Ulnar Collateral Ligament Strain of the Thumb Metacarpophalangeal Joint: Biomechanical Comparison of Two Postoperative Immobilization Techniques

Abstract

Background The aim of this study was to compare postopera t i v e i m m o b i l i z a t i o n t e c h n i q u e s o f t h e t h u m b metacarpophalangeal (MP) ulnar collateral ligament (UCL) in a cadaver model of a noncompliant patient. Methods A cadaveric model with fresh-frozen forearms was used to simulate pinch under two immobilization conditions: (1) forearm-based thumb spica splint alone and (2) forearmbased thumb spica splint with supplemental transarticular MP Kirschner wire fixation. Pinch was simulated by thumb valgus loading and flexor pollicis longus (FPL) loading. Ulnar collateral ligament displacements were measured and strain values calculated. Statistical analysis was performed using a repeated measures analysis of variance model. Results With valgus thumb loading, we noted a significantly lower UCL strain in the splint and pin group compared to splint immobilization alone. Increased load was associated with a statistically significant increase in UCL strain within each immobilization condition. FPL loading resulted in negative displacement, or paradoxical shortening, of the UCL in both immobilization groups. Conclusions While immobilized, valgus thumb force, as opposed to MP flexion, is a likely contributor to UCL strain during simulated pinch representing noncompliance during the postoperative period. Supplemental thumb MP pin fixation more effectively protects the UCL from valgus strain. UCL shortening with FPL loading likely represents paradoxical MP extension due to flexion of the distal phalanx against the distal splint, suggesting attempted thumb flexion with splint immobilization alone does not jeopardize UCL repair. Clinical Relevance This study provides a foundation to aid clinical decision-making after UCL repair. It reinforces the practice of surgeons who routinely pin their MP joints, but also brings to attention that the use of temporary MP pin fixation may be considered in difficult cases, such as those with potential noncompliance or tenuous repair.

Thumb Metacarpophalangeal Joint Ulnar Collateral Ligament Injuries: Management and Biomechanical Evaluation

“…Standard immobilization protocols postoperatively includes a thumb spica splint or cast with or without the use of a supplemental transarticular K-wire. 38 Lien et al 39 compared postoperative immobilization techniques of the thumb MCP joint in cadaver models to simulate a noncompliant patient. The authors loaded the cadaveric thumbs with the flexor pollicis longus (FPL) and separately with a valgus force.…”

Efficacy of a radial-based thumb metacarpophalangeal-stabilizing orthosis for protecting the thumb metacarpophalangeal joint ulnar collateral ligament

“…Previous investigations have examined the efficacy of thumb UCL immobilization with a forearm-based thumb UCL orthosis. 21 However, no similar investigation has been performed to determine if using a low-profile functional orthosis compromises the ability of the orthosis to reduce thumb UCL strain with valgus forces applied to the thumb. Accordingly, the purpose of our study was to determine the efficacy of a low-profile functional orthosis in resisting abduction across the thumb ulnar collateral ligament (UCL) and protecting it from reinjury.…”