The effect of internal fixation without arthrodesis on human facet joint cartilage.

Internal fixation of the spine combined with limited or no fusion has been advocated in the treatment of thoracolumbar fractures, spondylolisthesis, and severe juvenile spinal deformities. Internal fixation without arthrodesis of canine facet joints has been shown to result in the irreversible gross and histologic findings typical of osteoarthritis. Surgery was performed in eight patients for the treatment of thoracolumbar fractures. In each patient, Harrington distraction instrumentation was placed across at least two vertebral segments above and below the fused area. Instrumentation was removed six to 26 months following the initial surgery. A unilateral partial facetectomy was performed at the facet joint above the lower Harrington hook. Gross examination of the facet joints revealed areas of fibrillation, fissures, and thinning of the normal cartilaginous surface characteristic of osteoarthritis. Histologic examination revealed consistent areas of erosion of the vascular tidemark, osteophyte formation, subchondral remodeling, fibrillation, and loss of the normal cartilage cellularity. These findings were consistent with the histologic appearance of osteoarthritis. Internal fixation of the spine without arthrodesis is not an innocuous procedure and may be a predisposing factor in the development of symptomatic spinal arthritis.