An increasing number of patients are being admitted to hospital with infected knees after being injected with hyaluronic acid – despite the unproven arthritis treatment being discouraged by several medical bodies.

While a large body of evidence suggests the injections don’t work, they are being offered at radiology clinics across the country as a treatment for osteoarthritis.

Knee infections in people without knee replacements are rare. But three doctors who spoke to this masthead said they had each seen several patients who had infected knees after receiving the injections.

Orthopedic surgeon Ian Harris and his colleagues have seen three patients with infected knees in the past few months.

All had received injections of hyaluronic acid – a substance that is derived from roosters’ combs or created synthetically and often used in beauty products to hydrate the skin.

“We’re seeing a string of patients who have turned up in the emergency department of our hospital with infected knees, that have needed surgery and IV antibiotics,” Harris said.

“Rather than relieving their osteoarthritis – which is what the injections are purportedly for – they are making the patient worse by causing an infection.”

The Royal Australian College of General Practitioners and Arthritis Australia strongly recommends against the use of hyaluronic injections for joint pain.

The Therapeutic Goods Administration received two reports of infection following a hyaluronic acid injection last year. That’s likely an underestimate as the TGA’s own researchers estimate just 0.5 per cent of all adverse events actually end up being reported.

Hyaluronic acid injections to the knee are not covered by Medicare, but several radiology practices have been offering them bulk-billed with no out-of-pocket costs.

Harris suspects the practices are performing the injections while using a CT scan to guide the needle. CT scans attract a significant Medicare rebate.

“It’s not necessary to do a CT scan to inject a knee – you can inject a knee without a CT scan, easily,” said Harris.

CT scans also typically expose a patient to much higher doses of radiation compared to an X-ray.

Hyaluronic acid injections have long been sold to people with joint pain caused by arthritis. The theory is the acid cushions and lubricates the joint, easing pain.

But researchers have known for more than a decade the evidence for the treatment does not stack up, says Professor Rachelle Buchbinder, co-ordinating editor of Cochrane Musculoskeletal, the independent group that pulls together gold-standard evidence reviews.

A systematic review of the evidence, published in the BMJ in 2022, combined data from 169 trials of 21,163 patients.

It found “strong, conclusive evidence” the benefit from the injections was so minimal compared with a placebo a patient would not notice.

That lack of benefit is coupled with increased risks: across the trials, 3.7 per cent of patients had a serious adverse event. These include joint infections and inflammatory reactions.

“On balance, the risks outweigh the benefits,” said Buchbinder. “I would expect that most people would not want the treatment if the evidence was communicated effectively to them.”

Gold Coast-based orthopaedic surgeon Christopher Vertullo has treated four patients in the past two years who developed severe knee infections following the injections. He said the infections were due to the syringe picking up bacteria from a patient’s skin and transporting it into their knees.

He describes the consequence of an infection as “an absolute disaster”, requiring lengthy hospitalisation, antibiotics and surgical arthroscopic evacuation.

Infections can cause permanent knee damage and often prevent or complicate future knee replacement surgery.

“The risk benefit ratio is unacceptable,” he said of the injections.

Vertullo was an adviser for the updated clinical care standards for knee osteoarthritis, released by the Australian Commission on Safety and Quality in Health Care last year, which warned against the injections “due to evidence that they provide no meaningful clinical benefit and have a significant expense”.

He’s also concerned about the radiation risks to patients from repeated CT scans used to guide the injections.

Vertullo said safer and proven treatments for knee osteoarthritis included muscle-strengthening exercises, keeping weight under control and using appropriate pain medication.

Professor David Hunter, a clinical researcher at the University of Sydney and a member of Arthritis Australia’s scientific advisory panel, said while the injections were not supported by robust evidence, they were attractive to patients who wanted a quick fix.

Hunter, who works as a rheumatologist, said he regularly came across adverse reactions caused by the injections. About 5 to 10 per cent of people would present with significant swelling in their knee following the injections, he said.

“The injection has proteins that are often derived from a rooster’s comb so the avian proteins cause a local reaction in the human because we’re not used to having bird protein in our body,” he said. “It can be very painful.”

Last year, Robert Hooke received three injections of hyaluronic acid into his knees in a bid to relieve his persistent osteoarthritis.

The injections were prescribed by a surgeon and administered over three weeks under CT scan by a radiologist at a private clinic in Melbourne’s north.

The 76-year-old said the injections made no difference to his osteoarthritis. One left him in pain and with a swollen knee.

“I wanted to relieve my pain,” he said. “I wasn’t told that it probably wouldn’t have any effect.”

Hooke said he didn’t have to pay for the injections. He has also tried physiotherapy, crutches, braces, creams and steroid injections, but nothing had made a difference to his pain.

A federal Health Department spokesman said clinical studies had indicated that hyaluronic acid injections might provide short-term pain relief for some people with knee osteoarthritis. But he said the overall benefit was “modest and must be balanced against known risks such as pain, swelling, inflammation and, rarely, joint infection”.

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