ECU Tendinopathy / Subluxation

One of the ulnar-sided wrist problems, and the one you are most likely to feel under your fingers while you are examining something else.

Illness script in one line: ulnar-sided wrist pain along the dorsal ulna, with a snap or a slipping sensation on supination and ulnar deviation, worse with rotation and grip — in a racquet player, a golfer, a gymnast, or a wrist that was forced into supination in a fall.

Caseload frequency: uncommon as a referral, common as a coexisting finding. Read further: ECU pathology in patients having TFCC foveal repair [1]. The reason that paper exists is that these two travel together.

Snapping is normal. Painful snapping is not.

This is the organising idea.

Read further: ECU snapping in an asymptomatic population [2].

Why that matters to a student: a snap is dramatic. You feel it, the patient feels it, and it is enormously tempting to treat it as the diagnosis. Read further: ECU groove morphology and tendon instability [3], an accessory ECU tendon [4]. The anatomy varies between people, so what the tendon does is not automatically why it hurts.

So examine both wrists, and ask the only question that matters: does that reproduce what you came in with?

Main problem

"Something slips over the bone on the back of my wrist." That is the classic description of a slipping tendon.

That description is close to diagnostic on its own — patients do not usually invent it. The other version is duller and more common: ulnar-sided pain with rotation and grip, no slipping named, and a snap you find rather than one they report.

Body chart

Dorsal and ulnar, along the groove — over the back of the ulnar head and running distally. Ask them to point, and use the answer to sort the three candidates:

A finger tracing a line along the tendon is different from a fingertip in a hole. Watch which one you get.

Behaviour

The pattern: worse with rotation or grip. Snapping on supination / ulnar deviation.

Aggs: supination combined with ulnar deviation, a racquet backhand, wringing a cloth, opening jar lids, pushing up out of a chair, hammering, a golf swing through impact.
Eases: keeping the forearm pronated or neutral, a brace, avoiding rotation under load.
Severity: VAS 0–10 at best / at worst / right now.

The mechanical detail worth having: the tendon sits in a groove on the back of the ulna and is held there by its own subsheath, and supination with ulnar deviation is the position that loads that restraint. That is why the aggravating list is a list of supination tasks.

History

Two stories, and they are managed differently.

• The event. A fall or a forced supination with an immediate snap and a sensation of something jumping out. Section 4.
• The build-up. Weeks to months of gradual dorsal-ulnar pain in someone with a rotation-heavy sport or job, no single moment.

Then ask the wrist-and-hand question: have you ever broken this wrist or forearm? ECU tendinopathy has been reported following conservative treatment of a distal ulnar metaphyseal fracture [5]. It is the same lesson as the DRUJ page, from a different tendon.

Special / screening questions

• Any numbness over the back of the little-finger side of the hand? Dorsal ulnar cutaneous neuropathy has been described alongside ECU tendinopathy [6]. Section 4.
• Any hot, red, boggy swelling, or early-morning stiffness well past thirty minutes (UniSA coding: In), or other joints involved? Section 4.
• Sport, grip size and technique — racquet, golf, gymnastics, weight-bearing through the hand.
• Previous wrist surgery.

A standard ulnar-sided wrist pain table gives the top three. This is the third of them.

The discriminator that does most of the work: where the finger goes, and whether resisted extension with ulnar deviation is the thing that hurts.