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

Abstract

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 (Young's modulus, strength and maximum energy absorption E max) 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 Young's modulus, r=0.73 for strength and r=0.69 for E max, P<0.0001). The correlations of bone mineral density measured by quantitative computed tomography versus Young's modulus, strength and energy absorption E max were significant. Strength was predicted best ( r=0.82; P<0.0001), followed by E max ( r=0.79; P<0.0001) and Young's 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. Relevance The judgement of bone strength of the proximal femur is of major importance in clinical practice. The measurement of bone density of the cancellous bone of the proximal femur has been established, however this procedure is expensive and not widely available. The relevance of the Singh-index as a simple and inexpensive Method for the estimation of the cancellous bone quality of the proximal femur in comparison to the measurement of bone density remains to be explored.