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Matrix-induced Autologous Chondrocyte Implantation (MACI)

The ends of the bones in the knee are covered with articular cartilage, a smooth rubbery tissue that allows frictionless movement in the joint and acts as a shock absorber. The cells that form cartilage are called chondrocytes. Damage to the articular cartilage is called a chondral lesion. It is common especially among active people.

Think of chondral lesions as potholes. Filling potholes prevent wear and tear on the knee joint. Articular cartilage lesions in the knee do not heal spontaneously. This leads to pain and poor function and left untreated can progress to osteoarthritis. Osteoarthritis is the most common form of arthritis and increases the risk of disability. There are different treatments for osteoarthritis mostly non-surgical. Joint replacement is the established surgical procedure to treat end-stage osteoarthritis in older patients.

However, young patients with cartilage defects face the prospect of a partial knee resurfacing procedure with metal parts that have a limited life span and invasive revision surgery that is often needed. For these reasons, new techniques that promote cartilage regeneration are so important. ACI is autologous chondrocyte implantation. It offers the ability to repair symptomatic chondral lesions so that these patients can return to their activities and their lives. Autologous chondrocyte implantation provides excellent long-term results.

The suitability for an MACI is determined after careful considerations of the patient’s symptoms, clinical examination, and imaging studies.

Good patients are those motivated to improve their condition and who have joint pain and swelling due to a chondral defect. Best results are achieved in patients with knee symptoms for less than two years at the time of surgery; though patients with symptoms for longer still have a great prognosis.  Athletes must be willing to stop intensive training and competition for 9-12 months.

Autologous chondrocyte implantation is a state-of-the-art procedure to repair isolated cartilage defects. It aims to regenerate cartilage and rejuvenate the joint.  The new cartilage that is formed is hyaline cartilage just like natural articular cartilage.

Autologous chondrocyte implantation is an established technique for the treatment of cartilage defects of the knee. It is FDA approved to repair damaged cartilage using the cells from the patient’s own knee.

FDA approved the use of a Matrix Associated Chondrocyte Implantation (MACI) in 2016. It is designed for people younger than age 55 who have focal (localized) cartilage defects, usually caused by injury or repetitive microtrauma. The goal is to prevent the development of knee osteoarthritis.

All cartilage surgery is theoretically a two-step process. Step one is diagnostic arthroscopy. For ACI, during Step one, a small chondral biopsy is taken. During an arthroscopic examination of the knee, Dr. Patel will clean out debris and determine the size of the defect and whether the patient is a good candidate.  If so, in a short procedure he will take a cartilage biopsy, about the size of two Tic Tacs, from an area of the knee that does not bear weight.

The cartilage sample is sent to a lab where the chondrocytes are isolated and cultured to obtain a large number of chondrocytes. The chondrocytes are seeded onto a membrane matrix (MACI) in the lab. In about 3 – 5 weeks the cultured cells are sent back to Dr. Patel.

In the second surgical procedure, the defect is prepared and the MACI implant is placed into the defect. With this biodegradable scaffold matrix, the collagen is seeded with the new cartilage cells in the lab and implanted into the lesion. As the cells grow and mature, they replace the damaged cartilage with heathy cartilage.

For a period of about 6-8 weeks after the second surgery weight-bearing is restricted. During that time, the patient goes to physical therapy to improve strength and range of motion. A continuous passive motion machine may be recommended to keep the joint in motion to improve the cartilage healing success.

Return to sports can take 9-12 months. 85% of patients can return to pain-free activities. Studies report that ACI lasts at least 10-20 years!

Dr. Ronak M. Patel is a double board-certified orthopaedic surgeon and sports medicine physician. He completed his bachelor’s degree, medical degree, and residency training at Northwestern University. He, then completed his fellowship training at the Cleveland Clinic. He specializes in the treatment of complex knee, shoulder and elbow injuries and degenerative conditions. Contact him to schedule a consultation to learn more about how he can help you return to the life you love and the activities that make life worth living. He serves teens and adults in Chicagoland and NW Indiana.

At a Glance

Ronak M. Patel M.D.

  • Double Board-Certified, Fellowship-Trained Orthopaedic Surgeon
  • Past Team Physician to the Cavaliers (NBA), Browns (NFL) and Guardians (MLB)
  • Published over 49 publications and 10 book chapters
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