Spinal cord insults and heterotopic ossification in the pediatric population.

Fifteen of 152 pediatric patients with spinal cord insults (10%) developed heterotopic ossification (HO) at 19 locations. The average age of the patient was eight and one-half years. The spinal cord levels were 13 thoracic and two cervical. The average time to detection of the HO from spinal insult was six and one-half years. The hip was involved in 15 of 19 HO lesions. Decreased range of motion of the affected extremity was the most common sign of occurrence. Alkaline phosphatase was elevated in five of eight patients at the time of detection. Three patients had some resorption of the HO, and one had nearly complete resorption. Five patients (3.3%) with HO had no other etiologic agent other than the neurologic insult, and their average age at time of injury was 13 and one-half years. The hip was involved in six of seven instances. The average time to diagnose this HO was 14 months after injury. Ten patients had late concurrent etiologic factors such as surgery, decubitus ulcers, late neurogenic hip dislocation, and late acute local trauma influencing HO formation. Pediatric patients who developed HO appeared to have a lower incidence, delayed onset, and fewer associated signs and symptoms compared with their adult counterparts with spinal cord injury. Patterns of ossification about the hip differ from adults. The HO lesion has the potential to resorb. HO may be initiated years after the spinal injury by an incidental insult.