The shoulder is a ball-and-socket joint. The end of the humerus (ball) articulates with the scapula (shoulder blade). The acromion forms part of the upper border of the joint. It is held together mostly by the rotator cuff muscle, but also by the labrum (cartilage) and ligaments.
The most common cause of shoulder pain is impingement syndrome. This usually occurs when the humerus slides up and abuts the acromium. This can be caused by rotator muscle dysfunction and/or tightness in the shoulder capsule. The two structures that tend to become impinged is one of the rotator cuff tendons (the supraspinatus) and the bursa (fluid filled sac to cushion the tendon). Sometimes, particularly in the older population, prolonged impingement can lead to a rotator cuff tear.
Treatment usually involves manual mobilisation of the shoulder joint. Often it is useful to stretch the humerus downwards to reduce impingement. Stretching and massage the posterior capsule is also helpful. There is good evidence to show that strengthening the rest of the rotator cuff is beneficial so that they can stabilise the humerus and prevent it from sliding upwards. If this fails, your doctor may recommend a cortisone injection to reduce the inflammation in the bursa first. Surgical resection is the final option.
Some useful tips to help shoulder pain