Impaction bone grafting with freeze-dried irradiated bone. Part II. Changes in stiffness and compactness of morselized grafts: experiments in cadavers.

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 gamma-irradiated. 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 fresh-frozen 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.

Impaction bone grafting with freeze-dried irradiated bone. Part I. Femoral implant stability: cadaver experiments in a hip simulator.

Processed freeze-dried irradiated allografts seem to be used less than instead of fresh-frozen allografts for impaction bone grafting in revision hip arthroplasties. Although biologically acceptable, their use is discouraged because of their questionable mechanical properties following freeze-drying and irradiation procedures. To address this question, we impacted freeze-dried grafts in 6 cadaveric femurs and loaded with a cemented Charnley prosthesis. The routinely used fresh-frozen allografts were used as controls in the contralateral side. These constructs were compared simultaneously in a walking hip simulator for their stability during 900,000 loading cycles. The mechanical parameters were axial inducible displacement and subsidence of the implant. The former parameter was lower in the implant mounted on freeze-dried impacted grafts than that mounted on the fresh-frozen bone. The latter parameter was also lower in the freeze-dried group. At the end of the test, we found no implant loosening in either group and their 'pull out' resulted in cement-prosthesis debonding, which showed the mechanical integrity of the impacted grafts. Freeze-dried grafts provide more stable fixation of the stem than fresh-frozen morselized grafts, when tested in a hip simulator.