(3) Compared with the N or C1 group, there was a significant stress concentration on the screws and its surrounding proximal femur in the C2 group. (2) Compared with the C1 group, while only the lowest femoral calcar screw was removed, there was a similar stress distribution in the proximal femur, and the average stress of the femoral head increased only by 0.35% although that of the femoral neck increased by 63.62% however, removal by any other means resulted in a significant stress concentration in the proximal femur and a significant increase in the average stresses of the femoral head and neck (5.96–40.95% and 12.82–75.46%, respectively). Moreover, the average stress of the femoral head in C1 group increased by 37.85%, while that of the femoral neck decreased by 23.03%. (1) Compared with the N group, a uniform stress distribution was stopped by the addition of three screws in the C1 group in contrast, all screw removals resulted in the stress concentration on the screw holes and the disappearance of stress shielding. The stresses and displacements of the femur were determined. For the R1 or R2 groups, the screws in the model of the C1 or C2 individuals were gradually removed in seven or three types of different screw combinations, respectively. The established finite element models consisted of N, C, and R groups: N group, the normal femur C group (to simulate the femoral neck fracture healing after the internal fixation), the normal femur with three inverted triangular parallel cannulated screws (C1) or with two upper parallel screws (C2). The CT data of the femurs were obtained from a 69-year-old healthy female to establish the femur models. The purpose of this study was to determine the biomechanical changes of the femur before and after the screw removal using a finite element analysis. The removal of three inverted triangular parallel cannulated screws after the femoral neck fracture healing is sometimes accompanied by osteonecrosis of the femoral head (ONFH) or its refracture.
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