Calibby,
You are not actually missing a knuckle, it is just not in the correct place. The picture of your right hand from the dorsal aspect (the back of the hand) tells the story. You have a short fourth metacarpal. It looks like the phalanges (finger bones) are actually all of the correct length.
If you look at the position of the MCPJs (metacarpal phalangeal joints) across the dorsum of the hand, you will notice that the Ring Finger (RF) MCPJ is more proximal (towards the elbow) than the rest. The MCPJs are marked by the dimple when the hand is flat and the big knuckles when you make a fist.
The reason you are having pain, is most likely because the short metacarpal is putting stress across the adjacent MCPJs. There are stout ligaments that connect the metacarpal heads together (the transverse metacarpal ligaments). Also there are several muscles within the hand, which produce the complex, fine motions of the fingers (writing, manipulating small objects like screws, nuts, beads, pins, etc. These muscles and their tendons are now out of balance.
So, for some reason, when you were young, the RF metacarpal stopped growing or grew a lot slower than the other metacarpals. The most common cause is damage to the growth plate in the metacarpal. It does not take a significant injury to cause enough damage for the growth plate to fuse too soon.
When you were younger, the surgery that was proposed was most likely a bone graft to lengthen the metacarpal. This is more difficult than it sounds. You can't just lengthen the bone willy-nilly, especially now that you have grown up, because the bone is not the only thing that is short, as the muscles, tendons, nerves, and blood vessels are also shortened. If you just stretch out the bone, the muscles and tendons will no longer be at the proper tension and may not move the finger joints correctly. The nerves are very, very touchy. Stretching them just a little can lead to total malfunction, where the nerve just quits working. You would then lose sensation and some motor function.
One thing that is not done in the hand is cosmetic surgery. Hand surgeons will not compromise function just for appearance.
But, there are some things that can be done, some options are better than others. As to which procedure is chosen, depends upon many things, such as what type of activities will be required of the hand in the future. For example, the demands of a professional musician are different from those of a manual laborer.
The ringer finger can be removed, by what is called a ray resection. This is where the whole ringer finger, metacarpal and all, is removed and the small finger is moved over to close down the space left by the ring finger. This is a very successful operation and is done quite often after trauma or tumor resection. It has the advantage of returning the patient to full activity (activities of daily living, employment, recreational activities, etc) very quickly. It has a proven track record with few complications.
Another procedure would be a distraction lengthening of the metacarpal. Here, an external fixator is placed on the metacarpal and it is cut in half. Then, very slowly, the two fragments of the bone are distracted (pulled apart). Since this is done very slowly (over weeks), the soft tissues have time to also lengthen. As the bone is separated, it actually lays down new bone in the gap, thus it essentially "grows" in length. This is a more complex procedure, but it is done fairly regularly. It does have a much higher risk and complications rate. Some problems include nerve dysfunction, pin track infection, breakage of the hardware, and the bone not healing properly.
You need to see a hand surgeon, so that a proper examination can be done. X-rays, and other studies as needed, are performed to determine exactly what the problem is. Then, you and the surgeon can discuss what your options are.
Good luck.
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