The lateral trochlear sign. Femoral trochlear dysplasia as seen on a lateral view roentgenograph.

Dysplasia of the femoral trochlea is easily detected on an axial roentgenogram of the patellofemoral joint. A roentgenographic sign is described wherein severe trochlear dysplasia can also be readily appreciated on a plain lateral roentgenogram. The subchondral bone of the trochlea is normally seen as a dense white line, which remains parallel to the subchondral bone of the lateral femoral condyle. The intersection of those two lines is indicative of severe trochlear dysplasia and has been named "the lateral trochlear sign."