Three-Dimensional Analysis of Metacarpal Head Articular Defects Created by Headless Screws.

OBJECTIVES: Headless screw fixation used to treat metacarpal neck and metacarpal shaft fractures is gaining popularity. The aim of the study is to determine the proportion of the metacarpal head articular surface that is compromised during retrograde insertion of headless screws.

METHODS: Metacarpal screw fixation through a metacarpal head starting point was performed using fluoroscopic guidance on 14 metacarpals. Headless compression screws, with a tail diameter of 3.6mm, were used. The specimens were subsequently skeletonized and digitized using a 3-dimensional surface scanner. The articular surface defects created by the screws were then determined using computer software. Screw position in the dorsal aspect of the metacarpal head was expressed as a percentage of the total volar-to-dorsal distance.

RESULTS: The 14 metacarpals studied consisted of 2 index, 4 long, 4 ring and 4 small metacarpals, taken from 4 hands. The average total metacarpal head surface area was 284.6 mm2 (range, 151.0-462.2 mm2 ); the average screw footprint in the metacarpal head was 13.3 mm2 (range, 10.3-17.4 mm2 ), which compromised a mean of 5.0% (3.0-7.8%) of the total cartilaginous metacarpal head surface area. In the sagittal plane, screw placement was found to lie in the dorsal 37.4% of the metacarpal head (range, 20.7-58.6%).

CONCLUSION: The proportion of the articular surface area injured with retrograde insertion of headless compression screws into the metacarpal head is 5.0%. Screw placement is generally in the dorsal 37% of the metacarpal head.