Foot and ankle injuries are among the most common conditions evaluated at primary care visits; the differential diagnosis of such injury is broad.1 Although many of these injuries are easily identified on imaging studies, a number of subtle, yet important, conditions can be easily missed, especially if you do not routinely encounter them. Given that broad differential, a high degree of suspicion is required to make an accurate diagnosis, which allows appropriate treatment within a reasonable time frame and minimizes the risk of long-term morbidity.
This article outlines the diagnosis and initial management of 5 important, yet often elusive, types of foot and ankle conditions: Achilles tendon rupture, injury to the syndesmosis, ankle fracture, Lisfranc injury, and proximal fracture of the fifth metatarsal.
Achilles tendon rupture
The Achilles tendon is the most frequently ruptured tendon in the body (approximately 20% of all large-tendon injuries)2; as many as 25% of cases are initially misdiagnosed.3
Presentation. Patients frequently present with pain at the Achilles tendon—2 to 6 cm above the insertion into the calcaneus—and an inability to fully bear weight.4,5 A small percentage of patients are able to ambulate on the affected side, albeit with minor pain, which likely contributes to the rate of missed diagnosis. Absence of difficulty bearing weight is due to the presence of secondary plantar flexors, which can compensate for loss of chief plantar flexor function by the Achilles tendon.2
Examination of a patient with an Achilles tendon rupture typically reveals edema, bruising, and a palpable gap within the tendon, 2 to 6 cm proximal to insertion.3,4 The Thompson test—squeezing the calf with the patient prone and the knee on the affected side flexed—can aid in diagnosis. When the Achilles tendon is intact, plantar flexion occurs at the ankle; when the tendon is ruptured, plantar flexion is absent.5 The test can be modified when examining a patient who is unable to lie prone by having them rest the flexed knee on a chair while standing on the unaffected leg.
A diagnosis of Achilles tendon rupture is supported when at least 2 of the following conditions are met4,5:
- positive Thompson test
- decreased strength during plantar flexion of the ankle
- palpable gap or pain at the typical location (2-6 cm above insertion)
- increased passive ankle dorsiflexion upon gentle ranging of the ankle joint.
Imaging has a limited role in the diagnosis of Achilles tendon rupture; because the findings of the physical examination are reliable, reserve x-rays for cases in which the diagnosis remains uncertain after examination.2 Consider ordering plain x-rays to rule out an avulsion fracture at the insertion of the Achilles tendon; ultrasonography or magnetic resonance imaging (MRI) might assist you in detecting the rupture proper, along with the location of the tear for surgical planning, if surgery is deemed necessary by an orthopedic surgeon.3-5
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