The Shoulder PART 1

Understanding the Shoulder Complex and its Relationship  with the Rest of the Body:


The human shoulder is one of the most dynamic joints in the body.  It is essential to have healthy shoulder mechanics to perform well in athletics, but also to preform activities of daily living.  Shoulder health is often determined by the relationship between the shoulder and the rest of the body. Unfortunately, there are several factors that compromise that relationship and lead to shoulder injuries. I believe the three factors that lead to shoulder dysfunction are: posture, mobility, and stability.

 Stats:

 Statistically there is a high prevalence of shoulder injuries in America.  In 2006, approximately 7.5 million people went to the doctor's office for a shoulder problem; more than 4.1 million of these visits were for rotator cuff problems. (orthoinfo.com)  Shoulder injuries are the second most common injury to cause missed work time, lower back injuries are credited as the number one reason people miss time at work. However, shoulder injuries take the most time to recover and return to work, compared to other injuries.  On average it takes 30 days to return to work after a shoulder injury compared to 13 days after a back injury. (TDI,
TWC)

 Anatomy:

The primary joint people think of when they talk about the shoulder is the “glonohumaral joint” this is the ball and socket joint that attaches the humerus (arm bone) to the scapula (shoulder blade). The best analogy of this joint is of a golf ball on a tee.  The bony joint surface that connects the humerus to the scapula is not much bigger than the size of the head of a golf tee. The stability of the joint is mainly gained through soft tissues, meaning the ligaments, tendons, and muscles that surround the shoulder. The soft tissues try to keep the head of the humerus centered on the scapula; this concept is called centration and is fundamental to preventing injuries. 

The first layer on top of the bone is a covering of ligaments including the labrum and the shoulder joint capsule.  On top of the shoulder capsule are the muscles and tendons of the rotator cuff.  Technically the rotator cuff consists of 4 muscles: supraspinatus, infraspinatus, teres minor, and the often forgotten subscapularus. The cuff muscles attach on the head of the humerus and originate from the scapula.  I often include the long head of the biceps in the group of the rotator cuff because of its proximity and function in shoulder stabilization. The muscles of the cuff must perform several tasks to aid in shoulder function.  Each of the muscles moves the shoulder in a specific direction. For example, supraspinatus raises the arm overhead after the shoulder has reached 90 degrees.  When a person injures their supraspinatus, they are not able to lift their arm over their shoulder. Possibly the most important task of the rotator cuff is to stabilize the head of the humerus. There are constant small contractions from all of the cuff muscles to keep the head of the humorous centrated.

The final layer of protection comes from the muscles that stabilize the scapula. There are a total of 18 muscles that attach to the scapula. Most of the muscles that attach to the scapula originate from the spine and ribcage.  This group of muscles help move and stabilize the scapula. If the scapula does not move effectively or there is a weakness in the muscles supporting the scapula,increased stress is placed on the shoulder and the cuff muscles.  Without scapular motion, humans would not be able to raise their arms over 120 degrees. It becomes imperative that middle back, lower neck, and rib cage be mobile to allow the shoulder blade to move to reduce stress on the shoulder.

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Video By Young Lae, Moon M.D. Chair of 3D Based Medical Application Working group.
Chairman and Professor of Orthopaedics, Chosun University Hospital, Korea.
[CC-BY-3.0 (http://creativecommons.org/licenses/by/3.0)],
via Wikimedia Commons