Elbow Joint: Anatomy, Structure, Ligaments, Function, Imaging

Topic

Elbow joint

The elbow joint is a complex synovial hinge joint that connects the arm and forearm, formed by the articulations between the humerus, ulna, and radius. It allows flexion, extension, pronation, and supination of the forearm. Functionally, the joint combines two types of movements — hinge (between humerus and ulna) and pivot (between radius and ulna).

It is enclosed in a strong capsule reinforced by collateral ligaments and surrounded by a group of powerful flexor and extensor muscles. The joint provides both stability and mobility, essential for precise upper limb movements such as lifting, grasping, and positioning of the hand.

Synonyms

Cubital joint
Humeroulnar articulation
Humeroradial joint complex

Articulations

Humeroulnar joint: Between the trochlea of the humerus and the trochlear notch of the ulna — allows flexion and extension.
Humeroradial joint: Between the capitulum of the humerus and the head of the radius — permits flexion, extension, and rotation.
Proximal radioulnar joint: Between the radial head and the radial notch of the ulna — enables pronation and supination.

Type

Compound synovial joint combining hinge and pivot mechanics.
Capsule: Single fibrous capsule enclosing all three articulations.

Relations

Anteriorly: Brachialis, biceps tendon, median nerve, brachial artery.
Posteriorly: Triceps tendon, olecranon bursa, ulnar nerve (behind medial epicondyle).
Medially: Ulnar collateral ligament and flexor-pronator mass.
Laterally: Radial collateral ligament and common extensor origin.

Ligaments

Ulnar (medial) collateral ligament: Triangular band from medial epicondyle to coronoid process and olecranon; resists valgus stress.
Radial (lateral) collateral ligament: From lateral epicondyle to annular ligament; resists varus stress.
Annular ligament: Encircles the head of the radius, maintaining its position in the radial notch.
Quadrate ligament: Between radial notch of ulna and neck of radius, limiting rotation.

Capsule

Anterior and posterior parts: Thin and loose to permit flexion and extension.
Medial and lateral parts: Strengthened by collateral ligaments.
Lined by synovial membrane that produces synovial fluid for lubrication.

Synovial Membrane and Bursae

Lines the inner surface of the capsule and forms folds around the olecranon and coronoid fossae.
Olecranon bursa: Between olecranon and skin; inflamed in bursitis.
Bicipitoradial bursa: Between biceps tendon and radial tuberosity.

Nerve Supply

Musculocutaneous, radial, ulnar, and median nerves provide sensory and motor innervation through articular branches.

Function

Flexion and extension: Primarily at the humeroulnar and humeroradial joints.
Pronation and supination: Occur at the proximal radioulnar joint.
Stability: Maintained by congruent articular surfaces, collateral ligaments, and muscular support.
Load transfer: Distributes forces from hand and forearm to arm during movement or impact.

Clinical Significance

Dislocations: Posterior dislocation is most common, often with radial head fracture.
Fractures: Involve distal humerus, radial head, or coronoid process (terrible triad injury).
Ligament injuries: Ulnar collateral ligament tears common in throwing athletes.
Arthritis: Osteoarthritis or rheumatoid arthritis may cause pain and stiffness.
Bursitis: Inflammation of olecranon bursa due to trauma or infection.
Nerve entrapment: Ulnar nerve compression at cubital tunnel causes sensory and motor deficits.

MRI Appearance

T1-weighted images:
- Bone marrow: bright, reflecting fatty composition.
- Cortical bone: dark, smooth margins.
- Articular cartilage: intermediate-to-low signal lining humeral, ulnar, and radial surfaces.
- Joint capsule: low-signal band outlining the joint.
- Fat pads (anterior and posterior): bright, visible in normal extension.
- Pathology: fractures or bone contusions appear as low-signal lines or foci in bone marrow.
T2-weighted images:
- Bone cortex: dark; bone marrow: bright, slightly less than T1.
- Cartilage: intermediate-to-bright, smooth and uniform in normal joint.
- Synovial fluid: hyperintense in the joint recesses.
- Pathology: effusions and synovitis appear bright; osteochondral defects or edema more intense.
STIR:
- Normal bone: intermediate-to-dark signal.
- Pathologic areas (marrow edema, bursitis, soft-tissue swelling): bright hyperintensity.
- Useful for early detection of bone contusions, ligament sprains, and joint effusion.
Proton Density Fat-Saturated (PD FS):
- Bone: intermediate-to-dark; fluid: bright.
- Ligaments and tendons: dark linear structures.
- Pathologic findings: bright hyperintensity in partial ligament tears, synovial inflammation, or capsular edema.
T1 Fat-Sat Post-Contrast:
- Normal synovium: mild thin enhancement.
- Synovitis: thick, enhancing synovial folds.
- Infection or arthritis: diffuse synovial and pericapsular enhancement.
- Post-traumatic or post-surgical cases: granulation tissue shows variable enhancement.

CT Appearance

Non-Contrast CT:

Demonstrates bony architecture in fine detail.
Cortical bone: high attenuation with sharp margins.
Articular surfaces: smooth and congruent; cartilage space appears as low-density gap.
Pathology: visualizes fractures, bone fragments, loose bodies, and osteophytes with precision.
Useful in evaluating post-traumatic alignment and hardware position.

Post-Contrast CT (standard):

Enhancing synovium and capsule visible in inflammatory or infectious conditions.
Highlights pericapsular soft-tissue enhancement in arthritis or bursitis.
Helpful in detecting subtle joint effusions, erosive arthropathy, or vascular complications following trauma.

CT VRT 3D image