Effect of bone bank processing on bone mineral density, histomorphometry & biomechanical strength of retrieved femoral head.

BACKGROUND & OBJECTIVES: Standard processing of the bone grafts involves deep-freezing and sterilization with gamma irradiation which may alter mechanical properties of the bone graft. This study was aimed at measuring the effect of bone bank processing on the mechanical properties of bone allograft and its correlation with bone mineral density [BMD, dual-energy X-ray absorptiometry (DEXA Scan)] and histomorphometric indices. METHODS: Femoral heads retrieved from patients undergoing hip replacement surgeries were used as the material. Twenty femoral heads were under taken in the study. Each femoral head was cut into two equal cubes. One cube was subjected to BMD measurement using DEXA Scan followed by unilateral compression test. Histomorphometric indices such as trabecular number (Tb. N.), trabecular separation (Tb. S.), trabecular thickness (Tb. T.) and bone volume (B.V.) were calculated on the same specimen by a computer software. The other cube was kept in deep freezer (-76°C) for a minimum of three weeks, followed by gamma irradiation and subjected to similar tests. RESULTS: Results were compared in pre- and post-processed bone specimens. A significant loss of biomechanical strength (P<0.001) with mean a loss of 18.90 per cent was found in post-processed samples in uniaxial compression tests. Similarly, BMD (mean decrease by 13.8%, P<0.01) and histomorphometric indices such as Tb. T. (mean decrease by 12.37%, P<0.01), Tb. S. (mean increase by 12.60%, P<0.001) and B.V. (mean decrease by 20.84%, P<0.01) were found. However, Tb. N. was not significantly affected. INTERPRETATION & CONCLUSIONS: The current method of processing of bone allografts i.e. deep-freezing and gamma irradiation appeared to cause a significant reduction in the biomechanical strength of allogenic bone which was more suitable to be use in the morselized form. Appropriate consideration for decreased strength needs to be given when using allogenic bone graft as a structural graft.