Avoid the In-Out-In Posterosuperior Femoral Neck Screw: The Use of the Piriformis Fossa Radiographic Landmark

OBJECTIVES The most common screw placement across the femoral neck is the inverted triangle. The posterosuperior screw has high incidence of cortical breach, creating an in-out-in (IOI) screw. This study examined the use of the radiographic landmark of the piriformis fossa (PF) to prevent screws being placed IOI. The hypothesis was that posterior screws placed below the PF inferior margin would prevent femoral neck cortex breach. METHODS Five bilateral cadaveric specimens were used to place 10 screws along the femoral neck posterosuperior cortex. On the AP view, 5 screws were placed in a traditional manner, below the femoral neck superior cortex but above the inferior margin of the PF (APF screws), and 5 were placed below the inferior margin of the PF (BPF). All 10 screws were placed inside the posterior cortex on lateral view. After screw placement, each hip was dissected, and femoral necks were evaluated for signs of cortical breach. RESULTS All screws placed below the PF inferior margin were contained within the femoral neck with no incidence of being IOI. All screws placed above the PF inferior margin breached the cortex to varying degree. All screws were similar in relation to their distance from the posterior cortex on the lateral view, with the APF screws averaging 1.98 mm and the BPF screws averaging 1.82 mm (p-value=0.46). CONCLUSION Placing the posterosuperior screw of the inverted triangle caudal to the PF inferior margin on AP view appears to avoid cortical breach during percutaneous screw fixation of femoral neck fractures.