Identifying shoulder testing positions and movements that isolate infraspinatus from supraspinatus

Abstract

Background: Clinical diagnosis of rotator cuff pathology is inaccurate. The difficulty of differentiation of supraspinatus and infraspinatus may contribute to diagnostic inaccuracy. Objective: To identify the characteristics of infraspinatus function that might isolate electromyographic activity of this muscle from that of supraspinatus, forming the basis for a clinical test for infraspinatus pathology. Methods: Key databases were searched using the single term 'infraspinatus'. Inclusion criteria involved infraspinatus muscle activation. Two reviewers independently applied inclusion/exclusion criteria to title and abstracts. Quality of included studies was assessed. Actions involving markedly high infraspinatus electromyographic (EMG) activity and a high ratio of infraspinatus to supraspinatus activity were identified. Results: Fifty-three articles were included from an initial yield of 1175. For many movements supraspinatus was co-active with infraspinatus. Most isolated EMG activity was seen during resisted shoulder external rotation in a variety of positions and in flexion with a longitudinal humeral force.Conclusions: It appears difficult to isolate infraspinatus from supraspinatus in the clinical setting. However, infraspinatus may be relatively isolated from supraspinatus by resisting an external rotation force, potentially in the position of shoulder flexion with a longitudinal humeral force applied.