Objective To investigate the effect of arthroscopy-assisted latissimus dorsi transfer (LDT) on posterosuperior massive rotator cuff tear (psMRCT) and analyze factors related to the outcome.Methods A retrospective case cohort study was conducted to analyze 31 patients with psMRCT admitted from January 2013 to December 2015.There were 13 males and 18 females,aged 52-67 years [(58.4 ± 4.5) years].The mean duration of symptoms was (1.9 ± 0.9) years.All patients received arthroscopy assisted LDT combined with rotator cuff repair.Postoperative rehabilitation training was carried out according to the standard procedures.Before operation and at the last follow-up,X-ray films were taken to measure the acromiohumeral talus,and magnetic resonance imaging was obtained to check the integrity of repaired tissue.Visual analog scale (VAS),active range of motions,Constant-Murley score and Fudan University Shoulder Score (FUSS) were measured to assess the shoulder joint function,and complications were documented.Furthermore,subgroup analysis was made according to "concomitant subscapularis tendon tear or not","concomitant pseudoparalysis or not","Goutallier Ⅲ/Ⅳ level fatty infiltration","complete or partial rotator cuff repair",and " Hamada Ⅰ/Ⅱ level acromiohumeral distance".Pearson correlation analysis was performed to detect the relationship of subgroup factors with postoperative Constant-Murley score and FUSS score.Results All patients were followed up for (38.8 ± 13.0) months.No complications including fever,infection,adhesion or neural malfunction were reported.Mean acromiohumeral distance increased from preoperative (5.4 ± 0.9) mm to (7.0 ± 1.0) mm at the last follow-up (P ＜ 0.05).MRI image showed intact fixation of rotator cuff and transferred latissimus dorsi tendon.At the last follow-up,VAS score decreased from preoperative (4.8 ± 1.4)points to (0.6 ± 0.7)points;the active range of motions was restored significantly;the Constant-Murley score improved from (32.9 ± 9.5) points to (67.4 t 6.7) points;the FUSS score increased from (53.3 ± 9.1) points to (85.1 ± 4.8) points (all P ＜ 0.01).Pearson Correlation analysis indicated that,among subgroup factors,only partial rotator cuff repair was significantly inversely associated with ConstantMurley score (P ＜ 0.05) and FUSS score (P ＜0.01),and the Constant-Murley score and FUSS score of patients with complete repair were significantly higher than those of patients with partial repair (P ＜ 0.05 and P ＜ 0.01,respectively).Conclusions For psMRCT,the effect of arthroscopy-assisted LDT is confirmed,which can relieve pain,restore range of motion and improve shoulder function.Preoperative pseudoparalysis,subacapularis tendon tear,Goutallier Ⅳ level fatty infiltration and Hmada Ⅱ level acromiohumeral distance do not significantly influence postoperative outcome.The torn rotator cuff tear should be repaired as possible.