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Autologous Chondrocyte Implantation (ACI)
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Autologous Chondrocyte Implantation (ACI)

Damage to joint (articular) cartilage (known as chondral lesions), or damage to both the cartilage and the underlying bone (known as osteochondral lesions), does not repair itself spontaneously and results in joint pain and poor function.

Such damage, which is common after trauma, if left untreated can lead to osteoarthritis. The knee is the most commonly affected joint. Patients aged over 60 years with osteoarthritis are more likely to have total knee replacement. However, younger patients face a problem, as metallic resurfacing has a limited lifespan and in young patients invasive revision surgery is often needed.

Techniques that promote regeneration of the native hyaline cartilage are therefore extremely attractive, as they offer the possibility of both repairing the tissue and allowing younger patients to return to their previous activities. One such technique is autologous chondrocyte implantation (ACI).

ACI is a technique for regenerating hyaline cartilage in a diseased or damaged area of a joint through the implantation of cartilage cells. The technique has been used extensively since it was introduced in the 1980s. It has achieved excellent long term results, both in terms of cartilage repair and helping patients returning to previous activity levels.

ACI is recommended for younger patients who have symptoms of joint pain and swelling, related to a chondral articular lesion.

Intended audience

This article is intended for anyone suffering from damage to their articular cartilage and their families who would like to find out about autologous chondrocyte implantation, as well as anyone interested in cartilage problems.

What is Autologous Chondrocyte Implantation (ACI)?

In patients undergoing ACI, the surgeon performs an initial procedure (arthroscopy), in which small pieces of cartilage, including cartilage cells (chondrocytes), are harvested from a non-weight-bearing area of the joint. The cartilage pieces are sent to a laboratory, where the cells are isolated and cultured (multiplied) for 3–5 weeks to obtain sufficient number of cells (usually between 5 and 10 million cells).

The patient then undergoes a second operation. The surgeon first prepares and smoothens the damaged area, covers it with a membrane, similar to a patch, and then injects the chondrocytes that have been grown in the laboratory underneath the membrane. Nowadays it is also possible to use innovative biomaterials where the autologous chondrocytes can be seeded before surgery and this cell-based “scaffold” can be implanted onto the cartilage lesion site.

The cells then grow and mature in the joint, and gradually replace the damaged area with living, healthy cartilage.

ACI can be used in any joint that has hyaline cartilage. While the vast majority (90%) of operations are carried out in the knee, ACI is also performed in the ankle. Furthermore, cartilage disease or damage in joints such as the hip (in patients with isolated lesions), shoulder, elbow and the big toe may be treated successfully with ACI.

After the procedure, patients undergo a rehabilitation programme, and each hospital may have their own programme. Typically, rehabilitation will begin with motion training, including partial weight-bearing and continuous passive motion (CPM), in which a device keeps the joint in motion without assistance. This lasts for approximately 10–12 weeks. During these first 3 months, patients gradually increase the weight on their operated joint until full weight bearing is achieved. This is important for the proper nutrition of the cells.

Over the past 25 years, we have progressed from performing surgery in small areas of diseased or damaged cartilage (lesions) to surgery for multiple lesions in one knee (two to five lesions per procedure) and lesions in both the femur and tibia.

ACI is also a very good option for children, or paediatric patients, as an artificial body part (prosthesis) should be avoided for a child or young adult. Young patients may develop osteoarthritis if they do not get treatment. For a child aged 13 years or older who has osteochondritis dissecans (OCD), ACI is an excellent option for restoring bone and cartilage, alongside the use of osteochondral grafts. However, it depends on the stage of the disease.

ACI is an excellent option for top athletes providing they are willing and able to stay away from intensive training and competition for 9–12 months. This is particularly relevant if the athlete is approaching the end of his or her career and they want a good quality of life afterwards.

More widely, ACI has opened up opportunities for joint resurfacing, with scientists and leading companies involved in the development of biomaterials. This can support the cartilage cells (chondrocytes) after the initial procedure, as well as during the rehabilitation process to get patients active and back to work earlier.

Overall, ACI has the best outcomes in patients who have not previously had surgery to the bone, and in young patients.

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