Ulna

An anatomical and biomechanical study guide focusing on the stabilizing bone of the forearm — its bony landmarks, muscular attachments, and clinical significance.

1. Osteology of the Ulna

Divided into proximal epiphysis, diaphysis (shaft), and distal epiphysis

Region	Landmark	Description
Proximal	Olecranon Process	Large, thick, curved bony eminence that forms the pointed part of the elbow. Articulates with the olecranon fossa of the humerus.
	Trochlear Notch	Large depression that articulates with the trochlea of the humerus.
	Coronoid Process	Triangular eminence projecting from the anterior proximal part of the ulna.
	Radial Notch	A narrow, oblong, articular depression on the lateral side of the coronoid process that articulates with the head of the radius.
	Ulnar Tuberosity	Roughened area just distal to the coronoid process for the attachment of the brachialis muscle.
Shaft	Anterior Border	Rounded and smooth.
	Posterior Border	Sharp and palpable along its entire length.
	Interosseous Border	Lateral and sharp for the attachment of the interosseous membrane.
Distal	Head of Ulna	Rounded articular eminence at the distal end.
Distal	Styloid Process	A short, pointed projection from the posteromedial side of the distal end.

2 & 3. Muscular Attachments

Muscles originating from and inserting onto the ulna

These muscles have their proximal attachment on the ulna and typically act on the wrist, hand, and fingers.

Muscle	Origin Site	Action
Flexor Carpi Ulnaris	Olecranon process and posterior border of the ulna	Wrist flexion and ulnar deviation (adduction)
Pronator Teres (ulnar head)	Coronoid process	Forearm pronation and assists elbow flexion
Flexor Digitorum Profundus	Anterior and medial surfaces of the ulna	Flexion of the DIP joints of digits 2-5
Extensor Carpi Ulnaris	Posterior border of the ulna (via a shared aponeurosis)	Wrist extension and ulnar deviation (adduction)
Supinator	Ulnar crest (supinator crest) below the radial notch	Forearm supination
Abductor Pollicis Longus	Posterior surface of the ulna (and radius and interosseous membrane)	Thumb abduction and extension at the CMC joint
Extensor Pollicis Longus	Posterior surface of the middle third of the ulna	Extension of the thumb IP joint
Extensor Indicis	Posterior surface of the distal third of the ulna	Extension of the index finger

These muscles originate on the humerus or scapula and insert onto the ulna, primarily acting on the elbow joint.

Muscle	Insertion Site	Action
Triceps Brachii	Olecranon process	Primary extensor of the elbow
Anconeus	Lateral aspect of the olecranon and posterior proximal ulna	Assists elbow extension and stabilizes the elbow joint during pronation
Brachialis	Ulnar tuberosity and coronoid process	Primary flexor of the elbow (the 'workhorse' of elbow flexion)

4. Memory Tricks & Key Concept

Ulna memory tricks: F.P.E.S.A.A.E. origins mnemonic, TAB insertions mnemonic, and key concept showing ulna as the stable bone

Origins Mnemonic: F.P.E.S.A.A.E.

Remember all 7 muscles originating from the ulna:

FFlexor Carpi Ulnaris

PPronator Teres

EExtensor Carpi Ulnaris

SSupinator

AAbductor Pollicis Longus

AExtensor Pollicis Longus

EExtensor Indicis

Insertions Mnemonic: TAB

Only 3 muscles insert onto the ulna — easy to remember!

Triceps Brachii

Anconeus

Brachialis

Key Concept: Ulna = Stability

The ulna is the stable bone of the forearm. During pronation and supination, the radius rotates around the ulna. The ulna remains relatively fixed, providing a stable axis for the forearm's rotational movements.

5. Clinical Notes

Important clinical correlations — fracture zones and nerve vulnerabilities

$Ulna clinical notes: ulnar nerve danger zone, nightstick fracture zone, and Monteggia fracture zone$

Olecranon / Cubital Tunnel

Ulnar Nerve Danger Zone

The ulnar nerve runs in the cubital tunnel behind the medial epicondyle, directly adjacent to the olecranon.

Compression or trauma here causes 'cubital tunnel syndrome,' leading to numbness and tingling in the 4th and 5th fingers and weakness in hand grip.

Shaft (Posterior Border)

Nightstick Fracture Zone

The subcutaneous posterior border of the ulnar shaft is vulnerable to direct blows.

A direct blow (e.g., raising the arm in defense) can cause an isolated fracture of the ulnar shaft, known as a 'nightstick fracture.'

Proximal Ulna + Radial Head

Monteggia Fracture

A complex injury involving the proximal ulna and the radioulnar joint.

A fracture of the proximal third of the ulna combined with dislocation of the radial head. This is a serious injury that requires surgical intervention.