[Experimental examination for optimized stabilisation of trochanteric femur fractures, intra- or extramedullary implant localisation and influence of femur neck component profile on cut-out risk].

INTRODUCTION Fractures of the proximal femur are typical injuries of the elderly. Therefore immediate restoration of weight-bearing capacity and prevention of local complications with the need for of secondary surgical procedures are very important. METHODS In an experimental test the weight-bearing capacity under alternating load up to 2,000 N and 4,000 cycles was analysed in the newest implants for extramedullary fixation (the DHS with lateral buttress plate, DHS) and for intramedullary fixation (the gliding nail, GN). If no instability occurred a static maximum load test was performed. To avoid the influence of other variables the tests were performed with sowbone femora with A2, A31, (AO classification) subtrochanteric reversed and subtrochanteric transverse osteotomies. To analyse the influence of long term alternating load and of the biological bone, a pair of cadaver femora were tested with 100,000 cycles of 2,000 N alternating load after GN and DHS osteosynthesis. In a second examination the influence of the profile of the femur neck component on the migration and cut-out risk was tested. Nine head and neck parts of sowbone femora with a A2 osteotomy 1,000 alternating load tests at 1,000 and 1,500 N were performed after GN I beam plate, gamma nail and PFN screw fixation. Additionally, three pairs of cadaver femora were tested with 6,000 cycles from 1,000-3,500 N of alternating load comparing GN vs gamma, GN vs PFN and gamma vs PFN to avoid influence of the biological variability on the ranking. RESULTS The weight-bearing capacity of the GN (4,230-5,557 N) was about 100% higher than that of the DHS (2,465-3,049 N). The total deformation was 1/3 higher for the DHS (17.3 +/- 2.06 mm) than for the GN (10.73 +/- 4,33 mm). After 100,000 alternating load cycles no instability and a total deformation of 13.3 mm was found for the GN, but for the DHS instability occurred after 15,800 cycles. The migration of the I-beam GN plate at 1,000 N in sowbone femora was 0.7 mm for the gamma screw 1.69 mm and for the PFN 2 mm but one cut-out was observed. At 1,500 N the difference are even higher, all three PFN showed a cut-out and in two of the three gamma screws rotation of the head and neck around the screw was observed. In the cadaver tests similar differences were found with a migration at least double that of the GN I beam plate for the gamma screw and the PFN double-screw fixation. There was no difference between the gamma and PFN fixation in the cadaver pair test.