Active coating of implants used in orthopedic surgery

Complications still occur in trauma and orthopedic surgery in spite of improvements in operating techniques and optimization of implants. These complications include delayed fracture healing, non-unions and extensive osseous infections. This may be explained by more complex patterns of injuries, the shift of the population pyramid bringing increased frequencies of complex fractures linked to osteoporosis and more intricate operating procedures. Growth factors for local application (bone mor-phogenetic protein [BMP]-2, BMP-7) have been approved by the FDA and CE-marked in Europe, but have not become widely accepted. Reasons may be that, although these proteins are expensive and of limited availability, considerable quantities have to be implanted locally. Furthermore, local release from a bovine collagen carrier in tissue is not evident. The use of coated implants incorporating active ingredients could release drugs locally and thereby generate a high concentration directly in the area of interest without systemic side-effects. Compounds that could be used in this way include growth factors for the improvement of fracture healing and antibiotics for prophylaxis of implant-related infections. The coating of implants with biodegradable poly(D,L-lactide) (PDLLA) can facilitate the local controlled release of incorporated growth factors directly into the fracture. The coated implant thus serves both as a fracture stabilization device and as a carrier for active components. This review presents different models (fracture healing, intervertebral fusion, infection model) demonstrating the efficiency of the coating technology. These findings seem to justify the transfer of this technology into clinical settings. In a preliminary study, gentamicin-coated intramedullary tibial nails were implanted in six patients exhibiting fractures with severe soft tissue damage. The preliminary findings do not allow conclusions to be drawn in respect of therapy of fractures with severe soft tissue damage or revi-sion surgery. However, the coating seems to be suitable as a "key technology" for the incorporation of active ingredients. In addition, this technology could be helpful in endoprosthetic revisions. The proper choice of growth factors or suitable antimicrobial substances will require extensive clinical investigations.