The patellar J sign is used to evaluate for how the patella tracks at the patellofemoral joint. The patient is seated, leg hanging off the examination table. The patient is asked to bring the knee into full extension and then passively flex to 90. This may be repeated a few times. A positive test is lateral tracking of the patella suddenly shifts medially as it engages the trochlear groove of the distal femur.

Patellar J Sign
https://wikism.org/Patellar_J_Sign

SportsMedReview: Knee Pain
https://www.sportsmedreview.com/byjo...

Wiki Sports Medicine: Knee Pain
https://wikism.org/Knee_Pain_Main