Patient must undergo preoperative orthopedic assessment, MRI of the affected joint, routine blood work, EKG, and anesthesia evaluation. Strict NPO status for at least 8 hours prior to surgery. Patient should discontinue NSAIDs and blood thinners 7 days pre-op. Prophylactic antibiotics administered within 60 minutes of incision. Informed consent obtained for arthroscopic intervention and potential conversion.
Post-operative protocol includes strict non-weight bearing or touch-down weight bearing for 6 weeks, depending on lesion size. Passive range of motion (PROM) initiated early with Continuous Passive Motion (CPM) machine. DVT prophylaxis, pain management via multimodal analgesia, and physical therapy sessions focused on quadriceps activation. Discharge after stability of pain control and safe mobilization with assistive devices. Mandatory follow-up scheduled at 2 weeks, 6 weeks, and 3 months.
Arthroscopic Microfracture: A Comprehensive Clinical Guide to Cartilage Repair
1. Comprehensive Introduction & Overview
Arthroscopic microfracture is a marrow-stimulating surgical technique designed to treat full-thickness articular cartilage defects. Unlike healthy hyaline cartilage, which has a limited intrinsic healing capacity due to its avascular nature, the subchondral bone is highly vascularized. Microfracture leverages this biological reality by creating controlled micro-trauma to the subchondral bone plate, facilitating the release of mesenchymal stem cells (MSCs), growth factors, and marrow elements into the defect site.
These elements form a "super-clot" that differentiates into fibrocartilage, a repair tissue that, while biochemically distinct from native hyaline cartilage, provides a functional surface to reduce pain and improve joint kinematics. This procedure is predominantly utilized in the knee, though it has applications in the ankle and hip.
2. Technical Specifications and Mechanism of Action
The efficacy of microfracture relies on the "marrow stimulation" principle. The articular cartilage—the smooth, white tissue covering the ends of bones—is devoid of nerves and blood vessels. When it is damaged (chondral defect), it cannot heal on its own.
The Biological Cascade
- Debridement: The surgeon removes unstable, frayed cartilage edges to create a stable "vertical wall" of healthy cartilage.
- Perforation: Using a specialized surgical awl or high-speed burr, the surgeon creates small holes (1–2 mm in diameter) in the subchondral bone at the base of the lesion.
- Marrow Release: These holes penetrate the calcified layer into the subchondral bone, allowing blood and bone marrow elements (containing pluripotent stem cells) to flow into the defect.
- Clot Consolidation: The released elements form a fibrin-rich clot.
- Differentiation: Over the following weeks, this clot undergoes a maturation process, transforming into fibrocartilage. This tissue is characterized by a higher concentration of Type I collagen compared to the Type II collagen found in native hyaline cartilage.
3. Clinical Indications & Usage
Patient selection is the primary determinant of success in microfracture procedures.
Ideal Candidate Profile
- Lesion Size: Small to medium-sized lesions (typically < 2–4 cm²). Larger lesions often require osteochondral autograft transfer (OATS) or Matrix-Induced Autologous Chondrocyte Implantation (MACI).
- Patient Age: Generally younger patients (< 45 years) who are active and have a higher metabolic potential for healing.
- Activity Level: Patients who are motivated to adhere to a strict post-operative weight-bearing and rehabilitation protocol.
- Joint Alignment: Patients must have neutral mechanical alignment (or have had a corrective osteotomy) to prevent concentrated loading on the repair site.
Clinical Indications Table
| Condition | Clinical Relevance |
|---|---|
| Traumatic Chondral Defect | Acute injury in a young, healthy athlete. |
| Osteochondritis Dissecans (OCD) | Focal areas of subchondral bone necrosis. |
| Early-Stage Osteoarthritis | Focal lesions in otherwise "healthy" joints. |
| Failed Conservative Care | Persistent pain after 6+ months of PT/viscosupplementation. |
4. Pre-Operative Preparation
Preparation is critical to ensure optimal biological environment for healing.
- Imaging: MRI (T2 mapping or dGEMRIC) to assess the depth of the lesion and the quality of the surrounding cartilage.
- Mechanical Assessment: Full-leg weight-bearing radiographs to rule out varus/valgus malalignment.
- Optimization: Cessation of NSAIDs (which can inhibit bone healing) 7–10 days prior. Smoking cessation is mandatory, as nicotine significantly impairs mesenchymal stem cell migration and bone healing.
- Informed Consent: Patients must be educated on the nature of "fibrocartilage" versus "hyaline cartilage" to manage post-surgical expectations regarding longevity.
5. The Procedure: Surgical Steps
The procedure is performed arthroscopically, minimizing soft tissue trauma.
- Step 1: Diagnostic Arthroscopy: Thorough inspection of all joint compartments to ensure no secondary pathology exists (e.g., meniscal tears, ligamentous instability).
- Step 2: Debridement: Using a motorized shaver, the surgeon removes all loose, unstable, or fibrillated cartilage until a stable, vertical rim of healthy cartilage is achieved.
