What are the steps to diagnose Patellofemoral syndrome?

Diagnosing Patellofemoral Pain Syndrome

Patellofemoral pain syndrome is diagnosed primarily through clinical history identifying gradual onset diffuse retropatellar or peripatellar pain that worsens with squatting, stair ambulation, and running, combined with physical examination findings of pain with squatting and hip weakness, with radiographs reserved for initial evaluation in patients ≥5 years or when conservative therapy fails after 6-8 weeks. 1

Clinical History: Key Features to Identify

The diagnosis centers on recognizing specific pain patterns rather than relying on imaging:

• Pain characteristics: Gradual onset (not sudden) diffuse pain behind or around the patella that worsens with activities loading the patellofemoral joint 1, 2
• Aggravating activities: Squatting, stair ambulation (especially descending), running, and prolonged sitting 1, 3
• Functional impact: Limitations in daily activities, sports participation, and quality of life 1, 2
• Psychological screening: Assess for anxiety or depression, as patients with patellofemoral pain are six times more likely to experience these comorbidities 1, 2

Physical Examination: Specific Tests and Findings

Most Sensitive Clinical Tests

The physical examination should focus on tests with proven diagnostic accuracy:

• Eccentric step test: Sensitivity 0.82 (95% CI: 0.72-0.89) - the most sensitive single test 3
• Palpation test: Sensitivity 0.81 (95% CI: 0.70-0.88) with acceptable accuracy (AUC ≥70%) 3
• Pain with squatting: The most sensitive physical examination finding in clinical practice 4
• Prolonged sitting test: Sensitivity 0.73 (95% CI: 0.62-0.82) 3

Strength Assessment

• Hip abductor and extensor weakness: A consistent predictor of patellofemoral pain syndrome that should be assessed using hand-held dynamometry or manual muscle testing 1, 5
• Quadriceps weakness: Particularly important to evaluate as a contributing factor 6, 7

Additional Examination Components

• Patellar tilt test: Has acceptable accuracy (AUC ≥70%) 3
• Navicular drop test: Acceptable accuracy for identifying foot mechanics contributing to symptoms 3
• Stair descending test: Acceptable accuracy (AUC ≥70%) 3
• Q angle measurement: Predictive when measured using standardized protocol 5
• Crepitus: Supported as a predictor of patellofemoral pain syndrome 5

Highest Diagnostic Accuracy Combination

The strongest diagnostic combination is pain severity 3-10 during stair descending AND pain severity 6-10 during prolonged sitting, which yields a positive likelihood ratio of 19.47 (95% CI: 6.36-59.65) and posttest probability of 95%. 3

Imaging: When and What to Order

Initial Imaging Approach

• Radiographs are usually appropriate for initial evaluation in patients ≥5 years of age with chronic knee pain 1
• Standard views include: Anteroposterior, lateral, and axial radiographs to demonstrate patellar tilt or subluxation 1
• Weight-bearing axial radiographs: Recommended to better assess patellofemoral kinematics 8

Advanced Imaging Indications

• MRI without IV contrast: Indicated when radiographs show small osseous fragments along the medial patellar margin or clinical concern for patellar dislocation-relocation 1
• CT without IV contrast: May be indicated to evaluate patellofemoral anatomy in chronic pain related to repetitive patellofemoral subluxation 1
• Reassessment timing: If no improvement after 6-8 weeks of consistent conservative therapy, reassess diagnosis and consider imaging to rule out other pathologies 1, 2

Differential Diagnosis Considerations

Rule out these conditions that may mimic or coexist with patellofemoral pain syndrome:

• Patellar tendinopathy: May coexist with patellofemoral pain syndrome 1
• Osteochondral defects or loose bodies: Require MRI evaluation 1
• Meniscal pathology: Consider in patients with mechanical symptoms 1
• Intra-articular pathology: If effusion is present, potentially requiring aspiration for synovial fluid analysis 1
• Osteoarthritis, patellar fracture, osteochondritis: Can be excluded with plain radiographs 4

Common Diagnostic Pitfalls

• Over-reliance on imaging: Plain radiographs are not necessary for diagnosis in typical presentations; clinical diagnosis should be made first 4
• Ignoring hip weakness: Failure to assess hip abductor and extensor strength misses a key predictor 1, 5
• Single test reliance: Individual physical examination tests have low reliability; clustering findings improves diagnostic accuracy 5, 3
• Missing psychological comorbidities: Failing to screen for anxiety and depression overlooks important management considerations 1, 2