Knee Ligament Injuries

Knee Ligaments Overview - Anatomy Aces

• Cruciate Ligaments (Intra-articular):
  • Anterior Cruciate Ligament (ACL): Prevents anterior tibial translation & internal rotation. Attaches anterior intercondylar area of tibia to medial side of lateral femoral condyle.
  • Posterior Cruciate Ligament (PCL): Prevents posterior tibial translation. Stronger than ACL. Attaches posterior intercondylar area of tibia to lateral side of medial femoral condyle.
• Collateral Ligaments (Extra-articular):
  • Medial Collateral Ligament (MCL): Resists valgus stress. Attached to medial femoral epicondyle and medial tibial condyle.
  • Lateral Collateral Ligament (LCL): Resists varus stress. Attached to lateral femoral epicondyle and fibular head.

⭐ The ACL is the most commonly injured knee ligament, especially in sports involving sudden stops and changes in direction (e.g., football, basketball).

ACL Injuries - Pivot Powerhouse

• Mechanism: Non-contact valgus/pivoting, deceleration, hyperextension. Audible "pop".
• Presentation: Rapid hemarthrosis, instability ("knee giving way").
• Associated: Meniscal tears (often medial), MCL. 📌 O'Donoghue's (Unhappy) Triad: ACL, MCL, Medial Meniscus.
• Clinical Tests:
  • Lachman Test: Most sensitive. Knee at 20-30° flexion.
  • Anterior Drawer Test: Knee at 90° flexion.
  • Pivot Shift Test: Most specific for anterolateral rotatory instability; pathognomonic.
• Imaging:
  • X-ray: To exclude fractures (e.g., tibial spine avulsion).
  • MRI: Gold standard for diagnosis; details soft tissue injury.
• Management Algorithm:

⭐ Segond fracture (avulsion of anterolateral tibial rim with LCL/ITB) on X-ray is highly suggestive, often considered pathognomonic, for an ACL tear.

PCL Injuries - Dashboard Defender

• Mechanism: "Dashboard injury" (direct blow to anterior tibia, knee flexed), hyperflexion, fall on flexed knee (plantarflexed foot).
• Strongest knee ligament; less common than ACL.
• Clinical Tests:
  • Posterior sag sign (Godfrey sign).
  • Posterior drawer test (most sensitive).
  • Quadriceps active test.
• Grading: Grade I, II (partial, <10 mm posterior translation), III (complete, >10 mm).
• Management:
  • Non-operative: Isolated Grade I & II.
  • Operative: Grade III, combined injuries, chronic symptomatic instability.

⭐ Isolated PCL injuries often have minimal pain and swelling, leading to missed diagnosis; posterior sag is key.

Collateral Ligament Injuries - Sideline Supports

• Medial Collateral Ligament (MCL) Injury:
  • Mechanism: Valgus stress (e.g., blow to lateral knee).
  • Symptoms: Medial pain, swelling, tenderness, instability.
  • Test: Valgus stress at 30° flexion (isolates MCL) & 0° flexion (suggests severe injury/cruciate involvement).
  • Grades I-III based on laxity.
  • Management: Mostly non-operative (RICE, hinged brace, physiotherapy). Surgery for Grade III / multi-ligament injuries.
• Lateral Collateral Ligament (LCL) Injury:
  • Mechanism: Varus stress (e.g., blow to medial knee).
  • Symptoms: Lateral pain, swelling, tenderness, instability.
  • Test: Varus stress at 30° flexion (isolates LCL) & 0° flexion.
  • Often associated with Posterolateral Corner (PLC) injury.
  • Management: Conservative for isolated Grades I/II. Surgery often for Grade III / PLC involvement.
• Sideline Management (Acute):
  • PRICE protocol (Protection, Rest, Ice, Compression, Elevation).
  • Immobilisation (knee brace/splint), crutches if needed.
  • Prompt referral for definitive diagnosis.

⭐ MCL injuries are more common than LCL injuries. Valgus stress test at 30° of knee flexion best isolates the superficial MCL fibers for assessment of injury.

Multi-Ligament Mayhem & Dislocation - Joint Jeopardy

Knee dislocation (KD) / MLKI (≥2 ligaments): Ortho emergency! High-energy trauma.

• Key Risks:
  • Popliteal artery injury (30-50%); limb-threatening.
  • Peroneal nerve (esp. PLC).
• Actions:
  • ABCDEs, prompt reduction.
  • Vascular: Pulses, ABI. ABI <0.9 → urgent angio/explore.
• Imaging:
  • X-ray, MRI for ligament detail.
• Management:
  • Ex-fix if unstable. Surgical reconstruction.
• Complications:
  • Arthrofibrosis, OA.

⭐ Popliteal artery injury: most critical limb-threatening emergency with knee dislocations.

High‑Yield Points - ⚡ Biggest Takeaways

• ACL tears: most common, often non-contact pivoting with audible "pop"; Lachman test is most sensitive.
• O'Donoghue's Unhappy Triad: classically ACL, MCL, and medial meniscus injury.
• PCL tears: typically from dashboard injury; posterior sag sign is characteristic.
• MCL injury: valgus stress test positive; often managed non-operatively.
• LCL injury: varus stress test positive; crucial to assess peroneal nerve function.
• Pivot shift test: highly specific for diagnosing ACL insufficiency.
• Segond fracture on X-ray is pathognomonic for an ACL tear.