Multiple radiographic projections in detecting intra-articular screw penetration during fixation of femoral neck fractures.

The authors performed a cadaveric study to evaluate the efficacy of multiple fluoroscopic projections in detecting intra-articular penetration of the screws during femoral neck fracture fixation and also to determine the most suitable radiographic projection. Models of intra-articular penetration in 8 normal proximal femur specimens were created by placing the pins in different quadrants of the femoral head and extending 1 mm beyond the femoral head surface. The tip-to-surface distance was measured on anteroposterior (AP) and lateral views, with the femur positioned at varying degrees of rotation, flexion, adduction, and abduction. After correcting for differences in magnification, associations between the tip-to-surface distance and femur position were noted. In certain femur positions and K-wire placements, conventional AP and lateral views did not show that the wire extended beyond the surface of the femoral head. The tip-to-surface distance on an AP radiograph with the femur in the neutral position was not comparable to that on the lateral view with the femur positioned at 20° of adduction (P=.821). However, the tip-to-surface distance on an AP radiograph with the femur in the neutral position varied significantly (P<.001) from all other tip-to-surface distances on either the AP or lateral projection. A linear association was found between the tip-to-surface distance and femur rotation angles on AP views and between femur adduction and abduction angles on lateral views. In conclusion, fluoroscopy in varied projections at different angles can detect unrecognized intra-articular screw penetration during internal fixation of femoral neck fracture. Additional special projection methods are suggested to identify and prevent intra-articular screw penetration.