Don't discount the effects of some time off--my guy just finished about 5 months of carefully planned rest for a stifle injury (his was an acute injury and not bilateral, however). It was NOT, however, stall rest. The first couple of months were no riding, but turnout in a paddock with a long, gentle hill with a quiet buddy. From there, we moved to handwalking on hills and a little lunging, and then walking under saddle on the hills. From there, we gradually added a little trot work. He just last week got clearance to go back to flatwork with no restrictions, and he will slowly be brought back to fitness in dressage (with long warmups/cooldowns of more hill walking!) and then, if all goes well, jumping. The vet said there was no reason he can't do some low-level horse trials this fall. He is (knock on wood) sound and happy to be back in work!
So, while as a rider, a long time off sucks, it can help if it's the right kind of time off, which, in the case of my horse was never stall rest and planned rehab. For some horses, that will be different, of course, depending on the injury.
This is from back in November. We had only had him about 6 months at that time.
It's nearly impossible to tell if a horse is neurological or where they might be lame from a riding video. He's not forward and dragging his hind legs, not really articulating his joints or pushing off. It could be neuro, could be lameness. Many neurological horses are "10 movers" under saddle. You would need to have him seen by someone who knows how to properly test for neurological deficits as well as can do a comprehensive lameness evaluation.