Extensor Retinaculum — Definition and Attachments
Definition
The extensor retinaculum is an oblique fibrous band formed by thickening of the deep fascia on the dorsum (back) of the wrist.
It holds the extensor tendons in position as they cross the wrist joint and prevents them from bowstringing during wrist extension.
Orientation
- Directed downwards and medially (oblique band)
- Approximately 2 cm broad vertically
- Lies on the posterior aspect of the wrist, bridging the dorsal surface of the lower radius and ulna
Attachments
| Side | Attachment |
|---|---|
| Lateral | Lower part of the anterior border of the radius (anterolateral surface of the distal radius) |
| Medial | Styloid process of the ulna, triquetral bone, and pisiform bone |
The lateral attachment to the anterior border of the radius — rather than the posterior border — accounts for the oblique direction of the retinaculum (it runs from anterolateral to posteromedial).
Deep Surface — Septa and Compartments
From its deep surface, the extensor retinaculum sends five septa downward to attach to the dorsal aspects (ridges) of the lower ends of the radius and ulna.
These five septa divide the space deep to the retinaculum into six osseofibrous compartments, numbered I to VI from lateral (radial) to medial (ulnar).
Each compartment transmits one or more extensor tendons, each enclosed in a synovial sheath.
Functions
- Prevents bowstringing of extensor tendons during wrist extension
- Holds tendons in position on the dorsum of the wrist
- Forms the roof of each osseofibrous compartment — the septa and bones of the radius and ulna form the walls and floor
- Reduces friction via the synovial sheaths lining each tunnel
Comparison with Flexor Retinaculum
| Feature | Flexor Retinaculum | Extensor Retinaculum |
|---|---|---|
| Surface | Anterior (palmar) | Posterior (dorsal) |
| Shape | Rectangular | Oblique band |
| Width | ~3 cm | ~2 cm |
| Attachments | Scaphoid, trapezium (lateral); pisiform, hamate (medial) | Radius (lateral); ulna, triquetral, pisiform (medial) |
| Compartments | 1 main tunnel (+ FCR tunnel + Guyon’s) | 6 compartments |
| Structure passing superficial | 6 structures (ulnar N, ulnar A, etc.) | None of clinical note |
| Nerve at risk | Median nerve (carpal tunnel syndrome) | Superficial radial nerve (Wartenberg’s) |