Finite Element Analysis of Necessity of Reduction and Selection of Internal Fixation for Valgus-impacted Femoral Neck Fracture

Abstract BackgroundAlthough valgus-impacted fractures don’t displace obviously, a larger valgus angle and posterior tilt of the femoral head can cause hip joint dysfunction and femoral head necrosis. The optimal surgical approach for valgus-impacted femoral neck fractures remains controversial. This study compared the biomechanical characteristics of different treatment strategies based on finite element analysis.MethodsTen valgus-impacted femoral neck fractures were analyzed in terms of posterior tilt and valgus angle measured on X-ray radiographs. Using these data, we generated 7 finite element models that were compared in terms of von Mises stress distribution and displacement.ResultsIn the intact femur, von Mises stress was concentrated at the medial and inferior sides of the femoral neck. In valgus-impacted femoral neck fractures, von Mises stress was at the same locations but was 5.66 times higher than that in the intact femur. When 3 cannulated screws were used for internal fixation, anatomic reduction diminished the stress at the fracture end from 140.6 to 59.14 MPa, although displacement increased from 0.228 to 0.450 mm. When the fracture was fixed with a sliding hip screw (SHS) + cannulated screw, there was less stress at the fracture end and greater displacement with anatomic reduction than that without reduction (stress: 15.9 vs 37.9 MPa; displacement: 0.329 vs 0.168 mm).ConclusionsThe SHS + cannulated screw has superior biomechanical stability than 3 cannulated screws, and is recommended following anatomic reduction to treat valgus-compacted femoral neck fractures.