Rotational Stability of One Versus Two Intramedullary Screws for Proximal Phalanx Fractures: A Biomechanical Study.

Abstract

Intramedullary screws in single- or double-screw configurations are increasingly used for proximal phalanx (P1) fractures. Our purpose was to assess the biomechanical rotational stability of antegrade one- versus two-screw constructs in the fixation of simulated transverse mid-diaphyseal P1 fractures. We used matched pairs of fresh-frozen cadaver upper extremities. We harvested the P1s of all fingers and made transverse mid-diaphyseal osteotomies. Across each matched pair, we alternated between one- and two-screw antegrade fixation constructs on matched P1s. We placed one-screw constructs centrally in the P1s, ensuring appropriate sizing fit within each canal. We placed two-screw constructs in either a "V" or "lambda" configuration as able, such that the distal threads of both were distal to each simulated fracture. We secured each P1 in a material testing system frame and rotated the distal fragment relative to the proximal fragment at 2 degrees/second. Our primary outcome was the difference in group-level torque (Nm) required to produce 15 degrees of malrotation for each fixation group. We tested nine matched pairs of simulated P1 fractures, fixing one of each with a single intramedullary screw and the other with two screws. There was no statistically significant difference between one- and two-screw constructs in mean torque required to generate 15 degrees of malrotation at the simulated fracture site (0.16 and 0.26 Nm, respectively, P > .05). Properly fitted antegrade one- and two-screw intramedullary constructs for transverse mid-diaphyseal P1 fractures have similar biomechanical rotational stability. For rotational stability in the fixation of transverse P1 fractures, there is no advantage to using a two-screw construct over a one-screw construct.