Sports Medicine Research: In the Lab & In the Field: Minor Scapular Asymmetries May be Normal (Sports Med Res)
Monday, January 13, 2014

Minor Scapular Asymmetries May be Normal

Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations

Schwartz C, Croisier JL, Rigaux E, Denoel V, Bruls O, Forthomme B. J Shoulder Elbow Surg. 2013: S1058-2746(13)00449-7.

Take Home Message:  Healthy individuals exhibit subtle but significant asymmetries between the dominant and nondominant scapula during glenohumeral motion.  Therefore, we should be cautious when using the contralateral shoulder as a reference.

Scapular dyskinesis is an umbrella term describing abnormal scapular movement and kinematics, associated with various shoulder injuries including rotator cuff syndrome, impingement syndrome, and shoulder instability. When we evaluate scapular dyskinesis we often compare the pathologic side with the contralateral shoulder but this assumes that scapular movement is symmetrical between sides in healthy individuals, which may not be the case. Schwartz et al. investigated the effect of gender and type of glenohumeral motion on 3-dimensional scapular motion bilateral symmetry in healthy populations, with the hypothesis that sex and type of motion would influence symmetry. The authors recruited 22 volunteers without any complaints of shoulder pain and no history of participation in sports using the upper extremity (11 men and 11 women; mean age of ~22 years). An examiner evaluated the participants and ruled out any postural abnormalities, pathology or prior surgeries involving the upper extremities or spine, and any sub-coracoacromial or tendinous pathologies.  The authors tracked the 3 dimensional position and movement of the scapulae as the participant performed 3 motions for their dominant side: abduction in the frontal plane, flexion in the sagittal plane, and glenohumeral internal/external rotation with the arm abducted at 90 degrees and the elbow flexed at 90 degrees. The participants had symmetrical resting positions for their scapula; however, among men the dominant scapula may be a little more laterally or medially positioned (0.5 cm) compared with the nondominant scapula. Despite similar resting positions, the authors observed asymmetrical scapular motion during glenohumeral movements, especially glenohumeral flexion and abduction. Males tended to have more upward rotation of the dominant scapula compared with the nondominant side during glenohumeral elevation. Meanwhile, women had differences related to internal/external rotation and more upward rotation of the dominant scapula during glenohumeral elevation.

We can draw several conclusions with important clinical ramifications from this study. For one, since subtle scapular asymmetries may exist in the healthy population, clinicians should be parsimonious with treatment in the absence of symptoms; such as, pain and range of motion deficits. Furthermore, until the threshold between normal and abnormal asymmetries can be defined, one should be cautious in classifying these scapular asymmetries as pathology. Additionally, the authors found the scapulae can be fairly symmetrical in a resting position, which may highlight a kinematic origin for scapular asymmetries. Since previous research has implicated postural differences, particularly among an athletic population, we may still need to consider the resting scapula position when developing a rehabilitation regimen for our patient. The authors note there are difficulties to extrapolating the data from the current participants to other clinical populations given the influence of age, sex, and level of physical activity. Regardless of these limitations, one should be careful when using the contralateral shoulder as a reference given the inherent subtle differences in scapular motion between dominant and non-dominant sides. 

Questions for Discussion: How do you tailor rehabilitation regimens to patients with differences in scapular motion between the dominant and nondominant sides? What impact of age, sex, and level of physical activity have you noted on your own clinic populations?

Written by: Jason Brucker, MD; Kris Fayock, MD
Reviewed by: Jeffrey Driban

Related Posts:



Schwartz C, Croisier JL, Rigaux E, Denoël V, Brüls O, & Forthomme B (2013). Dominance effect on scapula 3-dimensional posture and kinematics in healthy male and female populations. Journal of Shoulder and Elbow Surgery PMID: 24280354

13 comments:

Jake Marshall said...

Off topic I know but I am currious if you have any suggestions for getting a hold of full text articles without having to pay for all the different journals or journal compilations (proquest, medline).

Jeffrey Driban said...

Hi Jake: Some articles are available for free via pubmed.com or via the journal's website (e.g., http://natajournals.org/). You can also sometimes gain access via university/college's libraries. Unfortunately, outside of those methods it can be challenging to get free access to full text articles. Fortunately, many funding agencies are requiring that studies they fund should be publicly available so hopefully more articles will be freely available; as they should be.

Liz said...

