Relationship Between the Critical Shoulder Angle and Shoulder Disease
This review implies a causative effect of the Critical Shoulder Angle (CSA) in both osteoarthritis and rotator cuff disease.
This review implies a causative effect of the Critical Shoulder Angle (CSA) in both osteoarthritis and rotator cuff disease.
"An increased CSA (>35°) is thought to alter deltoid vectors, which results in increased superior shear forces on the rotator cuff muscles. This increased loading of the rotator cuff may be a risk factor for the development of rotator cuff tears." This assumed causative relationship has even led some to consider arthroscopic lateral acromial resection as a means for optimizing long-term surgical outcomes after rotator cuff repair.
This article often refers to statements about "prediction": a higher CSA predicts a cuff tear, while a lower CSA predicts osteoarthritis. These are actually statements of association rather than prediction or causation. Evidence to prove prediction or causation would require data that young shoulders with higher CASs would be more prone to develop cuff tears in later years and that young shoulders with lower CASs would be more prone to develop OA in later years. To our knowledge such data are not available.
It seems at least equally likely that the observation that the CSA is higher in patients with cuff tears is due to the fact that when the cuff is deficient the humeral head rides up, eroding the superior lip of the glenoid and causing laterally extending spurs on the acromion, both of which would increase the CSA. So the presence of a cuff tear may cause the change in the CSA rather than the other way around. See these examples:
It also seems likely that the observation that the CSA is lower in patients with osteoarthritis is due to the fact that OA results in medial erosion of the inferior lip of the glenoid, which would reduce the CSA. So the OA may cause the change in CSA rather than the other way around. See these examples:
Those readers interested in what it takes to prove causation are invited to visit the post "Causation and Statistics - a lesson from Sir Austin Bradford Hill"
(link) and to look especially at #4.
=====
We have a new set of shoulder youtubes about the shoulder, check them out at this link.
Use the "Search" box to the right to find other topics of interest to you.
You may be interested in some of our most visited web pages arthritis, total shoulder, ream and run, reverse total shoulder, CTA arthroplasty, and rotator cuff surgery as well as the 'ream and run essentials'
