Partial wrist fusion

Partial wrist fusion is performed for painful, arthritic wrist conditions. Partial wrist fusion allows some of the wrist movement to be preserved, whereas a full wrist fusion prevents all wrist movements.

There are many different types of partial wrist fusions, which is not surprising when you consider that the large number of bones involved in the wrist joint (namely the radius, scaphoid, lunate, triquetrum, trapezium, trapezoid, capitate, hamate bones). The pattern of arthritis and degenerative change in your wrist will determine whether you are suitable for a partial wrist fusion and which bones should be fused. Broadly speaking, joints that are very arthritic need to be fused (or removed) and joints that are healthy can be left intact.

The upside of a partial wrist fusion is the preservation of movement. The downsides of a partial wrist fusion are 

• a prolonged recovery is involved, with at least 6 weeks in a cast, and 6-12 months before you are cleared for heavy lifting and contact sports
• the bones may fail to fuse. This is termed "non-union", because the bones fail to unite. The likelihood of non-union varies between the different types of fusions, but is 10-30%. The risk of non-union is higher in smokers and in patients who fail to adhere to the post operative period of immobilisation.
• incomplete relief of pain, because there is still some movement in the wrist
• a partial wrist fusion alters the wrist biomechanics, increasing the load on the remaining joints and increasing the risk of arthritis in the wrist joints that were not previously affected. If this occurs your wrist will become painful once more, and if your symptoms are severe a total wrist fusion may then be recommended.

To fuse bones it is necessary to remove the cartilage and joint space between the bones, so a surgical incision is required to gain access to the bones. Surgeons can use a variety of different ways to hold the bones together while  they fuse, including wires, staples, screws and plates. Usually bone graft will be used to increase the fusion rate. This bone is commonly taken from the wrist that is being operated on, but occasionally a graft from the hip bone (iliac crest bone graft) is used.

Your surgeon will be able to advise you on whether one of the following types of partial wrist fusions are suitable for you:

Types of partial wrist fusion

• Radiolunate arthrodesis (radiolunate fusion)

Radiolunate fusion is most commonly performed for rheumatoid arthritis.

• Scaphocapitate arthrodesis (scaphocapitate fusion)

Scaphocapitate fusion is most commonly performed for scaphoid instability, scaphoid non-union, Kienbock's disease and mid-carpal instability.

• Radioscapholunate arthrodesis (radioscapholunate fusion)

Radioscapholunate fusion is most commonly performed for arthritis resulting from distal radius intra-articular fractures, and in patients who have rheumatoid arthritis that has affected the proximal row of carpal bones (scaphoid, lunate, triquetrum) but spared the mid-carpal joint.

• Lunotriquetral arthrodesis (lunotriquetral fusion)

Lunotriquetral fusion is most commonly performed in patients who have an uncommon developmental condition where the lunate and triquetrum failed to form properly as separate bones. If this is painful then fusion of these two bones provides good relief.

• STT fusion (scaphotrapeziotrapezoidal fusion)

STT fusion is performed for osteoarthritis, often in the setting of scaphoid non-union, Kienbock's, scapho-lunate dissociation or midcarpal instability. This involves fusing three bones - the scaphoid, trapezium and trapezoid.

• Four corner fusion (fusion of the capitate, lunate, hamate and trapezium with scaphoid excision)

A four corner fusion is most commonly performed for conditions where the scaphoid bone is damaged and fails to heal. "SLAC wrist" is the condition of ScaphoLunate Advanced Collapse, while "SNAC" wrist is Scaphoid Non-Union Advanced Collapse. In this operation the scaphoid bone is removed and four of the remaining bones are fused. A 2 bone capitate-lunate fusion can be performed instead of a 4 bone fusion, but a 4 bone fusion is recommended because it provides the same movement outcomes with a lower risk of non-union.