Femoral stiffness after osteosynthesis of a subcapital osteotomy in osteoporotic bone: an in-vitro comparison of nine fixation methods.

Restitution of normal bone mechanics after osteosynthesis of a proximal femoral fracture in the elderly is assumed to be a prerequisite for optimal healing. To find the most appropriate fixation device for this purpose, the stiffness of 79 cadaver femora from donors with a history of osteoporosis was measured during axial loading before and after a subcapital osteotomy stabilized with one of nine different osteosynthesis devices. Only an osteotomy stabilized with an experimental device consisting of 2 von Bahr screws (Ericsson AB, Göteborg, Sweden) supported by acrylic cement gave similar mean values as the intact femur. A femur stabilized with the Deyerle device (Biomet, Bridge End, Wales, U.K.), with cannulated screws type Uppsala (Olmed AB, Uppsala, Sweden), or with von Bahr screws had an approximately 20-30% lower stiffness than tested intact. However, these devices provided a higher femoral stiffness than the hook-pin technique type LiH (Söderström AB, Gothenburg, Sweden), cannulated screws (Smith & Nephew, Memphis, TN, U.S.A.), a sliding screw plate (Smith & Nephew), a compression screw with variable length (Biomet), or an experimental screw providing expansion and compression. Despite attempted compression of the osteotomy by some of the devices, all of the commercially available devices resulted in a decrease of femoral stiffness after fixation, which may adversely influence the healing of femoral neck fractures in the elderly. Only a combination of screws and bone cement resulted in normal femoral stiffness, probably because of better device anchorage in the osteoporotic cancellous bone. However, this combination might have the potential risk of vascular damage.