Avoiding Fifth Metatarsal Intramedullary Screw Head Cuboid Impingement: A Weightbearing Computed Tomography Anatomic...

Area of Science:

• Orthopedic surgery
• Biomechanical modeling
• Radiology

Background:

• Symptomatic hardware complications, specifically screw head impingement on the cuboid, are reported with fifth metatarsal (MT) intramedullary fixation.
• A novel trajectory model was developed using weightbearing computed tomography (CT) data to investigate this issue.

Purpose of the Study:

• To assess the potential for cuboid impingement during simulated fifth MT intramedullary screw placement.
• To quantify the necessary screw countersinking depth to avoid cuboid impingement.

Main Methods:

• A 3D model was created from 20 weightbearing foot CT scans.
• An automated tool simulated ideal fifth MT intramedullary screw fixation (7-mm head).
• Measurements assessed the distance between the screw trajectory and the cuboid, and simulated screw advancement to avoid impingement.

Main Results:

• Ninety-five percent (19/20) of simulated fixations resulted in cuboid impingement without countersinking.
• The average ideal screw trajectory was 0.15 mm from the cuboid.
• An average countersinking depth of 8.1 mm was required to avoid impingement.
• The oblique fluoroscopic view reliably indicated screw-cuboid overlap.

Conclusions:

• Ideal guidewire placement for fifth MT intramedullary fixation is often directly adjacent to the cuboid.
• Without countersinking, nearly all patients (95%) are at risk for cuboid impingement.
• The oblique fluoroscopic view is a valuable tool for assessing screw head impingement on the cuboid.