Incomplete Rotator Cable Did Not Cause Rotator Cuff Dysfunction in Case of Rotator Cuff Tear: A Biomechanical Study of the Relationship Between Rotator Cable Integrity and Rotator Cuff Function

Abstract

This study seeks to evaluate the biomechanical relationship between the severity of rotator cable tears and the function of the rotator cuff. Twelve cadaveric shoulders with intact rotator cuff, existing rotator cable, and a critical shoulder angle below 35° were included. For each shoulder, a posterosuperior rotator cuff tear (PSRCT) (model 2) in the crescent area was formed. Then anterior insertion detached (model 3), anterior insertion detached together with the middle cable tear (model 4), and the whole rotator cable tear (model 5) were subsequently created. The rotator cuff that lay above the humeral head rotation center was detached as a global tear control (model 6), along with the primitive status as the intact control (model 1). Glenohumeral abduction was initiated by simulating deltoid and remaining rotator cuff force. Functioning of the remaining rotator cuff was evaluated using the middle deltoid force (MDF), as required for abduction. No statistically significant differences in peak MDF values were seen among the 4 PSRCT statuses (44.10 ± 7.30 N [model 2], P= .96; 45.50 ± 9.55 N [model 3], P= .86; 45.90 ± 3.53 N [model 4], P= 0.30; 44.20 ± 8.19 N [model 5], P= .80) and intact control status (39.79 ± 7.65 N [model 1]). However, significant differences in peak MDF values were found among the 4 PSRCT statuses and the global tear control status (54.53 ± 7.46 N [model 6], P < .01). The PSRCT, regardless of the severity of the rotator cable tear, does not induce functionally significant biomechanical impairment. Tear extension involving all rotator cuff tissue above the geometric rotation center of the humeral head results in obvious functional impairment. For PSRCT, the remaining rotator cuff tissue above the geometric rotation center may contribute to the preservation of shoulder function in RCT patients.