The disease, which affects more than five million people in the UK, is caused by the wear and tear of the smooth, hard cartilage tissue that covers the ends of bones allowing them to glide over one another at the joint.
Scientists have long known that cartilage gets its strength from interlocking millimetre-long collagen fibres that work in a similar way to the load-bearing steel rods in reinforced concrete.
But the precise structure of these fibres or 'fibrils' has remained a mystery for more than 40 years, so hindering any progress towards the development of potential therapies.
Now, a team from The University of Manchester has used sophisticated electron microscope techniques to uncover the molecular structure of the thinner of the two types of collagen fibrils.
Professor Karl Kadler, who led the research in the Faculty of Life Sciences, said: "The ability of cartilage to withstand cycles of compression and relaxation is directly attributable to the collagen fibrils.
"Osteoarthritis occurs when the fibrils are disrupted or lost ?just like concrete without the steel, the cartilage becomes mechanically weak and susceptible to wear and tear.
"Eventually, the cartilage breaks down altogether and sufferers experience severe pain as the two ends of the bones rub against each other."
The team's findings ?published in the journal Proceedings of the National Academy of Sciences ?also explain why mutations in cartilage collagen genes cause osteoarthritis.
"Without a detailed understanding of the structure of these fibrils, a treatment that prevents them deteriorating would always prove elusive," said Professor Kadler.
"This research, while just a beginning, at least establishes some basic scientific facts that coul d prove useful in future studies on osteoarthritis and related conditions."
The next stage of the team's work will be to determine the structure of the thicker fibrils and examine how collagen cells manage to produce these relatively large fibrous structures which are 1,000 times their own size.
Once scientists understand how the fibrils form and develop in healthy cartilage, they can then investigate what happens when things go wrong in diseases like osteoarthritis.