Knee Ligament Injuries

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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.

Knee Ligaments: Anterior, Posterior, and Patellar Views

⭐ 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. Lachman Test for ACL 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) & 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) & 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. Valgus Stress Test for Medial Collateral Ligament

⭐ 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.

Knee Dislocation with Popliteal Artery and Peroneal Nerve

⭐ 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.

Practice Questions: Knee Ligament Injuries

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Which of the following tests is not done for anterior cruciate ligament injury?

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Flashcards: Knee Ligament Injuries

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The _____ extends from the lateral femoral condyle to the anterior tibia.

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The _____ extends from the lateral femoral condyle to the anterior tibia.

anterior cruciate ligament (ACL)

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