Increased cortical remodeling after osteotomy causes posttraumatic osteopenia

Following a fracture, substantial bone mineral loss can occur at the affected limb. The aim of this study was to analyze the changes in cortical bone around the site of a fracture. We analyzed bone mineral density by quantitative computed tomography and quantified changes in cortical remodeling by histomorphometry adjacent to an experimental osteotomy in sheep metatarsals. In the cortical bone around the osteotomy, we found a statistically significant 16% reduction in app.BMD within 9 weeks following surgery. This reduction was explained (R=-0.71, P<0.01) by a more than 6 fold increase in bone remodeling activity within cortical bone at the affected limb. The remodeling activity significantly increased between surgery and week 6, but remained unchanged between week 6 and week 9. We conclude from these findings that posttraumatic bone mineral loss adjacent to a fracture is related to an elevated number of active osteons, indicating a significant increase in bone remodeling activity. Load shielding by the osteosynthesis material and local recruitment of bone mineral are likely causes for this increased remodeling. This post-traumatic bone loss is likely to contribute significantly to frequently observed healing complications like refracture, failure of implant fixation, implant loosening, or cut out.