Mechanical stability of structured bone grafts from the anterior iliac crest

Abstract

Background The anterior part of the iliac crest is frequently used as a donor site for autogenous bone grafts. Depending on the clinical scenario, the grafts are exposed to compression and shear stresses. Insufficient stability of a bone graft can lead to the collapse of a reconstruction. The object of this study was to quantify the influence of surgery-related parameters like the bony composition (cancellous, unicortical and bicortical), the donor site and the angle of removal on the failure load of the bone plugs (shearing and compression tests). Methods A total of 137 bone cylinders varying in bony composition and in their angles to the trajectories in the anterior iliac crest were taken from 48 human hemipelvises with diamond hollow cutters. The failure load was measured in a standardized manner, each bone plug being subjected to two shear tests and three compression tests. Possible differences between groups were evaluated using analysis of covariance techniques with BMI, bone density and cortical thickness as covariates. The statistical significance level was set to 5% ( P < 0.05), no adjustment for multiple comparisons was done due to the descriptive nature of the study. Findings Bicortical bone plugs were more resistant than unicortical plugs to both compression and shear stress, and both were more stable than cancellous bone plugs ( P < 0.05). On average, the compression failure load was about twice as high as the corresponding failure load with shearing tests: the factor was approximately 1.5 for cancellous, approximately 2 for unicortical and approximately 3 for bicortical bone plugs. We could not find a significant effect of the precise donor site and the angle of removal (parallel or perpendicular to the crista) on the mechanical stability of cancellous bone plugs. Interpretation Surgeons should rather focus on the cancellous or cortical composition of the graft than location of the harvesting site or drilling angle in order to obtain a useful bone plug from the iliac crest.