Reverse shoulder arthroplasty leads to significant biomechanical changes in the remaining rotator cuff

Abstract

ObjectiveAfter reverse shoulder arthroplasty (RSA) external and internal rotation will often remain restricted. A postoperative alteration of the biomechanics in the remaining cuff is discussed as a contributing factor to these functional deficits.MethodsIn this study, muscle moment arms as well as origin-to-insertion distance (OID) were calculated using three-dimensional models of the shoulder derived from CT scans of seven cadaveric specimens.ResultsMoment arms for humeral rotation are significantly smaller for the cranial segments of SSC and all segments of TMIN in abduction angles of 30 degrees and above (p ≤ 0.05). Abduction moment arms were significantly decreased for all segments (p ≤ 0.002). OID was significantly smaller for all muscles at the 15 degree position (p ≤ 0.005), apart from the cranial SSC segment.ConclusionsReduced rotational moment arms in conjunction with the decrease of OID may be a possible explanation for the clinically observed impaired external and internal rotation.

Reverse shoulder arthroplasty: The Singapore General Hospital experience and a simple method of measuring change in the center-of-rotation

“…Several studies have shown that internal rotation of the shoulder remains poor despite reverse shoulder replacement. 5,12 The exact causes remain unknown but it may be due to alterations in the biomechanics of the deltoid, changes in rotational moment arm of the subscapularis and the design of the prosthesis. 5,12 Hence, the outcome for this study is consistent with the existing literature.…”

“…5,12 The exact causes remain unknown but it may be due to alterations in the biomechanics of the deltoid, changes in rotational moment arm of the subscapularis and the design of the prosthesis. 5,12 Hence, the outcome for this study is consistent with the existing literature. On the other hand, several authors have found that restoration of shoulder external rotation post-surgery is dependent on the quality and integrity of the teres minor.…”

Reverse Total Shoulder Arthroplasty: Early Outcome and Complication Report

“…25) Postoperative external rotation difficulty is a cause of patient's dissatisfaction. Therefore, if patient has severe external rotation lagging and insufficient teres minor muscle, surgeon should anticipate patient's dissatisfaction and explain it to the patient before surgery.…”

“…Virani et al 26) declared no difference in glenoid loosening between standard RTSA and RTSA of 10 mm lateralized COR. However, Boileau et al 24) declared that bony lateralization has mechanical advantage compared to metallic lateralization, 6,25) improving shoulder rotation, and no prosthetic instability. More studies are necessary to confirm this issue.…”

Preoperative Deltoid Size and Fatty Infiltration of the Deltoid and Rotator Cuff Correlate to Outcomes After Reverse Total Shoulder Arthroplasty

“…The loss of the contribution of the anterior deltoid to internal rotation may be compensated for by the remaining intact internal rotators (subscapularis, latissimus dorsi, pectoralis major, teres major); however, with the loss of the posterior deltoid, the only power to external rotation comes from the infraspinatus and teres minor [1]. Furthermore, the rotational moment arms of the remaining intact rotator cuff may be reduced by the altered mechanics of RTSA [13]. Accordingly, several clinical studies have shown RTSA to be effective in improving active elevation and abduction but not external rotation [4,22,27].…”