Partial triceps tendon transfer for dynamic stabilization in posterolateral rotatory instability of the elbow: a biomechanical study

Abstract Purpose Posterolateral rotatory instability (PLRI) of the elbow results from lateral collateral ligament complex (LCLC) insufficiency. In the setting of failed conventional ligament reconstruction, no established salvage procedure is available. This study biomechanically evaluated partial triceps tendon transfer to the supinator crest as a dynamic stabilization concept for PLRI. Methods Nine fresh-frozen human elbow specimens underwent cyclic external rotational loading of 0.5 Nm. Specimens were tested sequentially in the native state, an LCLC/common extensor origin-deficient unstable state, after transosseous LCLC repair, and after partial triceps tendon transfer to the supinator crest with the LCLC detached. Testing was performed under combined biceps/triceps loading conditions with external forearm rotation relative to the humerus as the primary outcome. A two-factor repeated-measures analysis of variance (RM-ANOVA) compared unstable, repaired, and tendon-transfer conditions across loading conditions. The native state was assessed unloaded and reported separately in a one-factor RM-ANOVA. Results Intervention significantly affected external rotation (F(2,16) = 33.31, p < 0.001, η 2 p = 0.81). Across loading conditions, partial triceps transfer significantly reduced external rotation compared to the unstable state (mean difference [MD]=-3.38°, p = 0.005), while LCLC repair showed lower external rotation than triceps tendon transfer (MD=-3.13°, p = 0.012). External rotation also differed significantly across the combined biceps/triceps loading conditions (Greenhouse–Geisser corrected F(1.26,10.11) = 77.00, p < 0.001, η 2 p = 0.91), decreasing from 13.37° at 0 kg biceps/0 kg triceps to 2.42° at 0.5 kg biceps/4.0 kg triceps. Conclusion Partial triceps tendon transfer improved dynamic elbow stabilization and significantly reduced PLRI in a LCLC‑deficient in vitro model. However, it did not fully restore joint stability, supporting its role as a potential adjunct or salvage option rather than a primary procedure. The findings highlight the importance of dynamic muscle tension in lateral elbow stability, while the time‑zero, in vitro design limits direct clinical translation and warrants further in vivo investigations.