Correlation of sonographic posterolateral rotatory stress test and posterolateral rotatory instability of the elbow.

Background: Posterolateral rotatory instability (PLRI) of the elbow is challenging to diagnose using physical examination alone. This study aims to describe preliminary sonographic criteria for diagnosing PLRI using stress ultrasound to assess ulnohumeral joint instability in clinically unstable patients. Methods: This retrospective cohort study included 40 elbows from 28 patients (mean age, 45 ± 14 years), divided into 3 groups: symptomatic with clinical instability [elbow pain with a positive posterolateral rotatory drawer or lateral pivot shift test on physical exam] (n = 16); symptomatic with no clinical instability [elbow pain without positive physical exam tests above, eg, common extensor tendinopathy] (n = 13); and asymptomatic controls (n = 11). A sonographic posterolateral rotatory stress test assessed lateral ulnohumeral joint (L-UHJ) laxity by subtracting the L-UHJ measurement at rest from L-UHJ measurement under stress (stress delta). Receiver operating characteristic (ROC) curve analysis was used to determine the optimal threshold for stress delta predictive of PLRI. Results: The L-UHJ stress delta was significantly greater in clinically unstable elbows (2.2 ± 1.1 mm) compared to stable symptomatic (0.9 ± 0.7 mm) and asymptomatic elbows (0.6 ± 0.5 mm), Conclusions: Sonographic posterolateral rotatory stress test findings for PLRI in clinically unstable patients may be smaller than previously shown in cadaveric models. An L-UHJ stress delta ≥1.6 mm demonstrates high sensitivity and specificity in the assessment of L-UHJ laxity in the diagnosis of PLRI. Further research is needed to validate these findings across larger, more diverse patient populations and clinical settings.