The elbow joint is the convergence of bones, ligaments and muscles that enable the flexion, extension, pronation, and supination of the arm. Within the single elbow joint capsule, there are three distinct interfaces, which are often considered to be individual joints, allowing for these different types of movement. The primary function of the elbow is allowing for the placement of the hand with the extension and rotation of the arm. Understanding the anatomy of the elbow will ultimately help patients in determining the source of their pain.
The following components are all integral pieces of the functioning elbow:
Confining the elbow joint components, the joint capsule, or synovial membrane, provides the elbow stability. It is thickened on its side by ligaments and is reinforced by muscle fibers on the front surface.
There are three bones intersecting at the elbow:
- Humerus: The humerus is the large bone of the upper arm that extends from a socket of the scapula, or shoulder blade, to the elbow joint, where it connects to the ulna and radius. Where the humerus meets the ulna and radius at the elbow, it has two articular surfaces, called the capitulum and the trochlea.
- Ulna: As the longer of the two forearm bones, the ulna is the inner bone when the palm is facing forward.
- Radius: Parallel to the ulna, the radius also connects to the humerus at the elbow.
The elbow joint can be divided into three articulations:
- Humeroulnar Joint: The primary joint of the elbow, the humeroulnar joint is a synovial hinge joint that allows from flexion and extension movements. It is located between the trochlea of the humerus and the trochlear notch of the ulna.
- Radiohumeral Joint: As the secondary hinge of the elbow, the radiohumeral joint aids in the same flexion and extension movements facilitated by the humeroulnar joint. It extends from the head of the radius to the capitulum of the humerus.
- Proximal Radioulnar Joint: A pivot joint that allows for rotational movement, also known as pronation and supination, the proximal radioulnar joint extends from the head of the radius to the radial notch of the ulna.
The three primary ligaments supporting the elbow are:
- Annular Ligament (AL): Surrounding the head of the radius, the AL serves to sustain contact between the radius and humerus bones.
- Medial Collateral Ligament (MCL): Two bands compose the MCL in the elbow; one anterior and one posterior, both of which initiate at the medial epicondyle and attach to the ulna.
- Lateral Collateral Ligament (LCL): The LCL of the elbow is a short band that extends from the lateral epicondyle to the annular ligament.
The primary function of the muscles surrounding the elbow is the empowerment of the elbow’s flexion, extension, supination and pronation movements.
- Biceps Brachii
- Triceps Brachii (long, lateral, and medial heads)
- Extensor Carpi Radialis Brevis
Pronation and supination muscles:
- Pronator Teres
- Pronator Quadratus
- Biceps brachii
The individual components of the elbow work together to allow for the following average ranges of motion, by movement type: