Shoulder Pain
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Shoulder Pain
Your shoulders each have two joints, making them the most flexible parts of your body.
The main shoulder joint – the glenohumeral – is a ball-and-socket joint. It’s called this because the top of the upper arm bone – the humerus – is shaped like a ball. This ball fits into the shoulder blade bone, which acts as the socket, giving your shoulder a wide range of movement.
But, the shoulder socket is very small, compared to other ball-and-socket joints, such as the hip. It’s held together and controlled by a covering of muscles, which are secured to the bones by strong cords called tendons.
These muscles and tendons form a capsule around the joint and support its movements, but can make it more likely to dislocate than other joints.
Inside the capsule is the synovium, which produces fluid that lubricates the joint and keeps the cartilage healthy. The cartilage helps protect your bones from any impact and sits between the bones of your shoulder joints to stop them rubbing together.
Above the main shoulder joint there’s a smaller joint where the top of the shoulder blade – the acromion – meets the collar bone.
This is known as the acromioclavicular joint. It helps the larger joint below to move through its full range, particularly when you’re raising your arm, lifting or throwing.
