In our forearms we're supposed to have two bones. The kitty orthopedist said that Punkin is missing all or part of one of the bones, in each arm.
This is not something that is likely to be fixable. Months of uncomfortable treatment _might_ result in some improvement, but the vet recommends just letting Punkin be Punkin, keeping his nails trimmed for him, and periodically checking his arms for sores from how he runs on them. So that is the plan.