The Influence of Pain on Shoulder Biomechanics

 http://www.mikereinold.com/2014/10/influence-pain-shoulder-biomechanics.html

The influence of pain on how well the shoulder moves and functions has been researched several times in the past.  It is often though that impaired movement patterns may lead to pain the shoulder.

A recent two part study published in JOSPT analyzed the biomechanics of the shoulder, scapula, and clavicle in people with and without shoulder pain to determine in differences existed between the groups.  Part one assessed the scapula and clavicle.  Part two assess the shoulder.

The subjects with pain were not in acute pain, but rather had chronic issues with their shoulders for an average of 10 years.  The authors used electromagnetic sensors that were rigidly fixed to transcortical bone screws and inserted into each of the bones to accurately track motion analysis.

The studies were interesting and worth a full read, but I wanted to discuss some of the highlights.

The Influence of Pain on Shoulder Biomechanics

In regard to the scapula, the authors found:

• Upward rotation of the scapula less in subjects with pain
• This decrease in upward rotation was present at lower angles of elevation, not in the overhead position

It is important to assess scapular upward rotation in people with shoulder pain, particularly emphasizing the beginning of motion.  Realize that no differences were observed in upward rotation past 60 degrees of elevation, implying that the symptomatic group’s upward rotation caught up to the asymptomatic group.  This may imply that there is a timing issue, more than a true lack of scapular upward elevation issue.  They are upwardly rotating, but perhaps just too late?

The study also found the following in regard to shoulder motion:

• Shoulder elevation was greater in subjects with pain
• This increase in shoulder elevation was present at lower angles of elevation, not in the overhead position

Noticed how I intentionally presented it similar to the scapula findings?  if you put the two finings together, it appears that people with shoulder pain have a higher ratio of shoulder movement in comparison to scapular movement at the beginning of arm elevation.  The shoulder caught up again overhead, so it appears that the timing between shoulder and scapular movement may have an impact.

As you can see, it is important to assess both shoulder and scapular movement together, and not in isolation, as movement impairments at one join likely influence the other.  The brain is exceptionally good at getting from point A to point B and finding the path of least resistance to get there.

I should note that in studies like this, it is impossible to tell if the pain caused the movement changes or the movement changes caused the pain.  So keep that in mind.  Regardless of causation, our treatment programs should be designed with these findings in mind.

There are so many other great findings in the study that I encourage everyone to explore these further, but I thought these findings were worth discussing.  Based on these findings, it appears worthwhile to assess the relative contribution of scapular and shoulder movement during the initial phases of shoulder elevation.