The shoulder is one of the most complex joints and it has the greatest range of movements of any joint of the body. It allows positioning of the hand in space to perform various activities. To allow the shoulder to move, it has to be inherently 'unstable' and free. It is however held together by a variety of complex ligaments, muscles and tendons. The coordinated working of various muscles help it to move in a stable manner and perform various function. It is this unique complexity that makes it easily susceptible to injuries and problems.
A full & thorough understanding of the anatomy and working of the shoulder is essential to deal effectively with shoulder problems.
Bones & Joints of the shoulder
The shoulder consists of 3 bones and 4 joints. The bones are the arm bone (Humerus), the collar bone (Clavicle) and the shoulder blade (scapula). They form 4 joints - these are,
The main shoulder joint - (Gleno-humeral joint or the GHJ), this is a ball and socket joint between the upper end of the arm bone which forms a ball and a part of the shoulder blade which forms the socket.
The roof joint -(Acromio-clavicular joint or the ACJ) - this is the joint formed where the collar bone meets the shoulder blade.
The inner joint- (Sterno-clavicular joint or the SCJ)- this is the joint formed between the breast bone and the collar bone.
The joint between the shoulder blade and the back of the chest wall- Scapulo-thoracic joint.
Muscles of the shoulder
Muscles of the shoulder can be divided into three groups.
1. Outer or Extrinsic muscles
These are large, powerful muscles at the front, back and sides of the chest which support and drive the movements of the shoulder girdle.
They consist of the 'pecs' or the pectoralis major muscle at the front, the 'traps' or the trapezius at the back and the 'lats' or the latissimus dorsi at the side.
2. The deeper layer consist of the intrinsic musces. They are made up by the pectoralis minor, the subclavius, the serratus anterior and the most important Rotator cuff.
The Rotator cuff
The rotator cuff is the flat tendinous insertion of a group of 4 muscles which help to keep the ball of the humeral head centered on the socket and also helps in imparting strength to movements of the shoulder. The rotator cuff can undergo inflammation and tendinopathic changes, attrition and tears, resulting in a spectrum of shoulder problems.
3. Muscles of the arm- These are the biceps at the front along with the corachobrachialis and the the triceps at the back of the arm.
The shoulder has several other important structures:
The bursa is a small sac of fluid that cushions and protects the tendons of the rotator cuff.
A cuff of cartilage called the labrum forms a cup for the ball-like head of the humerus to fit into.
The humerus fits relatively loosely into the shoulder joint. This gives the shoulder a wide range of motion, but also makes it vulnerable to injury.
Dr Vinod Kumar Abu Dhabi
Shoulder surgeon Abu Dhabi
NMC Royal Hospital