Anterior distal tibeal physis is essentially the growth plate at the bottom of his shin but the front surface of it. The length in bones comes from this area growing while young and it will fuse as a late teen.
I'm a vet so all animal experience but I would certainly follow up. If he has damage to the growth plate that causes premature closure it may cause growth problems.
I'm sorry if this sounds scary (and I would find the idea scary if it was my kid) but I wanted to explain why I think you should check it out.