What is the Shoulder?
The shoulder is an important part of the body because it is the most movable joint. However, the shoulder is also an unstable joint because of its range-of–motion. This joint is an asset for everyday activities such as washing, lifting objects, swimming or working in the garden.
It is often susceptible to injury and overuse because the ball of the upper arm is larger than the socket of the shoulder. Shoulder pain may also occur because of injury to the muscles, tendons and ligaments in the shoulder. More serious conditions such as degenerative diseases may affect the shoulder and cause pain that passes along the nerves to the shoulder.
The shoulder consists of a group structures – bones, ligaments and muscles in the joint region.
It is made up of three interconnecting bones, the humerus (upper arm bone), the scapula (shoulder blade) and clavicle (collarbone). The scapula is built like a triangle consisting of smaller triangles. It runs up and around the shoulder joint at the back to form the roof, the highest point of the shoulder known as the acrimion. The scapula, in turn, extends around the shoulder joint to form the coracoid process.
Joints of the shoulder
There are three joints of the shoulder – the glenohumeral, acromioclavicular and sternoclavicular joints. The glenohumeral joint (shoulder joint) is the primary joint of the shoulder. It is the ball-and-socket joint that facilitates circular, forward and backward movement of the shoulder. It is formed where the ball of the humerus fits into a shallow socket known as the glenoid onto the scapula. The acrimio-clavicular (AC) joint is located between the scapula and clavicle (where the clavicle meets the acromion) while the sternoclavicular joint is located at the medial end of the clavicle.
There are several ligaments in the shoulder. Ligaments are soft tissue structures that connect bones to bones. The joint capsule is a very tight sac that surrounds the joint and refers to a group of ligaments that connect the humerus to the socket of the shoulder joint on the scapula. This helps to stabilize the shoulder and keep it from dislocating.
The muscles help support and rotate the shoulder in many directions. One of the most important components of the shoulder is the rotator cuff. It lies outside of the shoulder and consists of a group of muscles and tendons that connects the bones of the shoulder joint together. The rotator cuff muscles and tendons also stabilize the shoulder joint stable by holding the humeral head in the glenoid socket. The deltoid muscle is the large outer layer of shoulder muscle. The deltoid is the largest, strongest muscle of the shoulder. The deltoid muscle takes over lifting the arm once the arm is away from the side.