Knee cartilage damage does not automatically mean knee replacement, and cartilage restoration is not limited to young patients with otherwise perfect knees.
That distinction matters because newer joint-preservation options have expanded the group of patients who may reasonably be evaluated for cartilage restoration. One important example is CARTIHEAL AGILI-C (Agili-C), an FDA-approved, cell-free osteochondral scaffold. Its FDA indication includes International Cartilage Repair Society (ICRS) grade III or greater knee-joint surface lesions with a total treatable area of 1–7 cm² in patients with Kellgren-Lawrence (KL) grade 0–3 osteoarthritis. In other words, KL grade 3 osteoarthritis is not automatically outside the FDA-labeled indication. Severe KL grade 4 osteoarthritis is a contraindication. FDA prescribing information and Instructions for Use.
That does not mean every patient with grade 3 arthritis is a CartiHeal candidate. The pattern of arthritis, location and containment of the defect, alignment, meniscus function, ligament stability, subchondral bone, symptoms, activity goals, and other health factors still matter enormously.
From my perspective as an orthopedic surgeon, the more useful question is not simply, “Do I have arthritis?” It is:
Is there a treatable cartilage or osteochondral lesion in a knee that is still worth preserving?
The hero image above is a high-resolution patient-education illustration. It is not an actual patient, MRI, operative photograph, or treatment result.
What is articular cartilage?
Articular cartilage is the smooth surface covering the ends of the bones inside the knee. It reduces friction and helps distribute load across the joint.
When cartilage is damaged, the problem can range from a small focal defect to widespread osteoarthritis. Full-thickness articular cartilage has limited ability to restore itself to normal native hyaline cartilage, which is why some symptomatic lesions remain painful despite time and rehabilitation.
Symptoms may include swelling after activity, deep joint pain, catching, reduced tolerance for stairs or squatting, recurrent effusions, or difficulty returning to hiking, running or sports. But cartilage abnormalities can also be incidental. Treatment should therefore be based on the patient plus the knee, not the MRI report alone.
Focal cartilage damage can overlap with osteoarthritis
Older cartilage-restoration thinking often divided patients into two groups: focal cartilage defect or arthritis. Real knees are more complicated.
A patient can have a clinically important focal ICRS grade III or IV lesion and radiographic osteoarthritis. The question is how much of the joint is diseased and whether the mechanical environment can support a preservation procedure.
Kellgren-Lawrence grading is an X-ray classification commonly used to describe osteoarthritis severity. KL3 generally reflects definite osteophytes with definite joint-space narrowing and other degenerative changes. KL4 represents severe disease with marked joint-space loss and advanced structural changes.
For many traditional cartilage procedures, diffuse advanced arthritis remains an important reason to favor arthritis-focused treatment instead. However, Agili-C is notable because its FDA indication specifically includes KL0 through KL3, provided the lesion and patient otherwise fit the labeling. FDA PMA P210034.
What exactly is CartiHeal Agili-C?
Agili-C is a cell-free, off-the-shelf, biodegradable, biphasic scaffold made from aragonite, a form of calcium carbonate. It is designed for treatment of cartilage and osteochondral defects. It is not MACI, it does not use cultured cells harvested from the patient, and it is not a knee replacement. FDA Instructions for Use.
The FDA-labeled indication is for:
- ICRS grade III or greater knee-joint surface lesion or lesions
- Total treatable area of 1–7 cm²
- Kellgren-Lawrence grade 0–3 osteoarthritis
The pivotal randomized study included 251 patients and compared Agili-C with surgical standard of care, which consisted of debridement or microfracture depending on the clinical setting. The study enrolled adults with symptomatic cartilage or osteochondral lesions and excluded KL4 osteoarthritis. The FDA concluded that the available data provided reasonable assurance of safety and effectiveness for the labeled population. FDA Summary of Safety and Effectiveness Data.
A 2025 review of the clinical evidence likewise describes Agili-C as an option for focal chondral or osteochondral lesions, including selected knees with mild-to-moderate osteoarthritis up to KL3. Current evidence review.
So can CartiHeal be used in stage 3 osteoarthritis?
Yes, if by “stage 3” you mean Kellgren-Lawrence grade 3, KL3 is within the FDA-labeled OA range for Agili-C.
But that statement needs an important second sentence: KL3 alone does not establish candidacy.
The FDA labeling says safety and effectiveness have not been established in several situations that can be highly relevant to an arthritic knee, including significant malalignment, ligamentous instability, and total or subtotal meniscectomy or lack of a functional meniscus. The labeling also lists important lesion-specific restrictions, including uncontained lesions, subchondral bone defects or cysts deeper than 8 mm, and implantation within avascular necrosis. Patellar cartilage and osteochondral defects are not an indicated treatment site. FDA Instructions for Use.
So two people can both have “KL3 arthritis” and have completely different treatment plans.
One may have a contained symptomatic femoral condyle lesion, acceptable mechanics and a functional meniscus, making preservation worth discussing. Another may have diffuse tricompartmental cartilage loss, major deformity, instability and severe functional limitation, where replacing one focal surface would not address the overall disease.
What should be evaluated before cartilage restoration?
A cartilage-preservation evaluation should look beyond the MRI.
Weight-bearing X-rays show joint-space loss, osteophytes and the overall distribution of arthritis. Full-length standing alignment imaging may be useful when bow-legged or knock-kneed alignment is suspected. MRI helps characterize cartilage, subchondral bone, bone marrow changes, menisci, ligaments and other lesions. The physical examination helps determine whether the imaging actually matches the patient’s pain and function.
The major decision questions include:
- Is the lesion focal enough to treat?
- Where is it located?
- Is the surrounding bone healthy enough?
