KNEE · CONDITIONS & TREATMENT
Knee Cartilage Injuries & Restoration
How defect size, bone involvement, alignment and meniscus function guide OATS, OCA, MACI, BioCartilage, Agili-C and joint preservation.
Restore a Focal Defect; Understand the Whole Knee
Articular cartilage covers the joint surfaces. A focal defect differs from a meniscus tear and widespread arthritis. Not every MRI finding needs surgery.
Restoration aims to improve function while preserving the joint; it cannot guarantee normal cartilage.
[1]What Guides Treatment?
Examination, weight-bearing X-rays and MRI assess the joint. Arthroscopy may refine the size and stability of a defect. The plan considers surface area, depth, location, underlying bone, alignment, ligament stability and meniscus function, along with symptoms, prior surgery and activity goals.
[2]Nonsurgical care may include activity changes, strengthening, selected medication or injections and weight management when appropriate. Persistent symptoms from a focal defect may justify restoration; an acute displaced fragment may need earlier attention.
[2]How Defect Size Influences the Discussion
These are approximate clinical groupings—not fixed eligibility cutoffs. Area in cm² measures the damaged surface, not its diameter. Bone involvement or a patellar location can change the choice even for a small defect.
| Defect pattern | Options commonly considered |
|---|---|
| Small · roughly under 2 cm² | Osteochondral autograft transfer (OATS/OAT) for suitable focal defects. Selected small, contained lesions may be treated with marrow stimulation, with or without an adjunct. |
| Medium · roughly 2–4 cm² | OCA or MACI may be considered. Autograft use depends on location and available donor tissue; significant bone damage favors an osteochondral approach. |
| Large · roughly over 4 cm² | OCA or MACI are common restoration options. OCA addresses cartilage and underlying bone together; MACI may suit a cartilage-focused defect with an appropriate bone bed. |
| Diffuse advanced arthritis | Focal restoration is often a poor fit. Arthritis management and, when appropriate, joint replacement may be more useful. |
Compare the Restoration Options
OATS / OAT: Your Own Cartilage and Bone
A plug is moved from a less-loaded area of your knee to the defect. It restores cartilage and bone in one operation and is often useful for smaller focal lesions. The amount available for harvest is limited, and the donor area can cause symptoms.
[1]OCA: Donor Cartilage and Bone
Osteochondral allograft transplantation replaces a defect with donor cartilage and underlying bone. It may fit larger lesions or defects with substantial bone involvement. Graft matching, availability and incorporation matter, and donor tissue carries a small transmission risk.
[1]MACI: Cultured Cells on a Membrane
MACI uses your own cartilage cells, collected in a biopsy, expanded in a laboratory and implanted in a later procedure. It is FDA-approved for symptomatic full-thickness knee cartilage defects in adults, with or without bone involvement. Bone loss may require additional reconstruction; severe osteoarthritis is a contraindication. Meniscus, stability and alignment problems must be addressed.
[3]Microfracture and BioCartilage
Marrow stimulation creates small openings in the bone to form repair tissue. BioCartilage is a micronized donor-cartilage matrix used as an adjunct in selected contained defects—not a living cartilage-and-bone plug. Small clinical studies report improvement, but they do not prove superiority to OATS, OCA or MACI.
[4]Microfracture produces fibrocartilage, which is less durable than normal joint cartilage. It is generally reserved for selected small lesions and lower-demand patients; prior marrow stimulation can affect later restoration choices.
[1]Agili-C: a Resorbable Scaffold
Agili-C is a cell-free implant intended to support cartilage and bone repair. Its FDA indication covers deep knee joint-surface lesions (ICRS grade III or above) with a total treatable area of 1–7 cm², without severe osteoarthritis (Kellgren–Lawrence grade 0–3). It overlaps more than one size group above.
It is not appropriate for every defect: containment, healthy surrounding bone and defect depth matter. The labeling excludes, among other situations, uncontained defects and bone defects or cysts deeper than 8 mm. Eligibility does not establish superiority to every alternative.
[5]Why Osteotomies and the Meniscus Matter
A repair can remain overloaded if the leg’s alignment is not addressed. A high tibial osteotomy (HTO) or distal femoral osteotomy (DFO) can shift load away from a damaged compartment when malalignment warrants it. A tibial tubercle osteotomy (TTO) can change patellar tracking and load in selected kneecap defects.
[8][6]If a substantial portion of the meniscus is missing and causes symptoms, meniscal allograft transplantation may be considered in a carefully selected knee. It replaces the cushioning meniscus, not the articular surface, and may accompany cartilage restoration. Ligament stability and alignment must also be suitable or corrected; advanced arthritis reduces the likelihood of benefit.
[7]Expect a Plan, Not a Product Choice
Discuss why the defect causes your symptoms, whether bone or alignment needs treatment, and whether surgery would be staged. Cartilage healing often requires protected weight-bearing and prolonged rehabilitation. Return to impact activity depends on the procedure and your progress.
[1]Cartilage injury after a kneecap dislocation →
Questions for Your Visit
- How large and deep is my defect, and is the underlying bone healthy?
- Why does the recommended option fit this location and my activity goals?
- Do I also need an osteotomy, meniscus treatment or ligament stabilization?
Sources & Further Reading
Evidence checked October 3, 2026. General education; treatment is individualized after an examination.
- AAOS OrthoInfo — Articular cartilage restoration
- Hinckel et al. — Algorithm for focal knee cartilage defects
- FDA — MACI prescribing information
- Cole et al. — Prospective multicenter study of BioCartilage augmentation
- FDA — Agili-C instructions for use
- AAOS surgical education — Osteotomy and patellofemoral cartilage transplantation
- AAOS OrthoInfo — Meniscal transplant surgery
- AAOS OrthoInfo — Osteotomy of the knee