The is the last joint of your finger, just before the nail. In osteoarthritis, hard bony lumps called can form there, and the joint can ache, stiffen or start to lean sideways. How finger arthritis is diagnosed and treated without surgery is covered in the guide to finger osteoarthritis. This guide explains fusion of the end joint, also called : when it is considered, what it can give you and what it takes away.

What is a joint fusion?

During the operation, the surgeon removes the worn cartilage from both sides of the joint, for example through a cut on the back of the finger1. The two bones are then held firmly together until they heal into one bone. The fused joint no longer moves, so the pain that came with movement usually eases. A review of the published studies describes the operation as an effective way for many people to get a stable, pain-free joint2.
Only the end joint is fused. The middle joint of the finger and the knuckle are not fused, so your finger may still bend at those joints, but not at the fused joint. Arthritis of the middle finger joint is a separate topic with its own guide.

When is fusion considered?

Fusion is often the last step in treating severe pain from finger arthritis3. It is usually considered when pain carries on despite treatment without surgery. A joint that is unstable, so the fingertip slips sideways when you pinch, or a joint that has become deformed, can also be reasons45.
The review behind the European recommendations found no trial comparing surgery with non-surgical care for hand osteoarthritis6. So the decision rests on how much the pain or instability bothers you, what you need your hand for, and what you hope to gain. The European recommendations stress that treatment is tailored to the person and decided together with them7.
The main aim of fusion is less pain and a stable joint. It can also straighten a deformed finger, but it cannot promise a particular appearance38. A soft lump beside the nail fold is usually a mucous cyst, which is covered in the guide to ganglion cysts.

What are the alternatives?

More non-surgical treatment

Joint protection, splints, medicines and injections can ease symptoms. The guide to finger osteoarthritis explains them. If your pain is bearable, there is no need to hurry into surgery.

Joint replacement

Instead of a fusion, a small silicone joint replacement can sometimes be used. It keeps some movement. A review pooled seven studies covering 269 fingers. On average, movement at the joint went from 24° to 36°, 97.7% of people were satisfied, and the re-operation rate was 7.1%9. The authors point out that there are few studies and they are of low quality9.
One study compared the two operations an average of 4.4 years later. Joints with a replacement had an average range of movement of 28°, and pain was low in both groups8. But 21% of replaced joints and 15% of fused joints needed another operation. People with a replacement were also less happy with how the finger looked8. The authors suggest a replacement for people with higher demands on their hands whose joint is stable before surgery. They suggest fusion for an unstable joint, or when the look of the hand matters most8.

Cutting the joint's nerves

Another option is to cut the small nerve branches that supply the joint, called denervation, sometimes with trimming of the bony lumps. It keeps movement, but the evidence is weak. A review of denervation for hand arthritis could not draw any conclusions about whether it works, and side effects, mostly changes in feeling, were common10. A newer series of 27 joints in 11 people reported less pain, but it is one small study without a comparison group11.

What fusion gives and what it takes away

Pain

The main aim is less pain. In a series of 54 fingers with advanced arthritis, average pain fell from 5 to 0.47 on a scale of 0 to 1012. In another series of 102 fingers, people were fully satisfied in 89 cases and satisfied in 913. An average of 4.4 years after fusion, pain was scored at 0.6 out of 108.
These results come from case series, not from trials where people were allocated by chance. They show the results in the groups studied, but they cannot promise the same result for you.

Movement and grip

Movement in the fused joint is lost for good, and you should not expect to get it back. What matters is how much that loss will get in the way of your daily life.
Researchers have studied this by fitting healthy volunteers with splints that hold the end joint still. Grip strength fell more the closer the splinted finger was to the little finger: by 12% for the index finger, 18% for the middle, 24% for the ring and 25% for the little finger14. In another study, splinting the ring finger's end joint lowered grip by a median of 1.67 kg. Only 10 in 100 people lost more strength than the threshold the researchers judged important for hand function15. These were short tests in healthy people, not measurements after surgery.

Everyday tasks

In a dexterity test of placing small pegs, splinting the index finger got in the way more than splinting the middle finger16. Before you decide, think about what you use that finger for. It might be picking up small objects, typing or playing an instrument. Talk this through with your surgeon.
Studies use a splint that holds the joint straight to copy the effect of a fusion14. You could ask your surgeon whether a similar trial before surgery makes sense for you. It cannot predict the result of the operation.

What position will the finger be fused in?

