Humeral Movement vs. Scapular Motion

The shoulder is arguably one of the most complex joints in the body.  Due to its enormous range of motion and various muscle attachments, one could teach an entire course about its anatomy and function.  There are tons of informative sources all over the internet on this stuff so I’m going to cut the crap cake here and focus on one of the most common shoulder dysfunctions I see, difficulty separating humeral movement from scapular motion.  This is not a strength issue as much as a proprioceptive issue where repetitive strain over time has impacted the shoulders ability to move efficiently.  Eventually this could lead to anything from impingement, to rotator cuff tendonopathy, to bursitis, etc.  While the diagnosis is of course important, understanding what movement(s) the shoulder is having trouble achieving that is leading to such symptoms can be of greater value from a therapeutic perspective.  

                     

Without getting into detailed anatomy, lets call the humerus (arm bone) a golf ball and the scapula (shoulder blade) a golf tee.  As long as the golf ball is comfortably congruent on the tee then in theory shoulder range of motion should be good.  Throughout the shoulders range of motion different muscles (specifically the rotator cuff) act to keep the ball on the tee.  If there is asymmetry within the rotator cuff or other phasic muscles due to old injuries, postural constraints, etc then aberrant joint motion may result causing irritation of adjacent structures.  This irritation may lead to pain.

Now just like how the movement of a golf ball can be independent of the tee, so can movement of the tee be independent of the ball, especially during closed chain exercises where the hand is fixed (Ie. crawling, hanging).  The scapula’s only osseous articulation is to the clavicle at the AC joint so you know the tone of surrounding musculature is EXTREMELY important for proper mechanics.  One could also argue that the posterior thorax and scapula create a pseudo-articulation, but that’s semantics and semantics are boring.

source: conornordengren.com

In all movements the ball and tee rely on each other and work together.  When we reach our arm over head the golf ball abducts as the tee upwardly rotates at a ratio of 2:1 (see pic below).  When we lift our arm forward the ball flexes and if we reach far enough forward the tee may protract.  There is no question that the mechanics of each articulation within the shoulder rely on each other, but what happens when things go awry and movement at one is compensated for by movement at the other?

 As the arm moves into abduction many muscles including the rotator cuff help to keep the golf ball on the tee

Probably the most common direction of difficulty I see distinguishing ball motion from tee movement is in the transverse plane.  Specifically scapular retraction compensating for humeral adduction and/or horizontal abduction/extension.  This movement inefficiency is typically seen in a patient with “upper cross syndrome”.  In this presentation the pectoral muscles and anterior deltoid have shortened over time causing the golf ball to be rotated and pulled anteriorly (see below).  This posture puts chronic strain on the posterior shoulder muscles such as infraspinatus, posterior deltoid, lats, and middle trapezius among others.  You may find these poor, overworked, locked long structures to have high tone.  They might even be tender to the touch.  This is likely because they are constantly under strain and pissed off that they have to hang on for dear life just to keep the ball on the tee.  In this scenario you may considering not releasing tension from these painful muscles and strengthening them instead.  I should not that the treatment plan for each case will vary depending on a number of factors so please get assessed by a health professional to see if this type of approach is right for you.  

          

Over time compensation patterns like these can wreak havoc on shoulder mechanics leading to shoulder pains in various ranges of motion.  If inefficient movement persists then painful and conditions like “Bursitis”, “Impingement”, and “Tendonopathy” may develop.  Please do not forget that asymmetries within the system arising from the foot, pelvis, or spine may also effect shoulder mechanics so be sure to assess globally before zeroing in locally.

As with most of my blog posts the take home message here is to understand the movement habits, or lack there of, that have led to pain.  When we answer these questions and educate our patients accordingly then success rates go way up and re-occurrence goes way down.   The specific take home message from this post.. as long as the golf ball is safely in its home and stabilized by surrounding structures, then everyone is happy.