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Autologous Chondrocyte Implantation

Revolutionizing Joint Repair: The Comprehensive Guide to Autologous Chondrocyte Implantation

If you’re grappling with knee joint pain from cartilage damage, you might wonder if autologous chondrocyte implantation (ACI) is right for you. Aimed at younger, active adults, ACI utilizes your own cells to repair full-thickness cartilage defects. In this article, we’ll walk you through the ACI process, help you determine if you’re an ideal candidate, and give you a glimpse of what to expect post-surgery.

Key Takeaways

  • Autologous Chondrocyte Implantation (ACI) is a surgical procedure specifically approved to repair articular cartilage defects in the knee, which is performed by harvesting, culturing, and reimplanting a patient’s own cartilage-producing cells, covered with a membrane.
  • ACI is most suitable for younger patients with symptoms of joint pain and swelling due to full-thickness chondral lesions who meet specific criteria, including adequate bone alignment, range of motion, and compliance with rehabilitation; it is not recommended for individuals with advanced osteoarthritis or inflammatory arthritis.
  • Long-term results of ACI are promising, showing significant improvements in pain-free activities, sports performance, and quality of life, with economic analyses demonstrating its cost-effectiveness compared to other treatments, though patient selection and adherence to post-surgery rehabilitation protocols are crucial for success.

Understanding Autologous Chondrocyte Implantation (ACI)

Illustration of healthy cartilage cellsACI is a game-changer in the treatment of articular cartilage defects, primarily in the knee joint. This specialized procedure, approved by the Food and Drug Administration (FDA), addresses cartilage defects located at the end of the femur bone and is also performed for defects of the patella and other joints. But what is this articular cartilage that we’re talking about? It’s a soft, rubber-like substance that covers the ends of bones within joints such as the knee. Its primary role is to provide a smooth surface for movement and serve as a cushion to absorb shock.

The ACI procedure involves a series of steps:

  1. Harvest approximately 200 to 300 mg of cartilage from a non-weight bearing area of the knee.
  2. Process the harvested cartilage in the laboratory to isolate and expand chondrocytes – the cartilage producing cells.
  3. Reimplant the expanded chondrocytes into the defect.
  4. Cover the reimplanted cells with a membrane.

The Science Behind ACI

The science of ACI revolves around the challenge of chondrocyte dedifferentiation during in vitro expansion, a major hurdle in chondrocyte-based cartilage repair. This can lead to reduced quality of repair. However, using non–tissue culture treated surfaces for cell proliferation shows:

  • reduced dedifferentiation of chondrocytes compared to traditional tissue culture polystyrene surfaces
  • higher expression of chondrocyte markers
  • production of more sulfated glycosaminoglycans than those cultured on conventional surfaces

This innovative method offers promising results for improving knee articular cartilage repair, specifically targeting repair articular cartilage defects.

Research indicates that healthy cartilage cells, or chondrocytes, grown on non–tissue culture treated surfaces have increased levels of chondrocyte extracellular matrix compared to those on traditional surfaces, suggesting a better suitability for cartilage repair.

From Biopsy to Implantation

The journey from biopsy to implantation begins with an arthroscopic assessment, which is performed to harvest a small piece of articular cartilage from a non-weight-bearing area of the patient’s knee, commonly the intercondylar notch or the medial and lateral femoral condyle. The harvested cartilage undergoes processing in a laboratory, where the following steps are taken:

  1. Chondrocytes are isolated from the cartilage.
  2. The chondrocytes are cultured to expand their numbers.
  3. The cultured chondrocytes are prepared for implantation.

Once the chondrocytes have proliferated adequately, they are implanted underneath a collagen membrane into the prepared defect site on the joint surface, addressing deep cartilage defects in a two-stage surgical procedure.