- Is the defect contained?
- How much osteoarthritis exists elsewhere in the knee?
- Is the meniscus functional?
- Is the knee stable?
- Is malalignment overloading the damaged compartment?
- Has appropriate nonsurgical treatment been tried?
- Does the patient’s desired activity justify the recovery and risks?
This is why a cartilage procedure should not be chosen from MRI dimensions alone.
When can physical therapy be enough?
Not every cartilage defect needs surgery.
Physical therapy can improve symptoms by restoring motion, quadriceps capacity, hip strength, neuromuscular control and the knee’s ability to tolerate load. Activity modification, weight management when appropriate, bracing in selected alignment patterns and medications may also help.
A successful nonsurgical program does not necessarily mean cartilage regenerated. It means the knee became functional enough that surgery was unnecessary.
For patients with persistent swelling, mechanical symptoms or activity-limiting pain despite appropriate rehabilitation, further evaluation may clarify whether the cartilage lesion is actually driving symptoms.
How does Agili-C compare with MACI, OATS and osteochondral allograft?
There is no universally best cartilage procedure. The best option depends on the defect and the joint around it.
MACI
Matrix-induced autologous chondrocyte implantation uses the patient’s own cartilage cells. Cells are harvested, expanded and later implanted on a collagen membrane, making MACI generally a staged treatment. It can be useful for appropriately selected symptomatic full-thickness defects when the joint remains preservable.
OATS
Osteochondral autograft transfer moves cylinders of the patient’s own cartilage and underlying bone from a lower-demand area into a defect. It provides native hyaline cartilage and bone in a one-stage procedure but is limited by how much donor tissue can safely be harvested.
Osteochondral allograft
Osteochondral allograft uses donor cartilage and subchondral bone. It can be particularly useful for larger osteochondral defects, substantial bone involvement or selected failed prior cartilage procedures.
Agili-C
Agili-C is different from all three. It is an off-the-shelf, cell-free osteochondral scaffold. Its FDA indication is particularly notable because it expressly encompasses appropriately selected patients across KL0–3, rather than limiting the labeled population to knees with no radiographic OA.
The choice should be based on lesion size, depth, location, bone involvement, arthritis pattern, previous procedures and the mechanical environment of the knee.
Alignment, meniscus and stability can determine whether restoration makes sense
Cartilage does not function in isolation.
A bow-legged knee can overload the medial compartment. A deficient meniscus increases contact stress. Ligament instability can create abnormal shear. Patellar instability can repeatedly overload the patellofemoral joint.
In selected patients, successful joint preservation may therefore require treatment of the cause of overload, not simply the damaged surface. That can include osteotomy, meniscus preservation or reconstruction, ligament reconstruction or other mechanical correction.
This concept is especially important when considering cartilage restoration in a knee that already has radiographic osteoarthritis.
For more information about the preservation procedures evaluated at Pacific Bone & Joint, see our cartilage restoration service. If bow-legged or knock-kneed loading may be contributing, our guide to adult leg alignment problems explains why full-length imaging and mechanical-axis assessment can change the treatment plan.
When is knee replacement the better conversation?
Cartilage restoration is intended to preserve a knee, not to postpone replacement at any cost.
When pain comes from diffuse end-stage arthritis rather than a treatable focal lesion, partial or total knee replacement may be a more predictable strategy. KL4 osteoarthritis is specifically contraindicated for Agili-C under the FDA labeling. Even before KL4, the overall pattern of disease may make arthroplasty more appropriate for an individual patient.
The presence of KL3 therefore should not trigger either extreme conclusion. It should not automatically mean “too much arthritis for cartilage restoration,” and it should not automatically mean “CartiHeal candidate.” It means the knee deserves a more detailed structural and mechanical assessment.
What are the risks and limitations?
All cartilage procedures involve tradeoffs. Depending on the operation, risks can include infection, blood clots, stiffness, persistent pain, incomplete integration, graft or implant failure, swelling, progression of osteoarthritis and additional surgery.
Agili-C has its own warnings, precautions and potential adverse events. The FDA labeling should be reviewed as part of informed decision-making. Importantly, its labeling also notes populations and conditions in which safety and effectiveness have not been established. FDA Instructions for Use.
No cartilage-restoration procedure can guarantee avoidance of future knee replacement.
Questions to ask when you have cartilage damage plus arthritis
Useful questions include:
- Is my pain coming from one treatable lesion or from diffuse arthritis?
- What is my Kellgren-Lawrence grade on weight-bearing X-rays?
- Where is the cartilage lesion and is it contained?
- Is the subchondral bone healthy enough for restoration?
- Is my meniscus functional?
- Is the knee stable?
- Does my alignment need to be corrected?
- Am I a candidate for Agili-C under the FDA labeling?
- Why would Agili-C, MACI, OATS, allograft, osteotomy or arthroplasty be favored in my particular knee?
- What happens if I continue rehabilitation instead?
When should you seek an orthopedic evaluation?
Consider a cartilage-preservation evaluation when pain, recurrent swelling, catching or activity limitation persists despite appropriate rehabilitation, particularly when MRI has shown a focal chondral or osteochondral lesion.
An evaluation can be especially useful if you have been told that you are “too arthritic” for cartilage restoration based only on the phrase grade 3 osteoarthritis. Whether preservation remains reasonable depends on what “grade 3” means, the distribution of disease and the rest of the knee mechanics.
If you have a symptomatic cartilage defect, including a knee with KL grade 3 osteoarthritis, schedule an orthopedic evaluation with Pacific Bone & Joint to determine whether rehabilitation, cartilage restoration, mechanical correction or arthroplasty best fits the actual pattern of your knee disease.
