ObjectiveTo investigate the effect of unilateral rotator cuff repair on the contralateral shoulder in patients with bilateral rotator cuff tears.MethodsA clinical data of 46 patients with bilateral rotator cuff tears met the criteria between May 2016 and May 2019 was retrospectively analyzed. Of 46 patients, 23 patients underwent bilateral conservative treatment (conservation group), 23 patients underwent unilateral arthroscopic rotator cuff repair, and conservative treatment on the contralateral side (operation group). There was no significant difference in gender, age, disease duration, degree of rotator cuff tear, and comorbidities between 2 groups (P>0.05). Before operation and at 6 and 12 months after operation, the degree of the rotator cuff tear was measured by MRI, and the shoulder function was evaluated by the visual analogue scale (VAS) score, University of California Los Angeles (UCLA) score, American Shoulder and Elbow Surgeons (ASES) score, and range of motion (ROM) (forward flexion, external rotation, external rotation at 90° of abduction, and internal rotation). The evaluation results of the non-surgical side of shoulders in the operation group were compared with one side of shoulders in the conservation group.ResultsAll incisions healed by first intention without any complication after operation. All patients were followed up 12 months. MRI reexamination showed that the degree of rotator cuff tear of the contralateral shoulder in the operation group increased significantly after operation (P<0.05). There was no significant difference between the operation group and the conservation group before operation (P>0.05), but the rotator cuff tear of the contralateral shoulder in the operation group was more serious than that of the conservation group at 6 and 12 months after operation (P<0.05). At 6 and 12 months after operation, the VAS score, UCLA score, and ASES score significantly improved when compared with the preoperative scores in 2 groups (P<0.05). There was no significant difference in the VAS score, UCLA score, and ASES score between 2 groups before operation (P>0.05). The function scores in the conservation group were better than those in the operation group at 6 and 12 months after operation (P<0.05). There were significant differences in the ROM of shoulder between pre- and post-operation in 2 groups (P<0.05). And there was no significant difference between 2 groups at pre- and post-operation (P>0.05).ConclusionFor patients with bilateral rotator cuff tears, the unilateral rotator cuff repair can aggravate the rotator cuff tear of contralateral shoulder.