I’m a retired senior Prosthetic Technician and have met a lot of people who have had a Syme amputation and made limbs for them. With what they intend doing to your son it means he should be able to weight bear on the distal, or end, of his stump. If he has a Below knee amputation it’s unlikely he’ll be able to weight bear on the distal end, so thats more or less the only difference. As far as prosthetics go, a below knee amputation opens the door to a lot more types of devices to enhance his mobility like dynamic feet or running legs or rotational devices, whereas a syme restricts these devices and the products on the market are very limited.
I’ve been an amputee for 48 years and have only a 5inch stump and very bony but I can ski, ride a bike, play Ice Hockey, play golf and walk the 18 holes, ride horses climb ladders etc. Most surgeons believe that the longer the stump the more control you have but I’ve been able to prove that completely wrong. If a prosthesis is well made there should never be a problem and with most amputees that is where the problems lie through ill fitting devices. Here in Australia technicians used to do a course at university to learn the special skills but unfortunately they stopped running the courses and now the techs have to learn as they go so the quality of workmanship and skills are slowly disappearing. New amputees are recieving ill fitting limbs and because they dont know any better they just accept what they’re given which is very sad.
Anyway, sorry about the rant, getting back to your son, his decision on what amputation to have should depend on what he wants to do with his life. If he wants to run in the paralympics he will run ten times faster as a below knee than a symes. If he wants to walk around in the shower the symes is better for weight bearing, otherwise he hops or gets a shower leg, like I have.
I hope i’ve helped with his decision which should never be made hastily because it’s permanant and any amputation is never a good thing we just try to deal with it in a good way.