I think a couple questions the clinician should answer are, Does the athlete experience and pain or discomfort with their activity? and Is their ability to perform being hindered? Another factor to consider is the athlete's sport, their position and length of time playing the sport. We know that in many overhead athletes, and especially throwing athletes, who started at a young age have anatomical differences on their dominant side as bones have formed and changed in response to forces sustained during growth. These changes result in differences in humeral torsion that can impact movement patterns at the glenohumeral joint and have an impact on scapular movement. In these athletes the changes to the bone cannot be reversed so its important to address any muscle imbalances in the dominant shoulder as well as in the non-dominant shoulder so that the side to side scapular differences do not become pathological.

Jason Brucker said...

You bring up good points about the importance of addressing acquired asymmetries early on in an athlete's career before they become the 'new normal,' so to speak. The authors in this article attempted to limit this variable by recruiting asymptomatic young volunteers who had limited participation in sports involving the upper limbs. Certainly, the intrinsic differences found in this study between dominant and non-dominant arms could have been an "adaptive alteration" (to use he authors' words) due to some other unaccounted factor (i.e. posture). Nevertheless, this study seemingly sets a floor for tolerable scapular asymmetry even if the upper limit of normal for comparative kinematics remains to be defined. Furthermore, altered range of motion and pain may serve to further augment already present differences and should remain a focal point for clinicians.

Jason Brucker said...

You bring up good points about the importance of addressing acquired asymmetries early on in an athlete's career before they become the 'new normal,' so to speak. The authors in this article attempted to limit this variable by recruiting asymptomatic young volunteers who had limited participation in sports involving the upper limbs. Certainly, the intrinsic differences found in this study between dominant and non-dominant arms could have been an "adaptive alteration" (to use he authors' words) due to some other unaccounted factor (i.e. posture). Nevertheless, this study seemingly sets a floor for tolerable scapular asymmetry even if the upper limit of normal for comparative kinematics remains to be defined. Furthermore, altered range of motion and pain may serve to further augment already present differences and should remain a focal point for clinicians.

Anoopbal said...

Hello,

Interesting post! I doubt this is more like the abnormal findings in MRI scans in asymptomatic people. In fact, MRI scans are not recommended for acute back pain bcos it doesn’t say much about the onset, severity or the prognosis of back pain. Are there studies looking at people who have severe scapular asymmetries being prone to shoulder pain or injuries? Or are there studies showing improving scapular asymmetry improves performance or decrease pain? I think the previous poster makes a good point. The scapular asymmetry might very well be an adaptation that is giving them the advantage in that arm.

Thanks
Anoop

Jason Brucker said...

Although the limits for tolerable shoulder asymmetry in asymptomatic patients remains to be defined, symptomatic patients with abnormal scapular motion and position has been well studied. Termed scapular dyskinesis, there are a multitude of pathologic conditions that can lead to this abnormal state, ranging from rotator cuff syndrome to multidirectional instability, although multifactorial causes are not uncommon. Depending on the clinical situation, one may ask the proverbial ‘which came first: the chicken or the egg?’ question. For instance, did the scapular abnormality arise as a compensatory mechanism for an existing problem (i.e. internal joint derangement), or are acquired muscle imbalances and abnormal motion the cause (i.e. a throwing athlete with posterior shoulder inflexibility leading to a rotational deficit)? To answer this, clinical context is key, not only to treat the pain, but to focus on appropriate rehabilitation protocols that address the underlying issue and restore normal scapular muscle activation and movement.

For further reference, please see these articles published in the British Journal of Sports Medicine:

http://bjsm.bmj.com/content/early/2013/04/10/bjsports-2013-092425

http://bjsm.bmj.com/content/47/14/875.full



Anoopbal said...

Thanks for the studies. I looked at one recent one which seems to be one of the very few studies comparing scapular focused treatment program. Scapular-focused treatment in patients with shoulder impingement syndrome: a randomized clinical trial. And here is the interesting part: "The intervention proposed in this study includes an exercise program, based mainly on scapular motor control principles, that provides improvement in shoulder disability and pain. Surprisingly, pain reduction and function improvement is apparent without measurable difference in scapular function".

So basically says, pain went down, but scapular dyskinesis remained the same! But they do suggest that the measures may not be sensitive enough to capture the small changes. Very interesting.

Jason Brucker said...

