The elastic properties of morsellised cortico-cancellous bone graft are dependent on its prior loading

Confined compression experiments were carried out on cortico-cancellous bone taken from bovine femoral condyles to assess the effect of prior loading on the elastic confined modulus, EcEc of morsellised cortico-cancellous bone (MCB). Measurements were taken to find the values of EcEc for MCB subjected to cyclic loading resulting in axial stresses in the range of 0.5–3.0N/mm2. Two values of EcEc were considered: EicEic, the instantaneous modulus, and EdcEdc, the delayed modulus allowing for stress relaxation effects. It was found that the values of EcEc increased with increasing maximum axial stress. It was also found that for each stress level the values of EcEc increased as the number of load cycles increased. The dependence of EcEc on the maximum axial stress and the number of load cycles is seen to explain the wide range of values for the apparent modulus of MCB found in previous studies. Tests examining the stress relaxation behaviour of MCB are also discussed. The results indicate that a minimum of 10 compaction episodes are required for MCB to achieve around 90% of its predicted maximum stiffness for a given compaction force.