FEMORAL STIFFNESS AFTER OSTEOSYNTHESIS OF A SUBCAPITAL OSTEOTOMY IN OSTEOPOROTIC BONE - AN IN-VITRO COMPARISON OF 9 FIXATION METHODS

Restitution of normal bone mechanics after osteosynthesis of a proxima l 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 histor y of osteoporosis was measured during axial loading before and after a subcapital osteotomy stabilized with one of nine different osteosynth esis devices. Only an osteotomy stabilized with an experimental device consisting of 2 von Bahr screws (Ericsson AB, Goteborg, Sweden) suppo rted 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 similar to 20-30% lower stiffness tha n tested intact. However, these devices provided a higher femoral stif fness than the hook-pin technique type LiH (Soderstrom AB, Gothenburg, Sweden), cannulated screws (Smith & Nephew, Memphis, TN, U.S.A.), a s liding screw plate (Smith & Nephew), a compression screw with variable length (Biomet), or an experimental screw providing expansion and com pression. Despite attempted compression of the osteotomy by some of th e devices, all of the commercially available devices resulted in a dec rease of femoral stiffness after fixation, which may adversely influen ce the healing of femoral neck fractures in the elderly. Only a combin ation of screws and bone cement resulted in normal femoral stiffness, probably because of better device anchorage in the osteoporotic cancel lous bone. However, this combination might have the potential risk of vascular damage.