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How is hip prosthesis and proximal femoral nail stability affected by lesser trochanter fractures: A comparative finite element analysis.

OBJECTIVES
This study aims to evaluate the effects of lesser trochanter (LT) and iliopsoas tendon on implant stability by using finite element analysis (FEA).


MATERIALS AND METHODS
Effects of iliacus and psoas major muscles on hip joint was evaluated with inverse dynamics methods to calculate joint reaction and muscle forces. Intertrochanteric femur fracture was simulated according to AO (Arbeitsgemeinschaft für Osteosynthesefragen) 31A1 and 31A2 classifications in three-dimensional modelling software. Uncemented three-dimensional model of modular nail prosthesis combination was used in FEA. All analyses were performed with Ti6Al4V's 114 GPa elastic modulus value. Effects of LT on implant stability were evaluated with two different implant designs using the same femoral stems and four different femoral models, two of which with intact LT and two of which with fractured LT.


RESULTS
Reaction forces of the hip joint decreased by 10% in the 0-40° hip flexion range. Maximum stress distribution for proximal femoral nail (PFN) model with fractured LT was 204.68 MPa at the distal locking screw on the interconnection point of PFN, while it was 335.35 MPa for the hip prosthesis with fractured LT. The direction of stress distribution for PFN model with fractured LT varied from medial to lateral and anterior to posterior. Maximum stress distribution for the hip prosthesis model with intact LT was 357.42 MPa, with direction of stress distribution from lateral to medial and posterior to anterior.


CONCLUSION
Hip prosthesis models with intact or fractured LT were similar in terms of stress distribution and deformation values, while there were differences between PFN models with intact or fractured LT. Thus, intact LT was significant in PFN implant stability. Further clinical and experimental analyses are necessary on this topic.