Ulno-Carpal Abutment (UCA) or Ulno-Carpal Impaction (UCI) syndrome is the common reason for wrist pain on the ulnar, little finger, side of the hand. Symptoms arise because of unbalanced loading of this side of the wrist joint and/or repeated abutment/impaction (“squashing”) of the TFCC – triangular fibrocartilage complex, a highly specialized, ligament/cartilage-like structure, that lies between the forearm and wrist bones.

Causes vary, but with each one, in essence, a repetitive loading of ulnar side of the wrist can elicit pain and discomfort. This is particularly obvious during sideways movement of the hand in direction of the little finger. Ulno-carpal abutment is most commonly seen in people with positive ulnar variance. This is the condition whereby the ulna, forearm bone on the side of the little finger, is relatively longer than the radius, forearm bone on the side of thumb (Pic 2, Gallery below). Such arrangement stretches the TFCC and imposes greater biomechanical load resulting in degenerative changes in the wrist in the long term.

Although causes vary, broadly speaking, there are 2 main categories:

Congenital –individuals born with longer ulna bone, people who experience premature closure of the distal radius

Acquired forms most commonly arise after the wrist fracture. Radius fracture frequently results in its shortening making ulna relatively longer; less common are injuries of the growing areas of the radius, longitudinal forearm instability from radial head fractures and Essex-Lopresti injuries.

Occasionally, ulno-carpal abutment may occur as a result of repetitive loading of ulnar side of the wrist (golf, racquet sports etc.).

Characteristic symptoms and signs are the pain over the ulnar side of the wrist, sometimes with soft tissue swelling and decreased range of motion in the wrist. Discomfort is almost always triggered and/or aggravated by sideways movement of the wrist, forceful gripping and rotational loading of the wrist joint.

The diagnosis of UCI is made by patient’s history, clinical examination and imaging. Pinpoint tenderness is on the ulnar, little finger side of the wrist. Pain often begins insidiously and increases with gripping, loading and rotation of the wrist and over time, leads to progressive wrist weakness and swelling.

X-rays often, but not always, detect abnormal relationship between the two bones (Pic 3, Gallery below) and can detect changes in affected bones and/or surrounding soft tissue swelling. More sophisticated imaging like Magnetic Resonance Imaging (MRI) or arthrogram and /or wrist arthroscopy (key hole examination of the wrist joint) may be required in atypical, more discrete clinical presentation.

Initial management is often non-surgical: modification of daily living activities, splinting, anti-inflammatory medication, and in some cases, a steroid injection into the ulnar corner of the wrist, around painful TFCC.

Surgical treatment is aimed at eliminating the mechanical impaction of the ulna against TFCC and wrist bones. The most commonly performed are the Ulnar Shortening Osteotomy, arthroscopic (key hole) tiding up of degenerate TFCC, so called ‘Wafer’ procedure, etc.

Ulna shortening osteotomy is the gold standard treatment, considered by most wrist surgeons, including myself, the most reliable, physiological and predictably successful operation. It essentially shortens the ulna by removing its segment further up the forearm, away from the wrist itself (Pic 4, Gallery below). The amount of shortening varies from one patient to another, but in most cases, 2-6 mm is sufficient to automatically unload diseased side of the wrist and stop affected bones and ligaments impacting against each other. Two broken ends of ulna are pulled towards each other and fixed with specialized plates and screws. Bone ends will require 6-8 weeks to unite/heal.Picture 5 shows X rays before and after ulna shortening and radical change in skeletal alignment which can be achieved with surgery. In most cases, however even minimal bone shortening leads to almost imminent resolution of symptoms.

Wafer procedure involves resection of the distal most 2-3 mm of the ulna head i.e. area that forms the part of the wrist joint itself. All of the cartilage and the very end of the bone are shaven off and ulna gets shortened directly at the point of impaction inside the wrist. Operation can be carried out arthroscopically (key hole method) of via open method. Personally, I perform this operation rarely, in strictly selected group of patients as operation results in non-physiological changes within the joint. It does have its place and can improve the pain in conditions with significant pre-existing degenerative changes.

In rare cases patients may present with so advanced changes that ulna head replacement (arthroplasty) or a total ulna head removal (Darrach procedure) might need to be contemplated.

Pain relief after the ulnar shortening osteotomy becomes evident quickly, 2-3 weeks after the operation i.e. as soon as early side effects of surgery start to withdraw. Patient satisfaction is predictably very high. This is nevertheless, technically demanding and serious operation which should not be performed too lightly. Deliberately fracturing a healthy bone and making it heal again is not without risks. Advantages and risks should be clearly gauged in each individual case and exact degree of patient disability preoperatively carefully ascertained.

Rehabilitation takes between 8-12 weeks although a return to full hand and wrist strength might take a bit longer. Wrist has to be splinted for up to 8 weeks postoperatively. Original Plaster of Paris is exchanged for the light weight, custom made, long arm splint within the first week of surgery (Pic 6, Gallery below). A splint extends from hand to the elbow and is deliberately long in order to completely prevent rotation of the forearm bones and facilitate union between two ulna segments.

Complications are rare, but as with any surgical procedure, there are general and procedure specific risks which patients should be aware of:
General complications:
• Adverse reaction to general anaesthetic
• Skin/joint infection
• Hypertrophic (lumpy and itchy) scarring
• Reflex Sympathetic Dystrophy – RSD (bad reaction to surgery with painful and stiff hands – this can occur with any hand surgery from a minor procedure to a complex reconstruction)

Specific complications (Ulnar Shortening Osteotomy):
• Numbness due to the sensory, superficial nerve injury
• Neuroma (painful nerve lump extremely sensitive to touch)

• Non-union at the site of bone cut (1-2% risk); smoking significantly increases this risk so operation is not recommended in smokers
• Ongoing joint pain
• Stiffness
• Metalwork (plate/screw) tissue irritation (in 25% cases)- requiring a need for its removal and another operation

Specific complications (Wafer Arthroscopic resection):
• Joint infection
• Numbness due to the sensory, superficial nerve injury
• Neuroma (painful nerve lump extremely sensitive to touch)

• Ongoing joint pain
• Stiffness

– Anticoagulation medication (Aspirin, Brufen, Warfarin, Clopidrogel) should ideally be stopped few days before the operation to reduce the risk of bleeding, but advise from the clinician who prescribed them is wise beforehand. I would strongly advise you to stop smoking prior to surgery as this can badly affect the outcome of surgery and increase complication rates.
– Please make sure that you arrange to be collected from the hospital as you will not be able to drive after the surgery.
– Plan your time off school / work / sports.
– Allow at least few weeks after surgery before considering a holiday.