Alfie, I think your assumption may well be correct as a couple of years ago I underwent consultation at Wrightington for my damaged ankle and a couple of options were explained to me as potential fixes for my issue.
Fusion of the joint (to relieve the kind of pain associated with arthritis normally), however this can eliminate flexibility/ motion within the ankle joint. (Not an option for me).
Bone Graft and Pinning of the joint which has sustained damage of some kind, usually restricting (at least), some flexibility of the joint. (What I had carried out).
Removal of the pertinent Ankle/Leg joint bones necessary to effect the repair required, with prosthetic replacements. which would entail extensive surgical procedures and lengthy recovery.
See Wrightington Link -
HERE
From reading the report, I would assume that it is option 3 that Hutchy has had carried out on his ankle/leg joint.
As indicated, I had option 2, but still suffer pain (to a much lesser degree thankfully), and I have lost a lot of flexibility/motion in the joint itself.
Malcolm