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

Area of Science:

• Orthopedic surgery
• Radiographic anatomy
• Surgical technique

Background:

• The inverted triangle screw placement is common for femoral neck fractures.
• Posterosuperior screw placement risks cortical breach, leading to in-out-in (IOI) screws.
• Identifying reliable radiographic landmarks is crucial for preventing surgical complications.

Purpose of the Study:

• To evaluate the piriformis fossa (PF) as a radiographic landmark to prevent in-out-in (IOI) screw placement.
• To test the hypothesis that posterior screws placed below the PF inferior margin avoid femoral neck cortex breach.

Main Methods:

• Ten screws were placed in 5 cadaveric femoral specimens.
• Screws were positioned using the piriformis fossa landmark on anteroposterior (AP) views.
• Cortical breach was assessed after dissection and evaluation of the femoral necks.

Main Results:

• All screws placed below the piriformis fossa inferior margin remained within the femoral neck, with zero IOI occurrences.
• Screws placed above the piriformis fossa inferior margin consistently breached the cortex.
• No significant difference was found in screw distance from the posterior cortex between groups.

Conclusions:

• The piriformis fossa inferior margin serves as an effective radiographic landmark.
• Caudal placement of the posterosuperior screw relative to the PF inferior margin prevents cortical breach.
• This technique enhances safety in percutaneous screw fixation for femoral neck fractures.