Overview
Articular cartilage is the smooth, white surface that coats the ends of the bones inside the knee. It has almost no ability to repair itself. It has no blood supply, and no cells move in to fill a gap the way skin or muscle does. A focal cartilage defect is a distinct spot where the surface has worn through to the bone underneath. The edges of that spot take extra pressure. That pressure slowly pulls the healthy cartilage around it into the wear pattern. Left alone, a small defect can grow into a much larger one over years, damaging the healthy cartilage around it.
Cartilage restoration exists for a specific patient: someone younger with a contained defect. That patient is not a candidate for joint replacement but cannot simply wait. The goal is to fill the defect with a durable surface before the cartilage around it degrades further. Several techniques exist. Each suits a different defect size and patient. The main options are microfracture, osteochondral autograft transfer (OATS), fresh osteochondral allograft, and cell-based implantation. The choice depends on lesion size, depth, and patient age. It also depends on whether the leg's alignment spreads force across the repaired area or overloads it. Alignment that concentrates stress on the repair site will cause it to fail no matter the technique. Fixing leg alignment is often part of the same surgical plan.
How the Procedure Works
The choice of technique depends on the size, location, and depth of the defect. It also depends on your age and how your leg is aligned. There is no one-size-fits-all approach. For small defects in younger patients, microfracture is reliable. Your surgeon makes small holes in the underlying bone to release marrow cells. Those cells form a fibrocartilage fill (a tougher, fibrous substitute for the original surface). For larger or deeper defects, the answer is osteochondral autograft transfer (OATS). A plug of your own cartilage-and-bone is moved from a low-load area of the knee into the defect. This restores true hyaline cartilage (the original joint-surface type), which is more durable than fibrocartilage fill.
Very large defects often require fresh osteochondral allograft. Donor tissue from a tissue bank fills a crater too large for your own supply. Cell-based procedures such as MACI take a sample of your own cartilage cells, grow them in a lab, and reimplant them under a membrane. They are used when the underlying bone is intact and the defect size suits the technique. None of these work reliably in a leg that is poorly aligned. If your knee puts extra load on the repair site, a bone realignment procedure (osteotomy) is often added. It is done at the same time and planned in advance.
When to Consider Cartilage Restoration
Cartilage restoration is usually offered when symptoms, imaging, and a trial of non-operative care all point to surgery as the next step. The typical picture includes:
Focal defect in a healthy knee
A single, contained cartilage lesion with healthy cartilage around it, not widespread arthritis.
Younger patient
An age where joint replacement is not ideal and preserving the native knee is worth the longer rehab.
Correctable alignment
A limb axis that is either neutral or can be corrected (for example with an osteotomy) to avoid overloading the repair.
Treats: OCD Knee
Risks & Why We Still Recommend It
Every operation carries risk. This procedure is offered because the condition, when left untreated, can cause a defect that slowly enlarges and pulls the surrounding cartilage into the same wear pattern. The decision to proceed weighs the risks of surgery against the limitations the condition places on daily function. Surgery does not remove risk; it addresses a problem that is otherwise progressive. Whether it is appropriate is determined for each patient in consultation with the surgeon.
The risks we discuss with you before cartilage restoration include:
- bleeding and infection
- anesthesia risk
- stiffness
- incomplete fill or failure of the graft to integrate
- donor-site symptoms when autograft is used
- blood clot in the leg or lung
Surgery is appropriate when you have a contained, symptomatic focal cartilage defect in a well-aligned, stable knee. If that picture does not fit you, this operation is not offered.
Frequently Asked
questions we hear in clinicWhy won't the cartilage heal on its own?
Articular cartilage has almost no ability to repair itself. It has no blood supply, and no cells move in to fill a gap the way skin or muscle does. Left alone, a small defect can grow into a much larger one over years, pulling the healthy cartilage around it into the wear pattern.
Which technique would I get?
It depends on the size, location, and depth of the defect, your age, and how your leg is aligned. Small defects in younger patients are reliably treated with microfracture; larger or deeper defects use a plug of your own cartilage and bone (OATS); very large defects often require fresh donor tissue; and cell-based procedures such as MACI grow your own cartilage cells in a lab and reimplant them.
Is this the same as a knee replacement?
No. Cartilage restoration exists for a specific patient: someone younger with a single, contained defect who is not a candidate for joint replacement but cannot simply wait. The goal is to preserve the native knee by filling the defect with a durable surface.
Why might I also need my leg realigned?
None of these techniques work reliably in a leg that is poorly aligned. Alignment that concentrates stress on the repair site will cause it to fail no matter the technique, so if your knee puts extra load on that spot, a bone realignment procedure (osteotomy) is often added at the same surgery and planned in advance.
Where does the graft tissue come from?
For OATS, a plug of your own cartilage and bone is moved from a low-load area of the knee, which is why donor-site symptoms are one of the risks we discuss. For very large defects, donor tissue comes from a tissue bank. For MACI, a sample of your own cartilage cells is grown in a lab and reimplanted under a membrane.
Further Reading
External patient-education references and related OSI pages for additional background:
