a curved line with its superior end adjacent to the lesser trochanter, nearly continuous with the intertrochanteric line, and converging inferiorly with the pectineal line to form the medial lip of the linea aspera; forms the medial boundary of the distal attachment of the iliacus muscle. SYN: linea spiralis femoris.

The spiral line of the femur is a curved ridge-like projection that runs obliquely down the posterior surface of the femur bone in the thigh. It starts at the upper end of the linea aspera, which is another ridge on the posterior surface of the femur, and extends down to the medial condyle of the femur, which is the bony projection at the lower end of the bone.

The spiral line serves as a site of attachment for several muscles, including the gluteus maximus muscle, which is a large muscle located in the buttock region. Other muscles that attach to the spiral line include the piriformis muscle, which is a small muscle located deep in the buttock region, and the obturator internus muscle, which is a muscle that lies in the pelvis and rotates the thigh laterally.

The spiral line also marks the boundary between the anterior and posterior surfaces of the femur. The muscles that attach to the spiral line are primarily responsible for extending and rotating the hip joint, as well as stabilizing the femur bone during movements of the leg.