DEFATTED, GAS-STERILIZED CORTICAL BONE ALLOGRAFT FOR POSTERIOR LUMBARINTERBODY VERTEBRAL FUSION

In posterior lumbar interbody vertebral fusion operations, variously s ized rectangular shaped, defatted, freeze-dried, gas-sterilised cortic al bone allografts were used in combination with cancellous bone autog rafts from excised posterior elements. Single-level fusion, with or wi thout internal fixation, was undertaken in 38 patients aged 50 years o r less with disc herniation or a failed discectomy (the younger group) and in 33 women aged 60 years or more with degenerative spondylolisth esis (the older group). Of the various observable indicators of union, changes in the allograft-host interface alone proved to be of practic al use. The incidence of nonunion in patients managed with pedicle scr ews, 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 t he younger group, and 0 of 11 patients; 0 of 8 patients; and 2 of 14 p atients, respectively, in the older group. Of the six patients with no nunion, three had persistent low back pain and only two had mobility o f the fused segment which was evident on lateral radiographs during fl exion and extension. No patient had graft collapse. The decrease in th e 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 simplifi ed technique is mechanically sound and effective in maintaining the he ight of the intervertebral space. Even when the graft failed to unite, fibrous union could be obtained without graft collapse. Combination w ith a simple internal fixator; such as a compression rod facilitates b one union.