Intramedullary Headless Screw Feasibility for Anatomical Reduction in II-V Metacarpal Fractures: A CT-Based...

Area of Science:

• Orthopedic Surgery
• Biomedical Engineering
• Radiology

Background:

• Intramedullary headless screw (IMHS) fixation offers a minimally invasive and stable approach for metacarpal fractures.
• However, the narrow intramedullary canal morphology can limit the suitability of standard screw sizes.
• Understanding metacarpal isthmus dimensions is crucial for successful IMHS application.

Purpose of the Study:

• To evaluate the isthmus morphology of the second to fifth metacarpals using CT-based analysis.
• To assess the anatomical feasibility of various IMHS diameters within these canals.
• To determine the impact of age and gender on metacarpal canal dimensions.

Main Methods:

• Retrospective analysis of 75 hand CT scans (300 metacarpals).
• 3D reconstructions and serial axial CT analysis to identify and measure isthmus diameters.
• Virtual screw implantation simulation to calculate feasibility rates for screw diameters from 2.75 mm to 4.00 mm.

Main Results:

• The fourth metacarpal exhibited the smallest mean isthmus diameter (2.64 mm), while the fifth was largest (3.21 mm).
• Screw feasibility decreased with increasing diameter; the fourth metacarpal showed low compatibility (e.g., 4.0% for 4.0 mm screws).
• Positive correlation between age and isthmus diameter in the second and third metacarpals was observed.

Conclusions:

• Metacarpal isthmus morphology significantly impacts IMHS fixation feasibility.
• The fourth metacarpal presents anatomical challenges, especially for larger screws (≥ 3.5 mm).
• Individualized, CT-based preoperative templating is recommended over standardized implant selection to optimize screw fit and minimize cortical compromise.