A positive J Sign is demonstrated by which finding during knee extension from 90 degrees?

A positive J Sign is demonstrated by which finding during knee extension from 90 degrees?

• A. Sudden Lateral Deviation of the Patella
• B. Sudden Medial Deviation of the Patella
• C. Increased Tibial Translation
• D. Excessive Patellar Tilt

Answer: (A)

Patellofemoral tracking during knee extension is the key idea here. As the knee moves from 90 degrees of flexion toward extension, the patella should stay centered in the trochlear groove thanks to the medial stabilizers (like the vastus medialis obliquus and the medial patellofemoral ligament). If these stabilizers are weak or there’s trochlear dysplasia, the patella can suddenly drift laterally as extension begins. That abrupt lateral shift during extension gives a distinctive J-shaped movement—the J sign. So the best finding is a sudden lateral deviation of the patella when moving from flexed to extended. The other options describe different patellar or knee issues (medial deviation, increased tibial translation, excessive patellar tilt) that don’t capture this specific pattern of lateral maltracking seen with a positive J sign.

Patellofemoral tracking during knee extension is the key idea here. As the knee moves from 90 degrees of flexion toward extension, the patella should stay centered in the trochlear groove thanks to the medial stabilizers (like the vastus medialis obliquus and the medial patellofemoral ligament). If these stabilizers are weak or there’s trochlear dysplasia, the patella can suddenly drift laterally as extension begins. That abrupt lateral shift during extension gives a distinctive J-shaped movement—the J sign.

So the best finding is a sudden lateral deviation of the patella when moving from flexed to extended. The other options describe different patellar or knee issues (medial deviation, increased tibial translation, excessive patellar tilt) that don’t capture this specific pattern of lateral maltracking seen with a positive J sign.