Hey buddy, I have dealt with a bad knee most of my life, due to a PCL breakage and rebuild many years ago... I've never let this weakness stop me from pursuing what I like most in life: extreme sports, especially board sports

I've written several posts in this and other forums looking for technical solutions such as TT and surfboards types, down to foot pads quality and vibration / shock absorption.
The only way to ride for me is with my weak knee at the front (back leg being the strong one). I snowboard, skateboard, surf and kite this way, and my sessions seem to be the longest either on the beach or mountain

. This is because you always charge with your weight your back leg, especially on landings..
TTs are generally bad for knees due the high vibrations and the non-hydrodynamic edge profile: tt are square boards which are dragged at an angle unlike surfboards: are boats shaped like TTs or surfboards..

? Despite that, you can drastically improve things with a good freeride / all-terrain board and some comfy footpads. After testing several boards and pads I've finally found my luck on the Wainman Blunt, as it gives you an amazingly smooth ride even in chop / onshore mush / white water breaks, with no spray and incredibly soft landings. This board actually gave me the confidence not only of jumping, but even going hiGH! (I've never thought even to be able to jump with my weak knee).
Strapped surfboards

can be much worse than TTs due to the high vibrations and stiffness of the deck

. I go strapless most of the times and love it

. As a freerider I love the 'feel free' feeling of riding strapelss, you'll know if / when you've tried it. This is possibly the best ride for your knees, there is literally no twist on your feet / legs as they are entirely free from the board. The vibrations are still there though and I'm working on how to reduce them

Surfboards are stiff and kite-surfboards even stiffer.
I strongly advise an hinged knee brace, as it will help to prevent twisting / stretching of the knee.
I always ride with a neoprene hinged knee support, just to have that extra comfort and peace of mind and it also slow down my knee tiredness after hours of riding

!
Get yourself a good specialist and physiotherapist, it will be a good investment

I wish you all the best, and hope that this might help you.