Ulnocarpal Abutment Syndrome
What is ulnocarpal abutment/impaction syndrome?
Ulnocarpal abutment (or ulnocarpal impaction) syndrome results from the ulnar bone “knocking” against the lunate bone. “Abut” means “to rub against”. The pain occurs with ulnar deviation of the wrist or loading of the wrist in this position. It can develop following a fall or with repetitive tasks e.g. hammering. This issue is more likely if the ulnar bone is relatively longer than radius (ulnar positive variance). It can also occur if the radius bone has been shortened by a distal radius fracture.
What are the symptoms of ulnocarpal abutment syndrome?
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Pain with repetitive tasks that involve moving the wrist from side to side (e.g. hammering or repetitive tasks that require a similar motion).
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Swelling is uncommon
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The pain may be sharp or aching.
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Occasionally there can be some crepitus (a grinding or crunching sound).
What is ulnar positive variance?
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Ulnar positive variance is when the ulna bone is longer that the flat surface of the radius closest to the ulna.
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Ulnar variance is measured with x-rays performed with the shoulder, elbow and wrist in a standardized position. The shoulder is held 90 degrees away from the body, the elbow is bent 90 degrees and the wrist is in neutral position. (See image.)
ULNAR NEGATIVE
ULNAR NEUTRAL
ULNAR POSITIVE
How is it diagnosed?
The history of symptoms, wrist examination and imaging are used to diagnose ulnocarpal abutment.
X-ray
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The ulnar bone may be relatively longer than the radius (ulnar positive variance). This may be due to a person’s normal anatomy or due to a distal radius fracture.
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There may be small cysts in the ulnar head or lunate.
MRI may be required if plain x-rays are unhelpful.
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A central (traumatic type 1A) tear of the triangular fibrocartilage complex (TFCC) may occur as a result of the abutment syndrome. The central tear does not cause the pain and does not require treatment.
Cysts in lunate
Cysts in ulnar head
Ulnar positive variance
Treatment Options
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Non-operative treatment
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Ulnar-shortening osteotomy surgery
1. Non-operative treatment
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Rest in a wrist splint
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Anti-inflammatories
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Steroid injection
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Hand therapy rehabilitation
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If non-operative treatment does not sufficiently relieve the symptoms, surgery may be required.
Recovery after surgery
2 days
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Keep hand & forearm elevated and take pain relief prescribed.
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The wound is kept dry for the first 2 weeks by showering with a plastic bag.
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Waterproof covers can be obtained from most pharmacies.
2 weeks
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The bandage and the stitches are removed. A removeable forearm splint is provided.
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May shower hand normally.
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Hand therapy exercises commenced
4-6 weeks
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Many people will feel safe to drive (wearing their splint) between 4 to 6 weeks.
8-10 weeks
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Review with surgeon with x-ray to check bone healing.
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Wrist and forearm movement should be almost normal
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Still some mild swelling and stiffness
4-6 months
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Residual swelling and stiffness resolves.
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Normal function and return to all activities.
2. Ulnar-shortening osteotomy (USO) surgery
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This procedure involves removing several millimetres of bone from the ulna to make it shorter and applying a plate to hold the bone in position while it heals. Osteotomy means to cut bone.
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A surgical plating system designed for USO is used. The system has a highly accurate saw guide to cut the ulna bone. There is also a mechanism to compress the two bone ends together once the appropriate length of bone has been removed.
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USO is performed as a day surgery procedure under general anaesthetic.
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A fibreglass backslab to support your wrist and forearm is applied.
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A sling is provided and a prescription for pain relief.
Risks of ulna shortening osteotomy
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Persistent wrist/forearm stiffness - very infrequent.
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Persistent pain - due to other concurrent wrist conditions.
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Infection <1%
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Plate removal - required due to discomfort in ~25% patients. More likely in women with small forearms.
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Non-union - bone not healing and needing further surgery & bone graft.