The internal joint stabilizer in lateral ulnar collateral ligament injuries: a biomechanical study.

HYPOTHESIS: The internal joint stabilizer (IJS) effectively reduces varus angle deviations and mitigates maximum lateral ulnar collateral ligament (LUCL) strain during elbow flexion-extension, thereby improving elbow posterolateral rotatory stability.

METHODS: Eight cadaveric specimens underwent biomechanical testing in 4 conditions: intact LUCL (INTACT), intact LUCL with IJS (INTACT IJS), disrupted LUCL (DISRUPT), and disrupted LUCL with IJS. Varus angle and LUCL strain were measured with a LabJack T7 LabJack T7 data acquisition system (DAQ) and 2-camera (PROSILICA GC1350C) stereophotogrammetry systems. General additive mixed models were used to evaluate the impact of LUCL and IJS status across flexion-extension cycles.

RESULTS: Post-hoc testing uncovered significant effects between the INTACT to DISRUPT stages, INTACT IJS to DISRUPT stages, and DISRUPT to disrupted LUCL with IJS stages over all flexion-extension angle checkpoints, approaching intact ligament stability during flexion-extension. The most significance was captured in each of these 3 pairs at 75°. There was no significant difference in maximum strain between the INTACT and INTACT IJS stages.

DISCUSSION: The IJS significantly stabilizes the elbow during flexion-extension after LUCL disruption. Peak efficacy is observed in mid-flexion (60°-90°), where varus laxity is most pronounced. While the IJS does not fully replicate intact ligament stabilization, it succeeds in reducing varus angles in disrupted ligament conditions. These findings support the IJS as a viable treatment for posterolateral rotatory instability of the elbow.