Stabilizing characteristics of rotator cuff muscles: a systematic review

Abstract

Purpose: To systematically review the evidence in support of the purported function of the rotator cuff muscles as dynamic stabilizers of the glenohumeral joint.

Methods: Electronic searches were conducted using AMED, CINAHL, Medline and SPORT Discus. Studies were required to include at least one characteristic of a stabilizer muscle. Quality analysis was completed by two assessors independently. Data were extracted for four main characteristics of stabilizer muscles: (1) moment arm length, (2) onset of muscle activity, (3) joint stiffness as measured by contribution of muscle activity to prevent joint translation, (4) co-contraction as demonstrated by electromyography muscle activity and co-activation ratio.

Results: Twenty of the 1726 identified studies were selected for the review. Rotator cuff muscles can limit joint translation (five studies) and contribute to joint stiffness (one study), possess shorter moment arms in some movements (three studies), but show limited evidence for stabilizing characteristics of early onset (seven studies) and co-contraction (seven studies).

Conclusion: The rotator cuff muscles exhibited some stabilization characteristics but not all. On the basis of our current low to moderate quality evidence, the most likely, but as yet unverified, stabilization role for the rotator cuff muscles appears to be limiting of translation in a direction-specific manner.

Implications for rehabilitation: Diagnostic tests currently used are based largely on the assumption that the muscles of the rotator cuff can be individually recruited as prime movers. Our findings demonstrate the need for more research into the proposed stabilizing mechanisms of the rotator cuff muscles to increase diagnostic accuracy and more targeted shoulder rehabilitation programs. It may be that the rotator cuff muscles have a role in limiting glenohumeral joint translation which is not reflected in the current diagnostic tests and rehabilitation protocols. Further research is required to establish this stabilizing characteristic in living subjects. Knowledge of the contribution of rotator cuff muscle activation in limiting joint translation may be an important aspect in properly assessing and quantifying the proposed function of the rotator cuff muscles as dynamic stabilizers of the shoulder joint.

Keywords: Characteristics; rotator cuff; shoulder; stabilizer muscle.