The reason why I had my most recent surgery and my earlier ones is that I have rapidly degenerating discs that began causing pain when I was a teenager. This surgery was my third spinal surgery. The first has a discectomy in my lower back - and turned out to be no help whatsoever. By four years later, that disc level plus an adjacent one had to be fused because my body had digested the remnants of the discs, and the vertebrae sat 'bone-on-bone' with no remaining discs between them.
The surgery that I had two weeks ago was a similar surgery but in my neck region. I've known for years that this surgery would eventually become unavoidable because my discs (the red layer between the vertebrae below) are disintegrating. Indeed, at the three disc levels where I had surgery, the discs were almost completely gone, leaving my vertebral bodies scraping against each other.
As a response to the instability of having almost no discs, my body started building bony spurs to try to hold the vertebrae stationary relative to each other. Those bony spurs pressed on the spinal cord (the thick yellow cord in the top middle of the picture) and on the nerves leaving the spinal cord.
This pressure was damaging the nerves and causing myriad symptoms, including pain in my neck and arms, muscle atrophy, and lack of sensation in my right hand.

After cleaning up all the errant disc material and bone spurs, the surgeon carefully levered open the space between the vertebrae and placed bone grafts in the spaces. The goal is that my body will build more bone around the grafts, fusing the vertebrae to each other. Thus, four vertebrae will become one long bone.
The problem is that, during healing, the spine must remain stable, with little bending or twisting. To aid with this part, the surgeon placed metal plates on the front of my vertebrae to hold them in place relative to each other. In the picture below, only two discs have been removed so the plates are not as extensive as in my case.

In my case, we had a very tough decision to make. In fact, four neck discs are disintegrated, including one (C3-4) that we ultimately decided to leave alone. The reason is that C3-4 can still move, so it protects the discs above it from degenerating even faster than they would if C3-4 were fused. As soon as a joint is fused, the discs just above and below it begin self-destructing at a faster rate because the joints undergo much more motion to make up for the fused section of the spine.
So, my surgeon and I know that C3-4 is causing me pain and will continue to do so. In all likelihood, it'll need to be fused in the next couple of years. But, for the sake of my long term prognosis, we decided to leave it alone for now, to protect the other discs. Our fear is that, in the next 40 years of my life expectancy, I'm heading toward a completely fused neck. That would be very bad - I'd have no head twisting or chin lifting ability. I'd lose my driver's license. I'd have a lot of trouble riding a bike, although I just might figure out a way to ride one!
Yesterday was my first checkup. I had several xrays as I moved my neck through its range of motion to see how the fusion is going. The goal is to see no motion at the fused joints. It's unlikely that will happen yet for me but I'm still awaiting the results.
Everyday for three months, I apply a plate-like apparatus to my neck so that it can bombard my joints with a magnetic field. Bone responds to magnetic fields by growing so this should help my body form stronger fusions. Another thing that causes bone to grow is stress so I'm required to walk miles every day. Each time my heel hits the ground, a shock wave travels up my spine and stimulates the bony fusions to grow stronger.
I still have substantial surgery-related pain. My head gets heavier as the day goes on, and the muscles holding it upright rebel. Moreover, it feels like one particular spot in my spine starts to hurt as the day goes on - I'm not sure what that means. On the good news side, the long-term right arm pain has only visited once since surgery. And, to my utter surprise, the pain in my leg is much less frequent than before surgery. I suspect that the pressure on my spinal cord in my neck was transmitting pain all the way down to my toes. Only time will tell if the improvement in leg pain is permanent.
In terms of the recovery, I've been given a huge range of possible time tables. I suspect that I'll be back on my bike outdoors, riding gingerly, sometime this spring but the exact time depends on how quickly my body heals.