Fracture of the spine in patients with ankylosis due to diffuse skeletal hyperostosis: clinical and imaging findings.

OBJECTIVE Only 12 patients with a fracture through a portion of the spine ankylosed by diffuse idiopathic skeletal hyperostosis have been reported. The purpose of this study was to determine the types of causative trauma, spinal sites at risk for fracture, complications mortality, diagnostic difficulties, and abnormalities identified only with special imaging studies in a group of 15 patients with this complication seen at our institution. MATERIALS AND METHODS The study included 15 patients with diffuse idiopathic skeletal hyperostosis who had a spinal fracture through an area of ankylosed spine. The criteria for diffuse idiopathic skeletal hyperostosis include flowing calcification or ossification along the anterolateral margin of at least four contiguous vertebral bodies; preservation of disk height in the involved areas; and absence of bony ankylosis of the apophyseal joint and erosion, sclerosis, or bony fusion of the sacroiliac joints. All spinal radiographs, tomograms, CT scans, and MR images obtained in these patients were reviewed to determine diagnostic difficulties, site and level of fracture, displacement of fractures, and extent of anatomic injury. The hospital charts of all patients were reviewed for history, physical examination, clinical status, treatment, and outcome. RESULTS Fourteen fractures of the cervical spine, one of the thoracic spine, and one of the lumbar spine occurred in 15 patients. Five fractures were caused by high-energy trauma and 11 fractures by low-energy, seemingly trivial injuries. The spinal fracture caused complete quadriplegia in seven patients, incomplete quadriplegia in one patient, complete paraplegia in two patients, a central cord syndrome in two patients, and no neurologic deficit in three patients. In two of three patients in whom fracture diagnosis was delayed, paraplegia developed during the delay. Three patients died within 1 week and three more died within 6 months after injury. CT and conventional tomography enabled diagnosis of posterior element fractures not seen on plain radiographs in five patients. All fractures healed, except those in the three patients who died within a week of injury. CONCLUSION Trivial trauma was the most common cause of fracture in the spine ankylosed by diffuse idiopathic skeletal hyperostosis. The severity of spinal cord injury in our patients was greater than in previous reports. We suggest that this may be a function of the relatively long segments of ankylosed spine (average, 16 vertebrae) in our patients providing a long lever arm for any traumatic force to act on. Patients with shorter ankylosed segments had less severe cord injuries. Delay in diagnosis of a fracture through an area of ankylosed spine associated with diffuse idiopathic skeletal hyperostosis was common if no neurologic deficit was present, and led to permanent paraplegia in two of three patients. CT and MR studies were useful in determining the anatomic abnormalities present, but were performed only in a limited number of patients.