There are several types of arthritis that may affect the knee joint.
Although each can end up with a similar amount of joint destruction and result in total knee replacement, they may have different causes and onsets and the early progression of each type of arthritis may be different.
Osteoarthritis of the knee
Osteoarthritis of the knee can be considered related to wear and tear or sometimes an injury. Often it is triggered by a mechanical focus, such as a kneecap which does not track properly - this triggers a sequence of local inflammation and joint surface softening, then local joint surface destruction accompanied by release of chemical substances into the injured joint, which then in turn sets off a destructive process in the joint as a whole.
In contrast with some of the other types of knee arthritis the joint destruction may start in one knee without other joints necessarily being affected, and the arthritic pain is not generally accompanied by feelings of unwellness.
Rheumatoid arthritis of the knee
Rheumatoid arthritis is quite a different disorder from osteoarthritis. There are, in fact, a number of different variants of rheumatoid arthritis but they share common traits - the arthritis tends to come on in several joints at a time, and be associated with a feeling of unwellness - even feverishness. The distribution often includes the hand, often the knuckles. Blood tests reveal specific 'rheumatoid' factors. Rheumatoid arthritis is considered an 'auto-immune' disease - that is the body attacking its own tissues - rather than a 'wear-and-tear' disorder.
Gouty arthritis of the knee
Gouty arthritis is a form of joint damage initiated by the presence of crystals in the joint. It is a 'metabolic' disease, that is there is a faulty chemical pathway which leads to the crystal production. The distribution often includes the big toes at the joint where the toe joins the foot (metatarso-phalangeal joint).
In this form of arthritis, extreme pain and severe inflammation tend to come on suddenly - and this is frequently related to dietary indiscretion.
Infective arthritis of the knee
Several infections of the joint can give rise to joint destruction. The two which come immediately to mind are gonorrhoea (a sexually transmitted disease) and tuberculosis (TB). This kind of arthritis is relatively uncommon in western countries, but always needs to be considered when investigating destructive changes in a single joint.