Shoulder Anatomy & Function
So moving on from the neck, we are going to move just below the neck to the shoulder and discuss shoulder pain. When looking at the shoulder, we often think of the shoulder as the ball and socket joint where our upper arm bone (known as the humerus, the ball of the joint) attaches to our shoulder blade (known as the scapula), which anatomically is referred to as the glenohumeral joint. However, there is a lot more to the shoulder than just the glenohumeral joint. There are two other joints within the shoulder complex. The joint that connects our collarbone (known as the clavicle) and our shoulder blade, referred to as the acromioclavicular joint and the joint that connects our collarbone to our breastbone (known as the sternum), referred to as the sternoclavicular joint. These two joints primarily provide stability to our shoulder. The socket of our glenohumeral joint comes from our shoulder blade (scapula) which through muscular attachment lies directly on the backside of our rib cage (which can be referred to as the scapulothoracic joint). The rib cage attaches to the spine (specifically the thoracic spine), so as we can see the shoulder complex is truly complex!
The glenohumeral joint, as we’ve previously discussed in the joint-by-joint approach is a primarily mobile joint, which makes sense being a ball and socket type joint, it can just about move in any direction. However, in order to be a mobile joint, the glenohumeral joint forfeits some stability. In fact, the primary stability and control of the glenohumeral joint is provided by four smaller muscles, collectively known as the rotator cuff. Many of us think that the rotator cuff is one muscle in the shoulder, however it consists of four smaller muscles. These muscles anatomically are known as the supraspinatus, infraspinatus, subscapularis, and teres minor. As their name implies, they are very involved with rotary mobility and control of the glenohumeral joint. They also provide mobility, control, and stability of the glenohumeral joint when raising the arm overhead.
The primary stability of the glenohumeral joint comes from the scapula, which from a functional standpoint the scapula is basically the foundation of the glenohumeral joint. In other words, it provides the base for the ball (humeral head) of the joint to move around in the socket. This makes sense as we want the socket of the ball and socket to be in a good position and stable to allow for the best movement of the ball. Anatomically, there are 17 muscles that attach to the scapula, which help to stabilize it as it has no direct connection to any bone on the backside (it sits on top of the ribs but does not directly connect to any of them). In addition to providing stability to the scapula, the muscles that attach to it also help with motion to help keep the ball centered in the socket (known as the glenoid fossa, which is a part of the scapula) as we move the glenohumeral joint, particularly when we reach the arm forward and overhead. The scapula does have attachments to other bones from the front. It attaches to the collarbone (clavicle) and the upper arm bone (humerus).
The acromioclavicular joint (the joint between the collarbone and shoulder blade) and the sternoclavicular joint (the joint between the breastbone and the collarbone) provide stability to the shoulder from the front.
Mobility of the mid back (thoracic spine) is extremely important to overall shoulder function and mobility. This relationship is relative to the shoulder blade positioning being relative to the rib cage, which attaches to the mid back. As a result, we need good mobility in our mid back to assist in proper positioning of our shoulder blade as we move our shoulder. Proper positioning of the shoulder blade is necessary to allow for proper centration of the humeral head (ball) in the glenoid fossa (socket) as we move our shoulder. This provides a better opportunity for proper rotator cuff function as well.
Functionally, the shoulder may be the most complex joint in our body. It depends upon many parts working in harmony simultaneously. As a result, the shoulder is one of the most common areas where we can experience some pain and discomfort. The important thing to realize relative to everything that is required for proper shoulder function is that even though we may experience pain locally in the shoulder the actual issue resulting in our pain may be arising from a region away from the actual shoulder.
Let’s discuss some of the functional issues that can result in shoulder pain.
Functional Causes of Shoulder Pain
Similar to neck pain, poor posture can result in shoulder pain. The most common cause of shoulder pain relative to poor posture relates to upper cross syndrome and the tendency for a more forward rounded upper/mid back that forces the scapula into a forward position. The forward position of the scapula results in a reduction of space for the ball to move around in the socket. This process is a common cause for shoulder impingement, which can also result in tendinitis and tears in our rotator cuff, as well as bursitis of the shoulder. Three of the most common causes for shoulder pain. The takeaway here is that when treating these conditions, we cannot isolate treatment to just the site of injury or pain, as this would not address the root cause of how the injury originated. Certainly, rotator cuff (remember it could be any of the 4 muscles of the rotator cuff) tendinitis can also result from direct injury or repetitive stress, in which case it may be appropriate to only treat the source of pain. As we discussed during our last post on neck pain, The loss of position in the mid back due to poor posture also results in a reduction of scapular (shoulder blade) related to positioning of our shoulder blade and core (trunk) stability. As we will discuss later, core stability is also important to proper shoulder function. In addition, the loss of position of our mid back typically results in a decrease of mobility in this region. As we have previously discussed, scapular stability and thoracic mobility are both important to overall function and health of the shoulder joint. As a result, these are two of the most common areas that we need to commonly rehabilitate in the treatment of shoulder pain.
