Treatment of large diaphiseal bone defects after infection

• Grant number: 05/02885-3
• Support Opportunities: Regular Research Grants
• Start date: January 01, 2006
• End date: June 30, 2007
• Field of knowledge: Health Sciences - Medicine
• Principal Investigator: Cleber Antonio Jansen Paccola
• Grantee: Cleber Antonio Jansen Paccola
• Host Institution: Faculdade de Medicina de Ribeirão Preto (FMRP). Universidade de São Paulo (USP). Ribeirão Preto , SP, Brazil

Abstract

Post-traumatic bone infections not rarely end in a large bone defect after debridment. The mostly used solutions in these case are: Ilizarov technique, autologous cancellous bone graft or revascularized massive bone graft. Despite the fact that periosteum is extremely osteogenic, spontaneous regeneration not uncommonly ended in a hour-glass pseudarthrosis, usually in the middle of the defect. The treatment of bone infection with cement impregnated with antibiotic is well established in orthopedics surgery. The PMMA as a local drug delivery system offers the advantages of high local antibiotic concentration that could not be safely achieved with systemic administration, moreover antibiotic impregnated beads or spacers fill the dead space that result of debridement and prevent fibrous tissue invasion. After removal of dead bone preserving the surrounding periosteum, the defect could be filled with a PMMA spacer that act as a support for the periosteum, promoting a well organized regeneration of the defect. This "mould" will be removed as soon as the cortices formation begins. The new bone formation around the spacer produce a cavity with stable walls without the risk the of narrowing with soft tissue contracture. In this experimental study thirty rabbits allocated in tree group of ten will be used:Group 1: Bone defect filled with cement + ATB. Group 2: Osteoperiosteal defect filled with cement + ATB. Group 3: Defect left empty. In a rabbit forearm model, a direct approach is made over the ulna and an oscillating saw is used to excise a 15 mm segment. Periosteum will be retained or not depending on the group. A controlled strain of pathogenic Staphylococcus aureus is applied in the medulary canal of the bone segment. The segment is replaced in its original position and the wound closed. After an observation period of 2 weeks to select the infected animal, the necrotic and infected segment is removed together with a thorough debridement creating an infected segmental bone defect. The treatment of the defect will be done according to the respective group. At tree weeks, when the formation of the new cortices starts, the spacer will be removed(Group 1 and 2) permitting the remodeling of the medullary canal. All the animals will receive 6mg/Kg/d of gentamicin for tree weeks beginning after the debridment. At the eightieth weeks radiography study takes place and the animals will be killed for additional study. (AU)