Knee

Chondral (Articular Cartilage) Defects

Q: What is the difference between microfracture and MACI?

Microfracture stimulates fibrocartilage fill from bone marrow — a single-stage procedure with rapid recovery but inferior cartilage quality and durability for larger lesions. MACI implants cultured chondrocytes on a collagen scaffold to produce hyaline-like cartilage repair tissue — a two-stage procedure with superior histological outcomes for defects > 2 cm².

Articular cartilage — the smooth, glistening tissue lining the ends of bones within the knee joint — has virtually no capacity to heal itself. Even small full-thickness cartilage defects can progress over years to joint-wide osteoarthritis if left untreated in younger, active patients. At Maryland Orthopedic Specialists, our cartilage restoration specialists offer the full spectrum of evidence-based treatments, from arthroscopic microfracture for small lesions to sophisticated cell-based and osteochondral allograft transplantation for large or complex defects — giving patients with focal cartilage injuries a real chance at restoring joint surface integrity and delaying or avoiding total knee replacement.

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What is chondral (articular cartilage) defects?

Articular cartilage is a highly specialized hyaline tissue, 2–6 mm thick, composed predominantly of type II collagen and proteoglycans. Its avascular, aneural, alymphatic composition explains its lack of intrinsic healing capacity: without a blood supply to deliver inflammatory cells and progenitor cells, even partial-thickness defects do not heal spontaneously.

Causes of chondral defects:

Acute trauma (patellar dislocation, tibial plateau injury, direct impaction)
Repetitive mechanical overload
Osteochondritis dissecans (OCD) — subchondral bone disease that destabilizes the overlying cartilage
Prior meniscectomy — loss of meniscal shock absorption increases cartilage stress
Ligament instability (ACL deficiency) — abnormal shear forces accelerate cartilage damage

International Cartilage Regeneration Society (ICRS) Grading:

Grade 0: Normal cartilage
Grade 1: Superficial softening, fissuring, or fibrillation
Grade 2: Partial-thickness defect; < 50% cartilage depth
Grade 3: Deep defect; > 50% depth; down to but not through subchondral bone
Grade 4: Full-thickness defect through subchondral bone (OCD, full osteochondral lesion)

Treatment decisions are primarily driven by lesion size (cm²) and depth (chondral vs. osteochondral), as well as patient age, activity level, and associated pathology.

Treatment options

Treatment is based primarily on lesion size, depth, and patient factors. No cartilage restoration procedure works in isolation — concurrent problems such as malalignment, meniscal insufficiency, and ligament instability must be addressed at the same time to protect the repair and maximize durability.

Non-Operative Management

For low-grade lesions (ICRS Grades 1–2) and incidentally discovered asymptomatic defects, non-operative management is appropriate. A structured physical therapy program focused on quadriceps strengthening, hip abductor activation, and neuromuscular control reduces peak cartilage loading and is the foundation of conservative care. Anti-inflammatory medications and corticosteroid injections can calm inflammatory flares, and viscosupplementation may provide symptomatic relief in mild focal disease. For younger, active patients with Grade 3–4 symptomatic lesions, however, non-operative care rarely provides durable relief and surgical restoration is generally recommended.

Surgical Procedure

Microfracture (Cartilage Repair)

Marrow stimulation technique that penetrates the subchondral bone to recruit stem cells and form a fibrocartilage repair patch in a focal cartilage defect. Best suited for small defects in patients who have not had prior cartilage procedures.

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OATS — Osteochondral Autograft Transfer

Transfer of one or more osteochondral plugs from a low-weight-bearing area of the patient's own knee to fill a focal cartilage defect with living hyaline cartilage and intact subchondral bone — a durable single-stage restoration.

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Osteochondral Allograft Transplantation (OCA)

Transplantation of a size-matched fresh donor osteochondral plug to restore a large full-thickness cartilage defect with living hyaline cartilage. Used when defects are too large for autograft or when prior cartilage treatment has failed.

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Frequently Asked Questions

Can cartilage grow back on its own?

No — full-thickness articular cartilage defects do not heal spontaneously because cartilage has no blood supply to deliver healing cells. Partial-thickness defects (< 50% depth) also do not reliably repair; they may stabilize but typically do not fill. This is why focal defects in young, active patients are treated rather than observed.

What is the difference between microfracture and MACI?

Microfracture stimulates fibrocartilage fill from bone marrow — a single-stage procedure with rapid recovery but inferior cartilage quality and durability for larger lesions. MACI implants cultured chondrocytes on a collagen scaffold to produce hyaline-like cartilage repair tissue — a two-stage procedure with superior histological outcomes for defects > 2 cm².

Can I still get a knee replacement if my cartilage restoration procedure fails?

Yes — cartilage restoration procedures do not burn bridges for future joint replacement. Patients with failed cartilage procedures may undergo total knee replacement at any time, and outcomes are not compromised by prior cartilage surgery.

Do I need to address my alignment before a cartilage procedure?

Malalignment (varus bowing, valgus deformity) concentrates load on the defect and is the primary cause of cartilage restoration failure. Realignment procedures (high tibial osteotomy, distal femoral osteotomy) are often performed concurrently with cartilage restoration in patients with coronal malalignment.

How long is recovery after a cartilage restoration procedure, and when can I return to sport?

Recovery from cartilage restoration varies by procedure: microfracture typically requires six to nine months before return to sport, while MACI or osteochondral allograft transplantation can take nine to twelve months or longer because the graft needs time to fully integrate. Weight-bearing is usually restricted for six to eight weeks to protect the healing cartilage. Your MOS surgeon will use a structured, criteria-based return-to-sport protocol that includes strength testing and functional assessments to ensure the repair is mature enough to handle athletic demands. Patience during rehabilitation significantly improves long-term outcomes.