I view the shoulder as an engine covered with a lid.
The ball and socket joint, called the glenohumeral joint, is the centre point around which all things rotate. The labrum is the rim of the socket that helps stabilise the joint. The acromion and the acromioclavicular joint make up the roof of the shoulder.
The rotator cuff, the deltoid, the trapezius, the pectoralis muscles and the short head of biceps are the main muscles that move the joint. The outer muscle is the deltoid. The rotator cuff lies under the roof of the shoulder.
With the above concept, then we can broadly group problems into a few baskets.
Impingement – sharp roof outgrowth that pinches the rotator cuff and thus causes pain.
AC joint arthritis – ageing of the joint causes bony outgrowths that pinch the rotator cuff and inflammation in the AC joint causes pain when the joint is stressed while lifting and pushing things.
The rotator cuff has four muscles that move the shoulder in different directions, and if they tear, then we will have weakness in that direction of movement. Nerve injuries or problems in the neck and shoulder region can also cause similar weakness, and this must be excluded.
Ball & Socket Joint Problems
Arthritis – this causes stiffness, pain and a clicking or locking feeling in the shoulder.
Instability – the labrum can be torn in dislocation injuries of the shoulder. It can also become loose in people that overuse the shoulder in certain sports or in people that have a genetic ‘double-jointed’ (hyperlaxity) problems.