Arthritis, the word, is derived from "arthro" a word-root connoting joint and the suffix "itis" connoting inflammation. In general, then, arthritis is joint inflammation and it can have many causes.
Gout, a condition wherein a person has a high level of uric acid within the body due to a subtle kidney malfunction (kidneys excrete uric acid as a normal waste product and if they are awry then, of course, the uric acid serum level will rise). When the uric acid molecules reach a high enough concentration within the joint spaces, usually at cooler locations within the body such as feet, knees, and hands, the discrete molecules of uric acid undergo crystalization. The discrete crystals are immunologically determined to be "foreign" and the immune system responds normally and the patient involved experiences an inflammatory response with swelling, pain, redness and increased temperature of that part. Treatments are given to decrease the inflammatory response (colchicine, steroidal anti-inflammatories and non-steroidal anti-inflammatories and the arch-type of the latter is aspirin). Other treatments lower the level of uric acid and the most common one is allopurinal. Other medications attempt to aid the kidneys is secreting uric acid and thereby lower it's level within our bodies. At times a combination of the medications above are used. Other sterile inflammatory conditions are caused by calcium phyrophosphate crystal deposition in joints and the underlying cause is the same, I believe.
Traumatic arthritis could take place when a joint was severely strained or sprained and the internal damage to a joint would cause compensatory swelling, redness, heat, and pain as part of the healing process. A classic example of this would be a sprain to the ankle or the knee which was related to a physical over-stress in a sporting event such as skiing. Treatment is usually rest and occasionally surgery if a ligament or tendon is meaningfully torn.
An infection of a joint can cause a purulent arthritis. Micro-organisms can enter a joint via direct methods such as during a penetrating wound or rarely micro-organisms which circulate within our blood stream can manage to enter a joint space before our immune system destroys it. The treatment is rest and antibiotics and occasionally surgical drainage of the joint.
Most other types of arthritis are rheumatoid in nature. Rheumatoid arthritis is the visible arthritis which occurs with rheumatoid disease. The latter term should be used because it is truly an autoimmune disease of the total body and the main mechanism for total body spread is via a vasculitis. The endothelium of the bodies arteries, arterioles, capillaries, veins, and lymph vessels, even the heart itself are affected directly and made abnormal and thereafter the autoimmune factors can enter the body tissues and cause destructive effects, over time. The arthritis of lupus erythematosis, scleraderma, psoriasis, and the other rheumatic diseases, including osteo-arthritis are all really rheumatoid arthritis caused by rheumatoid disease. The classifications, above, simply try to organize those patients who have less or more rheumatoid disease with those with scleraderma having more physical findings and symptoms than those with rheumatoid arthritis and of course those with osteo-arthritis having less than those patients with clinical rheumatoid arthritis. Myositis, Dermatomyositis, and Wegener's granulomatoisis are likewise just more severe cases of rheumatoid disease. All the above feature vasculitis, neuropathy and arthritis and all are systemic in nature. The great variability in the condition is caused by: the time of onset in life, the intrinsic ability of various patients to immunologically defend themselves, the level of the autoimmune response to the stimulant, often thought to be a micro-organism, perhaps.
I have determined that the systemic condition appears predominantly in joints and synovial structures because the vasculitis is exacerbated by compression and abrasion (Triple Response of Lewis) so that patients who have rheumatoid disease have very red palms, knuckles, bottom of feet, chronically swollen joints with those of the hands, feet, jaws knees, hips,and wrists being prominent. All express meaningful dermographism, a general word for the intradermal inflammation created by scratching the skin with a mildly sharp object. Since the abrasion and compression of the arterioles, capillaries, and venules of the structures of the joints, including the intra-articular cartilages of the knees, wrists and jaws, causes more vascular inflammation and therefore capillary permeability, more auto-immunological factors enter those tissues and cause more obvious, observable damage over time. Trauma or over-use to a joint can cause increased problems for any joint and lead to joint damage and it may not appear clinically until a person is older. Joints that are weight bearing such as knees and hips feature such disturbances commonly and so total knees and total hips are common. The concept that osteo-arthritis is a separate disease is not true, but the other findings of rheumatoid disease are more subtle, but are present to the astute observer. Patients with what is termed osteo-arthritis often have subtle elevations C-reactive protein, for instance, the same inflammatory factor which is noted in all the other rheumatoid diseases.
I have determined that the cause of rheumatoid disease is the auto-inflammatory reaction triggered by Streptococcus pyogenes, a common bacteria, the one that causes strep throat, ear infections, bronchitis, pneumonia, tonsillitis, sinusitis and peridontal infections. Also, it can cause erysipilas, a soft tissue infection. Likewise it can cause rheumatic fever, scarlet fever, scarletina, and Streptococcal toxic shock syndrome, puerperal fever, impetigo, pyoderma (chronic skin infections), and potentially infections of any part of the body of humans and domestic animals. The organism is endemic in the human race and has truly evolved "with us" and the autoimmune response to the repeated infections, low grade, acute and chronic, and high grade, acute and chronic, cause, ultimately, rheumatoid disease and all of us have it with exacerbations and remissions during our lifetimes. The same autoimmune disease causes damage to the lining of blood vessels and it causes arteriosclerosis, over time and of course the most common organ in which that condition is noted is the heart. Both the above, rheumatoid disease and arteriosclerosis are caused by the autoimmune response to Streptococcus pyogenese infections. Rheumatoid disease causes many of the maladies of mankind (and our domestic animals)and the assault is chronic with exacerbations and remissions and results in many or most of the manifestations of aging! Gout, mentioned above, is caused by abnormal kidney function secondary to rheumatoid autoimmune vasculitis, so, ultimately, it and pseudo-gout are caused by the same underlying pathological condition.
I am writing a book on the condition mentioned above: "Rheumatism, Enigma Unraveled" and it should be available in 3 months from Amazon.com or via Trafford Publishing in Victoria, B.C.