Our daughter had this surgery in 2018, and it took a little over 6 months total rehab to get back to where she as before the injury (JO Level 10 gymnast). That was PT 3x/week and meeting with her surgeon 1x/month to evaluate (after seeing surgeon every 2 weeks for first two months post op).
Not sure if your son’s surgeon is planning to harvest from your son’s hamstring or if they are planning on using cadaver donation. DD’s hamstring was in very good shape so they harvested from that; she had friends who had same procedure with cadaver donation that ultimately failed, and needed to be redone.
Surgeon offered a pain port to be inserted at the hip during the surgery for post-op recovery/pain management. Because of the fact that sport rehab was going to start the same week, we choose to not have pain port inserted and she took oral prescription pain killers the first two nights (to ensure good sleep) but nothing but OTC pain relief past that point.
The surgeon won’t know the true scope of the surgurical needs before going in. DD had massive scarring buildup that had caused her patella to be permanently shifted that needed to be remediated as well as rebuilding the MPFL. She has 3 total scars, each one about 1 1/2" - 2" in length. Scars took about 18 months to heal/fade as completely as they were going to. Mederma scar gel (and liberal sunscreen) was recommended to be used once the stitches were removed/the wounds were fully closed.
For the first two weeks, in addition to the brace keeping her leg fully straight/locked, she had a cooling system that wrapped around her knee to keep swelling down and promote healing. It was basically a plastic box that we filled with ice and water that connected to a series of tubes in velour wrapping and a motor that pushed the water through the tubes to constantly cool the knee area. If your surgeon uses that, they will give it to you at the hospital after the surgery and instruct on its use. Really a pretty awesome system, we still have it and she continued to use it for post practice recovery on other minor injuries.
DD was basically completely prone and only got up to use the bathroom the first week of recovery. At the end of the week was her first post-op visit to her PT, that was an evaluation of healing and light massage to work with the swelling, even with the cooling system. Also used some leg squeezer contraptions that fit from hip to toes (both legs) and provided gentle pressure to promote good circulation during the early PT sessions.
Second week she was able to move around a bit more though leg remained locked straight. She also began PT in earnest.
Post op, surgeon had locked leg braced and didn’t unlock the brace until I think the 6 - 8 week mark. He then only ‘unlocked’ the brace for a very reduce amount of flex (30 degrees or so total I think). It took 3 1/2 months for DD to really relearn to walk ‘normally’, then another 6 weeks or so of learning to run on it in a very systematic fashion. Last couple of rehabs months was ensuring all the prep work was complete to really start stress testing the knee again.
It is a hard injury, but if your son was in good physical shape before the injury, rehab will be smoother. Hardest part for our daughter was learning to trust that her knee would hold up even after completing rehab and being told by her surgeon that her knee was stronger than it had been before the injury.