Autologous chondrocyte implantation (ACI)

What is autologous chondrocyte implantation (ACI) surgery?

Autologous Chondrocyte Implantation surgery, also known as ACI surgery, is a well-established but highly specialised treatment that is used to repair defects in the cartilage, which is the flexible, connective tissue found in joints, such as the knee.

Autologous chondrocyte implantation surgery is a two-step surgical procedure. In the first operation, your surgeon will extract some of your own cartilage cells, which are then sent to a specialist laboratory. The laboratory expands and grows these cells, ready to be implanted to treat the area where your cartilage is damaged. This is considered the ‘gold standard’ treatment for suitable cartilage defects, with a high success rate of approximately 85%¹.

What are the benefits of autologous chondrocyte implantation?

ACI is a powerful and reliable treatment when delivered by a specialist in joint-preserving surgery. Other key benefits of this treatment include:

• The ability to generate new, high-quality cartilage that is more durable and more closely resembles the natural joint tissue.
• Effectiveness for larger cartilage defects, where most alternative techniques are unsuitable.
• Helping to preserve the health and condition of the joint in the long term, which could delay the onset of osteoarthritis and more significant surgeries, such as joint replacement.

What else is autologous chondrocyte implantation surgery known as?

You may also hear autologous chondrocyte implantation surgery, known as ACI knee cartilage therapy, cartilage cell transplantation or a cartilage patch. It is also sometimes confused with matrix-induced autologous chondrocyte implantation or MACI.

What is the difference between ACI and MACI?

Both ACI and matrix-induced autologous chondrocyte implantation (MACI) use your own cells to repair damaged cartilage in a joint. However, the main difference is the technique: with MACI, your harvested cartilage cells are grown onto a supportive scaffold (also known as a matrix) before they are implanted into the joint. With ACI, your cells are implanted directly into the joint and then covered with a patch to keep them in position.

What conditions can ACI treat?

Autologous chondrocyte implantation is typically recommended to treat large, single areas of damaged cartilage (usually over 2cm²), which are usually caused by an accident or injury. This procedure is often chosen when the defect is too significant to be treated successfully with other cartilage repair methods.

How do I know if I need ACI surgery?

Your orthopaedic consultant (surgeon) will be able to advise you if you may need autologous chondrocyte implantation.

Who is suitable for an autologous chondrocyte implantation?

ACI surgery is generally recommended for healthy people with large areas of full-thickness cartilage damage, usually 2cm² or more. Good candidates are generally between the ages of 13 and 55, with little to no signs of osteoarthritis or previous joint injury and can commit to a fairly intensive six-month rehabilitation programme.

Who is not suitable for autologous chondrocyte implantation?

You may not be a good candidate for autologous chondrocyte implantation if you have:

• A high BMI, as studies suggest, is associated with significantly lower success rates³.
• Moderate to severe osteoarthritis.
• Been diagnosed with rheumatoid arthritis.
• An area of damage less than 2 cm².
• Previously had a failed cartilage surgery.
• An unstable joint (untreated).
• Malignment of the joint (untreated).

You may also be unsuitable if you aren’t able to commit to the rigorous rehabilitation programme.

What happens during autologous chondrocyte implantation surgery?

How can I prepare for autologous chondrocyte implantation (ACI)?

Whilst ACI may be the recommended treatment for your cartilage damage, your surgeon will also assess your knee alignment and knee stability. If you have a significant ‘knock-knees’ or ‘bow-legged’ alignment, then an osteotomy may be needed to offload and protect the new cartilage. If you have a ligament injury, such as an ACL injury, it is important that your knee is stabilised, often with a ligament reconstruction, before proceeding with ACI.

Pre-operative assessment for autologous chondrocyte implantation

Before autologous chondrocyte implantation surgery, you’ll have a pre-operative assessment to determine if you’re a suitable candidate for the procedure.

A member of our nursing team will review your medical history and record your baseline measurements, including your height, weight and blood pressure. If your nurse thinks it is necessary, you’ll also be given pre-operative tests such as blood tests, urine tests and MRSA swabs.

Your nurse will give you specific guidance on how to prepare for the day of surgery, including if and when you should stop eating or drinking, if you need to stop or pause any medications, and any other requirements – for example, not wearing jewellery or false nails.

What should I expect during an autologous chondrocyte implantation (ACI)?

ACI surgery is a two-stage procedure, with both parts typically being performed under general anaesthetic, meaning that you’ll be asleep during surgery.

Stage one: Cartilage cell harvest
Stage one is quick, minimally invasive surgery during which small incisions (cuts) are placed into the joint to remove a small section of healthy cartilage from a non-weight-bearing area of the joint. It typically takes around 30 minutes or less.

