Osteoarthritis of the knee is a common age related condition that is due to general wear and tear that causes a gradual degeneration of the cartilage at the knee joint.

Symptoms include pain which worsens with activity and improves with rest, stiffness, crepitus (a crunching or grinding sensation when you move), and swelling.  

The knee may give way because muscles have become weak or the joint structure is less stable.  There may be a restriction of normal movement and the alignment of the knees may become more bowed or knock knee, and in severe cases may also result in a leg length discrepancy.

Osteoarthritis is most common in people in their late forties onwards, although it can also affect those at a younger age; it affects more women than men.  Common risk factors include being over-weight, previous injury to the knee joint, a family history, and those who do a hard repetitive activity or have a physically demanding job. 

Knee arthritis may also be caused by other conditions such as Rheumatoid Arthritis or Gout.