Decreasing strength of bone allograft after recovery and preservation

Bone allograft is a commonly used implant for reconstruction in the orthopedic surgery. The strength of grafts is one of the most important properties. The study was conducted to find out the effects of the bone allograft recovery and preservation toward the strength of bone in the conditions of 1) being deeply frozen meanwhile having the rapid temperature change, 2) being deeply frozen and having the slow temperature change, 3) being freeze-dried and eventually having the gamma radiation sterilization. Sixteen fresh similar sized porcine femurs were used as the samples for the strength test. They were divided into 4 groups and each group consisted of four femurs: two right and two left. Group I was the control. The bones in Group II underwent the state of being deeply frozen mean while having the rapid temperature change during the preparation. In Group III, the bones underwent the state of being deeply frozen and having the slow temperature change during the preparation. Group IV was the freeze-dried group. Before using the compression load to the subjects, all of them were placed in the moist chamber until their bone temperature remained at room temperature. Then, all the samples were pressed down by the three-point bending, single load named Shimutzu AGB 2000 until the fracture occurred. The compression load was applied to the middle of the bone and to the other two fixed points which were designed at 10 cm away from both sides of the middle point. The load was applied at the rate of 1 mm per second under the ambient temperature of 25 degrees Celsius and 55% humidity. The maximum weights of each group was recorded and compared with the others by using Student-t-test. The control group was the strongest as its fracture happened at 675.90 +/- 5.11 Kg. The bone strength of the deeply frozen group that had the rapid temperature change was 467.21 +/- 3.02 Kg while the one that had the slow temperature change was 467.30 +/- 2.90 Kg. There was no significant difference in terms of the strength between the bone under the rapid temperature change and the one under the slow temperature change while being prepared. The freeze-dried group yielded the weakest bone strength; the bone was broken at 61.17 +/- 4.21 Kg. The process of bone graft preparation resulted in weakening the strength of bone for approximately 30% in the deeply frozen condition and approximately 90% in the freeze-dried group. Surgeons should know the changes in the strength of the bone allograft and hand the bone grafts with care. Furthermore, they must select the proper type of bone grafts with proper indication.