In the technique of impaction bone grafting, implant stability depends on the mechanical properties of the impacted morselized grafts. Although the procedure is usually performed with fresh-frozen femoral heads, there is still some concern about their supply and safety. Bone processing is a potential solution, but the mechanical properties of this material during and after impaction need to be determined.We used 6 osteoarthrotic femoral heads to prepare two paired batches of morselized bone. One batch was morselized and frozen. The other batch was chemically treated, morselized, freeze-dried and then gammairradiated. We impacted 18 samples from each batch in a contained cylinder. Freeze-dried bone grafts were tested after 30 minutes of rehydration. The changes in the compactness and stiffness of the material were monitored during the impaction. The compaction of the freeze-dried bone was faster than that of their freshfrozen control. The maximal stiffness reached by both materials was the same (55 MPa), but the freeze-dried grafts required three to four times fewer impactions to achieve that stiffness. After 3, 10 and 50 impactions the freeze-dried bone was stiffer than the fresh-frozen bone. As it is easier to impact, the freeze-dried bone may be mechanically more efficient than the fresh-frozen bone in surgical conditions. Moreover, the processed bone meets the highest safety standards, as regards the risk of disease transmission.
Background Defatted bone chips with or without freeze-drying and irradiation have mechanical advantages as compared to fresh-frozen controls in in vitro models of impaction. These improved results have been ascribed to replacement of viscous bone marrow by saline and embrittlement of the freeze-dried bone by irradiation.Material and methods To determine which of these hypotheses is correct, we compared the development of stiffness and compactness of morselized bone graft that had been: 1) fat-reduced with saline, and 2) fresh-frozen, solvent-detergent defatted, 3) freeze-dried irradiated and 4) not irradiated. We used 12 osteoarthrotic femoral heads to prepare these four batches of morselized bone, and impacted 18 samples from each batch in a cylinder. The frozen bone grafts were tested after thawing at room temperature for 2 hours and the freeze-dried grafts were tested after 30 minutes of rehydration. We monitored the development of compactness and stiffness of the material during impaction.Results The stiffness of the freeze-dried irradiated bone was greater than that of the other three series after 10, 50 and 150 impactions. The freeze-dried bone chips that were not irradiated and the chips defatted with saline alone were less stiff than the fresh-frozen control after 150 impactions.Interpretation The brittleness of freeze-dried irradiated bone, caused by loss of the capacity to absorb energy in a plastic way, increases the compactness and stiffness of the morselized grafts. Washing bone with saline alone or treating bone with solvent-detergent but no irradiation had no similar mechanical advantage and the bone did not impact better than fresh-frozen undefatted bone in our model.
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