Towards a clinical test for infraspinatus pathology

This thesis investigated the development of an accurate clinical test for infraspinatus pathology, a common source of shoulder pain. A systematic review of 25 studies found that most clinical tests for rotator cuff pathology were inaccurate. Moreover, all the clinical tests for infraspinatus pathology were inaccurate, except external rotation lag sign, in one study. For an infraspinatus clinical test to be accurate, the effect of the test on infraspinatus needs to be isolated from supraspinatus. A second systematic review suggested that differentiation was difficult, but if external rotation was resisted in flexion, in combination with the application of a longitudinal humeral force, infraspinatus might be isolated from supraspinatus. An electromyographic study, using surface and intramuscular electrodes, found that resisted shoulder external rotation from a position of flexion, might isolate infraspinatus from supraspinatus, on the basis of muscle activation. This study reported that both parts of infraspinatus are activated differently in resisted external rotation, with the oblique part being much more active than the transverse part. A cadaveric study using pressure sensitive transducers suggested that infraspinatus is subject to subacromial impingement on the posterior acromion in shoulder extension and external rotation. Supraspinatus is also subject to impingement on the anterior acromion in this position, so this movement would not serve as a clinical test specific to only infraspinatus. However, this movement will indicate subacromial impingement. The results from this thesis have suggested new directions for a clinical test for infraspinatus. This could involve resisted manual muscle testing or impingement of infraspinatus. While an accurate clinical test for infraspinatus pathology may or may not be possible in the long term, it is too early to declare it a goal out of reach. Further research effort is justified in the search for an accurate clinical test for infraspinatus pathology.

Submission note: A thesis written in partial fulfilment of the requirements for the degree of Doctor of Physiotherapy to the Department of Physiotherapy, Faculty of Health Sciences, La Trobe University, Bundoora.