Medial Epicondyle of Humerus: Anatomy, Relations, Function, Imaging

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Medial epicondyle of humerus

The medial epicondyle of the humerus is a prominent bony projection located on the medial side of the distal humerus, easily palpable on the inner aspect of the elbow. It serves as the common flexor origin for the forearm’s superficial flexor muscles and provides attachment for important ligaments stabilizing the elbow joint.

This structure projects more prominently and posteriorly than the lateral epicondyle, making it a key palpation landmark and a site of frequent overuse or traction injuries, such as medial epicondylitis (golfer’s elbow). It also forms the roof of the cubital tunnel, through which the ulnar nerve passes, making it clinically significant in ulnar nerve entrapment syndromes.

Synonyms

Internal condyle of the humerus
Medial humeral epicondyle
Common flexor origin

Location and Structure

Situated on the medial aspect of the distal humerus, above the trochlea.
Shape: Oval and prominent, projecting medially and slightly posteriorly.
Surface features:
- Anterior surface: Smooth and broad, giving origin to flexor muscles.
- Posterior surface: Rough and subcutaneous, easily palpable under the skin.
- Inferior border: Continuous with the medial supracondylar ridge.
- Superior border: Merges with the medial surface of the humeral shaft.
Epiphysis: Has a secondary ossification center appearing around age 5–7 and fusing by late adolescence.

Relations

Anteriorly: Pronator teres, flexor carpi radialis, and palmaris longus origins
Posteriorly: Groove for ulnar nerve (cubital tunnel) and overlying fascia
Medially: Subcutaneous tissue and skin
Laterally: Medial edge of trochlea and elbow joint capsule
Inferiorly: Common flexor tendon blending with muscles of the forearm’s superficial layer

Attachments

Muscular attachments (common flexor origin):
- Pronator teres
- Flexor carpi radialis
- Palmaris longus
- Flexor carpi ulnaris
- Flexor digitorum superficialis (humeral head)
Ligamentous attachment:
- Ulnar collateral ligament (anterior and posterior bands) attaches just distal and anterior to the epicondyle, contributing to medial elbow stability.

Function

Muscular anchorage: Serves as the common origin for forearm flexor muscles, allowing powerful wrist and finger flexion.
Joint stability: Provides attachment for the ulnar collateral ligament, supporting the medial aspect of the elbow joint.
Force transmission: Distributes tensile forces generated by wrist flexors during gripping or throwing motions.
Anatomical landmark: Used in clinical and radiological localization of the ulnar nerve and cubital tunnel.

Clinical Significance

Medial epicondylitis (golfer’s elbow): Chronic microtrauma at the common flexor origin causing pain and inflammation.
Avulsion fracture: Common in children and adolescents due to traction from the flexor-pronator muscles or valgus stress during sports (e.g., baseball pitching).
Ulnar nerve entrapment: The epicondyle forms the posterior wall of the cubital tunnel; swelling or deformity may compress the nerve.
Fractures: Can be associated with elbow dislocations, especially in pediatric injuries.
Post-traumatic ossification: Myositis ossificans may occur following repetitive trauma or surgery.
Surgical importance: Landmark in medial elbow approaches and ulnar nerve decompression procedures.

MRI Appearance

T1-weighted images:
- Cortical bone: Very low signal (dark).
- Bone marrow: Bright signal (fatty content in adults).
- Muscle and tendons at origin: Intermediate-to-low signal; clearly separated from subcutaneous fat.
- Inflammation or partial tear: Intermediate to bright signal in the common flexor tendon origin.
T2-weighted images:
- Cortex: Dark.
- Marrow: Bright, slightly less than on T1.
- Common flexor origin: Low signal normally; hyperintense in tendinopathy or strain.
- Edema or enthesopathy: Focal bright signal at tendon-bone interface.
STIR:
- Normal bone and tendon: Intermediate-to-dark signal.
- Pathology: Bright hyperintense areas in tendon origin or adjacent bone marrow (indicative of inflammation or avulsion injury).
- Useful for early detection of medial epicondylitis and marrow edema.
Proton Density Fat-Saturated (PD FS):
- Normal bone: Intermediate-to-dark signal.
- Pathologic: Bright hyperintensity in tendon, muscle, or periosteum with indistinct borders.
- Excellent for evaluating partial-thickness tears, edema, and periosteal inflammation.
T1 Fat-Sat Post-Contrast:
- Normal: Cortical bone non-enhancing; marrow shows mild homogeneous enhancement.
- Epicondylitis: Focal or diffuse enhancement at the common flexor tendon origin.
- Avulsion or fracture: Enhancing soft-tissue and marrow adjacent to cortical defect.
- Chronic fibrosis: Minimal or peripheral enhancement with central low signal.

CT Appearance

Non-Contrast CT:

Cortical bone: Dense and sharply marginated; clearly shows the medial projection of the epicondyle.
Trabecular pattern: Fine, consistent structure; marrow density similar to surrounding humeral bone.
Pathology:
- Detects avulsion fractures, calcifications, or enthesophyte formation.
- Reveals subtle cortical irregularities in overuse or post-traumatic conditions.
- Assists in preoperative planning for fracture fixation or nerve decompression.

Post-Contrast CT (standard):

Normal: Enhancing soft-tissue planes around the epicondyle; cortical bone remains non-enhancing.
Inflammatory change: Enhancement in periosteum, tendinous attachments, or soft-tissue swelling.
Fracture or avulsion: Enhancing margins at cortical disruptions with pericortical edema.
Useful for: Differentiating soft-tissue mass, post-traumatic inflammation, and chronic tendon injury.

CT VRT 3D image

MRI image

CT image

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