How to diagnose knee pain?

Diagnosing Knee Pain

Radiographs should be the initial imaging modality for evaluating knee pain in patients with focal tenderness, effusion, or inability to bear weight. 1

Initial Assessment

History

• Determine key characteristics of pain:
  • Age of patient (different diagnoses more common in different age groups) 2
  • Location (anterior, medial, lateral, posterior) 3
  • Onset (acute vs. gradual) 3
  • Duration (acute vs. chronic) 3
  • Quality (sharp, dull, aching) 3
  • Associated symptoms (popping, locking, catching, giving way) 4

Physical Examination

• Perform a systematic examination:
  • Inspection for deformity, swelling, erythema 3
  • Palpation for tenderness, effusion, warmth 1, 3
  • Range of motion assessment 3
  • Stability testing 5
  • Special tests:
    • McMurray test for meniscal tears (61% sensitivity, 84% specificity) 2
    • Joint line tenderness for meniscal tears (83% sensitivity, 83% specificity) 2
    • Anterior/posterior drawer tests for ligament stability 5
    • Patellofemoral assessment for tracking and pain 6

Imaging Algorithm

Initial Imaging

• Radiographs (minimum of anteroposterior and lateral views) are indicated for:
  • Patients >55 years old (Ottawa rules) or >50 years old (Pittsburgh rule) 1
  • Children <12 years old (Pittsburgh rule) 1
  • Patients with focal tenderness, effusion, or inability to bear weight 1
  • Patients with history of trauma and positive Ottawa or Pittsburgh criteria 1

Advanced Imaging

• MRI without IV contrast is indicated when:

  • Radiographs are normal but symptoms persist 1, 4
  • Radiographs demonstrate joint effusion or osteochondritis dissecans 1, 4
  • Suspicion of meniscal tears, ligament injuries, or cartilage damage 1
  • Need for accurate cartilage measurements in osteoarthritis 1

• CT without IV contrast may be indicated for:

  • Evaluation of patellofemoral anatomy in chronic pain related to subluxation 1
  • Confirmation of prior osseous injury 1
  • Evaluation of osteochondritis dissecans when MRI is not definitive 1

• Ultrasound can be useful for:

  • Confirming joint effusion and guiding aspiration 1
  • Evaluating popliteal cysts and detecting cyst rupture 1
  • Detecting synovial pathology and cortical erosive changes 1
  • Demonstrating meniscal extrusion suggesting underlying tear 1

Special Considerations

Joint Aspiration

• Indicated when:
  • Effusion is present and there is concern for crystal disease or infection 1
  • Therapeutic corticosteroid injection is planned 1
• Should be guided by ultrasound or fluoroscopy for accuracy 1

Common Diagnostic Pitfalls

• Obtaining radiographs for all knee pain without applying clinical decision rules leads to unnecessary imaging 1
• Failure to consider referred pain from hip pathology 1
• Overlooking mechanical symptoms (popping, locking) that may indicate internal derangement 4
• Not recognizing that bilateral structural abnormalities on imaging can be present with primarily unilateral symptoms 1

Age-Specific Considerations

• In patients >45 years, osteoarthritis is the most likely diagnosis for activity-related knee pain with minimal morning stiffness (95% sensitivity, 69% specificity) 2
• In patients <40 years who are physically active, patellofemoral pain is common (anterior knee pain during squat: 91% sensitivity, 50% specificity) 2
• In children and adolescents with knee popping and pain, osteochondritis dissecans should be considered 4

By following this systematic approach to diagnosing knee pain, clinicians can efficiently determine the underlying cause and develop an appropriate treatment plan to improve morbidity, mortality, and quality of life outcomes for patients with knee pain.