Objective To explore the biomechanical stabil ity of dynamic sleeve three-wing screw for treatment of femoral neck fracture and to provide theoretical basis for choosing dynamic sleeve three-wing screw in cl inical appl ication. Methods Nine human cadaveric femurs were selected and divided randomly into 3 groups (n=3), excluding deformities, fractures, and other lesions. The central neck of the specimens were sawn with hand saw respectively at Pauwels angles of 30, 50, and 70°. All cut ends were fixed with dynamic sleeve three-wing screw. Instron-8874 servohydraul ic mechanical testing machine was used to fixed the specimens which simulated uni ped standing, at the rate of 10 mm/minute and l inear load 0-1 200 N at 11 key points. The strain values of princi pal pressure side and princi pal tension side under different loads were measured. Results There was a peak at 6th point in the 1 200 N load. The strain values at Pauwels angles of 30, 50, and 70° were (—1 657 ± 171), (—1 879 ± 146), and (—2 147 ± 136) με; showing significant differences (P lt; 0.01). The strain values of princi pal pressure side and princi pal tension side of the femoral neck became higher with the increasing Pauwels angle under the same load, showing significant differences (P lt; 0.01). The strain values became higher with the increasing load under the same Pauwels angle (P lt; 0.01). Conclusion Dynamic sleeve three-wing screw has good biomechanical stabil ity for treatment of femoral neck fracture. It explains theoretically that the fracture is more unstable with the increasing Pauwels angle．
Objective To compare the biomechanical characteristics of the less invasive stabilization system (LISS) and the dynamic condylar screw (DCS) in the fixation of subtrochanteric fractures of the femur so as to provide theoretical basis for choosing internal fixator in clinical application. Methods Twelve cadaveric human femurs (35-50 years old) were selected with similar proximal femur, excluding deformities, fractures, and other lesions. The twelve femur specimens were randomly divided into 2 groups, 6 specimens per group. An 1 cm gap of osteotomy model was made in the proximal femur up to 1 cm below the lesser trochanter to simulate a comminuted subtrochanteric fracture of femur, and the distal end was embedded with denture acrylic and liquid for denture acrylic. Fracture was fixed by LISS in group A, and was fixed by DCS in group B. The specimens were fixed on Instron-8874 servo-hydraulic mechanical testing machine in a single-leg standing position, and the axial compression test and dynamic fatigue test were carried out to compare the compressive strength and the strain distribution at both sides of the fracture line. Results Axial compression test: the strain values of the 2 strain gauges in group A were significantly smaller than those in group B (P lt; 0.01); the vertical down displacement of the femoral head in group A was significantly smaller than that in group B (P lt; 0.01) under the same load; when the load was 600 N, the axial rigidity of group A was (209.06 ± 18.63) N/mm, which was significantly higher than that of group B [(65.79 ± 7.26) N/mm] (t=3.787, P=0.004). Dynamic fatigue test: the vertical down displacement of the femoral head in group A was significantly smaller than that in group B in the same cyclic loading cycle (P lt; 0.01); when the vertical down displacement of the femoral head was 0.5 mm, the force and the cyclic loading cycles in group A were significantly larger than those in group B (P lt; 0.01). Conclusion LISS, which has good mechanical stability, can meet the requirements for subtrochanteric fracture of femur fixation in biomechanics and anatomical structures. It can be proven that the LISS internal fixator is firmer than the DCS internal fixator by biomechanical comparison.