Meniscal Injuries

Anatomy & Function - Knee's Cushions

• Fibrocartilage discs: Medial (C-shaped), Lateral (O-shaped); between femur & tibia.
• Composition: Primarily Type I collagen.
• Blood Supply Zones (peripheral to central):
  • Red-Red (outer 1/3): Vascular, good healing.
  • Red-White (middle 1/3): Transitional.
  • White-White (inner 1/3): Avascular, poor healing.
• Functions: Shock absorption, load transmission, ↑ joint stability & congruity, lubrication, proprioception.
• Medial: Less mobile, attached to MCL (📌 "C" shape, Commoner injuries).
• Lateral: More mobile.

⭐ The peripheral vascular "red zone" (outer 10-30%) has healing potential, unlike the avascular "white zone" which relies on synovial fluid for nutrition.

Injury & Tears - Snap, Crackle, Pop!

• Mechanism: Twisting on flexed, weight-bearing knee; often valgus force. Associated: ACL/MCL (📌 O'Donoghue's Triad: ACL + MCL + Medial Meniscus).
• Symptoms: "Pop/snap", pain (may be delayed), effusion, locking, catching, giving way. Key: Joint line tenderness.
• Tear Patterns:
  • Longitudinal/Vertical: Can become bucket-handle.
  • Radial: Disrupts circumferential fibers.
  • Horizontal/Cleavage: Often degenerative.
  • Oblique/Flap.
  • Complex.
• Vascular Zones (Healing): Red-Red (peripheral, good), Red-White, White-White (central, poor).

⭐ A bucket-handle tear, a displaced vertical tear, is a common cause of true knee locking, often requiring urgent management to unlock the knee or repair the tear if possible based on tear characteristics and patient factors.

Clinical Features - Clicking & Locking

• Clicking:
  • Audible/palpable snap or click with knee movement.
  • Often painful; indicates catching of torn meniscal fragment.
• Locking:
  • Knee "stuck"; true inability to fully extend.
  • Caused by displaced fragment (e.g., bucket-handle tear) blocking motion.
  • Patient may "wiggle" or manipulate knee to unlock.
  • Differentiate from pseudo-locking (pain, hamstring spasm).

  ⭐ True mechanical locking (inability to fully extend knee) strongly suggests a displaced bucket-handle tear, often of the medial meniscus.

Diagnosis & Imaging - MRI's Magic Eye

• MRI: Gold standard. Accuracy >90%.
  • Details tear: type, location, extent.
  • MRI Grading (Stoller):
    • Grade 0: Normal.
    • Grade 1: Intrasubstance signal, no surface contact.
    • Grade 2: Linear signal, no surface contact.
    • Grade 3: Signal contacts articular surface (tear).
• Key Signs: Double PCL, absent bow tie, flipped meniscus.

⭐ Grade 3 signal (articular surface contact) on MRI confirms a meniscal tear.

Management - Repair or Remove?

Goal: Preserve meniscal tissue. Decision based on tear (type, location, stability), patient factors.

• Conservative: Small (<1 cm), stable, peripheral, asymptomatic, or degenerative tears in low-demand patients.
• Surgical Indications: Symptomatic, mechanical symptoms (locking), failed conservative, large tears.

Repair Criteria:

• 📍 Location: Red-Red zone (vascular) > Red-White.
• 📏 Size/Pattern: >1 cm, longitudinal, vertical.
• 🏃 Patient: Young, active; ACL recon.

Meniscectomy:

• Partial: Remove unstable fragment. Preferred.
• Total: Irreparable, complex. ↑ OA risk.

⭐ Meniscal repair in the "red-red" zone (outer third) has the highest success rate due to good vascular supply.

High‑Yield Points - ⚡ Biggest Takeaways

• Medial meniscus is injured more often than lateral.
• Common mechanism: Twisting force on a partially flexed knee.
• Classic signs: Joint line tenderness, locking, clicking, delayed effusion.
• Provocative tests: McMurray, Apley's grind, and Thessaly test.
• MRI confirms diagnosis and tear pattern.
• "Red zone" (peripheral) tears heal better than "white zone" (central) tears.
• Management: Conservative or arthroscopic surgery (repair/meniscectomy).