Aims: evaluate the relationship between Singh index (SI), bone mineral density (BMD) examining bone mechanical properties from ex-vivo human femoral heads.
Methods: we collected the femoral heads of 22 patients that underwent arthroplastic for fracture of femoral head under low energy trauma. 5 patients were male while 17 were female. In each patient a pelvis X-ray was performed to estimate Singh Index. From 2 to 3 bone cylinders of cancellous bone were obtained from each femoral head. 52 bone cylinders (7x10mm) were obtained. In each specimen densitometric scans were performed by means of a Hologic QDR 4500 X-ray densitometer, using a small animal software. The coefficient of variation (CV) was calculated by repositioning a sample for 5 scans by different operators. The data obtained were expressed as bone mineral content (BMC) and bone mineral density (BMD). Compression tests with a JJ Instruments T5K machine were conducted on 52 spongy bone cylinders. Each specimen was loaded in movement control; maximum failure load and Young modulus were recorded.
Results The CV for the precision was 1.8% for BMC and 2.7% for BMD. There are no differences between males and females in age, BMC, BMD and Young modulus, while there is a significant difference in maximum load and SI. As regards SI values, there are significant differences among different categories of SI for age, sex, BMC, BMD, Young modulus and maximum failure load. Considering each sample position, namely 1, 2 or 3, there was no significant difference in densitometric parameters and in mechanical properties Statistical analyses of correlations by Pearson’s coefficient showed significant inverse correlations between age and mechanical bone properties (Young modulus and maximum failure load), while the correlations between BMC, BMD and biomechanical bone behaviour were strictly direct Linear regression model demonstrated only maximum load predictors are Young modulus and BMD
Conclusions The maximum failure load is lower in females than in males with similar BMD but lower SI for different SI categories there are significant differences both in biomechanical behaviour both in densitometric parameters.The age is inversely correlated with bone densitometric features and bone biomechanical behaviour, while bone density is directly correlated with bone strength and elastic modulus.The bone strength is predicted with 93% accuracy by Young modulus and BMD.
