Rotator cuff tear is one of the main causes of shoulder function reduction in middle-aged and elderly people. Shoulder muscle strength is one of the essential factors to ensure shoulder stability. It is important to determine the degree of influence of insufficient shoulder strength on patients' symptoms to guide clinical treatment. Currently, the extent to which inadequate shoulder strength affects shoulder joint function in rotator cuff tears has not been determined.

To investigate the relationship between shoulder strength and shoulder function before rotator cuff tear surgery.

We selected 243 patients with full-thickness rotator cuff tear who underwent surgical treatment in our hospital from March 2016 to July 2019. Isokinetic muscle strength test is used to measure the patient's shoulder strength before surgery, and the clinical scoring system is used to measure the patient’s shoulder function. According to the degree of tear, the patients were divided into 4 groups: small tear group, medium tear group, large tear group, and massive tear group. The correlation between shoulder strength and shoulder function of each group of patients was analyzed.

There was a negative correlation between abduction function and VAS score in patients of small tear group (r=-0.307, P=0.018) . In patients of medium tear group, the abduction function and UCLA score (r=0.262, P=0.015) , SF-36 PCS score (r=0.226, P=0.038) were positively correlated, and the external rotation function and UCLA score are positively correlated (r= 0.289, P=0.007) . In patients of large tear group, the abduction function and Constant score (r=0.282, P=0.043) , ASES score (r=0.309, P=0.026) , SF-36PCS score (r=0.317, P=0.022) were positively correlated. The external rotation function and UCLA score (r=0.288, P=0.038) , Constant score (r=0.293, P=0.035) , ASES score (r=0.329, P=0.017) were positively correlated. The internal rotation strength and UCLA score (r=0.383, P=0.005) , Constant score (r=0.401, P=0.003) , ASES score (r=0.314, P=0.023) , SF-36PCS score (r=0.285, P=0.041) , SF-36 MCS score (r=0.304 , P=0.028) were positively correlated. In patients of massive tear group, the abduction function and VAS score (r=-0.308, P=0.035) were negatively correlated. It was positively correlated with UCLA score (r=0.413, P=0.004) , Constant score (r=0.489, P=0.000) , ASES score (r=0.473, P=0.001) , SF-36PCS score (r=0.772, P=0.000) , and SF-36 MCS score (r = 0.293, P=0.046) . The external rotation function and VAS score (r = -0.292, P =0.046) were negatively correlated. It was positively correlated with UCLA score (r=0.629, P=0.000) , Constant score (r= 0.413, P=0.004) , ASES score (r=0.695, P=0.000) , and SF-36 PCS score (r=0.583, P=0.000) . There was a negative correlation between the internal rotation function and VAS score (r=-0.309, P=0.035) . It was positively correlated with UCLA score (r=0.512, P=0.000) , Constant score (r=0.709, P=0.000) , ASES score (r=0.802, P=0.000) , and SF-36PCS score (r=0.501, P=0.000) .

The tear degree may be a key factor in determining the degree of correlation between shoulder strength and shoulder function. The partial repair of irreparable large tear is of great importance.