I ruined my left knee about 7 years ago - total ACL, total MCL, split meniscus, cracked femur. With a surf trip to Hawaii scheduled for 8 weeks later.
I ordered a ‘functional multiple instabilities’ brace online from DonJoy, it was about $300. I surfed with it, it was fine. I had ACL replacement surgery about a month later, 3 months post-injury. They wouldn’t do it any sooner, as the femur head had to be totally healed so they could drill & screw into it.
I hit the rehab hard & fast and was surfing & playing lacrosse again (in a brace) 6 months post-op. About 2 years post-op, no more brace needed. Yes, the brace dinged the hell out of the left rails of all my boards, but worth it.
Interestingly, I also was fitted for a custom, molded-leg, carbon fiber/titanium brace after surgery. My insurance co. paid for it ($3800 I think at the time). The DonJoy brace is better! It fits better, is lighter, the hinges are smoother, and it never rusted from saltwater exposure (unlike some of the washers & fittings on the expensive one). Its a tiny bit bulkier, but not problematically so - its the one I wore much more than the custom one.
My reconstruction was patellar tendon rather than allograft, cadaver donation, or hamstring tendon. Patellar tendon reconstructions can be more painful and produce more scar tissue - both mainly from the harvest site rather than the repair. But once healed, and if you really do your rehab well, they produce the tightest, most ‘normal’ feel afterwards. The other ones get results more quickly and with less rehab effort required, but end up with a looser repair and are more likely to fail again under severe strain.
My recommendation would be to ‘pre-hab’ as much as possible with lunges, bodyweight squats, ankle weights (for floor exercises, not walking or running) and resistance bands to strengthen all the muscles which will support your reconstructed knee. If you have the time & dedication to follow-through, get the patellar tendon reconstruction. And skip the fancy brace and get a DonJoy. Post-op, get a good stand for your bike, and a tv and watch surf videos in your garage while you ride every day. Don’t be tempted to ride outside - the risk of falling is seriously not worth it. I was on the bike, in the garage literally every single day for 6 months - I marked my calendar. That’s what it takes. Then lots of weights, heavy & light, and I took up Tai Chi too because the balancing, holding, & twisting are very good to get you ready to surf again.
7 years later, nothing is a problem. A little soreness sometimes, especially after a run. I’m a Crossfitter now and can even do the balistic movements & oly lifts without concern for the knee. And still play lacrosse. Compared to those, surfing is light duty. Good luck!