Defatted, gas-sterilised cortical bone allograft for posterior lumbar interbody vertebral fusion

In posterior lumbar interbody vertebral fusion operations, variously sized, rectangular shaped, defatted, freeze-dried, gas-sterilised cortical bone allografts were used in combination with cancellous bone autografts from excised posterior elements. Single-level fusion, with or without internal fixation, was undertaken in 38 patients aged 50 years or less with disc herniation or a failed discectomy (the younger group) and in 33 women aged 60 years or more with degenerative spondylolisthesis (the older group). Of the various observable indicators of union, changes in the allograft-host interface alone proved to be of practical use. The incidence of nonunion in patients managed with pedicle screws, with a hook and rod system or without internal fixation was 0 of 8 patients; 1 of 14 patients; and 3 of 16 patients, respectively, in the younger group, and 0 of 11 patients; 0 of 8 patients; and 2 of 14 patients, respectively, in the older group. Of the six patients with nonunion, three had persistent low back pain and only two had mobility of the fused segment which was evident on lateral radiographs during flexion and extension. No patient had graft collapse. The decrease in the height of the intervertebral space, chiefly due to settlement of the allograft into the vertebral bodies, in the younger and older groups averaged 1.1 and 1.6 mm, respectively. We concluded that this simplified technique is mechanically sound and effective in maintaining the height of the intervertebral space. Even when the graft failed to unite, fibrous union could be obtained without graft collapse. Combination with a simple internal fixator, such as a compression rod, facilitates bone union.