Intra-Articular Antegrade Intramedullary Screw Fixation for Proximal Phalanx Fractures: Impact of Articular Surface Defects on Joint Contact Pressures.

Background: Intramedullary headless screw fixation is increasingly used for fixation of proximal phalanx fractures. However, the impact of screw entry defects on joint contact pressures is not well defined and may have implications for arthrosis. The objective of this cadaveric biomechanical study was to assess joint contact pressures at the metacarpophalangeal (MCP) joint before and after passage of 2 sizes of antegrade intramedullary fixation.

Methods: Seven fresh frozen cadaver specimens without arthritis or deformity were included in this study. Antegrade intramedullary screw fixation of proximal phalanx fracture was simulated using an intra-articular technique. Flexible pressure sensors were inserted into the MCP joints and cyclic loading was performed. Peak contact pressures were determined and averaged across loading cycles for each finger in the native state, with 2.4- and 3.5-mm drill defects in line with the medullary canal.

Results: Peak pressure increased with the size of the drill hole defect. Contact pressure increases were greater in extension, with peak contact pressures increased by 24% for the 2.4-mm defect and 52% for the 3.5-mm defect. Increase in peak contact pressure was statistically significant with a 3.5-mm articular defect. Contact pressures were not consistently increased for the 2.4-mm defect. Testing in flexion of 45° resulted in reduced contact pressure for these defects.

Conclusions: Our study demonstrates that antegrade intramedullary fixation of proximal phalanx fractures can increase MCP joint peak contact pressures, particularly in an extended joint position. Effect increases with defect size. This has implications for the management of proximal phalanx fractures using this technique.