Acute thoracolumbar burst fractures: a new view of loading mechanisms.

STUDY DESIGN: An in vitro investigation of loading mechanisms in acute thoracolumbar burst fractures. OBJECTIVES: To assess the validity of the authors' hypothesis that anterior shear forces transmitted by the facet joints are responsible for causing the severe canal compromise associated with acute thoracolumbar burst fractures. SUMMARY OF BACKGROUND DATA: Thoracolumbar burst fractures created in the laboratory rarely match the severity of clinical cases. To date, no studies have examined in great detail the role of facet joint loading in the burst-fracture mechanism. An incomplete understanding of loading mechanisms may contribute to the controversies regarding management. METHODS: Nine human cadaveric motion segments were instrumented with strain gages and subjected to axial compression or axial impact coupled with an extension moment. Failure loads, strain information, and radiographs were collected. RESULTS: Fracture patterns characteristic of acute thoracolumbar burst fractures were observed in the three specimens tested with an extension moment. In this group, high strains were also recorded at the bases of the pedicles, indicating a probable site of fracture initiation. Specimens tested in a neutral orientation experienced crush fractures without an increase in interpedicular distance. Strain patterns were more uniform in this group. CONCLUSIONS: The severity and clinical relevance of the injuries sustained by the specimens tested in extension suggest that facet joint loading plays a critical role in the acute thoracolumbar burst-fracture loading mechanism. Fracture patterns and strain concentrations are in agreement with clinical observations as well as past experimental studies.

Inflammatory disorders of the cervical spine.

The most common inflammatory disorders affecting the cervical spine include adult and juvenile rheumatoid arthritis, ankylosing spondylitis, Reiter's syndrome, and psoriatic arthritis. These disorders are characterized by typical deformities and instabilities of the cervical spine that result from the destruction caused by synovitis in bony and ligamentous structures in the neck. The treatment of these inflammatory lesions differs from the treatment of similar lesions found in the posttraumatic or degenerative spine. This article attempts to outline the epidemiology, clinical manifestations, and natural history of these conditions. Various radiographic parameters for evaluating disease progression have been used over the years, and their usefulness is reviewed in the context of recent studies better defining the radiographic natural history of these lesions. An algorithm for the use of the various imaging methods including magnetic resonance scanning is provided, and recent progress in delineating the proper timing of surgical intervention and the predictors of neurologic recovery is presented. The current surgical procedures available to treat these conditions are discussed with emphasis on distinguishing those cases in which stabilization alone is required from those in which a decompression procedure is also necessary.