Matrix Autologous Chondrocyte Implantation (MACI) is a medical procedure that repairs damaged knee cartilage. It uses a patient’s own cartilage cells to regenerate new tissue, addressing symptomatic, full-thickness defects. MACI aims to restore knee function and reduce discomfort for individuals with localized cartilage damage, not widespread joint degeneration.
Understanding MACI: What It Is and Why It’s Used
MACI uses autologous chondrocytes (a patient’s own cells) to grow new knee cartilage. This two-stage process regenerates hyaline-like cartilage, similar to natural joint cartilage.
MACI treats symptomatic, full-thickness cartilage defects in adult knees. These often result from trauma or repetitive stress. Unlike widespread osteoarthritis, MACI targets localized damage, often called “potholes.” Articular cartilage has limited natural healing due to poor blood supply. MACI addresses this by implanting lab-grown cells into defect sites.
The MACI Procedure: A Step-by-Step Guide
The MACI procedure has two stages, starting with a minimally invasive cartilage biopsy. In the first stage, a surgeon uses arthroscopy to assess damage. If suitable, a small piece of healthy cartilage, containing the patient’s chondrocytes, is removed from a non-weight-bearing area.
The cartilage sample goes to a lab. Over four to six weeks, chondrocytes are expanded and grown. These cultured cells are then seeded onto a bioresorbable porcine collagen membrane, forming the MACI implant for the second stage.
The second stage is an open arthrotomy. The surgeon exposes and prepares the defect site by removing damaged cartilage. The MACI implant, trimmed to fit, is secured with fibrin glue or sutures. The implanted chondrocytes then proliferate and mature, forming new hyaline-like cartilage that integrates with native tissue, restoring the joint surface.
Who Is a Candidate for MACI?
MACI candidacy involves specific criteria. Candidates are typically adults aged 18-55, as younger, active patients often heal better.
Defect type and size are also important. MACI treats single or multiple symptomatic, full-thickness knee cartilage defects. These are localized lesions, not widespread degeneration from advanced arthritis. Defects commonly range from 2 cm² to 10 cm².
Patients must not have widespread arthritis or other significant knee pathologies. Commitment to a rigorous rehabilitation program is necessary. An orthopedic surgeon’s evaluation, including physical exam and imaging, determines candidacy.
Recovery and Expected Outcomes
MACI recovery is a gradual, multi-month process requiring commitment to rehabilitation. Immediately after surgery, patients begin limited or non-weight-bearing activities, using crutches and a knee brace to protect implanted cells. The initial phase (a few weeks) focuses on pain/swelling control and joint mobility through exercises like continuous passive motion (CPM).
From 3 to 6 months, patients gradually increase weight-bearing and strengthening exercises. Rehabilitation emphasizes regaining full range of motion and building knee strength. Full recovery can take 12 to 18 months or longer, as implanted cells mature into durable repair tissue.
Outcomes include reduced knee pain and improved function, allowing a return to daily activities and sports. Studies show MACI significantly improves pain and function, with outcomes maintained for several years. The procedure creates repair tissue that alleviates symptoms and restores joint function.
Potential Considerations and Risks
Like any surgery, MACI has potential risks. General surgical risks include infection, bleeding, and blood clots. Patients may also experience joint pain, swelling, and stiffness.
Specific risks include graft failure (implant not integrating), which may require reoperation. Persistent knee pain or stiffness can occur. Hypertrophic tissue (cartilage overgrowth) is another potential complication requiring treatment. Financial considerations, including cost and insurance coverage, can impact access.