Once the cells are removed, they are taken to a lab to be cultured (multiplied). This usually takes 6 to 8 weeks. Once the cells are ready, you’ll be scheduled to have the second stage of your procedure.

Stage two: Cartilage implantation
Stage two is an open surgery, which means a larger incision (cut) is made into the skin for your surgeon to access the joint. Your surgeon will first prepare the area by carefully removing damaged cartilage. A "pocket" is then created and a patch is placed over the area. Your lab-grown cartilage cells (chondrocytes) are gently injected underneath the patch into the space. Over time, the cells will form a smooth, functional surface.

Your surgeon will close the incision and apply a dressing. The entire procedure can usually be completed in under 90 minutes. 

How long does it take to recover after ACI surgery?

Before you undergo autologous chondrocyte implantation surgery, your consultant will explain that the procedure has a significant recovery period and you will need to commit to a rehabilitation programme that takes anywhere from 6 to 12 months. A physiotherapist will guide you through every stage – from protecting the joint immediately after surgery to gradually rebuilding your strength, mobility, and confidence over the coming months.

For the first 2 weeks, the focus of your recovery is to reduce swelling in the joint and carefully restore the range of motion. You will perform very specific, controlled exercises, often assisted by a specialised machine to help your joint heal correctly.

Weeks 2 to 8, you will continue your personalised rehabilitation programme and physiotherapy exercises. You may need to wear a knee brace and use crutches to limit the weight on the joint as it heals.

Most people can start to bear weight on their knee joint around 3 months after surgery, but you’ll still need to stick closely to your rehabilitation programme to achieve a full range of movement and ensure the best possible outcome from your treatment.

How soon can I go home after ACI surgery?

Some people may be able to go home the same day as their procedure, while others may be recommended to stay in the hospital for a night or two, to support the start of their recovery. Your consultant will be able to advise you on how long you can expect to stay.

How soon can I walk after autologous chondrocyte implantation?

Many people can begin to walk with crutches a few days after their surgery, but you can expect to continue to need them for 6 weeks or more, depending on the rate of your recovery.

How soon can I return to work?

This depends on the type of work that you do. If you have a desk job, you may be able to return to work a few weeks after surgery, provided you can manage the demands of your job and rehabilitation requirements. However, if you have a more manual job, it could be several months before you can go back to work. Always follow the recommendation of your consultant.

How soon can I drive?

Most people can start driving again around 6 weeks after surgery, but always follow the advice given to you by your medical team.

How soon can I exercise or play sports after ACI surgery?

Rehabilitation after ACI surgery is a gradual process, and while you may be able to take part in light physical activity a few months after your procedure, it usually takes up to 18 months to get back to high-intensity exercise.

Will I need physiotherapy after autologous chondrocyte implantation?

Yes, expect to need long-term physiotherapy for up to 18 months following your autologous chondrocyte implantation procedure. This is usually more intensive to begin with and then eases into routine appointments. You’ll need to complete your physical therapy exercises at home, as well as during your appointments.

What are the alternatives to autologous chondrocyte implantation?

There are several alternatives to ACI surgery. These include:

• Autologous matrix-induced chondrogenesis: This is a one-stage treatment that combines local bone marrow stimulation with a collagen matrix to help stabilise the repair site and improve the quality of the new cartilage.
• Osteochondral autograft transfer (OATs): Another single-stage procedure that takes healthy bone and cartilage from a non-weight bearing area of the joint and transfers it to the damaged area.
• Matrix-induced autologous chondrocyte implantation (MACI): A version of the ACI technique, during which the harvested cells are placed onto a scaffold to multiply, before being implanted into the joint as a single structure.
• Chondroplasty: A local procedure to stabilise and encourage healing of the cartilage defect through ‘bone marrow stimulation’. Chondroplasty is typically recommended for smaller defects.

Your consultant will recommend the most suitable treatment for you based on your individual circumstances.

How much does autologous chondrocyte implantation surgery cost at Nuffield Health?

For pricing information, please contact your local hospital. The hospital or your healthcare team will give you a fixed all-inclusive price for the treatment following your initial consultation.

Sources
1 https://www.engage.england.nhs.uk/consultation/copy-of-clinical-commissioning-wave5/user_uploads/d10...
2 https://pmc.ncbi.nlm.nih.gov/articles/PMC2795849/#:~:text=Our%20data%20demonstrate%20that%20autologo...
3 https://www.ncbi.nlm.nih.gov/books/NBK424062/
4 https://pubmed.ncbi.nlm.nih.gov/40169165/
5 https://pubmed.ncbi.nlm.nih.gov/20181804/#:~:text=Conclusion:%20Autologous%20chondrocyte%20implantat....