History

• Recent changes in activity frequency, type, and intensity
• Increased duration of wear or changes to current exercise footwear
• Anterior knee pain after prolonged sitting (“theater sign”), squatting, running, climbing/descending stairs
• Insidious onset of anterior knee pain with activity
• In-line “giving way” of the knee secondary to pain and not due to ligamentous or tendinous deficiency
• Effusion is not a typical finding of patellofemoral pain (PFP). Its presence is likely, but not necessarily, related to other pathology.
• Any subluxation versus dislocation episodes and/or history of direct trauma
• Prior treatments, including nonsteroidal anti-inflammatory drugs (NSAIDs), taping, physical therapy, orthotics, injections, or surgery
• The presence of crepitus is not helpful to make a diagnosis because most healthy women and almost half of healthy men also have crepitus on exam.

Physical Exam

• Physical examination tests have been reported to have sensitivities <50%, although specificity for some tests have ranged from 72% to 100% (1).
• Evaluate gait (Trendelenburg gait, quadriceps avoidance) and overall limb alignment (varus/valgus, leg length discrepancy), as mentioned in “Risk Factors.”
• Dynamic testing with single and double leg squats to assess patellar motion
• Evaluate lumbar spine, core strength, and hips.
• Evaluate neurologic system.
• Note any atrophy of the lower extremity, especially VMO.
• Assess strength of gluteus medius using Trendelenburg test or side-lying hip abduction test.
• Examine flexibility of quadriceps (Thomas test), iliotibial band (Ober test), hamstring (popliteal angle test), hip (Thomas test), and gastrocsoleus (ankle range of motion).
• Assess for presence of crepitus or J-sign (abrupt lateral motion of patella with full extension) during active flexion and extension of the knee.
• Assess for patellar height: patella alta, patella baja, squinting patella, or grasshopper eyes (proximal and lateral patellar rotation).
• Rule out patellar and quadriceps tendinopathy, ligamentous instability, and meniscal pathology.
• Evaluate the prepatellar, infrapatellar, and pes anserine bursae and presence of joint effusion.
• Examine for patellar facet and retinaculi tenderness; tenderness over lateral retinaculum present in 90% of patients
• Evaluate patellar glide and apprehension:
  • Divide patella into four quadrants.
  • If unable to move >1 quadrant laterally or medially, this is suggestive of a tight medial or lateral retinaculum.
  • If able to translate >3 quadrants medially or laterally, suggestive of hypermobile patella; hypermobility usually seen with positive patellar apprehension as the patient senses impending patellar dislocation
• Perform patellar tilt test: With knee in full extension or 30 degrees of flexion, press posteriorly on medial aspect of patella. Lateral patella should translate anteriorly; if examiner cannot get the lateral border of patella to horizontal with posterior pressure on medial edge, suggestive of a tight lateral retinaculum

Differential Diagnosis

• Patellar or quadriceps tendinopathy
• Patellofemoral osteoarthritis
• Patellar instability with subluxation or dislocation
• Osteochondral defect of the trochlear or patellar surface
• Osteochondritis dissecans
• Iliotibial band syndrome
• Infrapatellar fat pad inflammation or impingement
• Synovial plica
• Retinacular strain
• Osgood-Schlatter apophysitis (proximal anterior tibia)
• Sinding-Larsen-Johansson apophysitis (inferior patellar pole)
• Referred pain from the hip, often affecting the anterior distal thigh and knee
• Multiple other sources of knee pain and arthritis (e.g., gout, infection, reflex sympathetic dystrophy, neuroma, or sickle cell disease)
• Pigmented villonodular synovitis

Diagnostic Tests & Interpretation

• Imaging studies are not required for an accurate diagnosis of PFP syndrome. Multiple studies have evaluated sulcus angle, patellar height (determined by Insall-Salvati index), patellar tilt (determined by Laurin angle), and patellar displacement (determined by Merchant angle) and have found no significant difference between symptomatic and asymptomatic patients (1)[A].
• Imaging studies are recommended if there is clinical suspicion of another diagnosis, or if a patient has failed initial conservative management. Most radiographs will appear normal. Any structural abnormalities may need to be addressed when determining the appropriate care plan for an individual patient.
• Computed tomography (CT), magnetic resonance imaging (MRI), or bone scintigraphy may be considered only in difficult cases to determine presence of additional pathology causing anterior knee pain or to assist with surgical options when conservative management has failed.
• Plain radiographs:
  • Anteroposterior bilateral standing: may show varus or valgus orientation of femur, knee, or tibia
  • Lateral view of affected knee: Evaluate for patellar height with Insall-Salvati ratio (patellar tendon length to patella length). Ratio <0.8 consistent with patella baja; ratio >1.2 consistent with patella alta
  • Merchant view of bilateral patellofemoral joints: will not distort trochlea/patella appearance. Evaluate for a shallow sulcus angle, subluxation degree, and femoral condyle appearance. Standing, loaded Merchant view is more accurate representation of joint kinematics.
  • Tunnel view if osteochondral deficit lesion suspected
• CT:
  • Useful to evaluate patellofemoral relationships (e.g., tilt and subluxation), especially in patients with suspected subluxation at <30 to 45 degrees of flexion that cannot be visualized well on plain film
  • Useful to evaluate intraosseous lesions and to plan selective surgical realignment procedures
• MRI:
  • Useful in evaluation of soft tissue, including patellofemoral cartilage, other articular cartilage, tendinopathy, and retinacula
  • Stages III and IV chondromalacia can be evaluated reliably with accuracy of 89%.