Track sign (femur)

The track sign is the presence of two sclerotic lines, running parallel to the long axis of the bone, on a frontal radiograph of the femur. It represents visualization of the linea aspera-pilaster complex, an anatomic variant .

The linea aspera is the roughened vertical ridge of bone which runs down the posterior aspect of the femur acting as a site of insertion for several muscles. Frequently the linea aspera is more prominent due to an underlying bony ridge known as the pilaster. The combination of the linea and pilaster may produce the track sign.

The track sign may potentially be confused with the blade of grass sign of Paget disease of the bone .