Is this possible? I have a complex injury near one knee, and part of it is in the shin. What would this indicate about a mechanical or fit problem?

I know, "see a doctor". I have seen a parade of doctors, it's finding a really good one that's the problem.

It would seem pretty odd to be caused initially from cycling. It is usually an overuse injury caused by running or jumping. I'd be willing to bet however cycling could exacerbate the situation if you had the injury before starting to ride.

If it's shin splints, you could get it from horrible cycling mechanics. The tibialis anterior dorsiflexes (pulls up) your foot. If the muscle it under too much load while it contracts, an eccentric contraction results. These contractions are responsible for much of muscle soreness. If you are using toe straps, I could see it happening if your foot was not far enough into them, and you pulled up with your foot. Soreness could also result from locking your ankles in a dorsiflexed position, which could plausibly happen if your seat were too low.This would put a large torque across your ankle while you were contracting the tibialis anterior. The same thing happens to beginning runners who land hard on their heels.
Both of these possibilities would be obvious to an experienced
I don't mean to imply this is your problem, but I'm sure it has happened before.

I think I'm finally figuring out what happened. I was walking around quite a bit in my mountain bike shoes, due to traffic conditions forcing me off the bike or because I reached a nice destination and just wanted to linger and walk around. The unfitness of those shoes for walking, combined with my foot's tendency to overpronate, put forces into the shin which caused shin splints.

Biking then exacerbated the condition, but didn't directly cause it. There's an underlying imbalance in my left leg and I have to straighten that out or compensate for that. I'm in the process of seeing a podiatrist and it looks like another round of physical therapy.

I use toe clips but don't really pull up on them -- I just use them to keep my foot in a reasonably good place. I'm torn about going to clipless -- presumably they give you the best mechanics; yet, I've several times been injured by apparatus that locks you into a position.

I understand you being hesitant about going clipless, but I think that's just because you haven't gotten to know them. Most people would argue that they are actually safer than toe straps, as toe straps don't "give out" under any circumstance short of their ultimate strength. With clipless pedals, you can set them to have as much or little float (rotational movement) as you and your knees want.

I agree clipless pedales are a better and safer (imo) You need someone to help fit you to that bike and make sure you look off bike and on bike orthotic situations and if the doctor has no clue then you need to see someone who deals with cyclists. If you IM me your location I may be able to recommend someone I know.

Dr. Rosa