Finite element analysis of PFNA in the treatment of osteoporotic intertrochanteric A2.3 fractures of the femur.

BACKGROUND

Poor bone quality in osteoporosis can compromise implant fixation and stability in intertrochanteric fractures. This study employed finite element analysis to evaluate the biomechanical performance of short (170 mm), medium (240 mm), and long (320 mm) proximal femoral nail antirotation (PFNA) implants in osteoporotic intertrochanteric A2.3 fractures. By modulating the elastic modulus of cancellous bone to simulate varying degrees of osteoporosis severity, we aimed to identify the optimal PFNA length for clinical practice.

METHODS

A three-dimensional finite-element model of an osteoporotic intertrochanteric A2.3 femoral fracture was established. The elastic modulus of cancellous bone was assigned six levels (588, 445, 260, 115, 63, and 34 MPa), representing different osteoporosis severities. PFNA implants of 170, 240, and 320 mm lengths were assembled, with the 170 mm nail further evaluated at diameters of 9.5, 10, and 11 mm. Single-leg stance loading was simulated. Von Mises peak stresses in the PFNA implant, cortical bone, and cancellous bone, along with maximum displacement, were calculated and compared.

RESULTS

The 240 mm PFNA exhibited the lowest von Mises peak stress (442.86-560.44 MPa) across all bone quality conditions. The 170 mm PFNA exceeded 1000 MPa when bone quality was ≤260 MPa, surpassing the yield strength of titanium alloy (approximately 900 MPa). The 320 mm PFNA demonstrated intermediate stress (618.60-842.16 MPa). The 240 mm PFNA consistently produced the lowest cortical stress (85.191-91.948 MPa) and similar femoral displacement to the 320 mm PFNA, while cancellous bone stress decreased progressively with deteriorating bone quality (19.68→8.35 MPa). The 170 mm PFNA showed higher cortical stress (185.25-211.7 MPa) and the greatest displacement (8.05-9.44 mm), whereas the 320 mm PFNA exhibited a sharp increase when bone quality was ≤115 MPa, reaching 472.82 MPa at 34 MPa. For the 170 mm nail, increasing diameter from 9.5 mm to 11 mm reduced peak implant stress by 25.8%-49.0%, with the 11 mm nail remaining below the yield threshold in all but the most severe osteoporotic condition.

CONCLUSION

Within the constraints of the present finite element model, the 240 mm PFNA showed the most favorable overall comparative biomechanical performance among the tested configurations and may represent a reasonable biomechanical option for osteoporotic intertrochanteric A2.3 fractures.