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Purpose: proximal femur fractures occur mainly in old and very old people with osteoporotic bone. The cut out of the femur neck and head component is therefore one of the major complications after osteosynthesis of these fractures. The Hypothesis of this study was that the cross section of the implant is relevant to minimise the cut out risk of the device. Material and methods: the following fixation devices were tested:-an I beam plate (16x10mm) used in the Gliding nail (Plus Orthopedics), a single screw (12mm) fixation of the Gamma Nail (Stryker-Howmwdica) and a double screw fixation (11 and 6mm) used in the Proximal Femur Nail (Synthes). For testing 9 femur sowbones and 3 pair of corps femura obtained from 3 over 60 year old deceased were used. A A2 type of Osteotomy with a complete calcar defect was performed, the fixation device was mounted in the proximal femur and in a holding device with gliding possibility of the neck component as in the original implant. 3 sowbones were tested in each group and to avoid individual differences in the corpse femura test in a right to left comparison was performed between the 3 implants in 3 pair of corps femura. To determine only the deformation due to the cut trough of the device in the femur neck only the head and neck portion of the femur was used for testing. The tests considered inlOOO cycles alternating load tests at 1000N and 1500N in the sowbones and at 1000N, 1500N, 2000N, 2500N, 3000N and 3500N in the corpse femura. The plastic, total deformation and cut out events were recorded. 501 trochanteric fractures treated between al996 and 2001 and 73 medial femour neck fractures treated from 1999 to 2003 with the Gliding Nail were evaluated regarding the rate of implant related complications. Results: in the sowbones the I beam profile plate shows a total deformation of 1mm after 1000N and 2mm after 1500N test. For the 12mm screw the corresponding values were 2,5mm and 5.6mm. TH double screw fixation showed a total cut ou- t at 1000N in one femur and at 1500N in both others. In the corpse femura the differences were similar: The cut through was 3 times higher for the Gamma Nail as compared to the gliding nail and 4 Times higher for the Proximal Femur Nail(PFN) as compared to the Gliding Nail. In the trochanteric fractures group the wound revision rate was 2.5% and the implant related late complication needing revision 3.3%. For the femur neck fractures in 9.5% secondary joint replacement and in another 9.5% local wound or implant revision due to tractus irritation were needed. Discussion: The cut through of the I beam profile plate is reduced by 2/3 compared to single screw fixation and % as compared to the PFN double screw fixation. The cross section profile is very important to reduce the cut out risk of devices for proximal femur fracture fixation. The double plane support of the I beam increases the support surface and minimises the cut out risk. The rotation stability can be also relevant for the difference found. The worse results of the double as compared to the single screw fixation can be due to the very cranial position of the proximal small diameter screw and the probably not identical loading of the 2 screws because of the movement of the screws in the gliding holes of the nail/fixation device. The clinical results show a relevant reduction o implant related complications especially of the cut out rate.