import { HighYieldBox, ExamCheatSheet, Tabs, Tab, ComparisonTable, VivaScenario, ContentSection, SpecialTestCard , MedicalImage} from '@/components/content' # Knee Patellofemoral Examination Patellofemoral examination assesses tracking, instability, and anterior knee pain. Examiners expect you to recognize the J-sign, perform the apprehension test correctly, and understand the factors contributing to patellar instability (Q-angle, trochlear dysplasia, patella alta). ## Quick Reference One-Pager ## Anatomy and Biomechanics **Patellofemoral Joint:** - Patella articulates with trochlear groove of femur - Largest sesamoid bone in body - Improves quadriceps efficiency by 30-50% - Contact area changes with flexion (inferior pole in extension, superior in deep flexion) **Stability Factors:** - **Static**: Trochlear groove depth, MPFL (medial patellofemoral ligament), retinaculum - **Dynamic**: VMO (vastus medialis obliquus), quadriceps alignment - **Limb Alignment**: Q-angle, tibial tubercle position **Q-Angle:** - Angle between quadriceps pull and patellar tendon - Line from ASIS to patella center, and patella center to tibial tubercle - Normal: Male less than 15°, Female less than 20° - Increased Q-angle → increased lateral patellar force → instability risk ## Inspection **With Patient Standing:** - Lower limb alignment (valgus, varus) - Squinting patellae (excessive femoral anteversion) - Patellar position (central, lateralized) - Q-angle estimation **With Patient Seated (Legs Over Edge):** - Patellar position and height - VMO bulk compared to opposite side **Active Range of Motion:** - Watch patellar tracking during extension - J-Sign: Lateral deviation of patella as knee extends (suggests lateral instability) **J-Sign:** The patella suddenly moves laterally as the knee reaches terminal extension. This indicates: - Patella is "escaping" the trochlear groove in extension - Associated with trochlear dysplasia, patella alta - Risk factor for patellar instability ## Palpation **Bony Landmarks:** - Patella (medial and lateral facets, inferior pole) - Femoral trochlea (with knee flexed) - Tibial tubercle (for tenderness, prominence) **Soft Tissues:** - Medial retinaculum (may be tender after dislocation) - MPFL origin (medial femoral epicondyle) - Quadriceps tendon, patellar tendon - Pes anserine bursa (differential for medial knee pain) ## Patellofemoral Instability Tests ## Patellofemoral Pain Tests **Clarke's Test Limitations:** - High false positive rate in normal individuals - Pain may be from compression rather than pathology - Should be used in conjunction with other findings - More useful when correlated with history of anterior knee pain ## Contributing Factors Assessment **Q-Angle Measurement:** - Patient supine, knee extended, quadriceps relaxed - Line from ASIS to patella center - Line from patella center to tibial tubercle - Normal: Male less than 15°, Female less than 20° - Increased Q-angle = increased valgus vector = lateral instability risk **Patella Alta (High-Riding Patella):** - Assessed clinically: Patella appears high when knee flexed 90° - "Grasshopper eyes" appearance - Confirmed with Insall-Salvati ratio on lateral X-ray (greater than 1.2) - Risk factor for instability (patella not engaged in trochlea in early flexion) **Tibial Tubercle-Trochlear Groove (TT-TG) Distance:** - Measured on CT/MRI (axial images) - Normal less than 15mm - Greater than 20mm = significant lateralization ## Special Populations **Why Higher Risk:** - Wider pelvis (increased Q-angle) - Generalized ligamentous laxity - Reduced VMO strength relative to vastus lateralis - Hormonal factors **First-Time Dislocation Assessment:** - Usually traumatic but may be atraumatic - High recurrence rate in adolescents (up to 40%) - Assess anatomical risk factors for surgical consideration ## Differential Diagnosis ## Summary Presentation ## Theatre Sign and Functional Tests **Theatre Sign:** - Pain with prolonged sitting (knee flexed 90°) - Patient needs to straighten leg for relief - Suggests patellofemoral pathology **Stair Descent Pain:** - More specific for PF pain than stair climbing - Descent requires eccentric quadriceps control - Higher PF joint reaction forces going down **Squatting Pain:** - Pain at end range flexion - Deep flexion increases PF contact pressures ## Examiner Tips