Morphometric Evaluation of Second to Fifth Metacarpals for Retrograde Intramedullary Headless Screw Fixation

Abstract

Intramedullary headless screw fixation has come to the fore in the treatment of metacarpal fractures in recent years with its advantages. Our aim was to evaluate the metacarpal morphometry for retrograde intramedullary entrance and to determine the optimal entry point. Computed tomography images of 105 patients including 64 men and 41 women, were examined. Distal and proximal metacarpal widths, medullary cavity width, cortex thickness and the measurements of the optimal entry site in volar-dorsal and radio-ulnar directions were measured in both coronal and sagittal planes. In the sagittal plane, the second metacarpal had the widest proximal width (16.29 mm), distal width was greatest in the third metacarpal (14.34 mm) which was significantly different between the sexes (p<0.001). Third metacarpal had the widest medullary cavity width in the sagittal plane (4.12 mm). In the coronal plane, it was the second metarcarpal with the widest proximal (16.14 mm) and distal width (13.92 mm) and was also the longest (66.32 mm). Unlike the sagittal plane, the medullary cavity width in the coronal plane was at the widest (4.06 mm) in fifth metacarpal. The points determined for optimal entry were respectively (4.60 mm; 4.97 mm; 4.55 mm; 4.36 mm) in the dorsal-volar plane, close to the dorsal side. There was no significant difference between the sexes for optimal insertion point in the sagittal planes in all the measured metacarpals. Considering its three dimensional structure, metacarpal bones have irregular morphometric properties and these features differ in sagittal and coronal planes. The optimal entry site is located in the midline in the coronal plane, while it is located in the sagittal plane close to the dorsal part. Knowing these properties can reduce the complication rate by reducing entry attempts and help select the correct material.