Major knee problem

I got hit 45 years ago but a drunk at 85 in a big Merc., head on. What a thud! It shattered my kneecap cut two tendons clean into. It healed but it took a year before that leg would bend half way back. That leg is a little shorter than the other! Don't realize if till in the saddle, one stirrup is a hair shorter. Drove me nuts all these years. That probably had an effect on cartlidge in that knee.