The shoulder is like a ball-and-socket joint and is the most flexible joint in the entire human body. It is no wonder that this joint is the most susceptible to injury and instability. The humerus is considered the ‘ball’, which nestles neatly into the glenoid or the ‘socket’ that is a part of the scapula or commonly known as the shoulder blade.
The shoulder consists of several bones and soft tissues. The shoulder joint is made up of three bones: the clavicle or collarbone, scapula or shoulder blade, and humerus. The clavicle has an S-shape that connects the shoulder to the body in such a way that it provides functional support to maximize range of arm motion. It also serves as protection for underlying nerves and blood vessels. The scapula connects the upper arm bone with the collarbone. It is flat and has a roughly triangular shape, providing attachment to the muscles of the back and neck. The coracoid process is the extension of the scapula. The acromial process is the extension of the scapula around the shoulder joint at the back that forms a roof called the acromion. The humerus provides attachment to the muscles of the upper arm.
The soft tissues of the shoulder joint consist of the following:
- Rotator Cuff – consists of a group of four tendons that hold the head of the humerus in the socket of the shoulder joint.
- Biceps Tendon – long and cord-like attachment of the bicep muscle to the shoulder, helping stabilize the joint.
- Coracoclavicular Ligament – the connecting ligament for the clavicle and the scapula’s corocoid process.
- Acromio Clavicular Ligament – the connecting ligament for the clavicle and the acromion process.
- Glenoid Labrum – a ring of fibro cartilage surrounding the cavity of the scapula, helping stabilize the joint.
- Articular Cartilage – smooth, white tissue covering the bone ends that form joints.
- Capsule – a capsule that surrounds the shoulder joint and helps stabilize the alignment of the ball and socket.