The elbow: joint structure, movements and muscles

Do you know what a professional darts player and a hairdresser have in common? The elbow is the most important joint for both of them. Even if you are just a humble bodywork therapist using her elbow every now and then, knowing its structure and function can be beneficial ...

The elbow joint is the meeting place of the humerus in the upper arm with the radius and the ulna of the lower arm. The trochlea of the humerus articulates with the semilunar notch of the ulna. The capitulum of the humerus articulates with the superior surface of the head of the radius.

Three distinct articulations comprise the joint: humeroulnar, humeroradial and the less significant radioulnar.
 
The largest and the most stable one is the humeroulnar joint. It is a simple hinge that relies on the medial collateral ligament for its stability.
 
Lateral to the humeroulnar articulation lies the humeroradial joint. Here the shallow disc of the radial head articulates on the spherical humeral capitellum. This set-up also prevents proximal migration of the radius during the whole range of elbow flexion and extension. The rotation of the radius along its long axis about the ulna enables pronation and supination. Despite this rotation, the head of the radius remains in a fixed position relative to the ulna. A number of injuries can result from the forced hyperpronation of the arm.
 
Excessive movements can also injure the soft tissues about the elbow. An area that is particularly vulnerable to blunt trauma with haemorrhage, swelling, pain and inflammation is the olecranon bursa, located on the posterior aspect of the joint. The synovial lining of the bursal sac can become thickened and swollen when injured.
​
The elbow is a typical example of a hinge joint and it only permits flexion and extension in the transverse plane. 

Ligaments
 
Four distinct ligaments surround the joint forming a complete capsule. It attaches to the upper borders of the fossae on the anterior and posterior surfaces the humerus and the lower aspects of the condyles. It also goes around the olecranon, the inner and anterior margin of the coronoid process, and round the lower edge near the head of the radius. Within this capsule is enclosed the proximal radio-ulnar joint, which will not be discussed further here.
 
The anterior ligament attaches to the upper margins of the coronoid and supracapitular fossa above. Below it connects to the anterior surface of the coronoid process of the ulna and to the annular ligament of the proximal radio-ulnar joint. The strength of this ligament comes from the fact that its fibres are arranged in several directions.
 
The posterior ligament attaches superiorly to the humerus above the olecranon fossa and inferiorly to the olecranon.
 
The ulnar collateral ligament, also called internal lateral ligament, is a band consisting of three parts forming a triangle. The first one connects the anterior border of the medial condyle to the margin of the coronoid process. The second – the inferior and posterior border of the condyle to the olecranon process. The third – the olecranon process to the coronoid process.
 
The radial collateral ligament is also called external lateral ligament. Above, it extends from the lower border of the lateral epicondyle of the humerus. Below it connects to the annular ligament and anterior and posterior margins of the radial notch.
 
Additionally, the annular ligament can also be considered as part of the elbow. It surrounds the head and the upper part of the neck of the radius and attaches to the anterior and posterior margins of the radial notch.
 
The entire capsule of the joint is surrounded by a synovial membrane. It covers the pads of fat situated in the coronoid, supracapitular, and olecranon fossa. The articular ends of the bones are excluded, as they are covered with cartilage.

​Muscles & Movements
 
As a hinge joint, the elbow can only be flexed and extended by the muscles around it.

​Flexion is produced by the joint action of biceps brachii, brachialis, brachioradialis, pronator teres, the flexors of the wrist and fingers and the extensors of the wrist (in pronation). The famous fitness exercise biceps curl is an example of elbow flexion. Another everyday example is lifting the bags from a grocery trolley.
 
Extension is produced by the triceps, anconeus, and the extensors of the wrist and fingers. Everyday situations where we use triceps extension include pulling down a cord to turn a lamp or pushing ourselves up horizontally (getting up from lying on our stomach) or vertically (going out of a swimming pool).
 
Although it is much simpler in its structure and more limited in its movement than the shoulder, the elbow is an important tool in a therapist’s arsenal. It is important to know and take good care of our elbows so that they serve us and our clients over the long term. 

Related articles:
The knee: joint structure, movements and muscles
The hip: joint structure, movements and muscles
The ankle: joint structure, movements, muscles
The shoulder: joint structure, movements and muscles