The architecture of the shoulder girdle is nothing short of spectacular.
Its design allows for amazing feats of strength and athleticism, such as throwing a 100mph fastball or lifting a barbell more than double your own bodyweight over your head. Unfortunately, some of the very characteristics that make the shoulder so remarkable are also often the culprits that make it more susceptible to common shoulder conditions.
Shoulder pain and dysfunction is becoming more than a small trend. We tend to hold sedentary desk jobs and be less active than in the past. We are losing our mobility as a product of our surrounding environment. To make matters worse, many common training methodologies may be potentially pushing us towards further dysfunction.
The good news is that you can always change the way you train. The goal of this article is to introduce a couple of important points regarding the anatomy of the shoulder and to discuss how the body can respond to a breakdown in function of the shoulder or neighbouring regions of the body.
Figure 1: The overhead barbell snatch may just be the ultimate expression of mobility and stability.
The shoulder girdle has a high degree of mobility. It is through this mobility that we are able to accomplish so many great things. However, with great mobility comes great responsibility.
With so much opportunity to move, the shoulder girdle is incredibly unstable. It has one true bony articulation with the rest of the body: the sternoclavicular joint. We must therefore rely a lot less on its bony structure for support than other areas of the body. Full cooperation between the peripheral nervous system, the muscles of the shoulder and its ligamentous system become paramount for proper control.
There are numerous definitions of the concept of stability but the one that resonates with me the most is, “the ability to react or adapt in the presence of change”. In other words, stability is reflexive and happens automatically, preceding conscious joint movement.
We often think that if we train the shoulder to be stronger, it will become more stable. Strength does not equate to increased stability and it is not uncommon to have an individual with great strength but poor movement control of the shoulder. This is because stability is pattern-dependent.
You may be able to demonstrate great stability and control in one movement or position but be completely incapable of displaying the same level of control if your position is altered or some sort of change occurs to your environment.
When a breakdown in control of the shoulder occurs, the scapula is often public enemy number one and a key contributor. The scapula, also commonly referred to as the “shoulder blade”, reigns supreme when it comes to adapting and altering its movement to permit continued function. Whether dysfunction occurs directly within the shoulder girdle or at some part of the body far away from it, we compensate and adjust the way we use this oddly shaped flat bone to overcome any challenge we are faced with.
Figure 2: Posterior view of the right scapula overtop of the ribcage forming the scapulothoracic joint.
In order to understand the scapula a little better, let’s take a look at a few important facts regarding its anatomy.
The scapula helps form two true articulations in the shoulder girdle – the glenohumeral joint (shoulder joint) and the acromioclavicular joint (AC joint). Therefore, impaired control of the scapula will directly affect movement at these two articulations. It also forms a pseudo-articular joint with the ribcage and spine, referred to as the scapulothoracic joint. This is not a true joint because there is no bony articulation, rather the scapula slides along the ribcage through the actions of various muscles.
As previously mentioned, the shoulder joint relies less on its bony structure for support. Therefore, there needs to be a tremendous amount of cooperation from the surrounding muscles. The scapula alone has 17 different muscles that have attachments off it (18 if you consider that around 30% of the population has tendinous attachments of the latissimus dorsi on its inferolateral border).
With so much reliance on dynamic stability, a small imbalance in the function of the muscles of the shoulder can result in a large change in how the entire upper extremity performs. To make things even more confusing, there are some muscles in the shoulder that primarily act to resist and control movement (tonic muscles), and other muscles which primarily act to initiate and create movement (phasic muscles). The roles of these muscles can change depending on what position you are in.
Why, then, is the scapula the center of the universe? Its main function is to position the socket of the shoulder to be in an optimal alignment with the ball of the humerus (arm bone) to create proper “joint centration” check out here. When the glenohumeral (shoulder) joint is in a favourable position, we have greater surface contact area and better stability. We also have lower peak joint forces and are able to display our strength and athleticism to the best of our abilities due to an optimal length-tension relationship with the working muscles.
If we are not able to create proper joint centration in the shoulder joint due to poor mobility or stability, we are left with an altered joint surface contact and higher peak joint forces, improper muscle activation and sequencing and altered joint movements. The body, being as remarkable as it is, will quickly adapt and overcome these positional faults through various compensatory strategies so that we never even know there is a problem. We are great at compensating until we can’t compensate. When this point is reached, the shoulder will break down at its weakest link and dysfunctional movements will become painful dysfunctional movements. Pain is our body’s way of telling us it can’t keep this strategy up.
Figure 3: Altered resting scapular position as a result of long standing musculoskeletal adaptation.
Figure 4: Excessive upward rotation and hiking of the right shoulder in order to lift the arm overhead.
Many common shoulder conditions result from long-term overuse and breakdown due to poor movement quality. The small amount of microtrauma that is caused by long-term dysfunctional movement patterns can eventually lead to forms of macrotrauma such as rotator cuff tears.
These injuries often result from a combination of musculoskeletal dysfunction and an environment that reinforces poor movement strategies. Without adequate extension through the upper back, posterior rotation of the collarbone and upward gliding at the AC joint, the socket of the shoulder can’t position itself correctly for overhead arm movements. The muscles of the shoulder joint will respond by prematurely upwardly rotating and/or protracting the shoulder blade to overcome these mobility restrictions at other levels. Additionally, without sufficient compression and stabilization of the shoulder joint from the rotator cuff muscles, the head of the shoulder will translate superiorly via the unopposed strong actions of muscles like the deltoid during overhead arm movements.
Over time this often leads to symptoms of impingement of sensitive structures such as muscles, tendons, bursae and the joint capsule. If these movement impairments persist, a microtear from being repetitively squished by the head of the shoulder can eventually lead to a large tear or even a full-thickness tear following a trivial shoulder movement.
In closing, the shoulder is one of the more resilient areas of the body when it comes to overcoming impairment in a quest to maintain optimal function. However, since the body is so talented at hiding impairment through compensation, many individuals begin to experience the first signs and symptoms of a shoulder problem long after the impairment in joint function first began.
The shoulder is a conduit to the performance of the surrounding areas of the body and we can use it as a beacon to understand what is happening on many different levels.
By Sean Sutton, DC
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