Dorsal Cortical Alignment Predicts Functional Outcomes in Proximal Phalangeal Fractures Treated with Intramedullary Headless Compression Screws but Not in Metacarpal Fractures.

: Intramedullary headless compression screw (IMHCS) fixation has emerged as a minimally invasive and biomechanically robust method for treating metacarpal and proximal phalangeal fractures. While the clinical outcomes are generally favorable, the impact of anatomical fracture reduction on postoperative function has not been systematically examined. : We retrospectively analyzed 69 patients (41 metacarpal, 28 proximal phalanx) treated with IMHCSs between June 2020 and March 2025. Fractures were classified radiographically as reduced or non-reduced. Functional outcomes were assessed using the Total Active Motion (TAM) scoring system. The association between the reduction quality and TAM outcome was analyzed separately for metacarpal and proximal phalangeal fractures using the Fisher-Freeman-Halton exact test. : All fractures achieved radiographic union. In the metacarpal fractures, 90% of the patients attained good-to-excellent TAM scores, with no statistically significant association between the reduction quality and functional outcome ( = 0.1303). In contrast, for the proximal phalangeal fractures, anatomical reduction was significantly associated with superior TAM outcomes ( = 0.0014; Cohen's w = 0.802). The postoperative radiographs in this group revealed smooth dorsal cortical alignment in the patients with good outcomes, suggesting preserved tendon gliding surfaces. : Anatomical fracture reduction significantly predicts postoperative function in proximal phalangeal fractures treated with IMHCSs. In contrast, metacarpal fractures appear more tolerant of minor malalignment. These findings underscore the importance of achieving cortical continuity in phalangeal fractures to optimize digital biomechanics. A minimal open approach should be considered to ensure proper alignment during IMHCS fixation.