Purpose of the study: Osteomyelitis is rarely observed in the calcaneus; about 3 to 10% of the bone infections in children. The diagnosis is often established late because of the less pronounced symptoms in long-bone localizations. We report a series of 26 cases of osteomyelitis of the calcaneus observed in children.
Material and methods: We studied the clinical history, the diagnostic process and the treatments delivered. Outcomes were assessed in terms of complications, anatomy and function at mean two years follow-up (range one to seven years).
Results: There were 15 boys and 11 girls, mean age was seven years (range one month to 13 years). Mean time from symptom onset to consultation was 13 days and mean time from consultation to hospital admission was four days, range one to 29 days. The clinical presentation was not specific. Body temperature was not above 38.5 degrees C in 45% of patients. Symptoms were fever, pain in the rear foot and functional impotency of the lower limb. Eight patients (30%) complained of moderate pain, 18 (70%) of intense pain. The pain was focused far from the calcaneus in six patients, retarding the diagnosis. Laboratory tests did not always reveal signs of inflammation. White cell counts above 10,000 were noted in only 61% of patients. The diagnosis of osteomyelitis of the calcaneus was based on: the plain X-ray, which revealed a defect in the calcaneus (n=12), ultrasound (performed in 19 patients) which revealed calcaneal subperiosteal detachment (n=6), collections in the rear foot (n=3) and soft-tissue thickening (n=4). Bone scintigraphy was performed in one child and showed intense uptake in the calcaneus. Magnetic resonance imaging, performed in one patient, demonstrated an anomalous signal in the calcaneus (high-intensity T(2) and low-intensity T(1) with presence of a subperiosteal abscess). Bacteriology was positive in 53% of the children. Medical treatment was delivered for all patients and 23 underwent a surgical procedure. For one of the three patients treated medically, the diagnosis of osteomyelitis of the calcaneus was clinical, since the plain X-ray was normal, the ultrasound yielded no evidence of abscess formation and the bacteriology was negative; but after two months of antibiotic treatment, bone remodelling was in favour of osteomyelitis of the calcaneus. For the two other patients treated medically, the plain X-ray showed a defect in the calcaneus, which had filled after two months of antibiotics. For the 23 patients treated surgically, the procedure was an evacuation of a subperiosteal abscess for 13 (n=6 nonruptured and 7 ruptured). Surgery revealed a bone lesion in nine children allowing curettage of the defect. Articular involvement was noted in eight cases: subtalar osteoarthritis (n=6) and tibiotarsal arthritis (n=2). Two surgical explorations failed to find any abscess formation; blood cultures confirmed the diagnosis and enabled isolation of the causal germ. Outcome was assessed with a mean follow-up of two years, range one to seven years. Nineteen patients (73%) were free of sequelae. Seven patients (27%) presented poor outcome with significant limitation of motion in the rear foot and ankle ankylosis. Seven patients developed chronic fistules, with persistent discharge at last follow-up. The poor results were observed in patients treated late with mean 17 days before consultation. Six of the seven cases of poor outcome were associated with arthritis involving a calcaneal joint (subtalar and tibiotarsal in two patients and subtalar in four).
Discussion: The same pathophysiological phenomenon as observed in long-bone localizations is noted for osteomyelitis of the calcaneus; the calcaneus has an apophysis, which is equivalent to the metaphyseal region of long bones, leading to the bone's vulnerability to hematogenous infection. Late diagnosis can be related to the notion of trauma, the manifestations of osteomyelitis being attributed to ligament injury. The positive diagnosis of osteomyelitis of the calcaneus is often established late because of late consultation (13 days in our series) or the minimal expression of general signs. Magnetic resonance imaging contributes significantly to diagnosis by showing an abnormal bone signal; it can also disclose associated abscess formation. Authors differ in their descriptions of the complications. The analysis of our results shows that the prognosis of osteomyelitis of the calcaneus is related to early diagnosis and management. Associated septic arthritis is an element of poor prognosis.