Stress injuries of the calcaneus detected with magnetic resonance imaging in military recruits

Background: Calcaneal stress injuries are fairly common overuse injuries in military recruits and athletes. We assessed the anatomic distribution, nature, and healing of calcaneal stress injuries in a group of military recruits. Methods: Military recruits who underwent magnetic resonance imaging for the evaluation of exercise-induced ankle and/or heel pain were identified from the medical archives. The magnetic resonance images, plain radiographs, and medical records of these patients were evaluated with regard to fracture type and the natural history of the injury. Results: Over ninety-six months, magnetic resonance imaging revealed calcaneal stress injuries in thirty recruits in a population with a total exposure time of 117,149 person-years, yielding an incidence of 2.6 (95% confidence interval, 1.6 to 3.4) per 10,000 person-years. Four patients exhibited a bilateral injury. Of the thirty-four injuries, nineteen occurred in the posterior part of the calcaneus, six occurred in the middle part of the calcaneus, and nine occurred in the anterior part of the calcaneus, with 79% occurring in the upper region and 21% occurring in the lower region. The calcaneus alone was affected in twelve cases. In twenty-two cases, stress injury was also present in one or several other tarsal bones. A distinct association emerged between injuries of the different parts of the calcaneus and stress injuries in the surrounding bones. In only 15% of the patients was the stress injury visible on plain radiographs. With the numbers available, there were no significant differences between the patients with calcaneal stress injuries and unaffected recruits with regard to age, height, weight, body mass index, or physical fitness. Conclusions: The majority of stress injuries of the calcaneus occur in the posterior part of the bone, but a considerable proportion can also be found in the middle and anterior parts. To obtain a diagnosis, magnetic resonance imaging is warranted if plain radiography does not show abnormalities in a physically active patient with exercise-induced pain in the ankle or heel. Level of Evidence: Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.