The Ideal Candidate for ACI

Photo of knee joint with articular cartilage defectWho benefits the most from ACI? Younger patients displaying symptoms of joint pain and swelling related to chondral articular lesions are advised to undergo this procedure. It is a recommended option for their treatment. Specifically, ACI is indicated for symptomatic, full-thickness chondral lesions and for lesions caused by osteochondritis dissecans in the femoral condyles and trochlear groove. If you’re wondering about the size of the defect that can be treated, suitability for ACI includes having symptomatic defects larger than 1.5 cm in diameter.

However, it’s important to note that ACI is not for everyone. It is contraindicated for individuals with advanced osteoarthritis, bipolar sclerotic bone-on-bone lesions, active inflammatory arthritis, or infection. ACI is absolutely contraindicated in cases of generalized osteoarthritis, inflammatory arthropathies, or joint sepsis due to potential complicating factors. It’s important to carefully consider these conditions before proceeding with ACI. For potential ACI patients, the preoperative phase includes detailed counseling about expected outcomes and the extensive rehabilitation involved.

Factors Influencing Eligibility

When assessing the eligibility for ACI, several factors come into play. Preoperative planning includes a critical assessment of:

  • Bone alignment, since appropriate axial alignment is a prerequisite for a successful outcome
  • Range of motion (ROM), which must be adequate
  • Ligamentous stability
  • Compliance with postoperative rehabilitation to ensure the success of the procedure.

Assessing Joint Health

A crucial part of the ACI process is the assessment of joint health. This is done using arthroscopic assessment, which systematically evaluates the knee joint and harvests cartilage tissue from a non-weight bearing area. This step enables the surgeon to gather detailed information about the condition of the joint and plan the procedure accordingly. A health technology assessment review can provide valuable insights into the effectiveness of such assessments and their impact on patient outcomes.

Navigating the Procedure: Step-by-Step

The ACI procedure is a carefully planned and executed process. During the planning phase, various factors are taken into account, including:

  • the clinical picture
  • functional score
  • findings from MRI or CT arthrogram
  • the arthroscopy report from the cartilage biopsy

Additionally, the arthroscopy report from the cartilage biopsy is also considered. A tool called a sharp small gouge is utilized for scoring the articular cartilage, preparing the area for the ACI procedure.

An arthrotomy incision is crucial in ACI as it allows adequate exposure of the lesion and facilitates the implantation of the chondrocytes.

Preparing the Defect Site

The preparation of the defect site is a critical step in the ACI procedure. It involves debriding the area of all unstable cartilage until reaching healthy cartilage, with an emphasis on stable cartilage shoulders for cell attachment. The calcified cartilage layer is removed during the preparation to expose a vascular bed which aids in the secure bonding of new cartilage.

An intact subchondral bone plate is critical to prevent contamination from marrow cells. The ACI membrane is oriented with the rough side to the bone and smooth side facing the joint, secured with careful suturing to ensure a watertight seal.

Securing the Cells

Illustration of collagen membrane securing chondrocytesOnce the cells are ready for transplantation, they are secured using a collagen membrane, creating a secure environment for the cells to adhere and multiply. This is a critical second stage in the ACI procedure. The following steps are involved in securing the cells:

  1. Utilize a collagen membrane to affix the cells in place.
  2. Use fibrin glue to secure the membrane.
  3. Meticulously suture the area to prevent leakage of the cells and maintain the integrity of the implanted tissue throughout the early healing process.

Following implantation, the chondrocytes migrate from the collagen membrane to the subchondral bone, fostering the development of durable, hyaline-like repair tissue that fills the cartilage defect.

Post-ACI Recovery and Rehabilitation

The journey to recovery following an ACI surgery is a process that requires patience and dedication. Patients undergo a period of non-weight bearing of up to 8 weeks, utilizing crutches and a hinged brace to manage limited range of motion. During this non-weight bearing phase, Continuous Passive Motion machines are commonly employed to maintain knee flexibility and improve joint nourishment through the movement of synovial fluid.

As rehabilitation progresses, gradual and progressive increases in range of motion are implemented, along with isometric muscle exercises to strengthen the knee without strain.

