Shoulder Position During Magnetic Resonance Arthrogram Significantly Affects Capsular Measurements.

Area of Science:

• Orthopedic imaging
• Shoulder biomechanics
• Diagnostic radiology

Background:

• Shoulder instability diagnosis relies on imaging, but the effect of humeral rotation during MRA is not fully understood.
• Standardized capsular measurements may vary with shoulder position, potentially affecting diagnostic accuracy.

Purpose of the Study:

• To evaluate how changes in shoulder position (internal rotation vs. external rotation) during MRA affect capsular measurements.
• To determine the diagnostic utility of rotational views in identifying shoulder instability.

Main Methods:

• Retrospective analysis of shoulder MRA scans with internal rotation (IR) and external rotation (ER) views.
• Comparison of capsular length, area, glenoid retroversion, and humeral subluxation between patients with and without instability.
• Multivariate regression analysis to identify predictors of instability.

Main Results:

• External rotation (ER) views showed significantly greater capsular length, area, and humeral subluxation compared to internal rotation (IR) views (P < .001).
• Patients with instability had significantly larger ER capsular length and area than controls.
• External rotation capsular length demonstrated 86% sensitivity and 84% specificity for predicting instability.

Conclusions:

• Humeral rotation during shoulder MRA significantly influences capsular measurements.
• External rotation positioning enhances the assessment of capsular changes and improves the diagnosis of shoulder instability.
• Rotational MRA views, particularly ER, are valuable tools for diagnosing shoulder instability.