THE EFFECT OF INSTRUMENTATION ON HUMAN SPINAL-FUSION MASS

Study Design. This study is a prospective histomorphometric evaluation of human spinal fusion bone using video dimensional analysis. Objecti ves. Little information exists regarding the biology of fusion mass (F M) and the effect that instrumentation has on FM quality. Concerns reg arding potential for ''stress shielding'' of FM with rigid implants ha ve arisen. The goal of this study was to determine what effect spinal implants have on the quality and metabolism of FM bone. Methods. Fifty -six patients underwent surgeries to remove spinal implants or extend a fusion after pulse-dose labeling with fluorochrome. Twelve patients had undergone fusions without instrumentation. Duplicate biopsies of F M and iliac crest (IC) were obtained and evaluated blindly for mineral ized volume, trabecular thickness, mineralization rate, and bone forma tion rate. Iliac crest, instrumented FM, and noninstrumented FM were c ompared. Results. Instrumented FM had superior material properties rel ative to noninstrumented FM or IC. No significant difference in metabo lic activity was present.Conclusion. Instrumentation does not lead to FM ''stress-shielding.''