Work

Biomechanical evaluation of the gravity varus test in a cadaveric model of posterolateral rotatory instability of the elbow

Year: 2026

Type: article

Abstract: Background Posterolateral rotatory instability (PLRI) of the elbow is an uncommon sequela of elbow dislocation, most often resulting from incompetence of the lateral collateral ligament complex (LCLC). Diagnosis is challenging because symptoms are subtle and examination findings unreliable, and the pivot shift test is painful and poorly tolerated in awake patients. The gravity varus test is a passive maneuver in which the weight of the forearm generates the varus moment, but the joint motion it produces, and the influence of forearm rotation on that motion, have not been quantified. The purpose of this study was to quantify the kinematic effects of the gravity varus test in cadaveric elbows and to determine whether supination produces greater ulnar external rotation than pronation under conditions of LCLC insufficiency. Methods Twelve fresh-frozen cadaveric elbows (mean age, 71 years; range, 40–91 years) were mounted with the epicondylar axis perpendicular to the ground. A 3-Space Fastrak electromagnetic tracking system recorded humeral, ulnar, and radial motion. Each specimen was tested through five arcs of flexion-extension in full supination and in full pronation. The LCLC was then released to create PLRI and the protocol repeated. Kinematic data were analyzed in 5° increments. Ulnar external rotation was compared between the intact and sectioned states, and between forearm positions, using paired t-tests on the within-specimen differences with Holm–Bonferroni correction across the 29 flexion angles; the 40°–60° arc of flexion was designated the primary comparison on clinical grounds. Results Across the 40°–60° arc, sectioning increased ulnar external rotation in supination by 6.36° (95% CI, 5.72–7.01; p < 0.001), peaking at 6.74° ± 1.20° at 45° of flexion, while no change occurred in pronation (−0.26°; 95% CI, −1.04 to 0.52; p=0.48). In the sectioned state, supination exceeded pronation by 8.65° across the arc (95% CI, 7.11–10.19; p < 0.001). The increase was significant at every angle in supination and at none between 5° and 115° in pronation. In intact elbows, supination exceeded pronation by 1.92° (95% CI, 1.40–2.45). Conclusion In this cadaveric model, sectioning of the LCLC increased ulnar external rotation during the gravity varus test with the forearm supinated but not pronated, and the increase was greatest within the 40°–60° arc in which apprehension is reported clinically. These findings support the biomechanical plausibility of the test and confirm that pronation stabilizes the lateral elbow.

Source: JSES International

DOI: 10.1016/j.jseint.2026.101792