Abstract: BACKGROUND: For people of different ages, femoral neck fractures have different fracture line characteristics and different treatment strategies. It has become a common challenge for orthopedic scholars that how to improve the quality of reduction and avoid osteonecrosis of the femoral head and failure of internal fixation in surgical treatment. Through mechanical tests of models of the femoral head and neck, we expect to obtain the relevant data and point out the direction for the improvement of reduction stability and reduction quality.  
OBJECTIVE: To obtain the mechanical characteristics of different ways of inserting Steinmann Pins into the femoral head through the static anti-pull-out test and the fatigue test.
METHODS:  The Steinmann Pins with model ZLW02SJA produced by Tianjin Zhengtian Medical Equipment Co., Ltd., with a specification of φ3.5*300 mm, and a sample material of 317 stainless steel, were selected for the study according to two steps. Step 1: Static tensile test was the test that inserted one or two Steinmann Pins into the Sawbone with corresponding depth in the femoral head. The direction could be from front to back or from greater trochanter of femur into the femoral head, and the total kind of solution combinations was eight. The Steinmann Pins were injected into the specified depth. The pullout force of the Steinmann Pins was tested with the speed of 20 mm/min, and the pullout force was recorded. Step 2: Fatigue tensile test. The average pullout force of the first eight tests was summarized; 75% of the two maximum pullout forces were taken for fatigue tensile test.  
RESULTS AND CONCLUSION: (1) Through static tensile tests, it is concluded that the two schemes with the best pullout force were scheme 5 and scheme 7. In scheme 5 whose direction was from front to back into the femoral head: the thickness of cortical bone was 4.3 mm. The thickness of cancellous bone was 25.7 mm. The number of Steinmann Pins was 2. Insertion depth was 2/3 of femoral head. In scheme 7 whose direction was from greater trochanter of femur into the femoral head, the thickness of cortical bone was 3.0 mm; the thickness of cancellous bone was 26.3 mm; and the number of Steinmann Pins was 2. Insertion depth was 2/3 of femoral head. (2) After that, 75% of the maximum pullout force of the two schemes was selected for at least 300 fatigue cycles, and both schemes could complete the fatigue test. The most stable inserting mode of Steinmann Pins was scheme 5, which had a large pullout force, so it could produce stable traction relatively with the femoral head in the process of reduction of the femoral head. (3) Results verified that static tensile tests and fatigue tests showed that the insertion of two Steinmann Pins was better than that of one Steinmann Pin, and the insertion of two Steinmann Pins behaved better in inserting from front to back rather than inserting from lateral greater trochanter.

Key words: Steinmann Pin, femoral head, mechanics, femoral neck fracture, static tensile test, fatigue tensile test, model of the femur