Costly hip and knee replacements could be averted by giving patients a "breakthrough" drug costing less than STG1 ($A1.50) a day, trial results suggest.
The treatment is said to be the first to slow the progress of osteoarthritis (OA), the wear-and-tear disease that destroys joints.
Strontium ranelate, marketed as Protelos in the UK, is a powder that is mixed with water to make a lemon-flavoured drink.
It is already used to prevent fractures in post-menopausal women with the brittle bone disease osteoporosis.
The new findings, presented at the European Congress on Osteoporosis and Osteoarthritis (ECCEO) in Bordeaux, France, showed that Protelos reduced deterioration of knee joint cartilage in a group of OA patients by a third over three years.
It also led to a significant reduction in pain and improved day-to-day mobility.
An estimated 8.5 million people in the UK are affected by OA, which results in the gradual wearing away of cartilage and bone.
The painful and disabling condition is especially common in older people and associated with long-term degradation of the joints as well as mechanical injury.
Some "rapid progressors" are predisposed to the disease and more likely to develop symptoms.
Until now, pain management has been the only available treatment short of major surgery.
Many hip and knee replacements could be delayed or avoided by taking Protelos, the results suggest.
Trial lead investigator Professor Cyrus Cooper, from Oxford and Southampton universities, said: "This is a major breakthrough. Osteoarthritis is a painful and debilitating condition, and for over 20 years we have been searching for a treatment that would allow us to alter the course of the disease, rather than just manage the symptoms.
"The results today ... could totally change the way we treat osteoarthritis. For the first time we have a treatment that can slow the development of this debilitating disease and could reduce or even eliminate the need for expensive and painful joint replacement surgery."
The international Phase III trial involved 1,683 mostly female OA patients with an average age of 63. They were randomly treated with either 1g or 2g daily doses of Protelos, or an inactive placebo, and their condition checked at yearly intervals for up to three years.
The best results were seen with the 2g dose. For every three years of treatment, Protelos slowed progression of OA by an amount that would be expected in one year, the research showed.
Prof Cooper said the drug produced an almost 50 per cent reduction in the frequency of rapid progression. Patients who are rapid progressors have a five-fold increased risk of needing joint replacement.
"You would expect it might have an impact on joint replacement rates," said Prof Cooper.
It is thought the drug may exert an influence on stem cells that generate bone and cartilage.