| Objective: 1. To design and manufacture hip prostheses for rabbits, to observe the heat-stability of Vancomycin (VCM) , the release of VCM from Vancomycin-loaded polymethylmethacrylate (VCM-PMMA) in vitro and the mechanical properties of VCM-PMMA. 2. To establish an animal model of hemiprosthetic hip joint infections and then to study the roles of VCM-PMMA in prophylaxis of experimental hemiprosthetic hip infections in rabbits. 3. To study the roles of VCM-PMMA in treatment of experimental hemiprosthetic hip infections in rabbits.Methods: 1. (1) Diameters of femoral heads, lengths of femoral necks and neck-shaft angles together with widths of medullar cavities of 10 rabbits were measured and averaged. (2) The heat-stability of VCM during polymerization reactions of PMMA was analyzed by heating VCM powders to 120℃ for 20 minutes. (3) S-Ⅲ PMMA powders of twenty grams were mixed with one gram of Vancocin (VCM-PMMA), after which it was compared with PMMA without addition of VCM. Both the VCM-PMMA and the control PMMA were delivered into moulds to produce uniform cylindrical discs, the antibacterial activity of VCM-PMMA cylindrical discs against Staphylococcus epidermidis was assayed with Kirby-Bauer susceptibility model. (4) VCM-PMMA discs were immersed into PBS, which was changed daily. Samples of PBS were collected on day1, 2, 4, 8, 12, 16, 24 and 32, then VCM concentrations were determined with TDx to analyze the release of VCM. (5) The compress strength of VCM-PMMA and PMMA was examined, and the prostheses were fixed with PMMA or VCM-PMMA in rabbits and theprostheses extraction tests were conducted. (6) Scanning electron microscope was used to observe the surface characteristics of VCM-PMMA. 2. Forty-eight rabbits were divided into four groups, i.e., control group 1, VCM group 1, control group 2 and VCM group 2, with 12 rabbits in each group. Then the femoral heads were replaced with prostheses, which were fixed with PMMA in control group 1 and group 2, and with VCM-PMMA in VCM group 1 and VCM group 2. Immediately after the replacements, 1×106 CFU of Staphylococcus epidermidis was injected into the joints for control group 1 and VCM group 2, and 1×108 CFU for control group 2 and VCM group 2. The animals were sacrificed 4 weeks after injections, and X-ray graphs were taken, levels of serum CRP and ESR determined, pathological changes observed and bacteria cultures performed. 3. Then the infected hemiprosthetic hip joints were performed debridements and one-stage revision arthroplasties. According to the fixed methods 24 rabbits were divided into two groups, i.e., control group and experiment group, with 12 rabbits in each group. Prostheses were fixed with PMMA in control group and with VCM-PMMA in experiment group. All the animals were sacrificed 12 weeks later,X-ray graphs, level of serum CRP and ESR, pathological changes, bacteria cultures and rhodamine-labelled antiserum stains were observed.Results: 1. (1) Prostheses were successfully designed and manufactured with stainless steel with its heads of 7mm or 8mm in diameters after parameters of rabbits' femurs were obtained. (2) High temperatures had very little effects on the stability of VCM even when VCM was heated to 120℃ for 20 minutes. (3) Inhibition zones against Staphylococcus epidermidis were formed around the discs of VCM-PMMA, while around discs of PMMA no zones were formed. (4) VCM released from VCM-PMMA with bactericidal concentrations in vitro lasted for at least 32 days and a rapid decrease in release was detected during the first 8 days. (5) The extraction strength of the prostheses fixed withVCM-PMMA and the compression strength of VCM-PMMA showed no significant decrease compared with that for VCM(P＞0.05). (6) Scanning electron microscope demonstrated that PMMA had porous structures and that the similar structure was observed when VCM was added to. 2. After 1×106 CFU of Staphylococcus epidermidis was injected into the joints right after the revision surgery, 75% and 25% of hemiprosthetic hip joints were infected f...
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