Before surgery, you and your surgeon agree the position the joint will heal in: straight or slightly bent. There is no single right angle for everyone. Data on how the fusion angle affects the use of the hand are limited1716. In a small study of 6 people with a simulated fusion, the angle changed how the index finger moved and how hard some of them could grip17.
In a study of 46 healthy volunteers, splinting the index finger's end joint bent at 20° gave better dexterity and a stronger grip than holding it straight16. For the middle finger, no difference was found in the tests used. The authors suggest that other things, such as appearance, can guide the choice for that finger16.
The fixing method matters too. A screw passed along the bone limits how much the joint can be bent2. The final position depends on which finger it is, what you use your hand for, how much appearance matters to you and the shape of your bones. Discuss it before the operation.

How are the bones held together?

The bones must be kept still until they have joined. The most common methods are fine wires (Kirschner wires), a small screw without a head that sits inside the bone, and a loop of wire2. The screw is buried completely in the bone4. In several of the described techniques it is a cannulated screw, passed over a thin guide wire118.
There is no strong evidence that one method is best for everyone. In a review of the studies, screws were linked with more bones healing, but also with problems not seen with other methods. The screw can be as wide as the joint itself, or wider2. In a study of 149 fusions of finger end joints and thumb joints, the complication rate after wires and after screws was not significantly different3. But the screw group was small: 13 joints, against 136 treated with wires3.
Wires are taken out after a while. In a large series, taking them out too early was one of the things that stopped the bones joining19. A screw usually stays in for good, although a screw that sticks out can mean another small operation13. The choice of method depends partly on the size of the bones and the planned angle2.

Bone healing and risks

When the bones do not join

Most published series also include the thumb's end joint, and causes other than osteoarthritis. In selected series, the bones joined in 89 to 100 of every 100 fingers1220513. When the bones do not join, this is called a , and it is not always painful. In one series of 181 fusions, the bones did not join in 21. Thirteen of these were pain-free, and in 6 cases the bones joined after a second operation19. A painful non-union may need another operation5.

Other complications

Complications are not rare, and how often they happen depends on how each study counted them. In an older series, major problems happened in 20% of joints. These were non-union, healing in a poor position, deep infection and bone infection. Minor problems happened in 16%19. In the newer study of 149 fusions mentioned above, 35% had a complication, most often infection (25%), diagnosed from signs and treated with antibiotics, and of varying severity. Diabetes and the surgeon's experience were both linked with complications3. In another series, 9% of fingers had a complication20.
In that series, less serious problems included skin breakdown on the back of the finger, sensitivity to cold and stiffness of the middle finger joint. Tingling, a shallow wound infection and metalwork that can be felt were also listed19. In one series, 7.4% of fingers became sensitive to cold12. A screw can also damage the nail bed. This happened in 3 of 27 fingers in one series4, while other series saw no nail changes1320.
Your own risk depends on your health, your skin and bone, and the fixing method. Ask about it before the operation.

Recovery

Bone healing usually takes from several weeks to a few months. In two series, the bones joined after an average of 9.7 and 11 weeks211. For some people it took up to 30 weeks1.
Until the bones have joined, the joint is usually protected with a splint or dressing. How long depends on the method. One description of a screw technique used a splint reaching the middle joint for 4 weeks. Full use of the hand was allowed after 6 weeks18. This is not a rule for everyone; your team decides when you can load the hand more. A screw buried in the bone makes it easier to start moving the finger early4.
During this time, keep moving the middle joint and the knuckles as your team advises, so they do not stiffen. Stiffness of the middle joint is one of the reported complications19. A can teach you the exercises. When you return to work and heavier tasks depends on your job and the fixing method. When you can drive again is decided individually, once you can hold the steering wheel firmly without distracting pain. General advice on the weeks after surgery is in the guide to recovering after hand surgery.

When to seek help

If your finger becomes cold, pale or blue, or numbness is quickly getting worse, contact your surgical team straight away. If you cannot get help quickly, go to your nearest emergency department.
For other problems after the operation, contact your surgical team or your GP promptly if you notice:
  • increasing redness, swelling, warmth or pain in the finger, fluid leaking from the wound, or a fever;
  • redness or oozing around a wire coming out of the skin;
  • a wire, dressing or splint that has moved, especially if the finger has changed position;
  • pain that comes back or gets worse after it had settled.
If you have diabetes, keep a close eye on the wound, because diabetes was linked with more complications in one study3.