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.
Introduction Postoperative shoulder stiffness (POSS) is one of the most common complications following arthroscopic rotator cuff repair (ARCR) and is thought to be caused by pathological changes in the anterosuperior soft-tissue structures of the glenohumeral joint. The aim of this study was to determine whether objective ultrasonographic evaluation can predict the occurrence of POSS at one year after surgery and to investigate the reliability of a newly developed ultrasonographic measurement method. Methods This retrospective cohort study included patients who underwent ARCR at a single institution between April 2017 and June 2018. Ultrasonographic external rotation (UER) and the subscapularis (SSC) sliding rate, representing anterosuperior soft-tissue sliding mobility assessed by ultrasonography, were evaluated at 1 and 3 months postoperatively. POSS was defined as passive external rotation <30° and forward elevation <120° at 12 months. Patients were assigned to one of the two groups: Group N (without POSS) or Group S (with POSS). Propensity score matching was performed to minimize baseline differences between groups. UER and SSC sliding rate were compared between the groups. Receiver operating characteristic (ROC) curve analysis was also used to determine predictive thresholds values for POSS at 12 months after surgery, and intra- and inter-rater reliability were assessed using intraclass correlation coefficients (ICCs). Results After propensity score matching, 40 shoulders (20 per group) were analyzed. The SSC sliding rate at 1 and 3 months and UER at 3 months were significantly greater in Group N than in Group S. The greatest between-group difference was observed for the SSC sliding rate at 1 month postoperatively. Regarding ROC curve analysis, the thresholds for POSS at one year postoperatively were 48% for the SSC sliding rate at 1 month after surgery, 38% for the SSC sliding rate at 3 months postoperatively, and 7° for UER at 3 months postoperatively. Reliability analysis showed substantial to almost perfect intra- and inter-rater reliability for both SSC sliding rate and UER. Conclusion Early postoperative ultrasonographic evaluation is useful for predicting the development of POSS at one year after ARCR. Reduced SSC sliding rate and limited UER in the early postoperative period were significantly associated with subsequent POSS. Level of Evidence Level III, Retrospective Cohort Design, Prognosis Study
