Ulna

The ulna (plural: ulnae) is one of the two long bones of the forearm. It is located medially in the supinated anatomic position. It has a larger proximal end and tapers to a smaller distal end (opposite to the radius). 

Gross anatomy

Prominent features of the ulna include:

• proximal: olecranon, trochlear notch, coronoid process, radial notch (lateral), sublime tubercle (medial)
• shaft: ulnar tuberosity
• distal: head, styloid process, groove for extensor carpi ulnaris

Articulations

• proximal (elbow joint)
  • olecranon: ulnatrochlear joint (elbow floexion)
  • radial notch: proximal radioulnar joint (site of supination and pronation)
• distal
  • distal radioulnar joint
  • wrist via the TFCC

Attachments

Musculotendinous

Anteriorly

• proximal:
  • brachialis: ulnar tuberosity
  • pronator teres: ulnar head
  • flexor digitorum superficialis: ulnar head
• shaft:
  • supinator
  • flexor digitorum profundus
  • pronator quadratus

Posteriorly

• triceps, aconeus, supinator, flexor digitorum profundus, flexor carpi ulnaris (ulnar head), extensor carpi ulnaris (ulnar head), abductor pollicis longus, extensor pollicis longus, extensor indices

Ligamentous

• proximal:
  • medial collateral ligaments of the elbow
    • anterior band: inferior medial epicondyle to the sublime tubercle
    • posterior band: medial epicondyle to medial olecranon
    • middle band (Transverse or Cooper's ligament): medial olecranon to medial coronoid process
  • anterior and posterior capsular ligaments of the elbow
• medial:
  • anterior and posterior attachments of the annular ligament
  • quadrate ligament
  • oblique cord
  • interosseous membrane
• distal:
  • triangular fibrocartilage
  • ulnar collateral ligament of of the wrist

Relations and/or boundaries

The ulna and its attachments help to divide the forearm into anterior and posterior compartments. 

Its subcutaneous border lies postero-medially and the antebrachial fascia attaches on either end. 

Its interosseous border (anterolaterally) is attached to the interosseous membrane of the forearm.

Blood supply

The forearm (and ulna) is supplied by the ulnar artery and its continuation as the common interosseous artery with the anterior and posterior interosseous branches.

Nerve supply

Periosteum is supplied anteriorly by the anterior interosseous nerve (branch of median nerve).

Posteriorly, the periosteum is supplied by the posterior interosseous nerve (branch of radial nerve)

Lymphatic supply

Lymphatics of the hand and forearm drain either to the supratrochlear lymph node, or directly into the lateral group of axillary lymph nodes.

Radiographic features

Carrying angle of the elbow of 15-20 degrees. Increased in females.

Development

Intracartilaginous ossification begins in utero. Ossification centres include:

• shaft/diaphysis (8 weeks gestation)
• distal (5-7 years > 16-18 years)
• proximal (8-10 years > 13-15 years)

Ossification

• ossification centres of the wrist
• ossification centres of the elbow

Related pathology

• Monteggia fracture: fracture of ulna with dislocation of proximal radioulnar joint
• Galeazzi fracture: fracture of radius with dislocation of distal radioulnar joint
• Essex-Lopresti fracture: fracture of radial head with disruption of the interosseous membrane and dislocation of distal radioulnar joint
• Madelung deformity
• ulnotriquetrial abutment