hmmm, Kind of a tricky one without seeing it. Based on what you've said I would think that he strained the MCP joint and it has since healed but slightly out of place. The Mulligan "positional fault". It's a theory bout would require mobilising the joint and strengthening, I would suggest you see a physio for guidance as it would be hard though not impossible for you to apply the glide while strengthening.

Pudding