It's not a Bennett: How to identify chronic reverse Bankart instability on MRI

Chronic Reverse Bankart Lesion (CRBL) is a significant issue for athletes, and CRBL's radiographic appearance can mimic a Bennett lesion on radiographs. Delay in diagnosis and treatment can result in long-term sequelae. The hypothesis of this study is that specific features on Magnetic Resonance Imaging (MRI) exam can enable the radiologist to differentiate these two causes of posterior glenoid calcification. These features are 1) decreased glenoid volume, 2) displacement of the posterior labrum, and 3) posterior displacement of the humeral head.

A single-institution retrospective review of forty-four cases from 2005 to 2025 with posterior shoulder pain and glenoid calcification imaged with MRI were reviewed to identify the MRI features. One case presentation of each diagnosis exemplifies clinical symptomatology, imaging features, and management. As a secondary study, each case was independently reviewed by three raters to establish the reliability of the MRI features in confirming the diagnosis. The accuracy of each rater's diagnosis and inter-rater reliability (Fleiss's kappa) was determined.

Incorrect or incomplete diagnosis of CRBL was common. In a retrospective analysis, 3 MRI features consistently distinguished CRBL from Bennett lesions (>95% accuracy across three, independent raters), with comparative measurements provided. Fleiss's kappa was 0.73 or better across all assessments, indicating substantial or better agreement across all three raters, and reliability of the key MRI features in distinguishing between CRBL and Bennett's.

Despite similar appearances on radiographs and Computed Tomography (CT), CRBL and Bennett lesions can be accurately differentiated using three MRI features, improving diagnostic precision.