The Use of the Piriformis Fossa Radiographic Landmark to Predict “In-Out-In” Placement of the Posterosuperior Femoral Neck Screw

Objectives: To investigate the correlation between a screw's radiographic relationship to the piriformis fossa with position on CT in the clinical setting. Methods: Intraoperative fluoroscopic images of patients treated with cannulated screw fixation of a femoral neck fracture, who also had a postoperative CT scan, were retrospectively evaluated by 4 fellowship-trained orthopaedic trauma surgeons. The posterosuperior screw on the AP fluoroscopic view was determined to be above the piriformis fossa (APF) or below the piriformis fossa (BPF). Using CT scan to determine IOI placement, the ability to predict IOI position based on fluoroscopic imaging was evaluated by calculating accuracy, sensitivity, specificity, and interobserver reliability. Results: 73 patients met inclusion criteria. The incidence of IOI screw placement was 59% on CT evaluation. The use of the PF landmark accurately predicted CT findings in 89% of patients. A screw placed APF was 90% sensitive and 88% specific in predicting cortical breach, with near-perfect interobserver agreement (κ = 0.81). Conclusion: The use of the PF radiographic landmark is highly sensitive and specific in predicting the placement of an IOI posterosuperior femoral neck screw. Level of Evidence: Diagnostic Level II. See Instructions for Authors for a complete description of levels of evidence.