Find out what happens to your joints in osteoarthritis, one of the most common forms of arthritis.

Osteoarthritis most commonly affects the hands, neck, lower back, knees and hips.

A joint is where 2 or more bones meet. The ends of the bones are covered by a hard slippery substance called cartilage. Cartilage acts as a ‘shock absorber’ and allows the bones it covers to glide over each other smoothly.

Osteoarthritis used to be blamed on simple wear and tear of the joints. We now know the process is more complex. The structure and composition of the cartilage change at a microscopic level so that it becomes less resilient.

The cartilage becomes roughened and pitted. It thins and develops tiny cracks. This process deprives the bones of their normal cushioning. They respond by becoming denser just below the cartilage.

The body tries to repair the damage, but the cartilage is broken down faster than it can build up. In severe cases, cartilage completely disappears in some places. This puts the bones in direct contact with each other with no cartilage to absorb the pressure.

A defective repair process can cause bone overgrowth (bone spurs or osteophytes) at the ends of the joint. The bone can also form cysts or develop tiny fractures.

Pain in osteoarthritis can be caused by:

  • pieces of bone or cartilage breaking off and floating inside the synovial cavity;
  • inflammation of the synovial membrane;
  • pressure on the soft tissues around the joints; and
  • increased pressure and tiny fractures in the bones.

Osteoarthritis affects people in different ways. Some people have very few symptoms while others experience considerable pain and disability.

Osteoarthritis of the knee joint

In osteoarthritis of the knee joint, these processes result in reduced protective cartilage, a narrowing of the joint space, and sometimes bone spurs.

osteoarthritis of knee diagram


Osteoarthritis of the spine

In osteoarthritis of the spine, the disks between the vertebrae of the neck or lower back become narrowed. Bone spurs (projections that form along edges of bone) may occur. The bone spurs may be painless, but sometimes they can pinch the nerve roots in your spine, causing weakness in an arm or leg.

osteoarthritis of the spine diagram


Osteoarthritis of the hip joint

In osteoarthritis of the hip joint, the cartilage gradually wears away decreasing the joint space between the bones. Bone spurs may also occur in the hip joint.

osteoarthritis of hip joint


Last Reviewed: 11/06/2010



1. Osteoarthritis: introduction [revised March 2006]. In: eTG complete [Internet]. Melbourne: Therapeutic Guidelines Limited; 2010 Mar (Accessed 2010 Jun 17.)
2. Arthritis Australia [website]. Osteoarthritis (updated 2010, Apr). Available at: (accessed 2010, Jun 17)
3. National Institute of Arthritis and Musculoskeletal and Skin Disorders [website]. Osteoarthritis (updated 2006, May). Available at: (accessed 2010, Jun 17)