MACI: Eligibility Criteria, Evaluation, and Contraindications

Who is eligible for Maci?

MACI (Matrix-induced Autologous Chondrocyte Implantation) is a specialized surgical procedure for repairing symptomatic, full-thickness cartilage defects, primarily in the knee. Eligibility is determined by a strict set of criteria focusing on the patient's age, the nature and size of the cartilage lesion, and overall joint health.

Understanding MACI: A Cartilage Repair Solution

MACI is an advanced, two-stage surgical procedure designed to repair damaged articular cartilage, the smooth, slippery tissue that covers the ends of bones in a joint and allows them to glide effortlessly. Unlike less invasive treatments, MACI involves taking a small biopsy of healthy cartilage from the patient, sending it to a lab to grow new cartilage cells (chondrocytes) on a collagen membrane, and then implanting this membrane back into the defect area in the joint. This innovative approach aims to regenerate durable, hyaline-like cartilage, offering a long-term solution for focal cartilage damage that has not responded to other treatments. It is most commonly used for isolated, full-thickness chondral defects, often resulting from acute trauma or repetitive stress, rather than widespread degenerative conditions like osteoarthritis.

Primary Eligibility Criteria for MACI

Candidacy for MACI is a complex decision made by an orthopedic surgeon after a thorough evaluation. Key factors considered include:

• Age: MACI is generally recommended for younger, active individuals, typically between 15 and 55 years of age. This is because younger patients tend to have healthier chondrocytes with greater regenerative potential and are better able to withstand the rigorous rehabilitation required. While there might be exceptions, advanced age often correlates with more widespread degenerative changes, making MACI less suitable.
• Defect Size and Location: The procedure is most effective for focal, well-defined, full-thickness cartilage defects.
  • Size: The defect should ideally be between 1.5 cm² and 10 cm² (or up to 12-15 cm² in some cases). Very small defects might be managed with simpler techniques, while very large defects may exceed the regenerative capacity or structural support offered by MACI.
  • Location: While primarily used in the knee (femoral condyles, patella, trochlea), it can sometimes be considered for other joints, provided the defect is clearly defined and accessible.
• Defect Type: MACI is specifically designed for full-thickness chondral defects, meaning the damage extends through the entire layer of cartilage down to the subchondral bone. It is not indicated for superficial cartilage damage or widespread degenerative conditions.
• Previous Treatments: Candidates typically have persistent symptoms (pain, swelling, mechanical symptoms) despite having failed more conservative treatments such as physical therapy, activity modification, bracing, or less invasive surgical procedures (e.g., debridement, microfracture).
• Overall Joint Health and Alignment: The knee joint must otherwise be relatively healthy.
  • No Widespread Arthritis: Patients with widespread osteoarthritis or diffuse cartilage loss throughout the joint are generally not candidates, as MACI is for isolated defects.
  • Good Joint Alignment: Any significant malalignment (e.g., bow-legged or knock-kneed deformities) or instability that could lead to abnormal loading of the repaired area must be corrected either prior to or at the time of the MACI procedure.
• Patient Commitment to Rehabilitation: Successful outcomes with MACI heavily depend on strict adherence to a prolonged and intensive post-operative rehabilitation protocol, often lasting 6-12 months or more. Patients must be motivated and committed to this process.

Conditions That May Rule Out MACI Eligibility

Several factors can make a patient unsuitable for MACI:

• Widespread Osteoarthritis or Degenerative Joint Disease: If the cartilage loss is diffuse throughout the joint, MACI is not an appropriate solution.
• Significant Joint Malalignment or Instability: Uncorrected biomechanical issues will place excessive stress on the new cartilage, leading to failure.
• Inflammatory Arthritis: Conditions like rheumatoid arthritis, psoriatic arthritis, or other systemic inflammatory arthropathies are contraindications due to their impact on joint health and healing.
• Active Joint Infection: Any current infection within the joint must be resolved before considering MACI.
• Bone-on-Bone Damage: If the cartilage is completely gone and there is significant bone-on-bone contact or severe subchondral bone changes, MACI may not be able to adequately restore the joint surface.
• Morbid Obesity: Excessive body weight can place undue stress on the treated joint, potentially compromising the success of the repair.
• Unrealistic Patient Expectations: Patients must have a clear understanding of the procedure, its potential benefits, risks, and the demanding rehabilitation process.

The Evaluation Process for MACI Candidacy

The journey to determining MACI eligibility typically involves several steps:

• Detailed Medical History and Physical Examination: The surgeon will assess the patient's symptoms, past injuries, activity level, and perform a comprehensive examination of the affected joint.
• Advanced Imaging Studies:
  • X-rays: To assess bone structure, alignment, and rule out significant arthritis.
  • MRI (Magnetic Resonance Imaging): Crucial for visualizing the cartilage defect's size, depth, and precise location, as well as assessing surrounding soft tissues.
• Diagnostic Arthroscopy: In some cases, a minimally invasive arthroscopic procedure may be performed to directly visualize the cartilage defect, confirm its characteristics, and obtain the biopsy for cell culture. This also allows for addressing any concomitant joint issues.
• Consultation and Discussion: The orthopedic surgeon will discuss all findings with the patient, explaining whether MACI is a suitable option, outlining the expected outcomes, potential risks, and the extensive post-operative rehabilitation plan.

The Importance of a Comprehensive Rehabilitation Plan

While not an "eligibility" criterion in the strictest sense, a patient's capacity and willingness to commit to the post-operative rehabilitation plan is paramount for MACI success. The rehabilitation is lengthy, typically involving phases of non-weight-bearing, controlled range of motion, gradual weight-bearing, and progressive strengthening. This structured approach is critical for the maturation and integration of the newly formed cartilage. Without diligent adherence to this plan, the long-term success of the MACI procedure is significantly compromised, underscoring the holistic view a surgeon takes when evaluating a candidate.