The Path to Mobility

The path to mobility after ACI surgery is a journey of steady progress. The recovery process involves a commitment to rehabilitation, with patients generally allowed to return to light sports activities at about 6 months post-operation, and full sports activities possible between 9 and 12 months, dependent on individual recovery.

Post-operative rehabilitation includes the use of a continuous passive motion (CPM) machine and active knee flexion and extension exercises, which stimulate synovial fluid circulation and promote joint movement. Non-impact functional activities like walking and swimming are recommended in the first year.

Monitoring Progress

Monitoring progress after an ACI procedure is crucial. The cartilage matrix used in MACI shows expansion and fills in the defect over the course of a year, showcasing the progression of the healing process. Approximately 9 months after ACI, the implant matures sufficiently to endure high compressive forces.

Assessment of cartilage regeneration is performed using the International Cartilage Repair Score (ICRS)-Cartilage Repair Assessment (CRA) during arthroscopic follow-ups.

Long-Term Outcomes and Effectiveness

Photo of successful long-term outcomes after ACIACI has shown promising results in the long-term treatment of articular cartilage defects. Some key findings include:

  • Approximately 85% of patients return to pain-free activities post-ACI
  • 80% of competitive soccer players return to the same level after ACI
  • 92% of patients in a multicenter study are willing to undergo the procedure again
  • ACI has a success rate of 82% in the long-term
  • 210 patients displayed durable outcomes over 10-17 years
  • 96% of adolescents rated their results as good or excellent

These results demonstrate the effectiveness of ACI in treating symptomatic articular cartilage defects, specifically addressing the articular cartilage defect issue.

Comparing ACI with Other Treatments

When compared to other treatments like microfracture, ACI tends to produce a more hyaline-like, durable cartilage repair tissue, which can result in better long-term outcomes. Superior results in ACI treatments are often observed in defects larger than 4 cm2, suggesting that ACI may be particularly effective for larger chondral defects.

While the initial costs for ACI might be higher compared to microfracture, recent studies indicate that the long-term cost-effectiveness of ACI could be more favorable than previously thought.

Future Prospects in Cartilage Repair

The future of cartilage repair looks bright with ACI leading the charge. The ability to form cartilage-like tissues in vivo has been demonstrated, indicating progress in ACI techniques. Innovative culturing methods offer potential for enhancing ACI and cartilage tissue engineering, by expanding chondrocytes with reduced dedifferentiation.

However, survival analysis suggests that there is a recognized need for more comprehensive research to establish evidence-based rehabilitation protocols in ACI.

Economic Impact of ACI

The economic impact of ACI is significant. ACI demonstrates cost-effectiveness in relation to microfracture, with an incremental cost per QALY gained range of £14,395 to £15,598, aligning with accepted ranges for first repair procedures.

Decision-makers willing to invest £20,000 or more per QALY are likely to find ACI a more cost-effective option than microfracture when considered as a first line procedure, as evidenced by incremental cost effectiveness ratios found in the nhs economic evaluation database.

Understanding the Costs

While the initial costs for ACI are higher than microfracture, with ACI costing €14,804 in the initial year in Germany compared to €5458 for MF, it offers more quality-adjusted life years (QALYs) over a lifetime. In the second to fifth years following surgery, initial cost differences decrease as costs for ACI become comparable or less than MFX, specifically by the fourth and fifth years, where ACI costs drop to €2154 and €1478, respectively, compared to MFX at €2232 and €2061.



Cartilage in the knee has a poor blood supply, which is why it struggles to repair and regenerate. It is the oxygen and nutrients in our blood supply that helps to heal and regenerate structures in the body.

Prolotherapy is a non-invasive treatment that involves the injection of regenerative solution into these structures to provide a direct supply of what is required to heal and repair.

As the treatment is helping to treat the root cause of the problem, it is deemed to be a permanent fix.

