Right humerus bone lower part
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distal humerus anatomy lower part
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humerus bone anatomy labeled capitulum trochlea epicondyle fossa
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Here is a comprehensive overview of the distal (lower) end of the right humerus — its anatomy, key bony landmarks, articular surfaces, fossae, and related structures.
Distal Humerus — Anatomy
The distal humerus is the lower portion of the arm bone that forms the elbow joint, articulating with both the radius (laterally) and the ulna (medially).
Structural Overview — The Two Columns
As the humeral shaft descends distally, it becomes triangular in cross-section and bifurcates into two divergent cortical columns:
| Column | Direction | Termination | Divergence Angle |
|---|---|---|---|
| Medial column | Diverges ~45° from shaft (coronal plane) | Medial epicondyle | Stays in line in sagittal plane |
| Lateral column | Diverges ~20° from shaft (coronal plane) | Capitellum (curves 35–40° anteriorly in sagittal plane) | Curves anteriorly |
Together with the articular surface (the "base"), these two columns form a triangular (delta) configuration — the structural foundation of the distal humerus.
Articular Surfaces
1. Capitulum (Capitellum)
- Hemispherical projection forming the anterior and inferior surface of the lateral aspect
- Articulates with the radial head
- The articular surface encompasses approximately 180° arc in the sagittal plane
- Located at the terminus of the lateral column
2. Trochlea
- Spool- or pulley-shaped structure (Greek: "pulley") forming the medial articular surface
- Articulates with the trochlear notch of the ulna
- Covered by articular cartilage anteriorly, inferiorly, and posteriorly — an arc of nearly 270°
- Has a central sulcus matching the central ridge of the ulna's greater sigmoid notch
- Located more distally than the capitellum → creates 4–8° of valgus alignment in the coronal plane
The capitellar-trochlear sulcus is a small groove dividing the two articular surfaces.
Epicondyles (Non-articular projections)
Medial Epicondyle
- Blunt projection at the medial aspect of the distal humerus
- Terminus of the medial column
- The smooth posterior surface carries the ulnar nerve in a shallow sulcus (cubital tunnel) as it passes into the forearm
- Origin of the MCL (medial collateral ligament) — anterior bundle inserts on the sublime tubercle of the coronoid
- Site of origin for flexor-pronator muscle group
Lateral Epicondyle
- Occupies the non-articular aspect of the distal humeral condyle
- Gives rise to the lateral supracondylar ridge superiorly
- Origin of the LCL (lateral collateral ligament) complex — from an isometric point on the lateral epicondyle
- Site of origin for the superficial extensor muscles of the forearm
Fossae
Two hollow depressions lie between the two columns, separated by a thin bony septum (occasionally absent = septal aperture):
| Fossa | Surface | Accommodates | During |
|---|---|---|---|
| Olecranon fossa | Posterior | Olecranon of ulna | Elbow extension |
| Coronoid fossa | Anterior | Coronoid process of ulna | Elbow flexion |
| Radial fossa | Anterior (lateral) | Radial head | Elbow flexion |
Important: Screws must not be placed through the fossae — impingement will restrict elbow range of motion.
Alignment Angles
| Parameter | Value |
|---|---|
| Valgus alignment (trochlea vs. capitellum) | 4–8° in coronal plane |
| Carrying angle (full elbow) | 10–17° valgus in extension |
| Anterior tilt of articular surface | 35–40° in sagittal plane |
| Internal rotation of articular surface | 3–8° axially |
Key Neurovascular Relations
- Ulnar nerve — travels behind the medial epicondyle; the Arcade of Struthers (present in ~70%) is a compression point ~8 cm proximal to the medial epicondyle
- Radial nerve — at risk anterolaterally along the supracondylar ridge
- Median nerve — crosses anterior to the elbow
Ligament Attachments
- MCL (medial collateral ligament) — anterior bundle from medial epicondyle to sublime tubercle; primary restraint against valgus stress
- LCL complex — radial collateral ligament, LUCL (lateral ulnar collateral ligament), and annular ligament; restraint against varus and posterolateral rotatory instability
- Annular ligament — encircles the radial head, attaching to anterior and posterior margins of the lesser sigmoid notch
Sources: Imaging Anatomy: Bones, Joints, Vessels and Nerves (Vol. 3), p. 92–93; Rockwood and Green's Fractures in Adults, 10th ed., Chapter 39 (Distal Humerus)
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