[Experimental studies of the effectiveness of the sliding principle in dynamic hip screw osteosynthesis and its value in managing unstable pertrochanteric femoral fractures].

54 human corpse femora were tested. In 18 unstable pertrochanteric osteotomies were performed, in other 18 femora valgisation osteotomies were performed. 18 femora served as control. In the unstable pertrochanteric osteotomy-group 135 degrees-DHS-osteosynthesis was performed. In the valgisation-osteotomy-group a 150 degrees-DHS-osteosynthesis was performed. Half of the femora were tested under physiological load, the other femora were tested with the load acting from cranial-lateral (50 degrees difference to the physiological load direction). Under physiological condition the load capacity was 5769 N in the 135 degrees-DHS-group and 7261 N in the 150 degrees-DHS-group, and so 8 to 10 times higher as the body weight. In the groups with the false loading direction the mean stability of the osteosynthesis was 2937 N in the 135 degrees-DHS-osteosynthesis-group and 3942 N in the 150 degrees-DHS-osteosynthesis-group. The load capacity of the control femora was 7451 N. The deformation under physiological load was similar in both groups. Under unphysiological load the deformation was 2-3 times higher in the 135 degrees-DHS-group because of the higher bending compared with the 150 degrees-DHS and because of the medical cortical defect. The results demonstrate the effectivity of the sliding osteosynthesis technique of the DHS. After DHS-osteosynthesis of unstable pertrochanteric fractures with limited medial defect in all cases full weight bearing after operation is possible. Valgisation osteotomy is not necessary in this type of fracture.