The Anatomy of the Shoulder

I can already hear you screaming a question at me, "I dislocated my shoulder and its never recovered, why!"

Lets see if this helps...

The shoulder consists of three bones,  The clavicle, scapula and humerus.  The shoulder joint is very similar to the hip joint as they are both ball and socket joints.  However the key difference between the two is the fact that the hip is a much larger irregular structure that makes it harder to dislocate the joint in comparison to the shoulder.  By now you must be excellent on learning joint names...  It's simple just merge two bone names to form the joint name (look back over the knee, and foot and ankle entries).

Firstly I should make it clear we have numerous bony prominences protruding around our shoulder joint.  We have our acromial and coracoid process which can both be palpated.  We also have the spine of the scapula which is the only surface of the scapula you can feel along your back.  Right, now that's cleared up we can move on to the joint names.

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We have a joint situated between the superior and lateral surface of the sternum and the medial third of the clavicle.  This is called our sternoclavicular joint.  Also between the last lateral third of our clavicle and the acromion process is our acromioclavicular joint.  Finally we have our main joint of the shoulder which is known as our glenohumeral joint.  This joint is formed between the humeral head (head of the humerus) and the proximal surface of the glenoid fossa.  The glenohumeral joint is a synovial joint (ball and socket).  We have a substance called hyaline cartilage which covers the bony ends of the joint and hyaline membrane that holds the joint in place, aiding stability.

The shoulder joint is all about sacrificing stability for mobility.  Here's why...  The head of our humerus is 2/3 the size of our glenoid fossa which it inserts into, therefore it is only in contact with the glenoid fossa for 1/3 of the time.  This decreases the stability within the joint however increases the mobility.  The shoulder joint however is quite a deep socket joint that increases stabillity.  Labrum (a source of fibrocartilage) adds to stability by increasing the depth round the glenoid fossa, this is called glenoid labrum. 

I briefly touched upon the dislocation of the shoulder earlier telling you its easier to dislocate than the hip, however I never told you why...  The glenoid labrum that surrounds the socket can wear away when a dislocation is present within the joint.  Therefore when the joint is back in place its much easier to pop out.  Sounds gross?  Well that's cause it is!  The glenohumeral joint allows us to perform many movements, such as; rotation, flexion, adduction, abduction, medial and lateral rotation.  However in an individual with worn glenoid labrum these movements become hyper movements and can fall quickly into dislocation again.

We also have a shoulder girdle which is often confused with the glenohumeral joint joint.  The shoulder girdle is made up of the scapula and clavicle and allows us to perform; elevation, depression, protraction and retraction. 

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There are numerous ligaments in the shoulder joint.  These ligament names are very similar to the joint names and are a combination of two or more bone names.  The first ligament we have in the joint is the acromioclavicular ligament which connects the supra lateral third surface of the clavicle and the acromion process.  We then have the coracoacromial ligament which attaches the coracoid process to the clavicle.  This ligament sits on the superior surface of the coracoid and attaches on to the anterior surface of the clavicle.  Finally we have our coracoclavicular ligament which attaches the medial surface of the coracoid to the acromion.  These ligaments are known as our static stabilisers and keep the joint in place.
 

In addition to these stabilisers are another set known as our dynamic stabilisers.  These are what allow movement within the joint.  We can abbreviate these stabilisers as 'SITS'.  These are a group of muscles that all work together to enable rotation of the shoulder, also referred to as our rotator cuff muscles.

S - Supraspinatus
I - Infraspinatus
T - Teres Minor

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S - Subscapularis

If you play tennis or badminton or any sport/activity that require many arm over the head motions you will be familiar with rotator cuff problems.  These often occur in the sports above because our dynamic stabilisers become tight and hypertonic (short and over active).  Therefore when the muscles become extremely hypertonic it limits movement around the shoulder and actually causes extreme pain on this area in the picture (right).   Therefore these hypertonic muscles cause muscle impingement which means a task such as putting your hand up in class or stretching to get something out of the cupboard or playing a sport such as badminton becomes difficult.  Therefore our muscles become weak as they are hypertonic and makes it much easier to tear tendons.

Well how do we avoid it?  Unfortunately theres not a lot you can do.  I'd like to invite you to imagine this.  Above the spine of our scapula is a tendon that attaches the clavicle to the supraspinatous which inserts onto the supra surface of the humeral head.  Therefore when we perform these discomforting activities our tendon gets crushed between our clavicle and humeral head.  Doesn't sound nice right?  Its not very pleasant at all... 

Solution? 

Well like I said there's not a lot we can do, however if you are familiar with these problems, such activities such as massage therapy may be a good start or if you can't afford that, then daily stretching exercises of our dynamic stabilisers and our deltoids and pectoral muscles to avoid any upper cross syndrome of our upper appendicular extremities may too be a good place to start.