• Nick Aunkst

5 Minute Reads: The Shoulder.

One of the most common complaints fielded at the office these days is the complaint of shoulder pain. It’s not uncommon to see both acute and chronic shoulder pain cases, many times in overhead athletes, desk-workers and people who work with their hands for a living. Throughout hundreds of conversations about the shoulder, it seems as though there are common misconceptions about the region, and with good reason. The shoulder is one of the most complex regions of human musculoskeletal anatomy and biomechanics. Lets go over some of the basics to get a further grounded understanding of the shoulder and its importance to movement.

The shoulder is composed of a few major joints. For the sake of the topic today, we’re going to focus on one: the glenohumeral joint, which is the combination of the humerus (upper arm) and the scapula (shoulder blade).

The shoulder is a classic “ball and socket” type of joint, and one of the few independent regions of the body that can perform “circumduction”. Circumduction involves the movement of a limb so that the distal portion performs a circular motion, while the proximal end stays fixed.

The ever-important rotator cuff is a major player in shoulder health, and maybe the most commonly misunderstood portion of the shoulder. The rotator cuff is actually a combination of four different muscles, all connecting various different points of the scapula to the upper humerus. The four muscles are the: supraspinatus, infraspinatus, teres minor and subscapularis. All of these muscles have their own place and purpose and they all create their own important motions in the shoulder. But, the main function of the rotator cuff muscles is to provide stabilization for the shoulder. Being that the shoulder is inherently one of the most mobile regions of the body, you can see how it is important to have congruency in the rotator cuff musculature to provide the proper stabilization for whatever activities you may be doing. Lets go over the actions of the rotator cuff muscles:

The supraspinatus is the upper most muscle of the rotator cuff, living on the top of the scapula and traveling out underneath the acromion process to the upper humerus. The supraspinatus is an extremely important muscle. Outside of providing stabilization to the shoulder, it helps the deltoid abduct the arm (raise to the side) and is critical in deceleration of the arm in an eccentric fashion. Think of a baseball pitcher, finishing off their throwing motion and decelerating their arm. This action relies heavily on the supraspinatus. The supraspinatus is also commonly a pain generator in cases of shoulder pain. The supraspinatus can be “impinged” under the acromion overtime with aberrant shoulder motion. This is how a good deal of “rotator cuff tears” happen.

The infraspinatus lives on the bottom of the posterior aspect of the scapula and attaches to the upper portion of the humerus. The infraspinatus is a fan shaped muscle. Again, critical for stabilization of the shoulder, it’s largely responsible for creating external rotation of the humerus (think ‘open door’ position). The infraspinatus is an important muscle when it comes to physical activity. Our world tends to be very ‘internal rotation dominant”, meaning we tend to spend more time in internal rotation than external rotation. This leads to issues with the infraspinatus muscle that can later lead to injuries of the shoulder. It’s critical to train this region to be strong and stable.

The teres minor is a small muscle located on the lateral aspect of the shoulder blade extending to the upper humerus. The teres minor is also an external rotator (open door, again), of the shoulder. The teres minor is largely responsible for holding the head of the humerus stable in the glenoid fossa as the arm goes into abduction or flexion. There is a “roll and glide” mechanism present with these motions, where the ball region of the shoulder must be able to do both motions fluidly. The teres minor is largely responsible for stabilizing this motion.

The subscapularis is the only rotator cuff muscle that actually lives on the front of the scapula, located between the scapula and the thoracic cage (ribs). The subscapularis is a powerful internal rotator of the humerus, assisting in activities such as bench press, arm wrestling and muscle ups. A dominant muscle, it often overpowers the smaller and inherently weaker external rotators of the rotator cuff. This is one way instability in the shoulder occurs. Dominant internal rotators (there are others, to be discussed at a later time) tend to overpower other regions, which can lead to acute or chronic shoulder pain issues.

The classic “rotator cuff tear” is simply a tear in one of the above muscles. There are varying degrees of sizes of tears, some more serious than others. And depending on your pain threshold, rotator cuff tendinoses can present with similar levels of pain. Therapies and options for treatment vary on the degree and the severity of the injury.

Consistency and proactivity are the keys to good long-term shoulder health. Given proper education, evaluation and instruction on how to care for the region, it can be easy to be proactive in your approach to caring for your shoulders. Find a health professional who understands the shoulder to supervise your through a program to tailor to your shoulder needs. The current, and future health of your shoulders will thank you.

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