Relationship of donor variables and graft dimension on biomechanical performance of femoral ring allograft.

Structural femoral ring allograft is commonly used in interbody spinal arthrodesis. Fractures of implanted femoral ring allograft have been reported. Data to guide donor screening and tissue processing by allograft tissue banks for factors that affect graft strength are incomplete. Fresh frozen human femora from 34 cadaveric donors were sectioned into ten 20-mm thick specimens. Bone mineral density (BMD), donor age, and graft dimensions were recorded for each specimen. Three hundred twenty-seven specimens were tested in quasi-static axial compression. Linear regression models compared load to failure with BMD, sex-specific donor age, minimum/maximum cortical wall thickness, and minimum/maximum outer ring diameter. Correlations between minimum and maximum cortical wall thickness and load to failure were significant (r = 0.73, p < 0.001 and r = 0.74, p < 0.001, respectively). BMD showed a weaker negative correlation with load to failure (r = -0.11, p = 0.05). Correlations between load to failure and minimum and maximum outer ring diameter and age (r = 0.06, p = 0.31) were not significant. We found that the minimum and maximum cortical wall thicknesses of femoral ring allograft are strongly correlated with the axial compressive load to failure of the graft. Other tested parameters did not prove to be effective predictors of resistance to axial loading.