Mechanical strength of fracture callus in osteopenic bone at different phases of healing

Objectives: To quantify and compare peak bending force and stiffness of fra ctured femurs during healing of ovariectomized (OVX) and sham-operated (SHA M) rats. Design: Temporal biomechanical animal study. Setting: Rat femurs were fractured and surgically fixed by a qualified surg eon. The inherent instability of the fixation system employed produced dela yed union of the fracture. All biomechanical assessments were performed wit h servohydraulic test machines (Instron Inc., Canton, MA, U.S.A.; and MTS C orp., Eden Prairie, MN, U.S.A.). Intervention: OVX was performed sixteen weeks before femur fracture, and th e effect of OVX on healing fractures was determined. Main Outcomes: Peak bending force and stiffness of the healing femurs at fo ur, six, and eight weeks after fracture. Results: Peak bending loads of the healing fractured femurs in the OVX and SHAM animals were not significantly different. Peak bending loads for the O VX animals at four and six weeks were significantly lower than the peak loa d at eight weeks (p < 0.05), whereas no difference was founding the peak lo ad with respect to time for the SHAM animals. Both SHAM and OVX animals had greater bending stiffness of the healing fractured femur after eight weeks of healing than at four weeks (p < 0,05) Conclusions: OVX is known to reduce cancellous bone mass and strength, but the effect of OVX on healing of fractures in corti-cal bone is controversia l. This study, using a delayed-union model, found no significant difference s between OVX and SHAM animals in the breaking strength of healing fracture s.