🔑 Key Learning

  • ACL: sudden twisting → haemarthrosis, positive Lachman
  • PCL: dashboard injury → posterior sag sign
  • Meniscal tear: twisting on flexed knee → locking, joint line tenderness
  • MCL/LCL: valgus/varus trauma → local pain, stress test positive
  • Quadriceps/patellar tendon rupture: inability to extend knee or do straight leg raise
  • Tibial plateau fracture: high-impact trauma → severe swelling/bruising

🦵 Anterior Cruciate Ligament (ACL) Injury

⚙️ Mechanism

  • The ACL is responsible for restraint vs anterior/forward movement of the tibia
  • Sudden deceleration, twisting or pivoting on a fixed foot (e.g. netball)
  • Commonly associated with meniscal tears

👀 Clinical Features

  • Audible "pop" at time of injury
  • Rapid swelling (haemarthrosis within 2 hours)
  • Instability when walking

🧪 Examination

  • Positive Lachman test
  • Positive anterior drawer test
  • Tender lateral joint line

🖼️ Investigations

  • MRI to confirm diagnosis and assess associated injuries

🦵 Posterior Cruciate Ligament (PCL) Injury

⚙️ Mechanism

  • The PCL is responsible for restraint vs backwards/posterior movement of the tibia
  • Direct blow to proximal tibia while knee is flexed (e.g. dashboard injury)

👀 Clinical Features

  • Posterior knee pain
  • Mild effusion

🧪 Examination

  • Positive posterior drawer test
  • Posterior sag sign

🦵 Meniscal Tear

⚙️ Mechanism

  • Degenerative (osteoarthritis) or sudden twisting injury during pivot (sports-related)

👀 Clinical Features

  • Joint line tenderness (anteromedial or anterolateral)
  • Locking, clicking, catching
  • Joint effusion

🧪 Examination

  • McMurray test may be positive

🦵 Medial Collateral Ligament (MCL) Injury

⚙️ Mechanism

  • Direct blow to lateral aspect of knee (e.g. during contact sport)

👀 Clinical Features

  • Medial knee pain

🧪 Examination

  • Pain along MCL course
  • Positive valgus stress test

🦵 Lateral Collateral Ligament (LCL) Injury

⚙️ Mechanism

  • Direct blow to medial aspect of knee

👀 Clinical Features

  • Lateral knee pain

🧪 Examination

  • Pain along LCL course
  • Positive varus stress test

🦵 Quadriceps/Patellar Tendon Rupture

⚙️ Mechanism

  • Fall or sudden eccentric loading of the knee

👀 Clinical Features

  • Inability to perform straight leg raise
  • Inability to extend the knee
  • Patella displaced:
    • Patella alta = proximal migration of patella - patellar tendon rupture
    • Patella baja = distal migration of patella - quadriceps tendon rupture

🦵 Tibial Plateau Fracture

⚙️ Mechanism

  • High-energy trauma (e.g. fall from height or car bumper injury)

👀 Clinical Features

  • Severe pain, swelling
  • Extensive bruising

🖼️ Investigations

  • CT scan to delineate fracture and plan surgery

📝 Exam Clues & Clinchers

  • ACL tear: audible pop, rapid swelling (<2 hrs), positive Lachman test
  • PCL tear: dashboard injury, posterior sag sign
  • Meniscal tear: twisting + locking + joint line tenderness
  • MCL injury: lateral trauma + medial pain + valgus test positive
  • LCL injury: medial trauma + lateral pain + varus test positive
  • Tendon rupture: can't extend knee or perform straight leg raise
  • Tibial plateau fracture: severe bruising, often in high-energy injury