Predictive value of Singh index and bone mineral density measured by quantitative computed tomography in determining the local cancellous bone quality of the proximal femur

Objective. The purpose of this study was to assess the predictive value of the Singh index as well as quantitative computed tomography for the in vitro local mechanical competence of the cancellous bone of the proximal femur. Design. An experimental study examining the relation between mechanical properties and bone mineral density of the femoral neck determined in vitro and the clinical estimated Singh index on X-rays. Background. Evaluation of the predictive value of the Singh index, an inexpensive and simple technique for the mechanical properties of the cancellous bone of the proximal femur. Methods. The bone quality of the proximal femur of 34 patients undergoing total hip replacement was estimated by roentgenography using the Singh index. Bone mineral density was quantified by quantitative computed tomography using cylindrical cancellous bone biopsies harvested during the total hip replacement procedure by a new biopsy method. The mechanical properties of the bone specimens (Youngʹs modulus, strength and maximum energy absorption Emax) were measured by mechanical testing of the bone biopsies. Results. A strong correlation of the Singh index versus material properties of cancellous bone was noted (r=0.66 for Youngʹs modulus, r=0.73 for strength and r=0.69 for Emax, P<0.0001). The correlations of bone mineral density measured by quantitative computed tomography versus Youngʹs modulus, strength and energy absorption Emax were significant. Strength was predicted best (r=0.82; P<0.0001), followed by Emax (r=0.79; P<0.0001) and Youngʹs Modulus (r=0.73; P<0.0001). Conclusions. We conclude, that assessment of bone mineral density by quantitative computed tomography is a reliable and precise method for the estimation of cancellous bone material properties. The Singh index provides a rough estimate for the mechanical competence of the proximal femur. It is inexpensive, simply to assess and can in some cases replace the measurement of bone mineral density, notably in cases of marked decrease in bone density.