MACI Knee Cartilage Restoration

My MRI Says I Have Knee Cartilage Damage. What Does That Mean?

Your knee can feel manageable at rest, then swell after a run, catch during a squat, or ache after a long shift. An MRI can show an area of cartilage damage, but it cannot determine on its own whether that finding is causing your symptoms or whether MACI is the right treatment. The location and size of the damaged area, your symptoms, and the health of the rest of the knee all matter.

MACI is one option for selected adults with a full-thickness cartilage defect that matches their symptoms. It uses the patient’s own cartilage cells in a staged process. 

The goal is to determine whether the cartilage damage is causing your symptoms and whether MACI is an appropriate option for your knee. Your activity level, work demands, overall health, and the condition of the rest of the knee all play a role in that decision.

 

Why Can One Small Area of Cartilage Damage Affect Your Whole Day?

Articular cartilage is the smooth tissue that covers the ends of the bones inside the knee. A full-thickness defect means the cartilage is damaged through its full depth in one area. This can lead to swelling, aching, catching, or pain when going up or down stairs, squatting, running, working, or completing other daily activities.

The pattern of your symptoms can be more useful than the pain level alone. Your knee might handle a short walk but swell after running, hurt during a deep squat, or catch when you step out of a car. Several knee problems can cause similar pain or catching, so the examination and imaging are considered together to understand what is causing the symptoms.

What Could My MRI Finding Mean?

Not every MRI finding means the same thing. The location, size, and depth of the cartilage injury all help determine whether MACI could be an appropriate treatment.

 

What the MRI says	What it can mean for you	Is MACI used for this?
Focal full-thickness cartilage defect	One specific area of knee cartilage is damaged all the way through. This can cause swelling, catching, or pain with activity.	Possibly. MACI is designed for certain full-thickness cartilage defects when the finding matches the patient’s symptoms.
Meniscus tear	The cushioning tissue between the thighbone and shinbone is torn. It can also cause pain, swelling, or catching.	No. A meniscus tear involves different tissue and follows a different treatment path.
Osteoarthritis	Cartilage wear affects a wider area of the knee and often involves bone and other joint tissues.	Usually not. MACI is not used for severe osteoarthritis or inflammatory joint disease.

 

How Does the MACI Procedure Work?

MACI stands for matrix-induced autologous chondrocyte implantation. Autologous means the cells come from the same patient. Chondrocytes are the cells that make and maintain cartilage.

1. Evaluation and planning. The surgeon reviews your symptoms, examination findings, X-rays, MRI images, previous care, and activity goals.
2. Cartilage biopsy. A small sample of healthy cartilage is collected from the knee, usually during arthroscopy.
3. Cell preparation. The cartilage cells are grown in a laboratory and placed on a thin collagen membrane made from pig tissue.
4. Implantation. During a later procedure, the surgeon shapes the membrane to fit the damaged area and secures it in place. Arthroscopic delivery of MACI is approved for accessible lesions up to 4 cm2. Delivery via mini arthrotomy is available for lesions that are not accessible via arthroscopic delivery.
5. Recovery. Movement, weight bearing, strength, and activity return in stages while the repaired area heals.

The time between biopsy and implantation varies. Cell manufacturing, insurance authorization, procedure planning, associated knee problems, and individual circumstances can all affect the schedule.

Who Could Be a Good Fit for MACI?

MACI is designed for adults with one or more symptomatic, full-thickness cartilage defects of the knee. It is usually considered when pain, swelling, or catching continues after other treatments have not helped enough.

A surgeon will also look at the rest of the knee. MACI should not be used in patients with severe osteoarthritis or certain inflammatory joint diseases, and conditions such as infection, meniscus pathology, ligament instability, or malalignment may need to be addressed before or at the same time as MACI.

Some patients also need another knee problem treated before or during cartilage restoration. An evaluation helps determine whether MACI or a different option makes more sense.

 

 

What Should Patients Know About Recovery?

Recovery after MACI follows a gradual plan set by the surgeon. Early care often includes crutches, a brace, limits on weight placed through the leg, swelling control, and guided knee motion. Physical therapy is often part of recovery as strength, movement, and activity gradually improve.

What Results Have Studies Reported for MACI?

According to the two-year SUMMIT study, MACI was shown to offer greater pain relief and improvement in function compared with microfracture. Improvements in pain and function were maintained with MACI at year 5.

A 10-year study published in the American Journal of Sports Medicine found that improvements seen after MACI were generally maintained through 10 years. At the 10-year follow-up, 92% of patients reported being satisfied with MACI for knee pain relief.

MACI is FDA-approved for the repair of certain symptomatic, full-thickness cartilage defects of the knee in adults. Whether MACI is appropriate depends on the individual patient and their knee condition.

When Might MACI Not Be Recommended?

MACI is designed for a specific type of knee cartilage damage, and some health or knee conditions can make another treatment a better fit. A surgeon reviews these factors before recommending the procedure.

 

What the surgeon checks	Why it matters
Allergies and implant materials	MACI uses antibiotics during processing and a membrane made from animal tissue. Tell the surgeon about medication allergies or concerns about animal-based materials. MACI should not be used in patients with a known hypersensitivity to gentamicin, other aminoglycosides, or products of porcine or bovine origin.
The condition of the knee	Severe arthritis, inflammatory joint disease, or damage across a large part of the knee.
A recent knee operation	A recent knee operation can affect when MACI is performed. MACI should not be used in patients who have undergone knee surgery within the previous 6 months, except surgery to obtain the cartilage biopsy or a procedure performed to prepare the knee for MACI implantation.
Ability to follow recovery instructions	The repaired area must be protected as it heals, so patients need to be able to follow activity and physical therapy instructions.
Age and pregnancy considerations	MACI has not been studied in patients younger than 18 or over 55 years of age. It is not recommended during pregnancy, and breastfeeding safety has not been established.

An active infection, inflammation, poor alignment, ligament instability, or a meniscus problem can also need treatment first. These findings do not always rule out cartilage restoration, but they can change the timing or make another procedure more appropriate.

 

How Dr. Howard Evaluates Knee Cartilage Damage

Daniel R. Howard, MD, FAAOS, is an orthopaedic surgeon specializing in sports medicine who evaluates knee cartilage injuries along with the rest of the knee. During the visit, he reviews when the symptoms started, which movements cause pain or swelling, how the knee affects work or activity, and what treatments have already been tried. He also considers motion, strength, stability, alignment, kneecap movement, X-rays, and MRI findings.

These details help determine whether MACI, another cartilage procedure, nonsurgical care, or a different operation is the most appropriate treatment for your knee.

Frequently Asked Questions

Is MACI the same as stem cell therapy?

No. MACI uses the patient’s own cartilage cells. The cells are grown in a laboratory and placed on a membrane before they are implanted into the damaged area.

Can MACI treat arthritis?

MACI is not used for severe arthritis or inflammatory joint disease. It is designed for a clearly defined area of cartilage damage. The surgeon must look at the entire knee before recommending it.

How many surgeries