Histologic Study of Fractured Human Vertebral Bodies

Philadelphia, PA, USA

INTRODUCTION: In the elderly, spine fractures with collapse may occur after minimal trauma. Many of these fractures are clinically asymptomatic, and some remain occult, but many cause profound pain and morbidity. In addition, some compression fractures often lead to progressive spinal deformity and chronic pain, whereas others do not. This study focused on individuals with fractures secondary to osteoporosis.

METHODS: 46 human thoracolumbar spines were obtained from individuals at autopsy. Standard radiographs were made of all specimens. 12 of the 46 individuals had a total of 27 fractured vertebrae. Attention was focused on these fractured vertebrae as well as 24, unfractured vertebral bodies which were harvested from a level immediately adjacent to the fractured vertebrae. 12 vertebral bodies from 4 individuals with no evidence of fracture or inflammatory spondyloarthropathy were also studied for comparison. The vertebral bodies were graded by their mineral density as measured by DEXA, and sectioned into 3 mm sagittal cuts. High resolution contact radiographs were prepared for each section prior to decalcification and tissue sectioning on a large format microtome. Mid- and parasagittal tissues sections of each Vertebral bodies with fractures secondary to osteoporosis were consistently characterized histologically by focal endochondral new bone formation adjacent to avascular necrotic bone and unreactive marrow. Such on-going new bone and new vessel formation adjacent to un-healed areas was also documented in radiographically unfractured vertebral bodies. Myelinated nerve bundles were documented adjacent to these areas usually associated with blood vessels, but occasionally as solitary bundles. No areas of new bone formation or areas of focal necrosis were found in vertebral bodies from individuals without radiographic evidence of osteoporosis.

CONCLUSION: Avascular necrosis of the vertebral body is a common histologic finding in individuals with osteoporosis. Indeed, our histologic observations suggest sub-clinical fractures and micro-fractures of the vertebral body may be the underlying pathologic process leading to avascular necrosis in individuals with osteoporosis. Microtrabecular fractures and endplate fracture were commonly seen in osteoporotic vertebral bodies, often in vertebra that appeared to be uninvolved on specimen radiographs. It is possible that nerve bundles documented within and adjacent to osteoporotic, vertebral compression fractures may contribute to the variable patterns of pain production noted clinically.