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# Elbow cartilage (humerus)

The elbow cartilage of the [humerus](https://durgical.com/en/anatomy/humerus/) covers the lower end of the upper arm bone; the [radius](https://durgical.com/en/anatomy/radius/) and ulna glide on it as the elbow bends.

Official name: Cartilage of the capitulum and trochlea

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## What it is

The smooth covering of the lower end of the humerus, where the elbow bends.

## What it does

Lets the radius and ulna glide on the humerus.

## Key points

- Two surfaces: the spool-shaped trochlea for the trochlear notch of the [ulna](https://durgical.com/en/anatomy/ulna/) and the rounded capitulum for the radial head; trochlear cartilage covers front, bottom and back, the capitulum only front and bottom
- Osteochondritis dissecans of the capitulum in adolescent throwers and gymnasts comes from repeated valgus compression of the radial head; Panner disease is a milder, self-limiting form in younger children
- On a lateral X-ray the anterior humeral line should cross the middle third of the capitulum; if it passes in front, an extension supracondylar fracture is suspected in a child

## Key facts

**Where**
Capitulum (for the radial head) and trochlea (for the ulna)

**Function**
Hyaline cartilage; smooth, low-friction joint surface; wears in osteoarthritis

## Relations

**Below**
[Ulnar notch cartilage](https://durgical.com/en/anatomy/cartilage-of-the-trochlear-notch/) on the trochlea medially and [radial head cartilage](https://durgical.com/en/anatomy/cartilage-of-the-radial-head/) on the capitulum laterally

**In front**
Coronoid fossa and radial fossa just above, which receive the coronoid process and the radial head in full flexion; then the [elbow capsule](https://durgical.com/en/anatomy/elbow-joint-capsule/) and [brachialis](https://durgical.com/en/anatomy/brachialis/)

**Behind**
Olecranon fossa above the trochlea, which takes the olecranon tip in extension; the [triceps tendon](https://durgical.com/en/anatomy/triceps-tendon/) behind

**Medial**
Medial epicondyle with the [UCL (elbow)](https://durgical.com/en/anatomy/ulnar-collateral-ligament-of-the-elbow/) origin; the [ulnar nerve](https://durgical.com/en/anatomy/ulnar-nerve/) runs behind it

**Lateral**
Lateral epicondyle with the [RCL (elbow)](https://durgical.com/en/anatomy/radial-collateral-ligament-of-the-elbow/) and the [common extensor tendon](https://durgical.com/en/anatomy/common-extensor-tendon/)

## How to find it

With the elbow extended, a small hollow at the back, just below the lateral epicondyle, overlies the groove between the capitulum and the radial head; the trochlea cannot be felt. Both surfaces are exposed from behind, through an olecranon osteotomy or a triceps-sparing approach.

## On imaging

AP and lateral X-rays; on the lateral view a 'double-arc' sign marks a displaced capitulum shear fracture. MRI or MR arthrography stages osteochondritis dissecans. A notch at the back of the capitulum, where its cartilage ends next to the lateral epicondyle, is a normal pseudodefect, not a lesion.

## Clinical notes

- Capitulum shear fractures (Hahn–Steinthal with a large bony piece, Kocher–Lorenz mostly cartilage) follow a fall on the outstretched hand; the fragment flips up in front of the humerus
- Unstable osteochondritis dissecans fragments come loose as loose bodies that catch or lock the elbow; options range from rest from throwing to drilling, fixation or osteochondral grafting
- Intra-articular distal humerus fractures need exact restoration of the trochlea and capitulum; an olecranon osteotomy is a common way to expose them from behind

## Development

Elbow ossification centres appear in a fixed order, roughly every two years from about age 1 (ages vary between texts): capitulum, radial head, medial epicondyle, trochlea, olecranon, lateral epicondyle. The trochlea may ossify from several pieces, a normal look that mimics a fracture.

## Memory aid

CRITOE (or CRITOL) gives the order of the elbow ossification centres: Capitulum, Radial head, Internal (medial) epicondyle, Trochlea, Olecranon, External (lateral) epicondyle.

## Test yourself

Think of the answer, then tap the question to see it.

## Which bones articulate with the two surfaces of the distal humeral cartilage?

The trochlea with the trochlear notch of the ulna and the capitulum with the radial head.

## Who typically gets osteochondritis dissecans of the capitulum, and why?

Adolescent throwers and gymnasts, from repeated valgus compression of the radial head on the capitulum.

## On a child's lateral elbow X-ray, what should the anterior humeral line cross?

The middle third of the capitulum; if it passes in front, an extension supracondylar fracture is suspected.

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Educational information, not medical advice. For any symptom, see a health professional.

## Its names

**Official Latin (TA2)**
cartilago articularis capituli et trochleae humeri TA2 382

**Official Spanish (DeCS)**
Cartílago articular del capítulo y la tróclea del húmero

**English (TA2)**
Cartilage of the capitulum and trochlea

## Related

- [Humerus](https://durgical.com/en/anatomy/humerus/)
- [Ulna](https://durgical.com/en/anatomy/ulna/)

Sources: Terminologia Anatomica (TA2); [Anatomy, Shoulder and Upper Limb, Elbow Joint](https://www.ncbi.nlm.nih.gov/books/NBK532948/); Anatomy of the Human Body (20th ed.): Surface Anatomy of the Upper Extremity (Lea & Febiger (Gray's Anatomy, 1918), 1918) · adapted, Public domain.

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Representative model, for educational purposes only.

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Source: https://durgical.com/en/anatomy/cartilage-of-the-capitulum-and-trochlea/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anatomy/cartilage-of-the-capitulum-and-trochlea/