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ACI - Autologous Chondrocyte Implantation

What is autologous chondrocyte implantation (ACI)?

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Updated April 17, 2014

Autologous chondrocyte implantation, or ACI, is a procedure that was developed in the late 1980s to treat areas of cartilage damage in the knee. ACI has also been used rarely in other joints, such as the ankle, but it is most commonly performed in the knee.

The idea of an ACI procedure is to take a few cartilage cells from the knee, grow them in the lab, and once millions of cells have been grown they are implanted into the area of cartilage damage.

How is ACI performed?
ACI is a two step procedure:

  • Step One: Arthroscopy
    The first step of ACI is to perform an arthroscopic surgery to identify the area of cartilage damage, and determine if it is appropriate for an ACI procedure.

    During the arthroscopic procedure, cartilage cells are collected. These cells are sent to a cell expansion laboratory where they are multiplied by growing in a culture. Growing enough cells takes about 4-6 weeks. Once enough cells have been grown, they are sent to the surgeon, and the second surgery is scheduled.

  • Step Two: Implantation
    Once sufficient cartilage cells have been grown, a second surgery is scheduled. During this surgery, a larger incision is used to directly view the area of cartilage damage (not an arthroscopy). A second incision is made over the shin bone and an area of tissue called periosteum is harvested. The periosteum is the thick tissue that covers the shin bone. A "periosteal patch," roughly the size of the area of cartilage damage, is harvested.

    The periosteal patch is then sewn over the area of damaged cartilage. Once a tight seal is created between the patch and the surrounding cartilage, the cultured cartilage cells are injected underneath the patch. The periosteal patch is used to hold the new cartilage cells in the area of cartilage damage.

Who is the right patient for an ACI procedure?
ACI is a significant procedure. The recovery is lengthy, and patients must be prepared to participate with intensive physical therapy. ACI is only appropriate for patients with small areas of cartilage damage, not widespread wear of the cartilage characteristic of knee arthritis. Patients considering ACI should fit the following profile:

    • A focal area of cartilage damage, not widespread arthritis

    • Have pain or swelling that limits their activity

    • A stable knee with no associated ligament damage

    • Weight appropriate for height (not obese)
In addition, patients should have tried other nonsurgical treatments before considering this significant procedure. Furthermore, patients must have a firm understanding of the post-operative rehabilitation from ACI surgery. This step is critical to success of the ACI procedure and without proper rehab the results are usually less than ideal.

What are the complications of ACI procedure?
The success of ACI is quite variable, with different surgeons reporting varying levels of success. The most common complication is due to scar tissue formation around the edge of the periosteal patch, called periosteal hypertrophy. This problem often requires an additional arthroscopic surgery to remove excess scar tissue.

Other complications include failure of the implanted cells to properly integrate, infection of the knee, and knee stiffness.

Read more about ACI and the rehabilitation after an ACI procedure...

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