With increasing aging population and the incidence of rotator cuff tear, growing number of patients undergo rotator cuff repair on both sides. Purpose of the current study was to compare perioperative characteristics and postoperative outcomes of both shoulders in patients who underwent arthroscopic bilateral rotator cuff repair sequentially. Materials and Methods: Prospectively collected data of 2580 primary rotator cuff repair by a single surgeon between October 2003 and January 2015 was

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... spectively reviewed. Among them, 99 patients had bilateral rotator cuff repair (198 cases), and 36 patients were excluded (less than 1 year follow-up (27) , reoperation due to retear before postoperative 1 year (3), osteoarthritis (1), rheumatoid arthritis (1), avascular necrosis (1), partial repair (2) , open repair (1)), so finally 63 patients were enrolled who followed up at least 12 months and underwent MRI, CT arthrography or ultrasonography at least 12 months after surgery. The mean age at first surgery was 58.4 years (range, 43-77), and the mean follow-up was 55.6 months (range, 18-125). The interval between first and second surgery was 28.5 months (range, 4-96). Perioperative clinical characteristics, postoperative functional outcomes of 6, 12 months and final follow-up and imaging studies for the evaluation of healing failure were investigated. Functional evaluation included the visual analog scale (VAS) for pain and satisfaction of surgery, range of motions, American Shoulder and Elbow Surgeons (ASES) score, and Simple Shoulder Test (SST). The paired t-test or Wilcoxon signed rank test and logistic regression was used to compare clinical parameters and functional scores between first and second surgeries, and P < 0.05 was considered statistically significant. Results: There were no significant differences in duration of symptom, fatty degeneration of each cuff muscle between shoulders of first and second surgery, and there are no significant differences in function and integrity of repaired cuff according to the time of diagnosis for the rotator cuff tear of the opposite side between shoulders (all Ps > 0.05). Tear size of both shoulders were closely related (OR ¼ 20.0, P ¼ 0.001), however, no preoperative clinical factors (age, duration of symptom, diabetes mellitus, osteoporosis, preoperative VAS and ROMs) were significantly related with tear size (all Ps > 0.05). Postoperative functional outcomes at 6, 12 months and final follow-up of the first and second surgeries improved significantly compared to preoperative state (all Ps < 0.05). Between first and second surgeries, satisfaction at 12 months and functional outcomes (VAS for pain and satisfaction, SST, ROMs) at final follow-up visit were significantly better in first surgery (all Ps < 0.05). Regarding the interval between first and second surgeries, satisfaction VAS and functional scores (ASES and SST) were significantly lower in shoulders of second surgery at postoperative 6 months in patients whose surgical interval was shorter than 6 month compare to patients whose interval was longer than 6 months (all Ps < 0.05). The rates of healing failure were 15.9% (10 of 63) after first surgery, 22.2% (14 of 63) after second one. Larger tear size (OR¼2.1, p<0.05) and higher fatty degeneration of the supraspinatus (OR ¼ 2.2, P ¼ 0.005) and infraspinatus (OR ¼ 2.7, P < 0.05) were significantly related to the healing failure of both sides. However, the functional outcomes including VAS for pain and satisfaction, and ROM were not statistically different with respect to cuff healing, and no preoperative clinical factors (age, duration of symptom, whether the surgery was performed on dominant side first, diabetes mellitus, osteoporosis, preoperative VAS and ROMs) were significantly related to the healing failure of both sides. (all Ps > 0.05). Seven patients showed bilateral healing failure, and this meant 70% of initial failure followed subsequent failure in the other shoulder, and there was significant relationship between the failure of first and second surgeries (OR ¼ 15.3, P < 0.001). Discussion: In staged bilateral rotator cuff repairs, functional outcomes of second surgery were lower than first one, which corresponded to the comparative study of bilateral staged total knee arthroplasty that the expectation and satisfaction are relatively lower in second surgery, because expectation and satisfaction is too high after first surgery. 1) Furthermore, if bilateral shoulders are involved, more symptomatic shoulder usually repaired first, therefore, subjective evaluation might be better in first surgery. The close interval between two surgeries within 6 months negatively affected to functional scores of second shoulder at early postoperative period, as the rehabilitation usually depends on the opposite shoulder. Previously operated shoulder which had not been fully recovered might adversely affected the early outcome of second shoulder. Therefore, it would be recommended that the second surgery should be performed after at least 6 months after first surgery in patients of bilateral rotator cuff tears. However, this decision should be carefully made because there is chance of progression of rotator cuff tear. Interestingly, the healing failure of firstly repaired rotator cuff was significantly related to the healing failure of second shoulder. This might be explained by the correlation of tear size between both sides. The tear condition of both shoulders were seemed to be similar, so it could be expected there were similar results on healing of both shoulder. Being supported by the current study and several studies including authors' 2) , the tear size and fatty degeneration of rotator cuff were the independent prognostic factors for healing regardless of side. Therefore, we could carefully suggest that healing failure at first surgery could be a good predictor for the failure of second surgery. Conclusion: Though bilateral arthroscopic rotator cuff repair demonstrated good outcomes in each side, the second shoulder would be better to be repaired after at least 6 months after first