Topic Overview

Ulna

General Features

• Medial bone of the forearm (in anatomical position).

• Longer than radius.

• Bone of stability – forms major part of the elbow joint.

• Does not directly take part in wrist joint (separated from carpals by articular disc).

Parts of Ulna

1. Upper End

   • Olecranon process → large, curved projection, forms prominence of elbow, triceps insertion.

   • Coronoid process → anterior projection, brachialis insertion.

   • Trochlear notch → formed by olecranon and coronoid processes, articulates with trochlea of humerus.

   • Radial notch → on lateral side of coronoid, articulates with head of radius.

   • Ulnar tuberosity → below coronoid process, insertion of brachialis.

2. Shaft

   • Three borders: anterior, posterior, interosseous.

   • Three surfaces: anterior, posterior, medial.

   • Interosseous border → attachment of interosseous membrane.

3. Lower End

   • Head of ulna → rounded, articulates with ulnar notch of radius.

   • Styloid process → posteromedial projection, palpable.

Ossification of Ulna

• Primary center: shaft, appears in 8th week intrauterine life.

• Secondary centers:

  • Lower end → appears at 5 years, fuses at 18 years.

  • Olecranon → appears at 10 years, fuses by 15–16 years.

• Total centers: 1 primary + 2 secondary = 3 centers.

Clinical Anatomy

• Fractures

  • Olecranon fracture → common from direct trauma, may require surgical fixation.

  • Monteggia fracture-dislocation → fracture of proximal third of ulna with dislocation of radial head.

  • Night stick fracture → isolated fracture of ulna (defensive injury).

  • Shaft fractures usually associated with radius fractures.

• Dislocations

  • Rare at elbow, but displacement of radial head may occur with ulnar fractures.

• Clinical landmarks

  • Olecranon and medial/lateral epicondyles form a straight line in extension and an equilateral triangle in flexion → important for diagnosing dislocations.

  • Styloid process of ulna used in measuring ulnar variance in radiology.

• Ossification centers helpful in forensic age determination.