Wrist ultrasound is high-yield and fast. The structures are millimetres from the transducer, which means excellent resolution, and several of the most common diagnoses — carpal tunnel syndrome, De Quervain's, trigger finger — are made on a combination of a single measurement and a dynamic manoeuvre.

Probe: The highest frequency you have. 15–22 MHz if available; 12 MHz is a workable floor. Use a generous layer of gel or a standoff for the most superficial structures, and keep probe pressure light — heavy pressure compresses the very structures you are assessing.

Carpal Tunnel Syndrome

The single most common indication, and the one where ultrasound has largely earned parity with nerve conduction studies for diagnosis.

The Measurement

Position: Wrist supinated and neutral, slight extension over a rolled towel. Probe in short axis at the level of the pisiform, which is the standard measurement location and corresponds to the proximal carpal tunnel inlet.

Landmarks: The median nerve sits superficial and radial to the flexor tendons, deep to the flexor retinaculum. On short axis it has a characteristic honeycomb appearance — hypoechoic fascicles in a hyperechoic background.

Measure cross-sectional area by tracing the inner margin of the hyperechoic epineurium.

Median nerve CSA at pisiform	Interpretation
≤ 9 mm²	Normal
10–12 mm²	Borderline / mild
13–15 mm²	Moderate
> 15 mm²	Severe

Published thresholds vary somewhat between studies and laboratories — around 10 mm² is the most widely used cutoff for abnormality. Know what your department uses and be consistent.

Supporting Findings

Wrist-to-forearm ratio: CSA at the pisiform divided by CSA in the mid-forearm (about 12 cm proximal). A ratio above roughly 1.4 supports the diagnosis and is useful when a patient has diffusely large or small nerves.
Flattening ratio of the nerve within the tunnel at the level of the hamate
Palmar bowing of the flexor retinaculum
Loss of the fascicular pattern — the nerve looks uniformly hypoechoic and swollen
Hyperaemia within the nerve on power Doppler in more active disease

Do Not Miss the Cause

Most carpal tunnel syndrome is idiopathic, but ultrasound can identify a treatable structural cause that changes management entirely:

Tenosynovitis of the flexor tendons
Ganglion cyst within the tunnel
Persistent median artery, sometimes thrombosed
Bifid median nerve, which is a normal variant but changes surgical planning — report it
Amyloid deposition or synovial proliferation

Always look. Finding a ganglion compressing the nerve is a genuinely different report from idiopathic CTS.

De Quervain's Tenosynovitis

Anatomy: The first extensor compartment contains abductor pollicis longus (APL) and extensor pollicis brevis (EPB), passing over the radial styloid.

Position: Wrist in ulnar deviation, thumb accessible. Scan in short axis over the radial styloid, then long axis.

Findings:

Thickening of the extensor retinaculum over the compartment
Hypoechoic fluid or synovial thickening surrounding the tendons
Tendon thickening and loss of fibrillar pattern
Hyperaemia on power Doppler
Tenderness under the probe, which is diagnostically useful — sonopalpation localizes the problem precisely

Look for a septum. A vertical septum dividing APL and EPB into separate subcompartments is present in a substantial minority of people and is a recognized cause of injection failure — the steroid goes into one subcompartment and the other stays inflamed. If you see it, report it; it changes how the injection is performed.

Trigger Finger (Stenosing Tenosynovitis)

Position: Palm up, probe over the A1 pulley at the metacarpal head.

Findings:

Thickening and hypoechogenicity of the A1 pulley
Fluid within the flexor tendon sheath
Hyperaemia on Doppler

The dynamic test is the diagnosis. Keep the probe in long axis over the A1 pulley and ask the patient to flex and extend the finger. Watch for the tendon catching, then snapping through the pulley. A static image of a thickened pulley is supportive; the visible catch is confirmatory. Record a clip.

Ganglion Cysts

The most common soft tissue mass in the wrist.

Typical locations: Dorsal wrist over the scapholunate ligament (most common), volar radial near the radial artery, and the flexor tendon sheath.

Sonographic appearance:

Well-defined, anechoic, posterior acoustic enhancement
Lobulated or multiseptated in many cases
No internal Doppler flow — this is the key discriminator
A stalk connecting to the joint or tendon sheath may be visible and confirms the diagnosis

Volar ganglia: check the radial artery. Volar radial ganglia sit immediately adjacent to the artery, and this matters for anyone planning aspiration. Document the relationship with colour Doppler.

If it has internal flow, it is not a ganglion. Solid vascular masses in the wrist need a different workup — see soft tissue mass evaluation.

Other Structures Worth Knowing

Extensor carpi ulnaris (ECU): Sixth extensor compartment, ulnar side. Tendinopathy and subluxation are common in racquet sports. Test dynamically with forearm supination and ulnar deviation — the tendon can visibly snap out of its groove.

TFCC region: The triangular fibrocartilage complex sits between the ulnar head and the carpus. Ultrasound can assess the superficial portion and the distal radioulnar joint but cannot reliably exclude a TFCC tear — MR arthrography remains the standard. Say this in the report rather than implying a normal ultrasound rules one out.

Scapholunate ligament: The dorsal component is accessible. Widening of the scapholunate interval, particularly on dynamic stress with a clenched fist, suggests instability.

Ulnar nerve at Guyon's canal: Less common than cubital tunnel compression but a real entity. Scan short axis between the pisiform and hook of hamate; look for a ganglion, which is the most frequent compressive cause here.

Key Images to Capture

Median nerve short axis at the pisiform — with CSA measurement
Median nerve mid-forearm — for the wrist-to-forearm ratio
Median nerve long axis through the tunnel
First extensor compartment — short and long axis, with Doppler
A1 pulley — long axis plus a dynamic clip if triggering
Any cystic lesion — two planes, measurements, and Doppler
Contralateral comparison for any borderline nerve measurement

Reporting Language

Carpal tunnel syndrome: "The median nerve measures 14 mm² in cross-section at the level of the pisiform (normal ≤ 9 mm²) with loss of the normal fascicular architecture and palmar bowing of the flexor retinaculum. Wrist-to-forearm ratio 1.9. No ganglion, tenosynovitis, or persistent median artery identified. Findings consistent with moderate median neuropathy at the carpal tunnel; correlate with clinical findings and nerve conduction studies as indicated."

De Quervain's: "Hypoechoic thickening of the extensor retinaculum overlying the first extensor compartment with surrounding tenosynovial fluid and marked hyperaemia on power Doppler. A vertical septum separating APL and EPB subcompartments is identified. Focal tenderness under the transducer. Findings consistent with De Quervain's tenosynovitis."

SonoBuddy keeps nerve cross-sectional area cutoffs and MSK protocols one tap away — offline, in the scan room.

Wrist and Hand Ultrasound: Carpal Tunnel, De Quervain's, and Ganglion Cysts