Lateralized Reverse Shoulder Arthroplasty vs. Medialized Design with Latissimus Dorsi Transfer for Cuff Tear Arthropathy with Loss of External Rotation and ER Lag Sign

<b>Background</b>: The management of irreparable posterosuperior rotator cuff tears with an isolated loss of external rotation presents significant challenges. Latissimus dorsi tendon transfer in conjunction with medialized reverse total shoulder arthroplasty has been employed to rectify external rotation deficits; however, lateralized RTSA designs may yield similar outcomes with a reduced incidence of complications. The objective of this study was to compare the clinical outcomes of lateralized reverse total shoulder arthroplasty without latissimus dorsi tendon transfer against medialized RTSA with LDT in patients with ILER and a positive external rotation lag sign. <b>Methods</b>: This retrospective cohort study involved 34 patients diagnosed with CTA and severe external rotation deficiency, characterized by a positive ER lag sign and 0° active ER. The patients were treated with either lateralized reverse total shoulder arthroplasty (<i>n</i> = 21) or medialized RTSA with LDT (<i>n</i> = 13). Outcomes evaluated preoperatively and at the 24-month follow-up comprised range of motion, ER lag sign, Constant-Murley Score, SPADI, and radiographic offset parameters. Statistical analyses were adjusted for age, sex, and baseline values. <b>Results</b>: At follow-up, 70% of patients undergoing lateralized RTSA exhibited resolution of ER lag, compared to 23% in the LDT group (<i>p</i> < 0.05). Active external rotation improvement was more significant in the LDT group (34.6° compared to 18.5°, <i>p</i> < 0.05). However, both groups exhibited comparable final external rotation and functional scores (CMS: 63 ± 9 vs. 63 ± 16; SPADI: 73 ± 20 vs. 74 ± 22). Lateralized RTSA demonstrated superior preservation of internal rotation, as evidenced by a higher percentage of patients achieving a negative Apley scratch test (67% compared to 23%, <i>p</i> < 0.05). A greater glenoidal offset correlated with improved postoperative external rotation and resolution of external rotation lag. The influence of teres minor integrity was more significant in the LDT group. <b>Conclusions</b>: Lateralized reverse total shoulder arthroplasty without latissimus dorsi tendon transfer provides similar functional restoration of external rotation in irreparable posterosuperior rotator cuff tear patients, accompanied by reduced complications, shorter surgical durations, and improved preservation of internal rotation. LDT has the potential to provide enhanced ER gains from a low baseline; however, it is characterized by increased invasiveness and technical complexity. Prosthetic lateralization is a biomechanically effective method for restoring external rotation in patients with rotator cuff arthropathy and external rotation deficits.