Introduction: Percutaneous screws placed into the posterosuperior femoral neck are frequently extraosseous or "in-out-in" (IOI). These IOI screws are not readily identifiable on anteroposterior (AP) and lateral fluoroscopic images. The purpose of this study was to examine the ability of surgeons to identify IOI guide pins using sequential fluoroscopic rollover images.
Materials and methods: A 3.2-mm guide pin was placed into the posterosuperior quadrant of eleven synthetic femur models. Five samples were "all-in" (AI), and six were IOI. Sequential fluoroscopic rollover images were obtained starting with an AP image, then images at 10-degree rollover intervals ending with a direct lateral image. Images were reviewed in a blinded fashion by five attending orthopedic trauma surgeons and 20 resident surgeons to determine whether guide pins were AI or IOI. Accuracy, interobserver reliability, sensitivity, and specificity were assessed.
Results: The overall accuracy of responses was 86% with no difference between attending trauma surgeons and residents (p = 0.5). The sensitivity and specificity for an IOI guide pin were 98.0% and 71.2%, respectively. Interobserver reliability among surgeons was good (κ = 0.703).
Conclusion: The use of the sequential fluoroscopic rollover images after placement of the posterosuperior guide pin into the femoral neck was highly sensitive for detecting an IOI position. The 40-degree rollover image was the best view to evaluate the proximity of the guide pin to the posterior cortex.
Keywords: Avascular necrosis; Cannulated screw; Femoral neck fracture; Fluoroscopy; In–out–in; Percutaneous screw fixation; Rollover; Screw penetration.