Osteoarthritis has been classified into two types according to the causes and risk factors that lead to its development.
- Primary osteoarthritis, which has no apparent cause but is related to ageing. It is the most common type of osteoarthritis.
- Secondary osteoarthritis, which has several underlying causes.
Primary osteoarthritis causes and pathophysiology
Primary osteoarthritis occurs in persons of advanced age though age cannot be considered as the cause of this type of osteoarthritis. Primary osteoarthritis more commonly affects the knee but can be seen developing in other joints also.
What happens here is that, as age progresses, the cartilage in the joint affected loses water and its protein content and becomes less flexible.
Therefore, it is not able to perform the function of acting as a cushion between the two bones of the joint.
With movements, the cartilage begins to degenerate at places and the osteoarthritis worsens over time.
When you exercise the joint, the two bones grate against each other under friction.
With repetitions, spurs or osteophytes form on the surface of the bones. This can be quite painful.
Eventually, in advanced cases of OA, there is complete loss of cartilage material and the two bones of the joint touch and rub against each other.
Causes and risk factors of secondary osteoarthritis
Secondary arthritis develops due to certain causes and there are risk factors that increase your chances of developing osteoarthritis. These are the causes that change the microstructure of the joint cartilage.
- Hereditary traits: Studies show that OA does tend to run in families.
- Obesity is a very common cause of osteoarthritis and is due to the stress on the knee or hip joints by the excess weight of the body.
- Endocrine disorders such as acromegaly, hypothyroidism, and hyperparathyroidism can promote the development of osteoarthritis.
- Diabetes causes osteoarthritis. This is due to associated conditions of diabetes such as obesity, atherosclerosis where blood supply to the joint is reduced, and diabetic neuropathy.
- Trauma to the joint, if severe, can cause the osteoarthritis, which progresses rapidly. Example of such a trauma will be injury to the joint such as due to a fall or an accident causing the bone to break, or causing the bones to lose proper alignment, and lose stability, or damage to the cartilage and menisci.
- Surgical complications due to surgery of the joint can predispose to osteoarthritis.
- Gout wherein high uric acid levels cause degeneration of the cartilage
- Congenital deformity of the joint or a congenital deformity can cause osteoarthritis. For example a deformity, which has resulted in the unequal length of the two lower limbs causing more weight to be borne by the hip/knee of the shorter limb.
- Metabolic defects such as hemochromatosis and Wilson disease can cause osteoarthritis (excess of copper in the liver).
- In certain bleeding disorders, there is necrosis of the blood vessels, which leads to internal bleeding. If such bleeding occurs in a joint, OA can set in.
- Infection of the joint can give rise to post-infectious osteoarthritis.
- Occupational causes of osteoarthritis result over time where a particular occupation causes extra stress on a particular joint by repetitive movements resulting in its overuse.
- Certain disorders alter the inherent structure and function of the cartilage such as rheumatoid arthritis, gout, and chondrocalcinosis.