Stiffness and compactness of morselized grafts during impaction: an in vitro study with human femoral heads.

The mechanical properties of the impacted material is important when using impaction bone grafting in revision arthroplasty. We did an in vitro study to monitor the stiffness and compactness of morsellized bone grafts during impaction. Using human osteoarthrotic femoral heads as the bone source we prepared 3 types of morselized grafts with the same bone mill: (1) purely cancellous grafts, (2) cortico-cancellous grafts and (3) cortico-cancellous bone with cartilage remnants. 5 g of bone samples were progressively impacted up to 150 times in a contained cavity. All types of grafts became stiffer and stiffer during the first 30 impactions. After 30 impactions, the grafts' compactness continued to increase slowly without concomitant changes in their stiffness. Over-impaction was not useful, but did not jeopardize the implant stability. The presence of cartilage remnants considerably compromised the increase in stiffness. In contrast, the addition of cortical bone from the femoral neck did not affect the impaction and resultant stiffness.