How is Patellofemoral Pain Syndrome diagnosed?

Diagnosis of Patellofemoral Pain Syndrome

Patellofemoral Pain Syndrome (PFPS) is primarily diagnosed through a thorough clinical assessment, with imaging used selectively to rule out other conditions rather than to confirm PFPS itself. 1, 2

Clinical Assessment Components

History Taking

• Pain characteristics:
  • Anterior knee pain or retropatellar/peripatellar pain
  • Pain during activities that load the patellofemoral joint:
    • Climbing stairs (especially descending)
    • Squatting
    • Running
    • Cycling
    • Prolonged sitting with flexed knees ("theater sign")
  • Pain severity between 3-10 during stair descending and 6-10 during prolonged sitting has high diagnostic value 3

Physical Examination

The following tests have demonstrated acceptable diagnostic accuracy 3:

1. Palpation Test (Sensitivity 0.81)

   • Direct palpation of the patella and surrounding structures to identify painful areas
   • Tenderness along medial/lateral patellar facets or retropatellar region

2. Eccentric Step Test (Sensitivity 0.82)

   • Patient steps down from a step, loading the affected knee eccentrically
   • Positive if pain is reproduced

3. Patellar Tilt Test

   • Assessment of lateral patellar tilt by attempting to lift the lateral edge of patella
   • Positive if excessive tightness or pain is noted

4. Functional Tests

   • Squatting (pain reproduction)
   • Stair descending (pain reproduction)
   • Prolonged sitting test (Sensitivity 0.73)

5. Biomechanical Assessment

   • Navicular drop test (foot pronation assessment)
   • Q-angle measurement using standardized protocol
   • Assessment of hip and knee muscle strength, particularly:
     • Quadriceps strength
     • Hip abductor strength
     • Hip external rotator strength

Diagnostic Imaging

Radiography

• Standard radiographs (AP, lateral, and axial/skyline views) should be obtained first to:
  • Rule out fractures, tumors, or osteoarthritis
  • Evaluate patellar alignment, tilt, or subluxation on axial views 1
  • Not diagnostic for PFPS but helps exclude other conditions

MRI

• Not routinely indicated for initial diagnosis of PFPS
• Consider MRI when:
  • Symptoms persist despite appropriate conservative treatment
  • Suspicion of articular cartilage damage
  • Need to evaluate bone marrow edema or soft tissue structures 1
  • MRI can identify patellofemoral cartilage loss and bone marrow lesions associated with chronic knee pain 1

Ultrasound

• Emerging role in diagnosis:
  • Can evaluate vastus medialis oblique contraction ratio
  • May detect reduced contraction ratio in vastus medialis oblique but not vastus lateralis 1
  • Can assess quadriceps and patellar tendon thickness
  • Allows dynamic examination of patellofemoral tracking

Diagnostic Algorithm

1. Initial Evaluation:

   • Confirm anterior knee pain pattern with activities that load patellofemoral joint
   • Perform physical examination focusing on palpation, functional tests, and biomechanical assessment
   • Rule out red flags (locking, instability, significant swelling, history of trauma)

2. Diagnostic Testing:

   • If typical presentation with no red flags: diagnosis can be made clinically
   • If atypical features or persistent symptoms: obtain weight-bearing knee radiographs including axial view
   • Consider MRI only if:
     • Symptoms persist despite 6-8 weeks of appropriate treatment
     • Suspicion of intra-articular pathology requiring surgical intervention
     • Need to differentiate from other conditions (osteochondral lesions, plica syndrome)

3. Combination Testing:

   • The combination of stair descending test (pain 3-10/10) and prolonged sitting test (pain 6-10/10) has a positive likelihood ratio of 19.47, making it highly specific for PFPS diagnosis 3

Common Pitfalls and Caveats

• Avoid over-reliance on imaging for diagnosis; PFPS remains primarily a clinical diagnosis
• Don't mistake patellofemoral osteoarthritis for PFPS (consider age, history, and radiographic findings)
• Remember that crepitus alone is not diagnostic of PFPS (may be present in asymptomatic individuals)
• Consider other sources of anterior knee pain:
  • Patellar tendinopathy
  • Hoffa's fat pad impingement
  • Plica syndrome
  • Meniscal tears
  • Osteochondral lesions
• Failure to assess hip and foot biomechanics may lead to incomplete diagnosis and treatment planning

By following this structured approach to diagnosis, clinicians can accurately identify PFPS and develop appropriate treatment strategies focused on addressing the underlying biomechanical factors contributing to patellofemoral pain.