• Manav Mehta, Georg N Duda, Carsten Perka, and Patrick Strube.
• Center for Musculoskeletal Surgery and Julius Wolff Institute, Charité Campus Virchow Klinikum-Forum 4, Charité-Universitätsmedizin Berlin, Augustenburger Platz 1, 13353 Berlin, Germany.
• Clin. Orthop. Relat. Res. 2011 Nov 1; 469 (11): 3102-10.

BackgroundGender and stability of fixation independently influence bone regeneration but their combined effects are unclear.Questions/PurposesIn a pilot study we determined the combined influence of gender and fixation stability on the callus of middle-aged rats regarding (1) biomechanical properties; (2) bridging over time; (3) callus formation; and (4) callus size, geometry, mineralization, and microstructure.MethodsWe osteotomized the left femur of 32 Sprague-Dawley rats (12 months old). Femurs were externally fixed with a gap of 1.5 mm in four groups of eight animals each: female semirigid, male semirigid, female rigid, and male rigid. Qualitative and quantitative in vivo radiographic analyses were performed twice weekly. Six weeks postoperatively, harvested femora were evaluated using micro-CT and biomechanical testing.ResultsTorsional stiffness and maximum torque at failure were higher in male and in semirigidly fixed fractures. Radiographic analysis revealed earlier bridging and callus formation in both male groups. Micro-CT analysis showed a larger callus size, altered geometry, and microstructure in males and semirigidly fixed animals, whereas mineralization was similar in all animals.ConclusionOur data suggest female gender represents an independent risk factor for bone healing in middle-aged rats. Although healing in females was delayed compared with males, they exhibited a similar response (superior callus properties) to a more semirigid fixation.Clinical RelevanceWhile female gender appears to reflect a risk for impaired bone healing in middle-aged female rats, clinical studies would be required to confirm the finding in humans.

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