Wrist Anatomy on MRI

Overview

This lecture covers the detailed anatomy of the wrist as seen on MRI, focusing on bones, tendons, key ligaments, and the triangular fibrocartilage complex (TFCC).

Bony Anatomy of the Wrist

• The wrist connects the forearm (radius and ulna) to the hand (metacarpals) via the carpal bones.
• Radius (lateral) and ulna (medial) have styloid processes; radius also has Lister’s tubercle and sigmoid notch.
• The carpal bones are organized in two rows: proximal (scaphoid, lunate, triquetrum, pisiform) and distal (trapezium, trapezoid, capitate, hamate).
• Four structures lie anteriorly: scaphoid tubercle, trapezium tubercle, pisiform, and hook of hamate, forming the carpal tunnel floor.

Wrist Tendons

• Extensor (dorsal) tendons are grouped in six compartments, each with set tendons (e.g., abductor pollicis longus in compartment 1).
• Lister’s tubercle separates extensor compartments 2 and 3.
• Nine flexor (volar) tendons pass through the carpal tunnel: four flexor digitorum profundus, four flexor digitorum superficialis, and one flexor pollicis longus.
• Median nerve runs in the carpal tunnel; impingement here causes carpal tunnel syndrome.
• Flexor carpi radialis passes within, but not through, the carpal tunnel; flexor carpi ulnaris attaches to pisiform.
• Ulnar nerve and artery pass through Guyon’s canal.

Intrinsic and Extrinsic Ligaments

• Intrinsic ligaments connect carpal bones: scapholunate, lunotriquetral, and scaphotrapeziotrapezoid (STT) ligaments.
• Scapholunate ligament is thickest dorsally; lunotriquetral is thickest volarly.
• Extrinsic ligaments connect forearm bones to carpals: volar (radioscaphocapitate, radiolunate, ulnar triquetral, etc.) and dorsal (dorsal radioulnar, dorsal radiotriquetral, dorsal intercarpal).
• Volar extrinsic ligaments form the anterior wall of the TFCC.

Triangular Fibrocartilage Complex (TFCC)

• The TFCC stabilizes the distal radioulnar joint and transmits force from ulna to radius.
• Components: triangular fibrocartilage disk, dorsal/volar radioulnar ligaments, ulnar collateral ligament, meniscal homologue, and surrounding extrinsic ligaments.
• TFCC acts like a meniscus, cushioning between ulna and carpal bones.

Key Terms & Definitions

• Carpal tunnel — Passageway on the volar wrist bordered by carpal bones and flexor retinaculum, transmitting flexor tendons and median nerve.
• Intrinsic ligaments — Ligaments connecting carpal bones to each other.
• Extrinsic ligaments — Ligaments connecting the radius/ulna to carpal bones.
• TFCC (Triangular Fibrocartilage Complex) — A structure that stabilizes the ulnar side of the wrist.

Action Items / Next Steps

• Review the previous wrist radiograph tutorial for foundational understanding.
• Practice identifying bones, tendons, and ligaments on MRI and 3D rendered images.
• Familiarize yourself with the names and locations of all carpal bones and major wrist ligaments.