Thromboprophylaxis using a low molecular weight heparin delays fracture repair

Low molecular weight heparins are significantly superior to unfractionated heparin or warfarin in the prevention of thromboembolic episodes associated with orthopaedic surgery. Therapeutic doses of heparin and warfarin have b een shown to delay bone repair in a rabbit model. The current study investi gated the effect of prophylactic administration of a low molecular weight h eparin, enoxaparin, on the healing of a closed rabbit rib fracture. Fractur e healing was assessed using histomorphometric, histologic, and immunohisto chemical methods at 3, 7, and 14 days, and biomechanical testing with torsi onal loading was assessed after 21 days. Bone repair was significantly atte nuated at all times in animals receiving subcutaneous enoxaparin compared w ith that of the control animals, Numerous putative mechanisms for this phen omenon are discussed, and additional studies are proposed to elucidate the effects of this pharmacologically diverse group of compounds on an aspects of bone physiology and repair.