Cartilage Restoration: The Complete Treatment Algorithm

Articular cartilage is the "teflon" of the body—a frictionless, pain-free surface that lasts a lifetime. However, it has an Achilles heel: it is avascular, aneural, and alymphatic. Once damaged, it does not heal. It heals with scar tissue (fibrocartilage), which lacks the biomechanical durability of hyaline cartilage.

For the young patient with a focal chondral defect, this is a crisis. Left untreated, it progresses to osteoarthritis. This article outlines the modern treatment algorithm for cartilage restoration.

Phase 1: The Background Check

Before touching the cartilage, you must assess the Environment. A cartilage graft placed in a hostile environment will fail.

1. Alignment: Is the patient in varus/valgus? Correcting the axis (HTO/DFO) is often more important than the cartilage procedure itself.
2. Stability: Is the ACL/PCL intact? Shear forces will destroy any graft.
3. Meniscus: Is there a "shock absorber"? If the meniscus is gone, consider a Meniscal Allograft Transplantation (MAT).

Visual Element: A flow diagram starting with "Background Factors" (Alignment, Meniscus, Ligaments) before branching into specific cartilage procedures.

Phase 2: The Defect Assessment

Classify the defect based on:

• Size: Small (<2cm²), Medium (2-4cm²), Large (>4cm²).
• Containment: Shouldered (surrounded by healthy cartilage) vs Uncontained.
• Location: Femoral Condyle (Weight bearing) vs Patellofemoral (Shear).
• Bone: Is the subchondral bone involved (Osteochondral defect)?

Treatment Options

1. Palliative: Debridement & Chondroplasty

• Indication: Low demand, widespread disease, mechanical symptoms (catching/locking).
• Technique: Shaving unstable flaps to stable rims.
• Outcome: Symptomatic relief only. No restoration.

2. Reparative: Marrow Stimulation (Microfracture)

• Indication: Small (<2cm²), contained defects. First-line treatment.
• Technique: Awl or drill holes into subchondral bone to release marrow elements (MSCs/Growth Factors). Forms a "Super Clot."
• Biology: Produces Fibrocartilage (Type I Collagen).
• Pros: Arthroscopic, cheap, easy.
• Cons: Inferior wear characteristics. Deteriorates after 2-5 years. Not recommended for high-level athletes.

3. Restorative: Osteochondral Autograft (OATS / Mosaicplasty)

• Indication: Small-Medium (<2-3cm²) defects. High demand athletes. Bone loss involved.
• Technique: Harvest cylindrical plugs of bone+cartilage from non-weight bearing zones (Trochlear ridge) and press-fit them into the defect.
• Biology: Moves native Hyaline Cartilage.
• Pros: True hyaline cartilage. Bone-to-bone healing. Immediate structural integrity.
• Cons: Donor site morbidity. Limited supply (cannot treat large defects). "Cobblestone" surface.

4. Restorative: Cell-Based Therapies (MACI)

• Indication: Medium-Large (2-5cm²) defects. Failed microfracture. Pure chondral defects (no bone loss).
• Technique:
  • Stage 1: Arthroscopic biopsy of healthy cartilage.
  • Lab: Chondrocytes are cultured and expanded, then seeded onto a collagen membrane.
  • Stage 2: Open surgery. Membrane glued/sutured into defect.
• Biology: Hyaline-like cartilage (Type II Collagen).
• Pros: Can treat large areas. No donor site morbidity. Excellent long-term results.
• Cons: Two surgeries. Expensive. Slow rehab (graft maturation takes months).

5. Salvage: Osteochondral Allograft (OCA)

• Indication: Massive defects (>4cm²), Uncontained defects, Osteochondritis Dissecans (OCD), Failed prior surgeries.
• Technique: Fresh cadaveric condyle matched to patient size. The defect area is replaced with a large plug/shell of living allograft.
• Biology: Living Hyaline cartilage + Mature bone.
• Pros: One stage. Restores architecture. High success rate (80-90% at 10 years).
• Cons: Graft availability. Cell viability (must use within 28 days). Immunogenicity (minimal). Cost.

Rehabilitation: The 4 Phases

Biology takes time.

• Phase 1 (0-6 weeks): Protection. Non-weight bearing (or touch weight bearing). CPM machine to stimulate chondrocyte nutrition.
• Phase 2 (6-12 weeks): Transition. Progressive weight bearing. Closed chain exercises.
• Phase 3 (3-6 months): Strengthening.
• Phase 4 (6-12 months): Return to Sport. (Only when MRI shows graft integration and functional tests passed).

Evidence Corner

• Microfracture vs OATS: OATS superior for return to sport in athletes (Gudas et al).
• Microfracture vs MACI: MACI superior for defects >2cm² (SUMMIT trial).
• Allograft: Excellent salvage with >80% survival at 10 years, even in complex cases (Gross et al).

Conclusion

No single procedure fits all.

• Small (<2cm): Microfracture or OATS.
• Medium (2-4cm): MACI or OATS.
• Large (>4cm) or Bone Loss: Allograft (OCA).

Clinical Trap: Do not microfracture a lesion > 4cm². It will fail. Do not perform MACI if there is significant subchondral bone edema or loss; the membrane needs a stable bed.

References

1. Saris, D., et al. (2014). "Matrix-Applied Characterized Autologous Cultured Chondrocytes Versus Microfracture." Am J Sports Med.
2. Gudas, R., et al. (2005). "A prospective randomized clinical study of mosaic osteochondral autologous transplantation versus microfracture." Arthroscopy.
3. Gross, A. E., et al. (2008). "Fresh osteochondral allografts for posttraumatic defects in the knee." JBJS.