[Experimental study of anti-infective reconstructed bone xenograft]

To develop a new type bone graft material that can be used as primary graft in contaminated even infected bone defect.

Anti-infective reconstructed bone xenograft (ARBX) was developed by combining reconstructed bone xenograft (RBX) with gentamycin and gelatin. One piece of ARBX was implanted in the muscle pouch in right thighs of 32 mice. The implanted ARBX and surrounding soft tissues were taken out from the mice at different time point to make into homogenate and the concentration of released gentamycin in the supernatant and the diameter of the bacterial inhibition ring of each specimen were tested. One piece of ARBX was implanted into the muscle pouch at the right thigh of 16 mice and one piece of RBX was implanted into the muscle pouch at the right thigh of another 16 mice. Fourteen days after the grafts and surrounding tissues were taken out to be examined histologically or made into homogenate to test the alkaline phophatase (ALP) activity. Bone defect was made in the bilateral radii and then Staphylococcus aureus was injected and debridement was conducted. 10 pieces of ARBX were implanted into the bone defect at the left radius and 10 pieces of RBX were implanted into the bone defect at the right radius. The defect was then fixed and the wound was sutured. Gentamycin was injected for 1 week. Six months later X ray examination was conducted to the radius, then the radius was taken and half of specimens were examined histologically and half of them was made into homogenate to examine the amount of Staphylococcus aureus. Defect was made in the right tibia of 25 rabbits and Staphylococcus aureus injected therein. Then the rabbits were divided into 5 groups of 5 individuals: group 1 (3 pieces of ARBX were implanted), group 2 (3 pieces of RBX were implanted and gentamycin was used locally), group 4 (3 pieces of RBX were implanted and gentamycin was injected intramuscularly), and group 5 (control group, without born grafting). Eight weeks after, radiological, histological, and bacteriological methods were used to observe the recovery of bone defect and amount of Staphylococcus aureus.

Gentamycin was released slowly from the ARBX and the effective bacterium-inhibiting concentration lasted 30 days. There was no significant difference in osteoinductive activity and related ALP activity between the mice implanted with ARBX and RBX. The bone defect of the dogs implanted with ARBX recovered better than that of the dogs implanted with RBX; osteomyelitis was found in the specimens from the bone defect implanted with RBX and not in the specimens implanted with ARBX, and the positive rate of Staphylococcus aureus was lower in the specimens implanted with ARBX than in the specimens implanted with RBX. 8 weeks after the implantation the Norden score of osteomyelitis was the lowest in the rabbits of group 1 (P < 0.01). The bone defect recovered better in the rabbits of groups 1 and 2. The number of Staphylococcus aureus in the bone defect in rabbits of group 1 was significantly smaller than that in the rabbits of group 2 (P < 0.05), and was very significantly smaller then in the rabbits of the other 3 groups (P < 0.01).

ARBX has strong oeteoinductive and anti-infective abilities. It can be used in primary bone grafting to treat contaminated even infected bone defect.