Ford B.1, Halaki M.2, Diong J.3, Cohen M.4, Ginn K.5
1University of Sydney, School of Biomedical Science, Faculty of Medicine, Sydney, Australia, 2University of Sydney, Discipline of Exercise and Sports Science, Faculty of Health Sciences, Sydney, Australia, 3University of Sydney, Discipline of Biomedical Science, Sydney Medical School, Sydney, Australia, 4University of NSW, Faculty of Medicine, Sydney, Australia, 5University of Sydney, Discipline of Anatomy and Histology, Sydney Medical School, Sydney, Australia
Background: People with shoulder pain often present with abnormal shoulder muscle function and movement patterns. It is not known whether shoulder pain causes muscle dysfunction, or whether muscle dysfunction causes shoulder pain. If the former, any therapeutic intervention that concomitantly produces shoulder pain may be contraindicated. We can investigate how shoulder muscle function changes in the presence of experimentally-induced nociception. However, there is no established model of experimental shoulder pain.
Purpose: The aim of this study was to determine whether two currently used experimental shoulder nociception protocols validly replicate the clinical experience of shoulder pain.
Methods: Nine participants without shoulder pain (5 male) received two injections of hypertonic saline, one into the subacromial space and one into supraspinatus muscle, on separate occasions at least one week apart. In addition, participants received an injection of isotonic saline either into the subacromial of the supraspinatus muscle to act as a control. The injection sites were randomly allocated. Outcome measures of pain distribution, pain intensity at rest, pain intensity changes in response to clinical provocation tests, quality of pain and pain duration were assessed by investigators who were blind to the site of injection. Pain intensity was measured using an 11 point numerical rating scale (NRS). Pain distribution was recorded by an investigator on a body chart and quality of pain was assessed using the McGill Pain Questionnaire.
Results: There were no differences in the amount of induced pain experienced between sites following hypertonic saline injection (F(1,8)=0.876,p=0.38) nor an interaction effect (F(8,64)=1.263,p=0.28). At each injection site, participants reported pain that lasted 10 minutes with mean peak NRS of 7.0 (subacromial space site SD=2.18; supraspinatus site SD=1) occurring one to two minutes after hypertonic saline injection. Mean peak NRS following isotonic saline injection was 1.4 (SD=1.1) (supraspinatus site) and 0.25 (SD=0.5) (subacromial space site). Pain was most commonly felt in the deltoid region and did not extend beyond the elbow. Most participants reported a decrease in pain in response to provocative tests. The highest ratings on the McGill Pain Questionnaire were in the sensory and evaluative domains with very few responses in the affective domain.
Conclusion(s): Injection of hypertonic saline into the subacromial space or into supraspinatus induced a distribution of pain similar to that observed in clinical shoulder pain. However, both the behaviour of pain on provocation tests and the quality of pain induced by hypertonic saline injection were different from those observed in clinical shoulder pain.
Implications: Injection of hypertonic saline into either the subacromial space or the supraspinatus muscle induced a distribution of pain similar to that observed in clinical shoulder pain, but neither protocol of experimental shoulder pain could reproduce increases in pain intensity following shoulder provocation tests or the emotional distress commonly observed in people with clinical shoulder pain. Induction of acute shoulder pain from local shoulder nociception has significant limitations as a model of clinical shoulder pain.
Funding acknowledgements: None
Topic: Musculoskeletal: upper limb
Ethics approval: University of Sydney Human Research Ethics Committee Reference Number 2014/857
All authors, affiliations and abstracts have been published as submitted.
