Babies, thankfully, do not have arthritic big toe joints. I, unfortunately, do.
Would you suggest any crawling modality to accommodate?
I saw your post in the crawling log but it was just before getting ready for bed and I didn't have a good answer. Here is my two cents to this one:
Start with baby crawling with plantar-flexed feet (point your toes instead of curling them under your foot and crawl on hands and knees). Baby crawling might be made more intense by looping resistance bands around the wrists and/or dragging something, just like leopard crawling.
If baby crawling is not challenging enough, one alternative -for the upper body at least- is some kind of modified "plank walk." These are not really a one-to-one substitute for crawling, but combined with standing cross crawls and something like standing lunges you might be able to approximate all the movements.
Plank walks (I've never seen an official name for them) are a gymnastic exercise in which you drag your feet behind you with your arms. Place your feet or knees on top of something that will slide easily (frisbees, sliders, old socks, rags, etc). Now "walk" around using only your arms.
A full plank walk is like a plank, with full scapular protraction, posterior pelvic tilt and stiff core (the aim is to minimize side-to-side wiggle of the body), pulling oneself forward with straight arms. It's a little more awkward, but you can push with your arms to move backward as well. Modifications to work up to this (it's harder than it sounds) are pulling/pushing with two arms at a time and setting the knees down in-between pulls.