treated conservatively; however, surgery is often recommended.

Emerg Med 33(6):50, 2001

Dr. Roberts is professor of emergency medicine at the Medical College of Pennsylvania and chairman of the department of emergency medicine at Mercy Catholic Medical Center in Philadelphia. He is also a member of the Emergency Medicine editorial board.