Biomechanical comparison of three types of bone graft for anterior spondylodesis.

BACKGROUND

Anterior spondylodesis with bone grafting for fusion of spinal motion segments is a common procedure in clinical routine. Bone grafts for fusion include autologous, allogenic and xenogenic grafts that are inserted in the unstable spinal motion segment. Nevertheless, biomechanical data for autologous, allogenic and xenogenic grafts are rare.

OBJECTIVE

The purpose of this study was to conduct biomechanical comparison of native and conserved bone grafts used in spondylodesis of the spine.

METHODS

Grafts examined were native ovine tricortical iliac crest grafts, bovine cancellous bone blocks and ovine, tricortical iliac crest grafts, conserved in the same way as the bovine cancellous bone blocks. The grafts were tested biomechanically to failure. Compared parameters were maximum torque, maximum rotation angle and graft stiffness at failure. The Mann-Whitney-U test with Bonferroni adjustment was used for statistical analysis.

RESULTS

Maximum torque at failure of the bovine cancellous bone graft did not differ significantly from that of the native ovine tricortical graft. Comparison of the conserved ovine tricortical graft revealed significantly lower values compared to the native ovine tricortical bone graft.Maximum rotation angle at failure of the untreated ovine tricortical bone grafts was significantly higher compared to the other grafts tested. Regarding graft stiffness no significant differences were found.

CONCLUSIONS

Based on the functional demands exerted on the spinal motion segment, our results suggest that torsional strength and deformational behavior of the bone graft influence the stability of the spondylodesis. The native tricortical graft best fulfills this requirement.