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BACKGROUND: To determine postoperative stress distribution after cemented arthroplasty in elderly patients with comminuted intertrochanteric fracture, and assist in determining a rational prosthetic stem length.
METHODS: A three-dimensional (3D) model of intertrochanteric fracture was established using the Mimics and Unigraphics modeling software, which included the 3D model of comminuted intertrochanteric fracture, two long-stem(#4,#5) and one short stem(#3) prostheses, and the mantle layer of cement. The bone defect of the calcar femorale was replaced with a 5-mm thick cement. Then, the 3D finite element model of those materials was established, boundary conditions of force were imposed, and material parameters were set. Accordingly, a finite element analysis was performed to this model in stress.
RESULTS: (1) The stress of the femur in the three-stem replacement prosthesis models increased from proximal end to distal end in the same pattern, while a stress concentration region was found at 5 mm from within the distal tip of the short-stem prosthesis (#3), which had a peak value of 67.85 MPa. However, no stress concentration was found on the long-stem prosthesis model. (2) For the short-stem prosthesis, the stress distribution of the cement-prosthesis interface was significantly concentrated in the distal region around the prosthesis end, in which the peak value of the lateral interface exceeded the fatigue strength of the bone cement. However, the biomechanics for the long prosthesis was better appreciated.
CONCLUSION: Long prosthesis stems may theoretically be a better option for comminuted intertrochanteric fractures in elderly patients. However, the application of exceedingly long prosthesis stems would not be a better option.