Australian knee CT use has almost tripled in six years, raising questions about low-value imaging, CT-guided injections, and rapidly growing Medicare costs.
The use of CT scans for knee conditions has soared across Australia, with researchers warning the increase is unlikely to be explained by clinical need alone and may partly reflect growing use of CT-guided injections for osteoarthritis.
In a perspective published this month in the Medical Journal of Australia, researchers including rheumatologist Professor Rachelle Buchbinder and orthopaedic surgeon Professor Ian Harris, said CT traditionally had a limited diagnostic role in knee conditions, generally being reserved for indications such as fracture assessment and preoperative planning.
But an analysis of Medicare data found annual CT knee imaging services increased from 31,792 in 2019 to 88,230 in 2025 – a 178% rise. Adjusted for population growth, utilisation climbed 155%, from 1255 to 3196 services per million people.
Medicare expenditure increased almost as dramatically. In 2025 dollars, annual spending rose from $8.05 million in 2019 to $20.21 million in 2025, an increase of 151%.
The increase was largely driven by the number of scans rather than their individual cost. Average expenditure per CT knee service rose only modestly, from about $203 to $229 over the six-year period.
The pattern contrasted sharply with other forms of knee imaging. MRI services increased 16% between 2019 and 2025, while knee x-rays rose 17%. After adjusting for population growth, utilisation of each increased by less than 7%.
Plain x-ray also remains the recommended first-line imaging modality for most knee conditions.
“The absence of significant growth in MRI and plain x-rays suggests that the observed substantial growth in CT knee imaging is unlikely to be explained solely by increased clinical demand and prompts consideration of modality-specific and system-level factors that may be driving this growth,” the researchers wrote.
Several factors could be contributing to the trend, they said. CT was more widely available than MRI in many regions, while Medicare-funded MRI scans referred by GPs were restricted for some age groups, particularly patients aged 50 years and older. CT could therefore be used as an alternative where MRI access is limited.
“However, this explanation is unlikely to fully account for the observed growth, as knee plain x-rays, which are regarded as the first-line imaging modality, did not demonstrate a corresponding increase in utilisation over the same study period,” the researchers wrote.
The increasing uptake of robot-assisted total knee arthroplasty may also be contributing, as CT knee imaging was commonly used for preoperative planning.
However, the researchers said neither explanation necessarily accounted for the scale of the increase, and highlighted another potential driver – CT-guided knee injections.
“Despite high-certainty evidence demonstrating that hyaluronic acid injections provide no meaningful benefit over placebo and are not recommended by contemporary guidelines, they continue to be offered,” the researchers wrote.
“At one of our institutions, we observed six recent cases of septic arthritis following CT-guided hyaluronic acid injections for knee osteoarthritis.
“These cases are also concerning as CT guidance is unnecessary for knee injections because this joint is accessible using anatomical landmarks.”
The researchers said CT guidance was unnecessary for knee injections because the joint could be accessed using anatomical landmarks. It also exposed patients and staff to ionising radiation, which may become more clinically relevant when injections and scans are repeated.
The researchers identified radiology practices advertising CT-guided injections nationally, including hyaluronic acid injections for osteoarthritis. Some were marketed with no out-of-pocket expense and involved multiple treatment sessions, each requiring a separate CT scan.
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They suggested the Medicare funding structure could be influencing the practice.
“Given that there is no Medicare rebate for knee injections, the adoption of CT guidance may facilitate Medicare reimbursement for procedures that would otherwise not attract funding,” they wrote.
“Online searches easily identify multiple radiology practices nationally that are marketing CT-guided injections, often for hyaluronic acid for osteoarthritis, in which the procedure is provided with no out-of-pocket expense and is usually delivered on multiple occasions, with each occasion requiring a separate CT scan.”
The investigation was prompted partly by six recent cases of septic arthritis following CT-guided hyaluronic acid injections for knee osteoarthritis observed at one of the researcher’s institutions.
“While septic arthritis following a joint injection is uncommon, it can cause rapid joint destruction and long-term morbidity,” they wrote.
The researchers warned that if increasing CT utilisation reflected similar growth in CT-guided injections, even a rare complication could result in a notable burden of preventable harm.
There were important limitations to the analysis, they noted. Medicare data record services rather than their clinical indication and did not identify referral sources. Current MBS items also did not allow the researchers to reliably distinguish diagnostic knee CTs from scans performed in conjunction with image-guided procedures.
The increase could therefore reflect a combination of osteoarthritis diagnosis and management, CT-guided injections, fracture assessment following trauma, and preoperative planning for joint replacement.
Despite this, the researchers said the striking divergence between CT and other knee imaging warranted greater scrutiny.
They called for improved imaging stewardship, transparency, and informed decision-making around CT-guided procedures to minimise unnecessary radiation and procedure-related harm while ensuring growing Medicare expenditure translated into genuine benefits for patients.
“Septic arthritis following joint injection represents a potentially catastrophic complication, which may become a greater health concern as the volume of CT-guided knee injections continues to increase,” the researchers concluded.
“Appropriate imaging stewardship, transparency and informed decision-making in CT-guided procedures will be essential to ensure that CT knee imaging utilisation translates into true patient benefits, while maintaining the long-term sustainability of the Medicare system.”
