You should be talking about local soft tissue injury and disuse atrophy of surrounding muscles caused by joint dislocation. If the bone thinning, atrophy or even osteonecrosis caused by poor blood circulation occurs after the reduction of the phalanx of the thumb, it should be considered, but this must be diagnosed by X-ray. I feel that you just feel it yourself, and you can't feel the true thickness of the bone outside, because the whole soft tissue is surrounded by X-rays, so I suggest you take an X-ray and compare it with your hands if necessary.