The shoulder bones fit together to form a highly complex, highly mobile joint that allows our arms to move through a huge range in multiple directions. In fact, the shoulder is the most mobile joint in the entire human body.
It is also the least stable joint so relies on a complex network of ligaments, tendons and muscles to function effectively.
Whilst shoulder bone injuries are much less common that soft tissue injuries, fractures, dislocations and shoulder bone spurs can cause significant problems.
Here we will look at the different aspects of shoulder bone anatomy including each of the four shoulder joints, the surrounding soft tissues and common problems that can affect the shoulder bones.
There are three shoulder bones:
There are a number of different muscles, tendons and ligaments that attach to the shoulder bones that work together to provide stability and strength to this highly mobile joint so we can lift and carry things, throw, push and pull and perform many other actions with our arms.
The first shoulder bone we are going to look at is the upper arm bone, also known as the humerus bone.
The humerus is a long bone that runs between the shoulder and the elbow. It is the bone found in the upper arm and is the longest bone in the upper limb.
At the top of the upper arm bone is the head of humerus, a rounded area that resembles a ball. The head of humerus rests in a shallow socket in the shoulder blade forming the shoulder joint.
The humerus can be divided into three sections:
Key Function: the ball shaping of the head of humerus allows the shoulder to move through a huge range of motion, more than any other joint in the body.
The scapula, aka shoulder blade, is another important shoulder bone that forms the socket part of the shoulder joint.
The shoulder blades are large, flat, triangular shaped bones found at the back of the shoulder, lying over the upper rib cage. The outer corner is shaped into a shallow, inward facing dome, known as the glenoid fossa, which forms a shallow socket for the ball shaped head of humerus.
There are three distinct areas on the scapula bones that stick out forming important bony prominences for the attachment of muscles, tendons and ligaments:
Fun fact, no less than 18 different muscles attach to the scapula bone.
Key Functions: The scapula bone helps stabilise the upper arm bone and forms the socket for the shoulder joint
The clavicle bone is the front-most shoulder bone, also known as the collar bone.
The clavicle is a long, thin bone that connects the shoulder to the chest via the sternum and is the only long bone in the human body that sits horizontally.
Located directly above the first rib, the clavicle shoulder bone acts like a crane to support the shoulder blade in place so that your arm can hang down freely by your side and swing as you walk.
Fun fact – the clavicle is the first bone to start developing in embryos but one of the last to full develop, often not reaching full ossification until people are in their early 20s.
Key Function: the clavicle forms the roof of the shoulder joint and transmits forces between the arm and the trunk
The shoulder is often thought of as being just one joint, but the three shoulder bones actually join together in different places to form four different shoulder joints:
You can find out more about each one in the shoulder joint anatomy section.
The shoulder bones are connected to and surrounded by various structures that help the shoulder joint to function effectively including:
A number of muscles surround the shoulder bones and joints, working together to provide movement, support and stability to the shoulder. The two main groups of muscles that attach to the shoulder bones are the:
Each of the muscles attach to the various shoulder bones via tendons - strong, flexible cord like structures. It is really important to have good strength in the shoulder muscles to ensure the shoulder has adequate support - rotator cuff strengthening and scapular stabilisation exercises can really help.
The shoulder ligaments and tough, elastic bands of connective tissues that connect bone to bone. The shoulder ligaments play a vital role in shoulder stability, supporting the joints and limiting joint movement.
There are nine different shoulder ligaments that connect the various shoulder bones at the glenohumeral, acromioclavicular and sternoclavicular joints.
Common Problems: Over-stretching, tearing or degeneration of the shoulder ligaments, usually due to an injury or repetitive friction
Bursa are small, fluid filled sacs that sit between the shoulder bones and tendons to reduce friction and allow smooth movement. There are a number of different bursa located around the shoulder, including the subacromial, subscapular and subdeltoid bursa.
Common Problems: Inflammation of the bursa known as shoulder bursitis
The labrum is a special layer of cartilage that lines the outer rim of the shoulder socket on the scapula bone. The glenoid labrum helps to deepen the socket which improves the congruity of the ball and socket joint, improving shoulder stability.
Damage to the shoulder bones from injuries or wear and tear are a common problem. The most common injuries affecting the shoulder bones are:
If enough force is placed through the shoulder, then one or more of the shoulder bones can break. Shoulder bone fractures are usually caused by:
The most common fractures to affect the shoulder bones are:
Other possible fractures of the shoulder bones include:
Primary shoulder impingement is a common problem caused by bony abnormalities at the shoulder.
Changes in the shape or angle of the acromion, typically due to bone spurs (small outgrowths of bone) reduce the space between the shoulder bones at the top of the glenohumeral joint. This increases the friction on the soft tissues leading to inflammation and pain, which can limit shoulder movement, and is known as shoulder impingement syndrome.
Common symptoms of shoulder impingement syndrome include:
If your doctor suspects impingement syndrome you may be sent for x-rays to identify any spurs growing on your shoulder bones that may need to be surgically removed with a subacromial decompression.
Related Article: Shoulder Impingement - Causes, Symptoms & Treatment
Shoulder arthritis is caused by inflammation in one or more of the shoulder joints. The most common type of arthritis to cause shoulder pain is osteoarthritis.
Shoulder osteoarthritis causes gradual wear and tear of the shoulder bones, damaging the protective cartilage and causing it to wear away, fray and even tear. This reduces the space between the shoulder bones causing them to rub against each other which, in time, leads to pain and stiffness that can limit shoulder movement and daily activities.
Osteoarthritis is a particularly common problem affecting the shoulder bones in people over the age of 50. It can affect any of the shoulder joints, but is most common in the acromioclavicular joints.
The anatomy of the shoulder comprises of three shoulder bones, the humerus, clavicle and scapula, between them four different shoulder joints.
Shoulder bone injuries are less common than soft tissue injuries. The most common shoulder bone problems are:
If you have pain from a problem in your shoulder bones or the surrounding soft tissues and want help finding out what is wrong, check out our shoulder pain diagnosis charts.
Page Last Updated: 19/05/2022
Next Review Due: 19/05/2024