Matched Pair Analysis of Rotational Stability With 1 Versus 2-Screw Antegrade Fixation in Distal Metaphyseal Ulnar Shortening Osteotomy Constructs.

Abstract

The purpose of this study is to evaluate the rotational stability of 1-screw versus 2-screw antegrade fixation in distal metaphyseal ulnar shortening osteotomies (DMUSOs) using matched cadaveric forearm specimens. In addition, we aim to assess the mode of failure for each construct, specifically determining whether failure occurs due to hardware failure or peri-implant fractures. Sixteen fresh-frozen cadaveric forearm specimens, organized into 8 matched pairs, were used. Ulnas were harvested, transected at the midshaft, and all soft tissue attachments were removed. A 5-mm oblique shortening osteotomy was created in the distal metaphysis, proximal to the ulnar head. Fixation was performed using either a single Acutrak 2 Mini 3.5 mm screw or 2 Acutrak 2 Micro 2.5 mm screws. Under a constant 10 N axial compressive load, specimens were cyclically loaded at 5°/second, beginning at 0.25 N m, and increasing by 0.25 N m every 500 cycles. Testing continued until failure, defined as either 10° of rotational displacement or catastrophic structural failure. The 2-screw construct exhibited significantly greater torque resistance compared with 1-screw fixation (0.84 N m [95% confidence interval, CI: 0.61-1.08] vs 0.63 N m [95% CI: 0.52-0.73], <i>P</i> = .016). In all instances, failure occurred due to rotational displacement exceeding 10°. In a matched cadaveric study examining DMUSO constructs, 2 smaller headless compression screws provided greater rotational stability than a single larger headless compression screw. The antegrade 2-screw fixation may allow for improved rotational stability across the DMUSO, allowing short-arm immobilization postoperatively, with earlier wrist pronosupination.