Hey man thank you. Sorry for the delay in responding. Right here is a summation, which would be obvious to anyone with a background in foot and ankle disorders or rheumatology.
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>Hurr durr the PM photos don't show it.
His right foot is literally worse than the example I've posted below.
Ok, so here is a pic of MH tentatively checking out his right foot.
View attachment 264059
Now, we can't see the foot here unloaded, i.e. similar to the PM photos where he is on his back and not weightbearing. But even here (if we discount the fact that he clearly looks like he's inspecting it) the "big toe" and the bone (metatarsal) look relatively fine.
In contrast, if you haven't seen them, his post mortem photo of his right foot, the same as above (and I am more than willing to send the one in question if allowed and by request) looks almost identical to this...
If you notice, the "big toe" here, is noticeably riding on a lower "level" than the rest of the toes.
View attachment 264063
For context, this is the pic I clipped this from. It's from the radiological report of a rheumatoid arthritis patient.
https://ars.els-cdn.com/content/image/1-s2.0-S187705681630189X-gr9.jpg
This is his right hand obviously, when in Georgia just after he'd bought his new camping gear. Note middle finger. Not normal by an stretch of any imagination when under load i.e. he's holding something.
View attachment 264060
And here's his left...
View attachment 264062
Note the deviation of the far joint of the index finger.
Here's a comparison pic from the NHS website here in the UK for Psoriatic arthritis joint destruction. Rheumatoid left unchecked is similar however.
Psoriatic arthritis
Now if we compare the timeline from the very first pic, where he's looking at his right foot, to the PM photo, that shows a marked increase in the amount his 1st MTPj has dropped. Within just over a year basically. The degree to which his foot had deformed (actually worse than the photo I posted above) would have made even putting his foot to the floor excruciating, let alone walking and let alone walking with weight.
My take on his ability to endure the hike was that MH was probably fairly recently diagnosed or had just begun to experience the symptoms of whatever auto-immune arthritis he was suffering from. I believe, as evidenced by his blood results, that he was basically living on ibuprofen and whatever other analgesics.
It's my firm belief (having studied his notes extensively over the last few weeks) that MH simply found the diagnosis/advance of the condition too much to deal with, given he was clearly someone who very much liked to be in control to quite an extreme degree. Also, psoriatic or rheumatoid arthritis would very much have started to impede on his ability to use a computer mouse.
In regards to whether the hike caused it, this is an excellent question. This would take us away from the realms of auto-immune arthritis and into mechanical damage. Repeated heavy trauma can cause the foot deformity he had.
If he didn't have the finger joints as per Georgia photo, I would be tempted to err with that, and still don't discount it. The point still remains however, the destruction Mostly Harmless had in his foot joint would have been disabling.
Again, I am more than happy to send the PM photo of his foot, for people to compare.
Hope this helps folks!