Background: The sonographic posterolateral rotatory stress test may be a good preoperative diagnostic tool for posterolateral rotatory instability, especially in atraumatic or occult cases. However, there is lack of study on the living population or the normal elbow. Hypothesis/Purpose: This study evaluates the ulnohumeral opening gap difference between elbows in resting and stress positions while performing ultrasonography in normal healthy volunteers. The hypothesis is that the normal ulnohumeral opening gap difference is less than 2 mm. Methods: A total of 21 participants (9 males and 12 females) who presented at our institution between May and June 2021 were recruited. First, participants with elbow deformity, major elbow trauma, history of injection or surgery around the elbow, or evidence of elbow instability were excluded. Only healthy elbows without symptoms were included in this study. Participants’ both elbows were examined using ultrasonography. The ulnohumeral gap was measured in millimeters, and the difference was calculated from the means of ulnohumeral gap in resting and stress positions. Results: The mean age of participants was 36.14 years old. No samples with hyperlaxity were included. Overall, the means of ulnohumeral gap in resting and stress positions were 2.55 ± 0.69 mm and 3.16 ± 0.80 mm, respectively. The average mean of overall ulnohumeral opening gap difference was 0.61 ± 0.32 mm. There was no statistically significant difference between males and females ( p = .989). The intraobserver reliability was 0.89 and 0.9 for resting and stress positions, respectively. Conclusion: The sonographic posterolateral rotatory stress test shows that the ulnohumeral opening gap difference between resting and stress positions is less than 2 mm in healthy volunteers. Clinical Relevance: In patients with inconclusively-diagnosed PLRI, the sonographic posterolateral rotatory stress test may be a reliable preoperative diagnosis tool, providing its non-invasiveness and the ability to assess the contralateral side as a comparison.

Management and outcomesWe performed an arthroscopic lateral collateral ligament repair. At 6 months postoperative, her elbow gained stability and a painless full range of motion. ConclusionPeriarticular muscles are crucial in joint congruity maintenance when the static stabilizers are disrupted. However, in neuromuscular diseases, the dynamic stabilizers are inadequate in providing stability for ligament healing, causing elbow instability. Osteoligamentous stabilizers restoration is the key to joint stability in a paralytic limb. An arthroscopy is a good option restoring collateral ligaments by reducing damage to surrounding muscles.

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