The effects of freeze-drying and rehydration on cancellous bone

Processing technique significantly affects the strength and stiffness of bone for use as a structural alloimplant in reconstructive surgery. The effects of the rehydration of freeze-dried human cancellous bone were studied using 14-mm-diameter cancellous dowels taken from matched cadaveric sites. Three different methods of rehydration were evaluated and compared with unrehydrated freeze-dried and frozen grafts. All samples were biomechanically tested in anatomically matched pair groups to determine compressive strength and stiffness. The strength of each tested graft was expressed as a percentage of its matched pair control. Freeze-dried grafts rehydrated for 24 hours compared with frozen grafts showed no significant difference in mean compressive strength (92.6% +/- 13.3% of control). Analysis of in vacuo versus ex vacuo rehydration at one hour showed a 38% greater mean compressive strength and a 42% greater mean stiffness for the ex vacuo group. Unrehydrated grafts appeared to be both stronger and stiffer than their rehydrated counterparts. These results suggest that the rehydration of freeze-dried grafts may adversely affect graft strength and stiffness. Rehydration under a negative pressure may proceed more rapidly than the process at atmospheric pressures. These findings limit the acceptability of freeze-dried grafts as structural implants.