Predictive value of bone mineral density and Singh Index for the in vitro mechanical properties of cancellous bone in the femoral head

Objective: The purpose of this study was to assess the validity of two methodically different radiological parameters, bone mineral density and Singh Index, for the prediction of mechanical properties in femoral cancellous bone. Design: Coherence between in vitro evaluation of mechanical properties and bone mineral density on a femoral bone slice, combined with clinical determination of Singh Index on ordinary X-rays. Background: It is accepted that bone densitometry yields excellent prediction of mechanical bone quality, but is considered to be an expensive and not widely available method for routine diagnostics in clinical practice. In contrast, determination of Singh Index is an inexpensive and simple technique, but its predictive value for bone mechanics is still controversially discussed. Methods: We used cortically confined bone slices from 33 femoral heads. Bone mineral density was measured using quantitative computed tomography. Strength and elastic modulus were assessed by mechanical testing in up to 39 circular positions on each slice. Singh Index was evaluated on ordinary X-rays of the hip by two independent readers. Results: Bone mineral density showed strong correlations with strength (r=0.86) and good correlations with elastic modulus (r=0.68). Singh Index correlated well with strength (r=0.70), but only moderately with elastic modulus (r=0.52). Conclusions: The strong validity of bone mineral density in predicting mechanical bone quality was confirmed. Singh Index assessment permits a rough estimation of mechanical strength in particular and can therefore be used for first estimations of mechanical bone quality, provided that readings were performed by experienced clinicians.