Cell power on the NHS: Autologous Chondrocyte Implantation

How Arthritis UK research has helped treat thousands of people with knee cartilage defects

In the 1980s, treatment options for people with osteoarthritis were very limited. Some medicines were available to help minimise pain and inflammation, and joint replacement surgery offered to those with advanced, late-stage disease. This left a gap to help stop osteoarthritis in its tracks, which is why alternatives such as cell therapies, capable of repairing and regenerating a patient’s own joint, were explored around the world. This led to the 1987 discovery of a cell therapy called Autologous Chondrocyte Implantation (ACI) in Sweden. 

What is ACI? 

A type of cell therapy that treats knee cartilage defects which, if left untreated could develop into osteoarthritis. ACI involves removing a small sample of healthy cartilage from an individual’s knee. This tissue is then used to grow a fresh supply of cartilage cells in a laboratory. These cells are later implanted into the damaged area of the knee in another operation, where they form new cartilage to aid repair. ACI works for the majority of those eligible for it, and in some is effective lifelong – it could delay or avoid the need for joint replacement altogether.

What role did Arthritis UK play?

Researchers from the Arthritis UK Tissue Engineering and Regenerative Therapies Centre travelled to Sweden to learn about the procedure and on their return began developing ACI in the UK, at the Robert Jones and Agnes Hunt Orthopaedic Hospital in Oswestry. Evidence from their work helped secure approval for ACI on the NHS in 2017. Since then, it remains the only cell therapy available on the NHS for treating cartilage defects in the knee. ACI is now commercially available across multiple continents, helping tens of thousands of people to date globally. 

Who is ACI for?

The ideal patient is a physically active adult aged 50 or younger with a single cartilage defect (hole in the cartilage) larger than 2cm² in a single location, roughly the size of a fingernail. It is not recommended for people with widespread or advanced osteoarthritis. 

What’s happened since? 

Researchers at the Arthritis UK Tissue Engineering and Regenerative Therapies Centre are maximising the success of ACI by identifying those who benefit from this therapy the most. ACI works for the majority of those eligible for it, but roughly one-in-five cases will later need joint replacement surgery. This is why the Centre have built a tool to predict ACI success called ORKA-1. It takes into consideration factors such as age, gender and pre-surgery characteristics in the affected joint. 

Where is ACI available? 

ACI is currently available across a handful of specialist orthopaedic centres across the UK. A recent addition to this list is the Cambridge Surgical Hub, where Centre Director Professor Andrew McCaskie leads research and training for the Hub. It opened in 2023 and was designed to make orthopaedic care for patients more efficient, to tackle the waiting list backlog for joint replacements and reduce length of stay. In 2025, it was accredited by NHS England as a surgical hub.

What’s next? 

Centre researchers are next exploring new ways to improve the ACI technique. For example, they’re identifying top-performing cells that repair damaged cartilage most effectively and identifying joint fluid markers that correlate with how well someone’s joint heals after cell therapy. Finding these cells and markers could help them maximise the success of ACI for patients even further. 

Want to find out more?

Look out for more information in a future SKILLs newsletter, where we’ll sharing the Tissue Engineering and Regenerative Therapies Centre Impact Report in full.