ZTE MRI for Rotator Cuff Tear Arthropathy: Integrated Bone–Muscle Analysis and Its Association with Pseudoparesis

<b>Background/Objectives:</b> Evaluating glenoid changes in rotator cuff tear arthropathy (RCTA) is crucial for preoperative planning. MRI with zero echo time (ZTE) sequence, which produces CT-like images, allows for the assessment of osseous morphology as well as factors contributing to pseudoparesis in RCTA patients. <b>Methods:</b> In this retrospective study, using 3T MRI, glenoid version, glenoid vault depth, humeral subluxation index, humeral head medialization, critical shoulder angle, glenoid best-fit circle width, glenoid best-fit circle bone loss ratio (GBLR), and anterior, central, and posterior glenoid bone loss were measured on reformatted 3D ZTE images in 43 shoulders independently by three observers. The same measurements were repeated by one observer after 10 days. Muscle cross-sectional areas were measured. Patients' active ROMs, American Shoulder and Elbow Surgeons (ASES), and Constant-Murley scores were recorded. Patients unable to perform 90° forward elevation were classified as the pseudoparesis group. <b>Results:</b> Interobserver agreements were good to excellent, except for glenoid vault depth, anterior bone loss, and GBLR. Intraobserver agreements were good to excellent. The pseudoparesis group showed significantly less subscapularis muscle cross-sectional area (<i>p</i> = 0.006). Moderate correlations were found between subscapularis cross-sectional area and forward elevation, abduction, and internal rotation ([r = 0.471, <i>p</i> = 0.001]; [r = 0.447, <i>p</i> = 0.003]; [r = 0.464, <i>p</i> = 0.002], respectively). Moderate negative correlations were found between anterior glenoid loss and forward elevation (r = -0.411, <i>p</i> = 0.006) and abduction (r = -0.475, <i>p</i> = 0.001). <b>Conclusions:</b> MRI with ZTE sequence demonstrated good reliability for assessing osseous morphology in shoulders with RCTA. Glenoid anterior bone loss and loss of subscapularis muscle are both associated with pseudoparesis.