Let’s take a long look into a notorious joint – the shoulder. I say notorious because anyone who has had a shoulder issue understands how intricate, difficult and stubborn injuries to this joint can be. They are ‘like grumpy old men – always around, never going away and always complaining’. But just like grumpy old men, we have to love them and learn from them because they are vital to so much of what we want to do.
This week we will look at the anatomy of the shoulder before looking at specific conditions in later articles.
Shoulder injuries are amongst the most notorious and debilitating of beasts. They are amongst the most popular of issues presented to me in my working life and I will admit, one’s that will result in people giving you a random hug in a coffee shop months later when they remember that you helped fix their shoulder (TRUE). It’s not that the shoulder is the most painful of injuries or the most drastically impactive, but it is very much the most difficult one to get right. Due to it’s anatomy, it only responds to diligent treatment and adherence to treatment protocols. In other words – it’s a team approach (more homework for you).
The shoulder joint is amongst the most unique of articulations in the human body as at the core of it’s anatomy is the multitude of tendons, ligaments and muscles that connect to it, and act on it’s movement.
The shoulder is actually made up of 2 different articulations that create the primary function of the joint.
1. Glenohumeral joint – ball and socket joint where the arm meets the trunk
2. Acromio-clavicular joint – sliding joint that enables upward motion of the arm overhead.
Understanding the role of both of these joints is particularly important for any complete shoulder recovery. Due to the interdependent nature of both of these joints in movement of the arm means that the multidimensional biomechanics of the shoulder are very dextrous and complex. This is perhaps the most important aspect when it comes to looking at shoulder function. No one muscle is independent, so to enable complete recovery you must address all muscles involved in the action.
To add into the mix of this joint is a 3rd factor of the scapula. The stability of the ‘scapula’ (wing bone at the back of the shoulder that lies flat against the ribs) is all important in shoulder function. Without the scapula being stable the arm fails to have a solid base against which to push, swing, circle or move. As I so often say, it’s like doing a push up on a bosu ball – it’s harder because you don’t have a stable platform.
In anatomical terms you will read/hear phrases such as translational laxity, traumatic and atraumatic instability, net humeral joint reaction force... The poor shoulder is the ‘problem child’ of human anatomy, like the nerd at school with all the food intolerances. No wonder it can have glenohumeral apprehension. :)
Acromio-Clavicular Joint
The AC joint is a gliding joint that is located where the clavicle (collar bone) meets the acromion process. The acromion is an extension of the scapula and juts out like a balcony to from the articulation where the clavicle and the scapula actually meet. This gliding joint allows movement of the arm overhead, depressing the scapula to help the arm move higher and higher over the head. It’s like a crane arm, assisting with elevating movement higher than what would normally be possible.
This joint is by far more simpler than the glenohumeral joint and an injury here is usually a little easier to recover from. However it is vitally important for maintaining movement of the shoulder as without it, the arm cannot be raised past 100/110 degrees. No muscles act directly on the AC joint but injury to the joint space can impede movement and function. Muscles that act on the clavicle and the corocoid process as well as the downward rotation of the scapula do assist with this overhead movement and thus can be areas that influence the type of movement.
For in depth discussion visit our article here
Glenohumeral Joint
This ball and socket joint is the main articulation of the shoulder joint. The Nebuchanezzer of the thing we call ‘the shoulder’. The head of the humerus (arm bone) is about the size of a billiard ball and it inserts into the glenoid, which is about the size of a teaspoon. It is a marvel of evolution that we are able to throw, lift and move the shoulder in such a free manner with this ratio of size of the articulation. This joint must remain stable throughout all motions and whenever we lift, push or move our arm in a circular it is this ‘universal style’ joint that is responsible for that action.
Perhaps the most unique aspect of the shoulder joint is that no only do muscles move it, but also act as stabilisers for function. There are many ligaments in place to ‘hold’ the bony articulations of the glenohumeral joint and keep it stable. However due to the unique size of the ‘ball in the teaspoon’,it is the muscles that surround the joint, that hold the ball in the relatively small socket. It’s an egg and spoon race like no other! This one fact makes the glenohumeral joint a very difficult and intrinsic joint to ‘get right’.
At the core of the issues is that the ligaments in the both joints, don’t necessarily have a great amount of tension in them. Unlike the deep hip socket or knee where the ligaments are under tension and constantly checking movement, the shoulder ligaments are responding to when and where the movement occurs. In essence there is a certain amount of ‘slack’ in the shoulder ligaments where they don’t actually locate the head of the humerus in the socket at all. This is the job of the rotator cuff muscles.
The rotator cuff are the 4 muscles that keep the humerus in the glenoid fossa (egg in the spoon).
1. Supraspinatus
2. Infrapsinatus
3. Teres Minor
4. Subscapularis
They arise from the scapula at the back of the shoulder and insert in various points on the head of the humerus. So many people come in with the pinpoint pain in the front of the shoulder. This is the insertion of the supraspinatus. The Infraspinatus is the biggest of the rotator cuff and lies at the posterior aspect of the shoulder. Poor Teres Minor is the runt of the rotator cuff. Small and tucked away just underneath the infraspinatus he inserts just underneath his big brother assisting in lateral rotation. Subscapularis is another large rotator cuff that originates from underneath the scapula and inserts on the axillary (armpit) side of the humerus.
So you can understand how vital the rotator cuff is for keeping the integrity of the shoulder joint in place. They work very much as a team and can often 'carry' a weak team member, taking up the slack or working harder to enable the team to perform. Lax or weakness here means already you are working with an unstable articulation which is the recipe for disaster. When the rotator cuff isn’t active, the body will compensate by activating other muscles to create stability and assist with articulation. This will form another article later in the series on scapular stabilisation.
So this is really an introduction into shoulders. You can see how complex the joint is with it's 3 main factors of movement. At the fundamental level though, often it is about addressing these basic elements of shoulder function to get to the core of injury or incorrect function. Sometimes we have to strip away the elements of tightness in other larger, power movers to get to the basics and this is often where shoulder injury becomes dextrous. Working continually to get release or space BEFORE we can get activation and function at the basic level.
Look for further articles in this series to look at particular conditions and injuries.