Another common cause of shoulder pain is related to increased demand and strain on our shoulders with activities that involve lifting, pushing, pulling, and throwing as a result of weakness in our gluteal muscles. There is a direct connection of our gluteal muscles to our shoulders known as our posterior oblique sling. Think of this as a big “X” along our backside, as it connects our gluteal muscles to our opposite side shoulder through a muscle called the latissimus dorsi. The latissimus dorsi is very involved with producing movement and strength at our shoulder joint.
As a result of many of today’s occupations and leisure activities involving sitting, we can frequently observe issues with gluteal function as sitting results in the gluteal muscles shutting off as we are sitting on them. In addition, we also can cause restricted blood flow to these muscles with sitting, which can further weaken these muscles. Have you ever attempted to throw a ball standing still and just using your upper body to throw compared to using your lower body through a throw, it is obviously much easier to get velocity and distance on the ball when we combine our upper and lower bodies. Think of a baseball pitcher throwing a baseball or a football quarterback throwing a football, there is a reason why they use their lower body to assist with velocity or distance of the throw. Without the ability to properly utilize our gluteal muscles to improve power produced at our shoulder, we displace a significantly more strain to our shoulder and the muscles that surround it, particularly the rotator cuff. Therefore, it is common to see shoulder pain or tendinitis due to overuse relative to poor gluteal function. Again if we just address the region of pain, in this case the shoulder, we will miss the primary reason for the shoulder dysfunction and pain, the gluteal muscles, which may result in short term relief, but it is unlikely that we will see any long term benefit from this approach.
In discussing shoulder pain, we would be doing a disservice if we did not discuss the importance of core stability to proper shoulder function. The core is necessary to help improve overall stiffness (not as in tension, but as in resilience) to our spine and in doing so helps us with the ability to maintain a neutral spine position. This is very important given the fact that the rib cage attaches to the spine. When we are able to maintain a neutral spine position (compared to a rounded or slumped spine position) the rib cage is able to maintain its proper position. Proper positioning of the rib cage is very important to scapular positioning. Just as we discussed above, scapular positioning is important in allowing proper space in our shoulder joint for our ball to move around in the socket, which reduces the likelihood of common causes of shoulder pain, particularly shoulder impingement.
In addition to scapular positioning, good core stability is vital to good thoracic mobility, which is vital to proper shoulder function, as we previously discussed. This is relative to the core being the primary anchor for our thoracic spine (mid back) to move off of, this all goes back to our joint-by-joint approach.
In review, things that we need to assess and strongly consider in the treatment of shoulder pain include:
- Scapular stability
- Thoracic mobility
- Glute muscle function
- Core stability
As we can see there are a number of functional factors that can contribute to shoulder pain, hence why shoulder pain can be very common. The importance of understanding this relates to the fact that in order to properly treat shoulder pain, we must evaluate and understand if any of the above factors are contributing to the pain and determine if we need to include them into our treatment plan. Understanding that we will also need to address the acute pain related to the affected structures of the shoulder itself, most often the rotator cuff or bursa of the shoulder.
Other Factors that need considered with Shoulder Pain
When dealing with shoulder pain, obviously there are acute injuries to the shoulder related to direct injury or trauma, most commonly:
- Motor vehicle accidents
- Collision and contact sport injuries (football, hockey, martial arts, MMA, etc.)
- Falls, especially when attempting to catch ourselves with an outstretched arm
Obviously with these causes of shoulder pain we need to treat the injury related to the trauma, which often can be treated with conservative treatment options, however there are injuries such as dislocations and fractures that may require surgical intervention. In addition, there are other times such as complete rotator cuff tears that may also require surgery.
The other thing that needs to be strongly considered whenever we experience pain in the region of our shoulder, especially without any injury or trauma, is the cervical spine (neck). The cervical spine often refers pain to our shoulder region. Therefore, it is important to note that just because pain presents in an area does not always mean that the region is locally responsible for the pain. Pain can refer from an area away from the site of pain. As a result, we need to always rule out the possibility of the neck being the cause of shoulder pain. If the neck is discovered to be the cause of shoulder pain or a contributing factor, obviously we must address the neck in the treatment of the shoulder pain.
We hope that this post has provided some insight into some of the common factors for why shoulder pain can be so prevalent in our society today. There is certainly a need for all of the treatment options that we have today from the most conservative to the most invasive, however determining what the best option is for the individual by way of understanding what the causative factors of their shoulder pain are and not just treating them from a symptomatic standpoint is the key to having better and more positive outcomes. Along with reducing the potential for future recurrencies.
…Till Next Time!
