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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.

What are the advantages and disadvantages of Autologous Chondrocyte Implantation (ACI)?

What are the advantages of Autologous Chondrocyte Implantation (ACI)?

The main advantage of ACI is that it is the first treatment to be developed that gets close to achieving cartilage regeneration – creating almost identical tissue to the original – as opposed to merely repairing the tissue, which results in fibrous cartilage.

What are the disadvantages of Autologous Chondrocyte Implantation (ACI)?

ACI is an expensive procedure to perform, and the institutions that regulate access to treatment have not so far understood the benefit to patients of this technique or the potential national economic gains over the long term. Consequently, regulatory systems have put up barriers to the adoption of ACI, which are difficult to overcome.

Another disadvantage of ACI is that, for people who want to return to competitive sport or intense activity early, waiting 9–12 months for the tissue to mature is a long time. However, the aspect of tissue maturity has not really been studied for other treatments and may also be a factor.


As with all surgical procedures, complications can occur with ACI. The most common complication is thickening (hypertrophy) of the ‘patch’ used to cover the cartilage defect. The thickening is due to increased friction and poor surgical technique.

In the early days of ACI, the patch was a periosteal membrane taken from the outer surface of the upper shinbone (tibia), and the complication was seen in 24% of patients, between 3 and 18 months after surgery. In half of the cases, it disappeared with continuous physiotherapy, in the other half, the thickening was removed by shaving during arthroscopy, and the symptoms disappeared with CPM. When handled correctly, this complication did not affect the long-term result.

Today, bio-engineered membranes have replaced the periosteal membrane and the number of complications has fallen to below 10%. The most serious complication is a partial or total graft loosening (delamination), which occurs in approximately 5% of patients and may require reoperation.

Frequently Asked Questions (FAQs)

How long will the treatment last?

Studies have shown that ACI lasts for at least 10–20 years, with good recovery both on an objective, scientific, level, and also in terms of how patients feel and manage activities of daily life.

How long do I need to stay away from sport or from work after ACI? How long before I can return to previous activity levels?

How long it takes to return to previous levels of activity depends on your level of activity before the operation. If you do not use your knee at work (for example, in an office job), you can regain your previous activity levels within a couple of days. If you work in a factory and have a job that requires heavy manual labour, or your job involves standing all day, it will take at least 6 months to return to previous activities. For jobs involving hard labour, such as mining or carpentry, the recovery period is 6–9 months.

It is important in all cases to resume your activities gradually, in a step-by-step process, as full healing takes between 12 and 15 months.

Further reading

There have been a number of studies looking at the outcomes for ACI. These have shown good results not only in terms of the regeneration of hyaline-like cartilage but also looking at the durability of results, with patients able to return to sports and other intense activities. Some key papers include the following:

  • Brittberg M, Lindahl A, Nilsson A, Ohlsson C, Isaksson O, Peterson L. Treatment of deep cartilage defects in the knee with autologous chondrocyte transplantation. N Engl J Med. 1994;331(14):889-895.
  • Minas T, Von Keudell A, Bryant T, Gomoll AH. The John Insall Award: A Minimum 10-year Outcome Study of Autologous Chondrocyte Implantation. Clin Orthop Relat Res. 2013
  • Peterson L, Brittberg M, Kiviranta I, Akerlund EL, Lindahl A. Autologous chondrocyte transplantation. Biomechanics and long-term durability. Am J Sports Med. 2002;30(1):2-12.
  • Peterson L, Vasiliadis HS, Brittberg M, Lindahl A. Autologous chondrocyte implantation: a long-term follow-up. Am J Sports Med. 2010; 38(6):1117-1124.
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