What is the appropriate workup for anterior knee pain?

Appropriate Workup for Anterior Knee Pain

The appropriate workup for anterior knee pain should include a thorough clinical examination focusing on patellofemoral alignment, strength testing, and specific provocative tests, followed by plain radiographs as the initial imaging modality, with MRI reserved for cases where specific structural pathologies are suspected. 1

Clinical Examination Components

History

• Duration and onset of symptoms (acute vs insidious)
• Activity-related pain patterns (worse with stairs, prolonged sitting)
• Mechanical symptoms (catching, locking, giving way)
• Previous trauma or injuries
• Activity level and sports participation
• Previous treatments attempted

Physical Examination

1. Patellofemoral Assessment:

   • Patellar tracking during active knee extension
   • Patellar mobility and alignment
   • Q-angle measurement

2. Provocative Tests:

   • Hawkins' Test: Pain with forcible internal rotation with arm passively flexed forward at 90 degrees (sensitive 92%, specific 25% for impingement) 1
   • Neer's Test: Pain with full forward flexion between 70-120 degrees (sensitive 88%, specific 33%) 1
   • Decline Squat Test: Places increased load on patellar tendon to reproduce pain 1

3. Strength Testing:

   • Quadriceps strength assessment (particularly eccentric control)
   • Vastus medialis/vastus lateralis balance evaluation
   • Hip muscle strength (particularly abductors and external rotators)

4. Functional Assessment:

   • Gait analysis
   • Single-leg squat mechanics
   • Step-down test

Imaging Studies

Initial Imaging

• Plain Radiographs: Appropriate as first-line imaging for chronic knee pain in patients ≥5 years of age 1
  • Views should include:
    • Weight-bearing AP view
    • Lateral view
    • Merchant view (axial patellofemoral view)
    • Optional: Standing 45° flexion posteroanterior view

Advanced Imaging

• MRI without IV contrast: Indicated when:

  • Radiographs show osseous fragments along medial patellar margin
  • Clinical concern for patellar dislocation/instability
  • Need to assess medial patellofemoral ligament integrity
  • Evaluation of Osgood-Schlatter or Sinding-Larsen-Johansson syndrome 1

• Ultrasound: Limited utility as comprehensive examination but can be helpful for:

  • Detecting synovial pathology and effusions
  • Evaluating meniscal extrusion
  • Assessing synovial blood flow with power Doppler 1

• CT: May be indicated to evaluate patellofemoral anatomy in cases of suspected repetitive subluxation 1

Additional Diagnostic Procedures

• Joint Aspiration: Usually not indicated for chronic anterior knee pain unless there is:
  • Concern for crystal disease
  • Suspicion of infection
  • Painful, tense effusion requiring drainage 1

Common Diagnostic Pitfalls

1. Failure to assess hip and foot biomechanics: Anterior knee pain may originate from biomechanical issues in the hip or foot.

2. Overlooking vastus medialis/lateralis imbalance: This common finding needs correction before initiating general quadriceps strengthening 2.

3. Attributing all anterior knee pain to patellofemoral syndrome: Multiple conditions can cause anterior knee pain, requiring specific diagnosis.

4. Premature advanced imaging: Plain radiographs should be the initial imaging study before proceeding to MRI or CT 1.

5. Neglecting psychosocial factors: Recent research suggests anterior knee pain involves a combination of biomechanical, neuromuscular, behavioral, and psychological factors 3.

Algorithmic Approach

1. Initial Evaluation:

   • Clinical examination with specific provocative tests
   • Plain radiographs (AP, lateral, Merchant views)

2. If radiographs normal but symptoms persist:

   • Trial of conservative management with physical therapy
   • Focus on vastus medialis/lateralis balance
   • Address biomechanical factors

3. If no improvement after 4-6 weeks:

   • Consider MRI to evaluate for:
     • Cartilage damage
     • Ligament integrity
     • Meniscal pathology
     • Bone marrow edema

4. If mechanical symptoms or instability present:

   • Earlier MRI may be warranted
   • Consider referral to orthopedic specialist

By following this structured approach to anterior knee pain workup, clinicians can efficiently diagnose the underlying cause and develop an appropriate treatment plan that addresses both structural and functional components of the condition.