They are separate injuries. It is possible it was strained or weaken 20 some years ago. Once tendons, ligaments etc get twisted, stretched, sprained, they never heal quite the same. So it may have had slight damage from before.. and then when you twisted your knee, you then tore it. (because it was never as strong as if you had no prior knee problem) So in one aspect, they are not related.. in another aspect they are.
Hope this makes sense and helps, If you need anything else please feel free to ask. If you found this helpful don’t forget to click the *accept* button
