Simvastatin locally applied from a biodegradable coating of osteosynthetic implants improves fracture healing...

Many clinical and experimental investigations address the influence of statins on bone formation and fracture healing. Simvastatin was shown to increase the expression of Bone morphogenetic protein (BMP-2), which is one of the most potent growth factors targeting bone formation. In this study, the effect of simvastatin locally applied from a bioactive polymer coating of implants on fracture healing was investigated. A closed fracture of the right tibia of 5-month-old Sprague-Dawley rats was performed. Intramedullary stabilization was achieved with uncoated vs. polymer-only coated vs. polymer plus drug coated titanium Kirschner wires. Test substances (either simvastatin low- or high dosed or BMP-2) were incorporated into a biodegradable layer of poly(d,l-lactide). Tibiae were harvested after 28 or 42 days, respectively and underwent biomechanical testing (torsional stiffness and maximum load) and histomorphometric analysis. Radiographic results demonstrated progressed callus consolidation in the BMP-2- and simvastatin-treated groups compared to the uncoated group at both timepoints. The simvastatin-high-dosed group revealed an increased torsional stiffness and significantly elevated maximum load (d 28) compared to control group as well as a significant increase in both parameters at d 42. BMP-2-treated animals showed significantly elevated maximum load and stiffness at the early timepoint and elevated torsional stiffness after d 42. The histomorphometric analysis revealed a significantly decreased cartilage area for BMP-2 treated animals at d 28. Even though an increase of mineralized areas among periosteal callus was found at d 42 for simvastatin-high as well as BMP-2 treated animals, no significant difference could be detected at both timepoints compared to the uncoated group. However, simvastatin-high treated animals revealed significantly reduced cartilage areas within the periosteal callus at d 42. The present study revealed a dose-dependent effect and improved fracture healing under local application of simvastatin. Biomechanical, radiographic and histomorphometric properties showed comparable results to BMP-2- treated animals in this study.