Correlation of bone mineral density and femoral neck hardness in bovine and human samples

Abstract

Bone mineral density (BMD) is a predictor of fracture risk. The purpose of this study was to determine whether a correlation exists between femoral neck BMD and an indicator of mechanical bone strength in human and bovine samples. Human proximal femurs were obtained from seven men and two women undergoing total hip arthroplasty (THA), mean age 60.3 years. Preoperative BMD measurements of the femoral neck were obtained (Lunar DPX). A 3 cm² area of interest on each excised femoral neck corresponding to the preoperative BMD measurement site was carefully marked and BMD was remeasured postoperatively. Ten excised bovine femoral necks were also measured for BMD. A bicortical core, each cortex 2.8 cm² in area, containing the center of the area of interest was removed from the human and bovine femoral necks, cut into multiple 7-mm thick, multiple cross-sectional discs, and measured for hardness by indent depth (Rockwell International Hardness Tester, Wilson Mechanical Instruments, New York, NY). In vivo human femoral neck BMD measurements correlated with in vitro BMD measurements (r=0.99). BMD measurements of human femoral necks were significantly lower than BMD measurements of bovine femoral necks (P<0.05). Inverse relationships were found between in vivo and in vitro human BMD measurments and indent depth (r=-0.58 and -0.59, respectively). Bovine BMD measurements and indent depth were also inversely related (r=-0.64). When combined, the in vitro human and bovine samples showed an increased correlation between indent depth and BMD (r=-0.77). In conclusion, in vivo and in vitro BMD measurements of the femoral neck are virtually identical. BMD values correlate inversely with indent depth in both human and bovine femoral samples. The data indicate that indent depth is a measurement that assesses biomechanical properties of bone which are reflected in BMD measurements.