Subscapularis Partial Thickness Tears by Yoo and Rhee Classification: Identifying MRI Predictors for Type IIB, Requiring Surgical Repair

<b>Objectives</b>: This study aimed to assess the significance of a novel subclassification for partial thickness tears of the subscapularis tendon (SSC) by Yoo and Rhee and to identify key MRI findings predictive of the newly adopted surgical indicator (Yoo type IIB). <b>Methods</b>: Between June 2021 and January 2024, 190 patients undergoing preoperative MRI and arthroscopic rotator cuff repair were enrolled. Patients with arthroscopically confirmed Lafosse type 1 tears (n = 148) who underwent debridement were included. Preoperative MRIs were retrospectively evaluated for SSC tear according to Yoo and Rhee classification, muscle atrophy, fatty infiltration, lesser tuberosity cyst, and long head of the biceps (LHBT) pathologies. Patients were divided into the control (Yoo type I + IIA) and study (Yoo type IIB) groups, and significant associations of MRI findings between the groups were investigated. <b>Results</b>: Among Lafosse type 1 patients, the control group (Yoo type I [n = 70] and Yoo type IIA [n = 41]; n = 111; mean age, 61.8 years ± 9.6, 48 men), and the study group (Yoo type IIB, n = 32; mean age, 66.2 years ± 7.8, 16 men) showed significant differences in age (<i>p</i> = 0.017), but not in gender (<i>p</i> = 0.634). Preoperative MRI findings, including muscle atrophy (<i>p</i> < 0.001), fatty infiltration (<i>p</i> < 0.001), lesser tuberosity cyst (<i>p</i> = 0.033), and LHBT pathologies (full thickness tear, <i>p</i> = 0.040; partial thickness tear, <i>p</i> < 0.001; tendinosis, <i>p</i> = 0.003; subluxation, <i>p</i> < 0.001), differed significantly between the groups. Multivariate analysis identified muscle atrophy (odds ratio [OR] = 33.83, <i>p</i> = 0.008) and LHBT subluxation (OR = 22.83, <i>p</i> < 0.001) as independent predictors for Yoo type IIB. <b>Conclusions</b>: In partial thickness tears of SSC, significant MRI differences were found between the Yoo and Rhee classifications. Notably, muscle atrophy and LHBT subluxation were valuable indicators for predicting Yoo type IIB as a surgical indication.