- Step 3: Calcified Layer Removal: The calcified cartilage layer at the base of the defect must be removed (curetted) to expose the subchondral bone.
- Step 4: Microfracturing: Using a 30-degree or 90-degree awl, holes are placed 3–4 mm apart. The holes must be deep enough to visualize marrow elements (the "fat droplet sign").
- Step 5: Irrigation and Closure: The joint is flushed, and portals are closed with sutures or steri-strips.
6. Post-Operative Recovery Protocol
The rehabilitation protocol is arguably as important as the surgery itself.
Phase 1: Protection (Weeks 0–6)
- Weight Bearing: Strict non-weight bearing (NWB) or touch-down weight bearing (TDWB) with crutches. This prevents the "washing out" of the marrow clot.
- Range of Motion (ROM): Use of a Continuous Passive Motion (CPM) machine is often recommended to stimulate synovial fluid circulation, which provides nutrition to the clot.
Phase 2: Progressive Loading (Weeks 6–12)
- Weight Bearing: Gradual transition to full weight-bearing as tolerated.
- Strengthening: Focus on closed-chain exercises (mini-squats, leg press) to maintain muscle mass without excessive shear force.
Phase 3: Return to Activity (Months 4–12)
- Impact Loading: Gradual introduction of impact activities (jogging, sport-specific drills) only after adequate muscle strength and proprioception are verified.
- Return to Sport: Usually permitted between 6 and 12 months, pending clinical assessment.
7. Risks, Side Effects, and Contraindications
Potential Complications
- Fibrosis/Arthrofibrosis: Excessive scar tissue formation leading to stiffness.
- Subchondral Bone Overgrowth: The formation of "bony bumps" at the site of the repair.
- Infection: Standard risk for any arthroscopic intervention (< 0.1%).
- Failure of Repair: The fibrocartilage may degrade over time, leading to recurring symptoms.
Contraindications
- Advanced Osteoarthritis: Diffuse, multi-compartment cartilage wear.
- Morbid Obesity: High BMI significantly increases contact forces, leading to premature failure.
- Inflammatory Arthritis: Conditions like Rheumatoid Arthritis require systemic, not focal, management.
- Malalignment: Uncorrected varus/valgus deformity will cause the repair to fail under excessive mechanical load.
8. Alternative Treatments
| Treatment | Best For | Mechanism |
|---|---|---|
| MACI | Large lesions (> 4 cm²) | Cultured autologous chondrocytes on a collagen membrane. |
| OATS/Mosaicplasty | Deep, localized lesions | Transfer of bone/cartilage plugs from non-weight bearing areas. |
| Allograft Transplantation | Massive defects | Using donor cartilage/bone to fill large gaps. |
| Viscosupplementation | Mild OA/Pain control | Injecting hyaluronic acid to lubricate the joint. |
9. Frequently Asked Questions (FAQ)
1. Is microfracture the same as a knee replacement?
No. Microfracture is a "joint-preserving" procedure intended to repair a small, focal defect. A knee replacement is a "joint-replacing" procedure for widespread osteoarthritis.
2. How long does the fibrocartilage last?
Clinical results show that fibrocartilage provides good pain relief for 5–10 years in the majority of patients, though it does not have the same wear-resistance as native hyaline cartilage.
3. Why do I need to be on crutches for so long?
The clot formed after microfracture is fragile. Early weight-bearing can shear the clot off the bone before it has a chance to mature into tissue.
4. Can I play sports again?
Yes, many athletes return to their pre-injury level of play, but it depends on the location of the lesion and the quality of post-operative physical therapy.
5. Does microfracture hurt?
Most patients report significant post-operative pain for the first 2 weeks, which is managed with multimodal analgesia (nerve blocks, anti-inflammatories, and cryotherapy).
6. What happens if the procedure fails?
If microfracture fails, the joint is usually still eligible for other procedures like MACI or, in older patients, a partial or total joint replacement.
7. Does insurance cover this?
In most cases, yes, as it is a standard of care for focal chondral defects. However, pre-authorization is required to prove medical necessity.
8. Can this be done on the hip?
Yes, microfracture is frequently used to treat acetabular cartilage defects in the hip, often in conjunction with labral repair.
9. Is smoking a deal-breaker?
Smoking is a major risk factor for non-healing. Most surgeons will require patients to stop smoking at least 4 weeks before surgery.
10. How do I know if I am a candidate?
Consultation with a fellowship-trained orthopedic sports medicine surgeon is required. They will perform a physical exam and review your MRI to confirm the lesion is focal and the joint alignment is sound.
10. Clinical Conclusion
Arthroscopic microfracture remains a cornerstone of cartilage restoration surgery. While it does not recreate native hyaline cartilage, its ability to produce a functional, durable fibrocartilaginous repair makes it an essential tool for the active patient. Success is highly dependent on rigid adherence to post-operative non-weight bearing protocols and careful patient selection regarding lesion size and joint alignment. When executed correctly, it provides a viable path to pain-free function and continued athletic participation.