Magnetic Resonance Arthrogram Outperforms Standard Magnetic Resonance Imaging 2 Weeks After First Shoulder Dislocation for Labral Tear Diagnosis.

PURPOSE:To determine the comparative accuracy and precision of routine magnetic resonance imaging (MRI) versus magnetic resonance (MR) arthrogram in measuring labral tear size as a function of time from a shoulder dislocation. METHODS:We retrospectively evaluated consecutive patients who underwent primary arthroscopic stabilization between 2012 and 2021 in a single academic center. All patients completed a preoperative MRI or MR arthrogram of the shoulder within 60 days of injury and subsequently underwent arthroscopic repair within 6 months of imaging. Intraoperative labral tear size and location were used as standards for comparison. Three musculoskeletal radiologists independently interpreted tear extent using a clock-face convention. Accuracy and precision of MR labral tear measurements were defined based on location and size of the tear, respectively. Accuracy and precision were compared between MRI and MR arthrogram as a function of time from dislocation. RESULTS:In total, 32 MRIs and 65 MR arthrograms (total n = 97) were assessed. Multivariate analysis demonstrated that intraoperative tear size, early imaging, and arthrogram status were associated with increased MR accuracy and precision (P < .05). Ordering surgeons preferred arthrogram for delayed imaging (P = .018). For routine MRI, error in accuracy increased by 3.4° per day and error in precision increased by 2.3° per day (P < .001) from time of injury. MR arthrogram, however, was not temporally influenced. Significant loss of accuracy and precision of MRI compared with MR arthrogram occurred at 2 weeks after an acute shoulder dislocation. CONCLUSIONS:Compared with MR arthrogram, conventional MRI demonstrates time-dependent loss of accuracy and precision in determining shoulder labral tear extent after dislocation, with statistical divergence occurring at 2 weeks. LEVEL OF EVIDENCE:Level II, retrospective radiographic diagnostic study.