High Yield Overview

MICROFRACTURE TECHNIQUE

Marrow Stimulation | Fibrocartilage Repair | First-Line for Small Lesions

Critical Microfracture Exam Points

Fibrocartilage NOT Hyaline

Key exam point: Microfracture produces Type I collagen fibrocartilage, not Type II collagen hyaline cartilage. Biomechanically inferior with lower compressive stiffness and wear resistance.

Size Matters

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.

Rehabilitation Critical

Non-weight-bearing 6-8 weeks is essential. CPM or aggressive ROM promotes fibrocartilage maturation. Premature loading causes fibrocartilage failure.

Time-Limited Benefit

Deterioration at 2-5 years is well documented. Short-term results good (85%) but decline over time. May serve as bridge to definitive treatment.

Quick Decision Guide - Cartilage Treatment Selection

Mnemonic

MICROMICRO - Key Principles

Memory Hook:MICRO-fracture has MICRO results in MICRO lesions - small holes for small defects!

Mnemonic

HOLESHOLES - Surgical Technique

Memory Hook:Make HOLES properly - spacing and depth determine success!

Mnemonic

YOUNGIdeal Patient Selection

Memory Hook:YOUNG patients do best - microfracture works in ideal candidates!

Overview and Epidemiology

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.

Common Indications

Full-thickness cartilage defect
Lesion under 2cm²
Intact subchondral bone
Contained lesion with stable shoulders
Failed conservative management

Contraindications

Lesion over 4cm²
Degenerative OA (diffuse disease)
Bipolar (kissing) lesions untreated
Uncorrected malalignment
Inflammatory arthropathy
Subchondral bone disease

Pathophysiology and Mechanisms

Fibrocartilage vs Hyaline Cartilage

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.

Hyaline vs Fibrocartilage

Why It Works

Subchondral penetration releases marrow elements
Mesenchymal stem cells populate the defect
Blood clot forms as scaffold for healing
CPM stimulates cartilage-like differentiation
Fibrocartilage fills the defect over 6-12 months

Why It Fails

Fibrocartilage is mechanically inferior
Subchondral changes develop over time
Cyclic loading degrades repair tissue
Large lesions cannot fill adequately
Type I collagen lacks resilience of Type II

Classification Systems

ICRS Cartilage Lesion Grading

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.

Clinical Assessment

History

Mechanism: Traumatic vs degenerative onset
Symptoms: Mechanical (catching, locking) vs pain
Duration: Acute vs chronic symptoms
Activity level: Sport demands and expectations
Previous treatment: Conservative measures tried

Examination

Effusion: Suggests synovitis/cartilage damage
Joint line tenderness: Over affected compartment
Range of motion: Usually preserved unless severe
Alignment: Varus/valgus assessment
Stability: Ligamentous integrity

Alignment Assessment is Critical

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.

Investigations

Imaging Protocol

First LineX-rays

Weight-bearing AP, lateral, Rosenberg (45° PA), skyline. Assess joint space narrowing, alignment, and OA grade. Normal X-rays do not exclude cartilage damage.

Key InvestigationMRI

Cartilage-specific sequences essential. Assess lesion location, size, depth, containment. Evaluate subchondral bone for edema or cysts. Identify associated meniscal or ligamentous pathology.

If Malalignment SuspectedLong-leg Films

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.

Management Algorithm

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.

Factors Favoring Good Outcome

Lesion under 2cm²
Age under 40
Acute traumatic defect
Single lesion
Normal alignment
Compliant with rehab

Factors Predicting Failure

Lesion over 4cm²
Age over 40
Multiple lesions
Degenerative (vs traumatic)
Malalignment
Early weight-bearing
Subchondral bone disease

Evidence Base and Key Trials

Microfracture Long-Term Outcomes

Mithoefer K, McAdams T, Williams RJ, et al • AJSM (2009)

Clinical Implication: Microfracture provides time-limited benefit; outcomes deteriorate after 2 years. Best for small lesions in young patients.

Limitation: Systematic review of level 4 studies.

STAR Trial - Microfracture vs ACI

Saris DB, Vanlauwe J, Victor J, et al • AJSM (2014)

Clinical Implication: ACI provides more durable results than microfracture for larger lesions. Microfracture may be acceptable short-term bridge.

Limitation: High dropout rate at 5 years.

Subchondral Bone Changes After Microfracture

Mithoefer K, Steadman JR, et al • AJSM (2005)

Clinical Implication: Microfracture may compromise subchondral bone, making future OATS/ACI more difficult. Consider in young patients.

Limitation: Retrospective review.

AMIC vs Microfracture

Volz M, Schaumburger J, Frick H, et al • Cartilage (2017)

Clinical Implication: AMIC may improve tissue fill without adding surgical stages. Consider for medium lesions (2-4cm²).

Limitation: Short follow-up, small sample.

Failed Microfracture and Subsequent Treatment

Minas T, Gomoll AH, Rosenberger R, et al • CORR (2009)

Clinical Implication: ACI remains an option after failed microfracture, though outcomes may be slightly reduced. Plan accordingly.

