MR arthrographic characterization of posterior capsular folds in shoulder joints.

Methods:: This was a retrospective study of 604 consecutive shoulder MR images and MR arthrograms obtained from April 2010 to January 2018. Extension in the vertical-oblique plan of the posterior synovial fold on MR arthrography was identified according to the posterosuperior, posteroinferior, superoposterior, and inferoposterior portions. The morphologies of the posterior synovial folds on MR arthrography were divided three subtypes. Morphologic appearances of the posterior labrocapsular complex on conventional MR images were described with four subtypes.

Results:: A posterior synovial fold in the shoulder joint was identified in 35 of 604 (5.8%) MR arthrography patients. 8 of 35 posterior synovial fold identified on MR arthrography were confirmed at arthroscopy. The most common MR arthrographic type of the posterior synovial fold was triangular-this was detected in 17 of 35 (48.6%) patients. The most common MRI morphology of the posterior labrocapsular complex was doubled posterior labrum. This was detected in 15 of 35 (42.9%) patients. 17 % of patients with posterior synovial folds who were diagnosed with MR arthrography had normal MRI features. The most common localization of the posterior synovial fold was posterosuperior and posteroinferior portions of the posterior labrocapsular structures. The mean of the shortest distance between the posterior synovial fold and the posterior labrum was significantly higher in the positive arthroscopic synovial fold group than in the negative arthroscopic synovial fold group (p = 0.047).

Conclusion:: Posterior synovial folds, normal capsular anatomic variants, are seen rarely on MR arthrography, and tend to be in the posterosuperior and posteroinferior portions of the posterior capsule. Some types of the posterior synovial fold can mimic a posterior labral tear in conventional MRI.

Advances In Knowledge:: On a direct MR arthrographic image, a posterior capsular synovial fold may be a normal anatomic variant. A fold is more commonly occur in the posterosuperior and posteroinferior capsular portions. The results of our study may allow differentiation of normal variations from abnormalities in patients with symptomatic shoulder joint.