Courtesy: Justin Arner MD, Associate Professor, University of Pittsburgh, Pennsylvania, USA
Meniscus Anatomy and Function
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The medial meniscus is C-shaped; the lateral meniscus is more U-shaped and mobile.
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Composed primarily of:
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Type I collagen (predominantly peripheral)
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Type II collagen (more central)
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High water content
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Glycosaminoglycans
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Functions:
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Load transmission
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Shock absorption
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Stability
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Lubrication
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Proprioception
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Vascular Zones
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Peripheral “red zone” has vascular supply.
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Central “white zone” is avascular.
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Central tears have limited intrinsic healing potential.
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Peripheral tears demonstrate better fibrocartilaginous healing.
Why Meniscus Preservation Matters
Evidence consistently demonstrates:
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Reduced long-term osteoarthritis compared with meniscectomy.
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Improved patient-reported outcomes.
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Higher reoperation rates compared with partial meniscectomy.
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Failure rates reported between 16 percent and 29 percent depending on tear type and follow-up duration.
Bucket-handle tears have particularly high reoperation rates, approaching 20 percent or more in some studies.
Repair Techniques
Inside-Out Technique
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Traditional approach.
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Requires posterior incision and capsule tying.
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Considered technically reliable with strong fixation.
All-Inside Technique
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Faster and technically less demanding.
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Modern devices improve efficiency.
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Clinical outcomes similar to inside-out techniques in many studies.
Key Observation
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Failure rates increase with longer follow-up.
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Medial meniscus repairs fail more often than lateral.
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Poor preoperative function and use of allograft in associated anterior cruciate ligament reconstruction may increase failure risk.
Biological Requirements for Healing
Successful meniscus healing requires:
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Appropriate cell types
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Adequate cell numbers
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Extracellular matrix formation
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Growth factor signaling
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Controlled inflammatory response
Positive Growth Factors
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Fibroblast growth factor
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Platelet-derived growth factor
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Transforming growth factor beta
Platelet-derived growth factor appears particularly important for:
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Cell proliferation
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Matrix production
Negative Factors
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Tumor necrosis factor alpha
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Matrix metalloproteinases
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Excess inflammatory cytokines
Balancing inflammation after injury and surgery is critical but often underappreciated in clinical practice.
Mechanical Methods to Enhance Healing
Rasping
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Refreshes tear edges.
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Encourages synovial ingrowth.
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Simple and inexpensive.
Trephination
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Creates vascular channels using a needle.
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Theoretical benefit in improving blood supply.
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Concerns exist regarding structural weakening.
Bone Marrow Venting (Notch Microfracture)
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Stimulates marrow elements to enter joint.
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Mimics biological effect seen during anterior cruciate ligament reconstruction.
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Some randomized studies show improved healing rates.
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Simple and cost-effective.
Fibrin Clot Augmentation
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Provides scaffold with platelets and cytokines.
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Historically used.
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Some early studies showed lower failure rates.
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Technically demanding.
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Limited modern large-scale data.
Platelet-Rich Plasma
Mechanism
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Concentrated platelets release growth factors.
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Promotes fibrocartilage formation.
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Enhances extracellular matrix production.
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Stimulates chemotaxis and angiogenesis.
Challenges
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No standardized definition.
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Variability in:
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Leukocyte concentration
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Platelet concentration
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Preparation techniques
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Timing of injection
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Cost varies significantly.
Clinical Evidence
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Some studies show:
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Lower failure rates
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Improved magnetic resonance imaging healing
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Other studies show:
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No significant difference
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Possible increased stiffness when combined with anterior cruciate ligament reconstruction
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Overall, evidence remains mixed but promising.
Bone Marrow Aspirate Concentrate
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Contains mesenchymal stem cells and growth factors.
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Animal studies show improved healing, including avascular tears.
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Limited human clinical data.
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Higher cost and more invasive.
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Some database studies show no clear reduction in revision rates.
Scaffolds and Meniscus Wrapping
Emerging options include:
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Collagen matrix wrapping
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Synthetic scaffolds
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Hydrogel systems
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Extracellular matrix-derived materials
Preclinical studies are promising.
Early clinical data suggest:
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Acceptable failure rates
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Good patient-reported outcomes
However:
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No consensus on ideal material.
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Cost remains a major limitation.
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Technical demands are higher.
Repurposing Approved Medications
An innovative concept involves using medications already approved for other indications.
Example: Losartan
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Traditionally used for hypertension.
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Inhibits transforming growth factor beta.
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May reduce fibrosis.
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Animal studies suggest improved cartilage quality.
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Potential to enhance biological repair response.
Other agents under investigation:
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Montelukast
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Simvastatin
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Anti-inflammatory modulators
These strategies may offer regulatory advantages in certain healthcare systems.
Key Clinical Questions
Does Technique or Biology Matter More?
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Proper repair technique is essential.
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Biological augmentation may be the limiting factor once fixation is optimized.
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Healing assessment remains challenging:
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Magnetic resonance imaging is imperfect.
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Clinical outcomes do not always correlate with structural healing.
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Timing of Repair
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Earlier repair likely preferable.
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Delays of several months may reduce healing potential.
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No definitive time cutoff established.
If Only One Biological Option Is Chosen
Common practical choices:
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Bone marrow venting (simple and inexpensive).
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Platelet-rich plasma (most commonly used augmentation).
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Selection often depends on cost and availability.
Osteoarthritis and Injectable Trends
In early osteoarthritis:
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Platelet-rich plasma is increasingly favored over hyaluronic acid in many practices.
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Often administered in series of three injections.
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Leukocyte-poor formulations commonly preferred.
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Bone marrow aspirate concentrate used selectively due to cost.
Use of corticosteroids in younger patients is increasingly questioned.
Current Limitations
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Lack of standardized preparation methods for biological products.
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Limited high-quality randomized controlled trials.
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Cost and insurance coverage barriers.
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Difficulty objectively measuring meniscus healing.
Future Directions
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Better translational research between laboratory and clinical practice.
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Standardized biological protocols.
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Cost-effective augmentation strategies.
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Tissue engineering approaches integrating cells and scaffolds.
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Repurposed medications targeting inflammatory and fibrotic pathways.
Conclusion
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Meniscus preservation is critical to long-term joint health.
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Failure rates remain clinically significant.
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Surgical technique is important but likely not the only determinant of healing.
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Biological augmentation represents the next frontier.
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Current options include:
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Rasping
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Bone marrow venting
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Platelet-rich plasma
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Bone marrow aspirate concentrate
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Scaffold augmentation
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More high-quality clinical trials are needed.
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The field is evolving, and significant advancements are expected in the coming decades.
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