Headless Compression Screw Fixation for Proximal Phalanx Fractures: A Biomechanical Study.

Proximal phalanx fractures are common injuries of the hand with multiple treatment options. Intramedullary (IM) screw fixation has become more widely used, and early outcomes are promising. However, biomechanical data regarding this type of fixation are sparse. Two methods of IM screw fixation of proximal phalanx fractures were tested in cadaver specimens. All specimens were treated with a single antegrade headless compression screw, with half getting the addition of a blocking screw. To test the most common deforming force of flexion-extension, each phalanx was subjected to apex volar 3-point bending using the Materials Testing System test frame. There was no significant difference in the stiffness of 3-point bending with single antegrade screws alone and with a blocking screw (mean, 63.1 vs 52.2 N/mm; = .27). When comparing smaller with larger specimens, stiffness of the small group was significantly greater than that of the large group when both fixation methods were included (85.3 vs 30.1 N/mm; < .0002). When comparing stiffness with percent fill of the screw within bone, there was a moderately positive correlation (0.51). Addition of a blocking screw did not increase the stability of the IM screw fixation construct for proximal phalanx fractures. When comparing specimen size, the smaller bones were stiffer under 3-point bending load, regardless of the type of fixation. In addition, those specimens that had a larger longitudinal screw length to bone length ratio were stiffer. These findings provide valuable information as techniques for IM screw fixation of proximal phalanx fractures continue to evolve.