What is patellofemoral pain syndrome?

What is Patellofemoral Pain Syndrome?

Patellofemoral pain syndrome (PFPS) is a condition characterized by gradual-onset diffuse pain behind or around the kneecap (retropatellar and/or peripatellar) that worsens during activities that load the bent knee—specifically squatting, stair climbing, running, and prolonged sitting with the knee flexed. 1, 2, 3

Key Clinical Features

Pain Characteristics

• Pain develops gradually rather than from a single traumatic event 3
• Pain intensifies with weight-bearing activities when the knee is flexed 4
• Prolonged sitting with bent knees (the "theater sign") commonly provokes symptoms 5, 4
• Descending stairs typically causes more pain than ascending 4

Diagnostic Criteria

• Pain with bilateral squatting is the most sensitive physical examination finding 2
• No anatomic malalignment, history of trauma, patellar instability, or clinical evidence of patellofemoral crepitus should be present 5
• Plain radiographs are not necessary for diagnosis but can exclude other conditions like osteoarthritis, patellar fracture, or osteochondritis 4

Associated Impairments and Risk Factors

Biomechanical Contributors

• Lateral retinacular and iliotibial band tightness are frequently present 5
• Dynamic valgus of the lower extremity leads to lateral patellar maltracking 6
• Hip abductor and extensor weakness is a consistent predictor and should be assessed bilaterally regardless of whether pain is unilateral or bilateral 2
• Weak hip muscles and rearfoot eversion with pes pronatus valgus contribute to dynamic valgus 6

Structural Factors to Screen For

• Patella alta (high-riding patella) may modify exercise selection 1
• Generalized joint hypermobility can influence intervention choices 1

Prognosis and Impact

Long-Term Outcomes

• Over 50% of patients report persistent pain more than 5 years after diagnosis despite treatment, indicating poor prognosis 1, 3

Quality of Life Impact

• Functional limitations in daily activities and sports participation are common 3
• Patients with PFPS are six times more likely to experience anxiety or depression 3
• The condition is associated with reduced physical activity and poorer health-related quality of life 1

Epidemiology

• PFPS is one of the most common causes of anterior knee pain in adolescents and adults younger than 60 years 4
• The incidence in the United States is between 3% and 6% 4
• It particularly affects athletes, especially young runners 7, 6

Important Clinical Distinctions

What PFPS Is NOT

• PFPS occurs without structural patellofemoral joint damage in younger patients 6
• Older patients with similar pain patterns but with signs of patellofemoral osteoarthritis represent a different clinical entity 6
• Traumatic causes including patellofemoral instability post-dislocation or PFP in the presence of hypermobility are excluded from the PFPS diagnosis 8

Assessment Priorities

Subjective Evaluation

• Assess pain levels and tolerance during functional activities 3
• Evaluate fear of movement and fear-avoidance beliefs during functional tasks, as high fear may necessitate additional interventions 1, 3
• Determine self-efficacy related to symptoms and perceived joint resilience 3
• Understand the impact of symptoms on daily life and recreational activities 3

Objective Evaluation

• Measure hip and knee muscle strength objectively using hand-held dynamometry or manual testing 1
• Observe single-leg squat performance to identify maladaptive movement patterns 1
• Conduct pain-provocation tests to assess tissue tolerance to load 1
• Examine gait, posture, and footwear to identify contributing causes 4

Common Pitfalls in Understanding PFPS

• Assuming pain correlates directly with tissue damage—education should clarify that pain does not necessarily reflect structural harm 1, 3
• Overlooking bilateral muscle deficits in unilateral presentations—treatment should address both limbs even when symptoms are one-sided 2
• Failing to recognize the chronic nature—patients need realistic expectations that recovery requires several months of consistent conservative care 1