Limitation: Retrospective single-center.

Exam Viva Scenarios

Practice these scenarios to excel in your viva examination

VIVA SCENARIOStandard

Scenario 1: Small Cartilage Defect (~2-3 min)

EXAMINER

"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?"

EXCEPTIONAL ANSWER

This young patient with a small (1.5cm²) cartilage defect on the medial femoral condyle is an ideal candidate for microfracture. My rationale: The lesion is under 2cm² which is optimal for microfracture. He is young (under 40), which is associated with better healing. The defect is on a weight-bearing surface where intervention is warranted. At this surgery, I would: 1. Complete the planned meniscectomy first 2. Assess the lesion fully - confirm size, containment, stable shoulders 3. Check alignment - if normal, proceed with microfracture 4. Debride to stable vertical cartilage edges 5. Remove the calcified cartilage layer 6. Create microfracture holes 3-4mm apart, 2-4mm deep 7. Confirm marrow bleeding with pump off Post-operatively: Non-weight-bearing 6-8 weeks, CPM or aggressive ROM immediately. Return to sport 9-12 months. I would counsel him that microfracture produces fibrocartilage (Type I collagen) not native hyaline (Type II), and that results may deteriorate after 2-5 years. For this small lesion in a young patient, initial outcomes should be good.

VIVA SCENARIOChallenging

Scenario 2: Failed Microfracture (~3-4 min)

EXAMINER

"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?"

EXCEPTIONAL ANSWER

This is a failed microfracture - not unexpected given the 2.5cm² size was at the upper end of optimal range. My assessment would focus on: 1. Symptoms: Confirming mechanical symptoms from cartilage, not other pathology 2. Alignment: Re-check for any malalignment that needs addressing 3. MRI: Assess subchondral bone status (cysts, edema, bone quality) 4. Associated pathology: Ensure no meniscal or ligamentous issues My treatment options for this failed microfracture: **First choice - ACI or MACI:** - Most appropriate for this 2.5cm² lesion - Two-stage procedure (harvest, then implant 6 weeks later) - Produces more hyaline-like cartilage (Type II collagen) - Prior microfracture does not preclude ACI, though outcomes may be slightly reduced **Alternative - OATS (if under 2-2.5cm²):** - Can cover with 2-3 plugs if lesion contained - Single stage - True hyaline cartilage transplanted - Donor site morbidity is a consideration I would need to assess the subchondral bone carefully - if there is significant bone loss or cystic change from the failed microfracture, I may need bone grafting before or during the definitive cartilage procedure. If there is any malalignment, I would address this with osteotomy either staged before or combined with the cartilage procedure.

VIVA SCENARIOCritical

Scenario 3: Large Lesion Discussion (~2-3 min)

EXAMINER

"A 42-year-old presents with a 5cm² cartilage defect on the lateral femoral condyle. The referring surgeon suggests microfracture. What are your thoughts?"

EXCEPTIONAL ANSWER

I would respectfully suggest that microfracture is not the optimal treatment for this lesion, and here's why: **Why microfracture is suboptimal:** 1. Size over 4cm² - microfracture outcomes are poor for large lesions 2. Age 42 - at the upper limit, healing potential reduced 3. Literature shows 50-60% good results at 2 years, declining to 20-30% by 5 years for large lesions **Better options for a 5cm² lesion:** **First choice - Osteochondral Allograft (OCA):** - Fresh allograft with live chondrocytes - Addresses large defects in single stage - True hyaline cartilage with mature matrix - Can address subchondral bone if needed - Best for large lesions **Alternative - ACI/MACI:** - Two-stage procedure - Can cover large lesions well - May produce hyaline-like cartilage - No donor site morbidity (vs OATS) **OATS mosaic** is possible but would require many plugs (5cm² = likely 5+ plugs), creating significant donor site morbidity. I would also assess alignment - if there is valgus malalignment contributing to lateral compartment overload, this must be addressed with a distal femoral osteotomy, either staged or combined. The key message is that while microfracture is technically simple, it is not appropriate for all cartilage lesions. Size matters - under 2cm² favors microfracture, over 4cm² should have alternatives.

MCQ Practice Points

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.

Australian Context and Medicolegal Considerations

Australian Practice

Microfracture remains common first-line treatment
Increasing use of AMIC for medium lesions
Access to OCA limited in Australia (availability)
ACI/MACI available through specialized centers
PBS does not cover cartilage cell implantation

Documentation Standards

Document lesion size precisely at arthroscopy
Record alignment assessment
Document technical parameters (spacing, depth)
Record marrow bleeding confirmed
Consent for time-limited benefit

Medicolegal Considerations

Key documentation requirements:

Consent discussion must include: fibrocartilage vs hyaline limitation, time-limited benefit (2-5 years), possibility of deterioration and need for further surgery
Document lesion size at surgery - if over 4cm², document why microfracture chosen (if it was)
Record rehabilitation compliance in follow-up
If failure occurs, document was appropriate initial choice for lesion size