During old age, the joints become weak, as the loss of bone and its associated structure occurs at a higher rate than its formation.
Osteoarthritis is a condition, in which the protective cartilage present on the end of the bones are degraded or wear down over a period of time. The condition of osteoarthritis result in pain, inflammation and stiffness of the joints.
Hence, in this case, Helen is suffering from the condition of osteoarthritis, which occurs normally in old age.
