Ulnar Impaction Syndrome: When the Ulna Is Simply Too Long

Written by Nigel Chua, hand occupational therapist · 21 years treating fingers, hands, wrists, forearms and elbows · Singapore

When the Ulna Bone in The Forearm Is Simply Too Long?

Ulnar impaction syndrome is pain on the little-finger side of the wrist caused by the ulna being slightly LONGER than the radius, so it repeatedly presses into the small wrist bones sitting above it.

A few millimeters is enough.

It is a loading problem, not a tearing one — which is why rest calms it and gripping, twisting or pushing up from a chair brings it straight back.

The pain is worse with the forearm turned palm-down and the wrist deviated towards the little finger.

Opening jars.

Wringing cloth.

Press-ups.

Many more examples.

The mechanism

At the wrist, the radius carries about 80 percent of the load and the ulna about 20.

That split depends on their relative lengths, and it is not a gentle curve. Roughly speaking, 2.5mm of extra ulnar length can push the ulnar share from 20 percent to over 40.

Double the load, through a cartilage disc designed for half of it.

Over years, that disc — the TFCC — wears centrally, then the lunate and triquetrum beneath show bone edema, then cysts, then true cartilage loss.

This is why the MRI report so often says “degenerative central TFCC tear” in someone who never injured their wrist. The tear is the consequence. The length is the cause.

Why the ulna ends up long

Congenital — some people are simply built ulnar-positive
After a distal radius fracture that healed shortened, so the radius dropped relative to the ulna
Premature closure of the radial growth plate, as in gymnast’s wrist
Functionally, in pronation and grip — the ulna becomes relatively longer with the forearm turned over, which is why symptoms are position-dependent

How it is distinguished

The clinical picture overlaps heavily with a straightforward TFCC injury, and the two often coexist.

What separates them:

TFCC tear: usually a specific injury — a fall, a twist. Sharp, often clicking
Ulnar impaction: gradual onset, no injury, ache that builds with load
Imaging: a PA X-ray taken with the forearm pronated and the fist clenched shows ulnar variance properly. A relaxed film underestimates it
MRI: bone edema or cysts in the lunate and triquetrum is the giveaway

If the bone underneath is bruised, the problem is not the disc that sits on top of it.

Treatment

Non-surgical first, and it is worth a real attempt.

Activity modification — avoid loaded pronation and ulnar deviation; press-ups on fists or handles rather than flat palms
Wrist widget or ulnar-sided support to limit the compressive position
Strengthening the muscles that offload the ulnar side, particularly ECU and pronator quadratus, once pain allows
Corticosteroid injection into the ulnocarpal joint for a settling window
Give it 3 to 6 months before calling it failed

Surgery, when load reduction doesn’t hold. The point is the same in all versions: shorten the ulna or decompress it.

Ulnar shortening osteotomy — a segment of the ulna removed and plated. Reliable, but it is a bone healing timeline: 6 to 12 weeks to union, 4 to 6 months to full loading, and the plate is often removed later
Wafer procedure — a few millimeters of the ulnar head shaved arthroscopically. Faster recovery, around 6 to 12 weeks, but limited to smaller amounts of variance

The window

This one runs on years, not weeks, and it is about cartilage rather than tissue healing.

Bone edema only: fully reversible once load is corrected
Cysts: still correctable, structure largely preserved
Cartilage loss and joint space narrowing: shortening the ulna no longer resurfaces what’s gone. Salvage surgery replaces reconstructive surgery at this point.

Nobody is going to spot this on a normal X-ray glanced at in a corridor. It is a millimeter problem, and millimeters need to be measured, not eyeballed.