Funding and Insurance Considerations

The funding and insurance coverage for ACI varies across countries and insurance plans, affecting its accessibility and affordability. ACI has been covered by insurance in Japan since April 2013, expanding treatment options for patients with extensive knee cartilage damage. However, ACI has been subject to restrictions by the National Institute of Clinical Excellence (NICE), potentially affecting its availability and insurance coverage.

Challenges and Considerations

While ACI offers promising results, there are several challenges and considerations to be mindful of. Medial-to-lateral suturing technique is important for long femoral condylar defects in ACI. Improper suturing or surgical techniques can contribute to periosteal hypertrophy, a complication involving scar tissue formation around the repair site.

Risks and Complications

Illustration of potential risks and complications of ACIPotential complications of ACI include:

  • Periosteal hypertrophy
  • Graft failure
  • Knee infection
  • Knee stiffness
  • Delamination (a serious risk post-ACI leading to partial or total graft loosening and may necessitate reoperation)

Post-operative infections can occur after ACI, although they are rare, requiring additional treatment or surgery.

Achieving Optimal Results

Achieving optimal results with ACI requires proper patient education, adherence to rehabilitation protocols, and a personalized healing timeline. Proper management of patient expectations through preoperative education is essential for improving long-term outcomes after ACI.

Providing patients with a personalized and clear healing timeline can facilitate a more successful recovery process.


The revolution in joint repair through Autologous Chondrocyte Implantation (ACI) offers a transformative potential for patients with articular cartilage defects. By harnessing the body’s own healing abilities, ACI provides a promising solution to repair damaged cartilage, restore mobility, and improve the quality of life. It is a journey of patience, commitment, and hope, leading to a future of pain-free activities. As Ralph Waldo Emerson said, “The first wealth is health,” and ACI is a significant step towards regaining this wealth.

Frequently Asked Questions

Who is the ideal candidate for autologous chondrocyte implantation?

The ideal candidate for autologous chondrocyte implantation (ACI-C) is a younger patient with higher pre-operative modified Cincinnati scores, a short history of symptoms, a single defect, and fewer than two previous procedures on the index knee. These factors are favorable for successful ACI-C.

Is ACI available on the NHS?

Yes, ACI is available on the NHS for specific patients with small areas of cartilage damage or early osteoarthritis, as per NICE guidelines.

How long does autologous chondrocyte implantation last?

Autologous chondrocyte implantation can take up to 24 months for full maturation of the repaired tissue, as estimated by Niemeyer et al. It provides a durable solution with good clinical results even 10 to 20 years after implantation.

How much does autologous chondrocyte implant cost?

Autologous chondrocyte implantation can cost around £16,000 per patient. In some cases, the cost can be higher depending on the particular circumstances and requirements regarding the procedure.

What is Autologous Chondrocyte Implantation (ACI)?

Autologous Chondrocyte Implantation (ACI) is a specialized procedure that treats articular cartilage defects, mainly in the knee joint, by harvesting, culturing, and reimplanting chondrocytes.


    1. Minas, T., Ogura, T., & Bryant, T. (2016). Autologous Chondrocyte Implantation. JBJS essential surgical techniques, 6(2), e24. https://doi.org/10.2106/JBJS.ST.16.00018
    2. Mistry, H., Connock, M., Pink, J., Shyangdan, D., Clar, C., Royle, P., Court, R., Biant, L. C., Metcalfe, A., & Waugh, N. (2017). Autologous chondrocyte implantation in the knee: systematic review and economic evaluation. Health technology assessment (Winchester, England), 21(6), 1–294. https://doi.org/10.3310/hta21060
    3. Beck, J. J., Sugimoto, D., & Micheli, L. (2018). Sustained Results in Long-Term Follow-Up of Autologous Chondrocyte Implantation (ACI) for Distal Femur Juvenile Osteochondritis Dissecans (JOCD). Advances in orthopedics, 2018, 7912975. https://doi.org/10.1155/2018/7912975

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