What is the appropriate approach for a physical examination of the knee?

Comprehensive Physical Examination of the Knee

A thorough physical examination of the knee should include inspection, palpation, range of motion testing, and specific maneuvers to evaluate ligaments and menisci, followed by appropriate imaging when indicated by clinical findings. 1

Initial Assessment

Inspection

• Observe for:
  • Gross deformity
  • Swelling/effusion
  • Erythema/warmth
  • Quadriceps atrophy
  • Gait pattern
  • Alignment (varus/valgus)

Palpation

• Evaluate for:
  • Joint line tenderness (medial and lateral - highly specific for meniscal tears)
  • Patellar tenderness
  • Effusion using bulge sign (highly reliable with R₍c₎ = 0.97) 2
  • Bony swelling (highly reliable with R₍c₎ = 0.97) 2
  • Tibial plateau tenderness
  • Fibular head tenderness

Range of Motion Testing

• Compare with uninjured knee
• Assess:
  • Active and passive flexion/extension
  • Presence of flexion contracture
  • Crepitus during movement (highly reliable with R₍c₎ = 0.96) 2

Ligament Testing

Anterior Cruciate Ligament (ACL)

• Lachman test (most sensitive and specific for ACL tears) 3

  • Position: knee at 20-30° flexion
  • Technique: stabilize femur with one hand, pull tibia forward with other
  • Positive: excessive anterior translation with soft endpoint

• Pivot shift test (specific for ACL tears) 4

  • Position: knee extended, internally rotated, valgus stress applied
  • Technique: flex knee while maintaining rotation and stress
  • Positive: sudden reduction of subluxated tibia at 20-40° flexion

Posterior Cruciate Ligament (PCL)

• Posterior drawer test (highly sensitive and specific) 3

  • Position: knee at 90° flexion, tibia in neutral rotation
  • Technique: push tibia posteriorly
  • Positive: excessive posterior translation

• Posterior sag sign (tibial sag test)

  • Position: both knees flexed to 90°
  • Observation: posterior displacement of tibia relative to femur
  • Positive: visible posterior "sag" of tibia

Medial Collateral Ligament (MCL)

• Valgus stress test
  • Position: knee at 30° flexion and at full extension
  • Technique: apply valgus force at knee
  • Positive: excessive medial opening

Lateral Collateral Ligament (LCL)

• Varus stress test
  • Position: knee at 30° flexion and at full extension
  • Technique: apply varus force at knee
  • Positive: excessive lateral opening

Meniscal Testing

• McMurray test (highly specific but low sensitivity) 3

  • Position: knee fully flexed
  • Technique: rotate tibia while extending knee
  • Positive: click or pain during maneuver

• Apley's grind test

  • Position: patient prone, knee flexed 90°
  • Technique: apply axial compression and rotation
  • Positive: pain with compression and rotation

Patellofemoral Assessment

• Patellar grind test (highly reliable with R₍c₎ = 0.94) 2

  • Position: knee extended
  • Technique: push patella into trochlear groove, ask patient to contract quadriceps
  • Positive: pain with maneuver

• Patellar apprehension test

  • Position: knee slightly flexed
  • Technique: push patella laterally
  • Positive: patient appears apprehensive or resists movement

When to Order Imaging

Radiographs

Radiographs should be the initial imaging study when any of the following are present 1:

• Focal tenderness
• Effusion
• Inability to bear weight
• Inability to flex knee to 90°
• Age greater than 55 years
• Gross deformity
• Penetrating injury
• Suspected patellar fracture or dislocation

Standard views should include:

• Anteroposterior (AP)
• Lateral (knee at 25-30° flexion)
• Additional views as needed:
  • Patellofemoral (sunrise/Merchant) view
  • Tunnel view
  • Oblique views

Advanced Imaging

• MRI is the preferred next study when radiographs are negative but internal derangement is suspected 1
• CT may be useful for suspected occult fractures 1

Pitfalls and Caveats

• Always examine the uninjured knee first for comparison 5
• Standardization of examination techniques improves reliability 2
• Instability testing (especially at 30° flexion) has lower reliability even after standardization 2
• Clinical decision rules (Ottawa Knee Rule) should not be applied in cases of:
  • Gross deformity
  • Palpable mass
  • Penetrating injury
  • Altered mental status
  • Neuropathy
  • Multiple injuries 1

By following this systematic approach to knee examination, clinicians can accurately diagnose common knee pathologies and determine appropriate next steps in management to optimize patient outcomes related to morbidity, mortality, and quality of life.