What is the main characteristic of osteoarthritis?

The main characteristic of osteoarthritis is indeed related to inflammation of the joints, but it's important to clarify the context. Osteoarthritis is primarily a degenerative joint disease that results from the wear and tear of cartilage, leading to the breakdown of cartilage in the joints. This can cause an inflammatory response as the body attempts to repair the damaged tissue, resulting in pain, stiffness, and swelling in the affected joints.

In osteoarthritis, the inflammation is not as pronounced as in other types of arthritis, such as rheumatoid arthritis, but it does contribute significantly to the symptoms experienced by the patient. Therefore, while osteoarthritis is chiefly characterized by the degeneration of joint structures, the inflammatory component plays a key role in the disease process and affects the patient's quality of life.

The other options do not accurately represent the main characteristics of osteoarthritis. Bone tumor formation, increased bone density, and joint swelling due to infection do not pertain to the degenerative aspect of osteoarthritis but instead may relate to other conditions or diseases affecting the skeletal system or joint health.