However the arthritic process in the knee is triggered, the destruction tends to follow a common pathway.
The common kind of arthritis in the knee is 'osteoarthritis', not the crippling sort of arthritis called 'rheumatoid' arthritis. Osteoarthritis in the knee may have several triggers. Often it is triggered by a mechanical problem setting off a sequence of local inflammation and joint surface softening, followed by local joint surface destruction accompanied by release of chemical substances into the injured joint, which then in turn sets off a greater destructive process in the joint as a whole.
Note that osteoarthritis of the knee can arise without a mechanical trigger, but our point is that it is very often the end result of long term problems in the knee - a torn meniscus, a maltracking patella, a fracture, or even inappropriate or over-enthusiastic surgery!