I would be interested in seeing the article, if you have a link. I certainly would have expected some improvement in control in the motions of scapular external rotation and the translation of scapular retraction, although it is conceivable that pain could improve prior to motion deficits. Perhaps you are correct that subtle improvements were not measurable due to the complexity of scapular motion (not to mention the deep position and overlying muscles of the scapula). Another explanation harks to a study by Timmons et al, who found that in shoulder impingement, scapular kinematic deviations typically have been small in magnitude and inconsistent in direction (2012 J Sport Rehabil). In addition, shoulder impingement itself is a broad term that encompasses different entities and is more of a physical condition than a specific diagnosis, so different etiologies (i.e. bursitis, rotator cuff pathology) could have divergent courses. Nonetheless, one would expect strength deficits (i.e. serratus anterior activation) to show measurable improvement with therapy. I would still maintain that without addressing pathologically abnormal shoulder movement, the impingement and subsequent pain would ultimately return.

Anoopbal said...

Here you go Jason:

Clin Rheumatol. 2013 Jan;32(1):73-85. doi: 10.1007/s10067-012-2093-2. Epub 2012 Oct 2.
Scapular-focused treatment in patients with shoulder impingement syndrome: a randomized clinical trial.
Struyf F, Nijs J, Mollekens S, Jeurissen I, Truijen S, Mottram S, Meeusen R.
Author information
Abstract
The purpose of this clinical trial is to compare the effectiveness of a scapular-focused treatment with a control therapy in patients with shoulder impingement syndrome. Therefore, a randomized clinical trial with a blinded assessor was used in 22 patients with shoulder impingement syndrome. The primary outcome measures included self-reported shoulder disability and pain. Next, patients were evaluated regarding scapular positioning and shoulder muscle strength. The scapular-focused treatment included stretching and scapular motor control training. The control therapy included stretching, muscle friction, and eccentric rotator cuff training. Main outcome measures were the shoulder disability questionnaire, diagnostic tests for shoulder impingement syndrome, clinical tests for scapular positioning, shoulder pain (visual analog scale; VAS), and muscle strength. A large clinically important treatment effect in favor of scapular motor control training was found in self-reported disability (Cohen's d = 0.93, p = 0.025), and a moderate to large clinically important improvement in pain during the Neer test, Hawkins test, and empty can test (Cohen's d 0.76, 1.04, and 0.92, respectively). In addition, the experimental group demonstrated a moderate (Cohen's d = 0.67) improvement in self-experienced pain at rest (VAS), whereas the control group did not change. The effects were maintained at three months follow-up.

And i think that's the question: Is it pathological or abnormal? If it is, can it predict pain or injuries? Maybe it has more of an affect in athletes and not in the general population? And maybe you are right that pain may not be a reliable indicator.

And a suggestion: Can you make the comment box bigger? It is just a bit small.

Jeffrey Driban said...

Anoopbal, in most browsers the comment boxes can be enlarged by clicking on the bottom right corner and then holding and dragging the corner.

Many bios are also listed at http://www.sportsmedres.org/p/collaborators_25.html. Once a writer has several posts they are invited to submit a bio.

Jason Brucker said...

Anoopbal, thank you for providing the article link and synopsis. Given the small sample size and multiple limitations as noted by the authors, it is hard to extrapolate the results at large, but the study lends support for a rehabilitation regimen directed towards scapular motion control. Since the primary outcome investigated was improvement in pain with scapular-based treatment, and patients were recruited based on positive impingement tests on exam rather than abnormal scapular kinematics, I would not give as much credence to the paucity of changes in the scapular measurements. Tying things back to the Schwartz article, it might have been edifying (but decidedly not useful) if the authors decided to examine the contralateral arm for comparative motion and position analysis.

Anoopbal said...

I agree. But I do think if you come up with a treatment program, it is important to show that your specific treatment is working due to the specific effects and not due to the non-specific effects of your treatment.. And it can only help a profession to have the intellectual curiosity to know "why" their treatments or modalities work or don't work.

Post a Comment

When you submit a comment please click 'Subscribe by Email" (just below the comments) or "Subscribe to: Post Comments (Atom)" (at the bottom of this page) if you would like to receive a notification when another comment has been submitted to this post.

Please note that if you are using Safari and have problems submitting comments you may need to go to your preferences (privacy tab) and stop blocking third party cookies. Sorry for any inconvenience this may pose.