Common painkillers can make the misery of osteoarthritis even worse, according to new research. Ibuprofen, naproxen and diclofenac are prescribed to relieve aching joints, but they may aggravate inflammation of the knee over time.
They belong to a class of medications known as NSAIDS (non-steroidal anti-inflammatory drugs). The study, based on over 1,000 patients, is one of the first to investigate the long term effects.
Lead author Dr Johanna Luitjens, of the University of California, San Francisco, said: "To date, no curative therapy has been approved to cure or reduce the progression of knee osteoarthritis. NSAIDs are frequently used to treat pain, but it is still an open discussion of how NSAID use influences outcomes for osteoarthritis patients.
"In particular, the impact of NSAIDs on synovitis, or the inflammation of the membrane lining the joint, has never been analysed using MRI-based structural biomarkers."
The US team found no benefit in 277 patients with moderate to severe osteoarthritis and sustained NSAID use. In fact, joint inflammation and cartilage quality got worse over the next four years compared to a group of 793 controls who did not take the drugs.
Dr Luitjens and colleagues looked at the link between NSAIDs and synovitis and assessed how the therapy impacted joint structure over time. She said: "Synovitis mediates development and progression of osteoarthritis and may be a therapeutic target.
"Therefore, the goal of our study was to analyse whether NSAID treatment influences the development or progression of synovitis and to investigate whether cartilage imaging biomarkers, which reflect changes in osteoarthritis, are impacted by NSAID treatment."
All participants underwent 3T MRI of the knee at the start and end of the study period. It generates a magnetic field twice as strong as normal magnetic resonance imaging. Scans were scored for cartilage thickness, composition and other measurements that served as non-invasive biomarkers of inflammation and arthritis progression.
Dr Luitjens said: " In this large group of participants, we were able to show there were no protective mechanisms from NSAIDs in reducing inflammation or slowing down progression of osteoarthritis of the knee joint. The use of NSAIDs for their anti-inflammatory function has been frequently propagated in patients with osteoarthritis in recent years and should be revisited, since a positive impact on joint inflammation could not be demonstrated."
Osteoarthritis blights the lives of around 8.5 million people in the UK. There are several possible reasons why NSAIDs increase synovitis.
Dr Luitjens said: "On the one hand, the anti-inflammatory effect that normally comes from NSAIDs may not effectively prevent synovitis, with progressive degenerative change resulting in worsening of synovitis over time.
"On the other hand, patients who have synovitis and are taking pain-relieving medications may be physically more active due to pain relief, which could potentially lead to worsening of synovitis, although we adjusted for physical activity in our model."
She called for prospective, randomised studies to provide conclusive evidence of the anti-inflammatory impact of NSAIDs.
Osteoarthritis is the most common form of arthritis, affecting more than 32 million adults in the US and more than 500 million worldwide.
It occurs most frequently in the hands, hips and knees. In patients, the cartilage that cushions the joint gradually wears away.
Arthritis is often accompanied by inflammation, or swelling, of the joint, which can be painful.
NSAIDs are commonly prescribed. The study was presented at a meeting of the Radiological Society of North America.
