1st compartment sheath !

The first compartment sheath wraps two thumb tendons on the thumb side of the wrist; it lets them glide and swells in de Quervain tenosynovitis.

Official name: Tendon sheath of the 1st dorsal compartment

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What it is

The sleeve around the APL and EPB tendons in the first tunnel at the thumb side of the wrist; it swells in De Quervain's tenosynovitis.

What it does

Lets the thumb tendons glide; it swells in De Quervain's tenosynovitis.

Key facts

Where: Over the radial styloid, under the extensor retinaculum (1st dorsal compartment: APL, EPB)
Function: Lets the thumb tendons glide; thickens in De Quervain tenosynovitis

Relations

Contents: APL and EPB tendons in a shared synovial sheath, sometimes split by a septum
Superficial: Extensor retinaculum, branches of the superficial radial nerve and the start of the cephalic vein
Deep: Shallow groove on the lateral side of the radial styloid
Below: Beyond the retinaculum the tendons form the front border of the anatomical snuffbox, with the radial artery in its floor

How to find it

With the thumb extended and pulled away from the palm, the APL and EPB tendons stand out together along the thumb side of the wrist; followed upward, the sheath lies over the radial styloid, the tender spot in de Quervain tenosynovitis.

Examination

Finkelstein test: the examiner holds the thumb and tilts the wrist toward the little finger; sharp pain over the radial styloid suggests de Quervain tenosynovitis
Eichhoff test (thumb tucked into the fist, then ulnar deviation): more false positives, since it can hurt in normal wrists

On imaging

Ultrasound shows a thick retinaculum and sheath with fluid and increased Doppler flow, and whether a septum splits the EPB off. X-ray excludes arthritis at the base of the thumb.

Common problems

De Quervain's tenosynovitis: the tendons and their sheath swell in the first tunnel, causing pain at the thumb side of the wrist.
Common in new parents lifting a baby and with repeated thumb use.

How it is diagnosed

Pain when the thumb is tucked into the fist and the wrist is tilted toward the little finger (Finkelstein-type test).

Treatment

Thumb splint, activity changes and a steroid injection, which helps most people.
Surgical release of the first tunnel's roof, protecting the superficial radial nerve.

Clinical notes

Surgical release opens the dorsal roof of the sheath; injury to the superficial radial nerve branches over it can leave a painful neuroma
Intersection syndrome: pain and crepitus a few centimetres above the wrist, where the APL and EPB muscle bellies cross over the second-compartment tendons (ECRL, ECRB)
Differential diagnosis: thumb base (carpometacarpal) arthritis, scaphoid problems and Wartenberg syndrome (compression of the superficial radial nerve)

Anatomical variants

Extra APL slips are the rule rather than the exception, and a separate EPB sub-compartment is frequent; reported frequencies vary widely

De Quervain tenosynovitis

Test yourself

Think of the answer, then tap the question to see it.

Which tendons run in the first extensor compartment sheath, and over which bone?

The abductor pollicis longus (APL) and extensor pollicis brevis (EPB), over the radial styloid.

What is the Finkelstein test, and what does a positive result suggest?

The examiner holds the thumb and tilts the wrist toward the little finger; sharp pain over the radial styloid suggests de Quervain tenosynovitis.

Why can a de Quervain release or injection of the first compartment sheath fail?

A common septum gives the EPB its own sub-compartment; if it is missed, the tendon stays tight.

Which nerve is at risk when the first compartment sheath is released?

Branches of the superficial radial nerve, which cross over the sheath; injury can leave a painful neuroma.

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Educational information, not medical advice. For any symptom, see a health professional.

Its names

Official Latin (TA2): vagina tendinum abductoris longi et extensoris brevis pollicis TA2 2577
Official Spanish (DeCS): Vaina tendinosa de los músculos abductor largo y extensor corto del pulgar
English (TA2): Tendon sheath of the 1st dorsal compartment

Sources: Terminologia Anatomica (TA2); Anatomy, Shoulder and Upper Limb: Hand Anatomical Snuff Box; Anatomy, Shoulder and Upper Limb, Wrist Extensor Muscles.

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Representative model, for educational purposes only.

1st compartment sheath highlighted on the Durgical 3D model