I had my left thumb fused in 2003 - the middle (MCP) joint. I was having horrible instability and dislocations just doing very simple things and movements and due to the complex nature of my condition, fusion was the only way forward.
I had the surgery done under general and as a day case. They created an S shaped incision, exposing the joint, then they removed the surfaces of the ends of the two bones that create the MCP joint, to encourage new bone to form and make one long solid bone. To stabilise it during the healing and fusion process, in my case they used two wires (called K wires) inserted through the joint to pull it together and keep it still as it healed. In some cases they will use bone grafts or metal plates though, depending on the surgeon and situation.
They used dissolvable stitches on the wound, then I was then placed into a very large and heavy POP cast, that weighed a tonne and hurt my shoulder. It was quite painful afterwards, but on the whole was bearable with medication, rest and elevation .The original cast stayed on for 2 weeks until I returned to clinic for x-rays and wound checks. The K wires protrude through the skin, so if they are used don't be too alarmed when you see your thumb out of cast! After checking wire positions etc I was then placed into a large fibre glass cast, which was much lighter and manageable. I was in that for another 10 weeks, then returned to have the wires removed.
This was done in clinic, with the OS just pulling them out. because I don't react to local anaesthetics, it was done without, but in most cases they will offer you some numbing agent first if you require it. To be honest it wasn't that painful, just unpleasant more than anything. It was very sore afterwards and bled quite a bit from the wire entry wounds, but again it was manageable. I was then placed into a removable, rigid plastic splint for another few months, before gradually weaning off as the bone fully fused.
The surgery certainly solved the problem with the joint dislocating as it's perfectly solid and stable now, so in that sense it was a success. However, as with any fusion surgery, the knock on effects for the surrounding joints is always an issue, and I've found that the remaining joints are looser now, although not as bad as the original problem thankfully. As for loss of mobility, I have found my hypermobility has helped me adapt very easily and I haven't really lost that much ability to do things. I can still grip and hold things just fine, it just takes time to develop and adjust to. I have actually since also had my entire wrist joint fused on that arm too, and still manage to cope quite well with most tasks.
Basically, my thumb fusion was a success and if given the option all over again knowing what I do now, yes I would do it again. Having said that though, there are draw backs that must be considered and addressed fully before going ahead and to be perfectly honest, I would recommend that any fusion surgery in HMS or related hypermobility conditions is a very last resort. I am in a difficult position of knowing due to my situation and complex issues, that fusions are largely my only option and face several more in years to come sadly. But please, if anyone is considering a fusion surgery make sure you have exhausted every other option first, as they are brutal, invasive operations, with long, painful rehabs and a very definite, final outcome that can't be undone. If it really is your last resort, I would recommend that you spend a few months wearing a very rigid splint that totally immobilises your joint to give you an indication of how and if you will cope.
I hope that helps and your surgery goes well. If you have any more questions please feel free to ask or PM me.
Best wishes........Jo x