Is it Time to Normalize Scapular Dyskinesis?
And a better question
A new paper (Salahm 2023) asks: “Is it Time to Normalize Scapular Dyskinesis?” It's a systematic review examining the evidence that “abnormal” scapular movement can cause shoulder pain. It reminds me of another paper from a few years ago by (McQuade 2016) called “Critical and Theoretical Perspective on Scapular Stabilization: What Does It Really Mean, and Are We on the Right Track?”
Here are some key points from each paper.
Scapular dyskinesis is hard to define
Scapular dyskinesis is usually defined as pathological “abnormality” in scapular movement or positioning. What counts as abnormal movement? Several different tests have been proposed, and these involve looking for subtle or obvious signs of increased medial border prominence and superior translation, and/or reduced posterior tilt and upward rotation.
Why are these movement patterns considered pathological as opposed to normal variations? Part of the rationale is that they may cause instability or shoulder impingement. McQuade points out that this theory is questionable: dividing movements into right and wrong is inherently difficult given the complexity and variable nature of movement, and especially difficult with the scapula, whose movements are especially complex and variable. In many ways, the scapula is an unusual bone:
it “floats” on the rib cage without a strong bony attachment to the rest of the body;
it is free to translate and rotate in many different directions;
even though it has major freedom of movement, end ranges of motion do not place other joints in danger;
scapular movements are specific to the task, and there are many different scapular tasks (e.g. throwing, reaching, pushing, supporting body weight, etc.).
For these reasons, it is very hard to make rules defining right and wrong movement patterns in a way that applies to all people and all contexts.
Scapular dyskinesis is common, and poorly associated with pain
The Salahm study reviews 34 studies examining the connection between scapular dyskinesis and shoulder pain in 2,400 individuals. It found that scapular dyskinesis was extremely common (48%) in people without shoulder pain, and just a little higher (60%) in people with shoulder pain.
For overhead athletes, the correlation appears stronger: 81% of athletes with shoulder pain have scapular dyskinesis compared to only 42% of athletes without pain.
However, this does not prove that abnormal movement is causing the pain. Perhaps the pain causes the abnormal movement. Further, there is evidence suggesting that “abnormal” scapular movements in swimmers may be an adaptation to the demands of the sport, because it tends to increase with training in the short and long term.
At first glance the initial perception may be that these results are suggestive of weakness or some compensatory mechanism that requires attention, however, it is possible that there is a normal adaptation related to the overall shoulder complex that causes this change to occur, particularly since these athletes were all competing at a high level without symptoms. This would not be unlike what is known regarding the increase in external rotation range of motion at the gleno- humeral joint within a single game and over the course of the season in a baseball pitcher. Within baseball pitchers this adaptation is not only normal, but necessary to perform at a high level.
On the basis of this evidence Salahm concludes that:
Until longitudinal studies are completed that monitor the predictive value of scapular dyskinesis over time amongst asymptomatic populations, the relevance of this finding will remain uncertain.
The McQuade paper reaches a similar conclusion:
we propose that most observed scapular dyskinesia likely represents normal movement variability …
The traditional orthopedic biomechanical model has assumed that variability is evidence of incorrect movement patterns. However … dynamic systems theory argues that variability reflects the variety of coordination patterns used to complete a task and suggests that variability is evidence of the flexibility and adaptability of the neuromuscular system in exploring new movement solutions.
McQuade also notes that common corrective exercises for scapular movement may develop skills that do not translate to common tasks, and that such exercises can reduce pain even when no correction occurs.
McQuade therefore recommends that efforts to improve scapular performance should focus more on developing comprehensive movement capacity in a wide variety of functional shoulder tasks, and less on looking “normal” during artificial movements that are disconnected from real world function.
Is scapular dyskinesis a thing?
So is it time to normalize scapular dyskinesis? I find that question a bit odd - kind of like asking whether it's normal to be abnormal. I think it would be better ask whether scapular dyskinesis as currently defined is a useful concept. Based on current evidence, I would say probably not.