Hi. I am assuming it's for your Son. Thank you for the question. It is not very clear here as to which part is hurt and which ligament might have been compromised. I am just stating in general, your son is 17 so chances of recovery is great if correct rehabilitation program starts for him soon.
Ligament injuries are of 3 grades depending on the impact and extent. Grade 1 & 2 can be treated well with rest, support and Physiotherapy. Grade 3 may need surgical repair. So first get a proper diagnosis done. If needed than MRI can confirm the injury. If you need further help, please feel free to write.