Comprehensive guide to microfracture for articular cartilage repair - surgical technique, patient selection, rehabilitation, and outcomes for orthopaedic examination
Reviewed by OrthoVellum Editorial Team
Orthopaedic clinicians and medical editors • Published by OrthoVellum Medical Education Team
Marrow Stimulation | Fibrocartilage Repair | First-Line for Small Lesions
Key exam point: Microfracture produces Type I collagen fibrocartilage, not Type II collagen hyaline cartilage. Biomechanically inferior with lower compressive stiffness and wear resistance.
Under 2cm² optimal. Larger lesions have progressively worse outcomes. Over 4cm² should be treated with OATS, ACI, or allograft. Examiners will test size threshold knowledge.
Non-weight-bearing 6-8 weeks is essential. CPM or aggressive ROM promotes fibrocartilage maturation. Premature loading causes fibrocartilage failure.
Deterioration at 2-5 years is well documented. Short-term results good (85%) but decline over time. May serve as bridge to definitive treatment.
| Lesion Size | First-Line | Alternative | Avoid |
|---|---|---|---|
| Under 2cm² | Microfracture | OATS (single plug) | Large procedures for small lesions |
| 2-4cm² | OATS or ACI | Microfracture if contained | Microfracture as first choice |
| Over 4cm² | ACI or OCA | OATS mosaic | Microfracture (poor outcomes) |
| Bipolar (kissing) | Address alignment first | Combined procedure | Isolated cartilage surgery |
Memory Hook:MICRO-fracture has MICRO results in MICRO lesions - small holes for small defects!
Memory Hook:Make HOLES properly - spacing and depth determine success!
Memory Hook:YOUNG patients do best - microfracture works in ideal candidates!
Why This Topic Matters
Microfracture remains a first-line treatment for small cartilage lesions due to its simplicity, low cost, and single-stage nature. However, understanding its limitations is crucial for exam success - the fibrocartilage produced has inferior mechanical properties and outcomes deteriorate over time.
The critical distinction: Microfracture produces fibrocartilage (Type I collagen) which is mechanically inferior to native hyaline cartilage (Type II collagen). Fibrocartilage has lower compressive stiffness, less water content, and poorer wear characteristics. This fundamental limitation explains the time-limited benefit.
| Property | Hyaline Cartilage | Fibrocartilage (Microfracture) |
|---|---|---|
| Collagen type | Type II | Type I (inferior) |
| Compressive stiffness | High | Lower (50-80%) |
| Water content | 65-80% | Lower |
| Proteoglycans | High aggrecan | Less organized |
| Wear resistance | Excellent | Inferior |
| Durability | Decades | 2-5 years degradation |
| Grade | Description | Depth | Microfracture Suitability |
|---|---|---|---|
| Grade 0 | Normal cartilage | Intact | No treatment needed |
| Grade 1 | Softening or superficial fissures | Superficial | Conservative management |
| Grade 2 | Lesion depth under 50% | Partial thickness | Usually conservative |
| Grade 3 | Lesion depth over 50% | Near full-thickness | Consider microfracture |
| Grade 4 | Full-thickness with subchondral bone exposed | Full-thickness | Microfracture indicated |
Microfracture for Grade 4
Microfracture is primarily indicated for ICRS Grade 4 lesions (full-thickness defects exposing subchondral bone). Grade 3 lesions may be suitable if symptomatic and unresponsive to conservative measures.
Malalignment is a major cause of microfracture failure. Always assess alignment clinically and radiographically. If significant varus (medial lesion) or valgus (lateral lesion), consider osteotomy before or with microfracture.
Weight-bearing AP, lateral, Rosenberg (45° PA), skyline. Assess joint space narrowing, alignment, and OA grade. Normal X-rays do not exclude cartilage damage.
Cartilage-specific sequences essential. Assess lesion location, size, depth, containment. Evaluate subchondral bone for edema or cysts. Identify associated meniscal or ligamentous pathology.
Full-length standing alignment films if clinical concern for malalignment. Calculate mechanical axis deviation.
MRI Findings
Look for: cartilage defect location and size, subchondral edema (may indicate ongoing damage), cyst formation (relative contraindication), bone marrow lesions, and associated meniscal/ligamentous pathology that needs addressing.
The 2cm² Rule
Under 2cm² is the magic number for microfracture. Outcomes are significantly better in lesions under this threshold. Over 4cm², microfracture should generally be avoided in favor of OATS, ACI, or allograft.
Practice these scenarios to excel in your viva examination
"A 28-year-old recreational footballer has a 1.5cm² full-thickness cartilage defect on the medial femoral condyle found incidentally during meniscectomy. How would you manage this?"
"A 35-year-old female presents 18 months after microfracture for a 2.5cm² medial femoral condyle lesion. She has recurrent pain and swelling. MRI shows incomplete fill with subchondral edema. How do you approach this?"
"A 42-year-old presents with a 5cm² cartilage defect on the lateral femoral condyle. The referring surgeon suggests microfracture. What are your thoughts?"
Collagen Type Question
Q: What type of collagen is produced after microfracture? A: Type I collagen - Microfracture produces fibrocartilage containing Type I collagen, not the Type II collagen found in native hyaline cartilage. This is mechanically inferior and contributes to long-term deterioration.
Hole Spacing Question
Q: What is the optimal spacing between microfracture holes? A: 3-4mm - Holes should be 3-4mm apart to preserve subchondral bone bridges. Closer spacing can cause subchondral collapse; wider spacing leaves inadequate marrow access.
Size Threshold Question
Q: What is the optimal lesion size for microfracture? A: Under 2cm² - Best outcomes occur in lesions under 2cm². Lesions 2-4cm² have acceptable but reduced outcomes. Lesions over 4cm² should be treated with alternatives (OATS, ACI, allograft).
Weight-Bearing Question
Q: How long should weight-bearing be restricted after microfracture? A: 6-8 weeks non-weight-bearing - Strict non-weight-bearing for 6-8 weeks is essential to protect the forming fibrocartilage. Premature loading is the most common cause of failure.
Outcome Deterioration Question
Q: When do microfracture results typically begin to deteriorate? A: 2-5 years - Short-term results are good (85% at 2 years) but deterioration occurs after 2-5 years in the majority of patients. This is due to the inferior mechanical properties of fibrocartilage.
CPM Rationale Question
Q: Why is CPM recommended after microfracture? A: CPM is thought to promote fibrocartilage differentiation toward a more hyaline-like phenotype. It also prevents adhesions and maintains ROM. The mechanical stimulus during early healing influences tissue quality.
Key documentation requirements:
High-Yield Exam Summary