Every bone in the body has distinguishing marks or features that give it the ability to connect with other bones through fibrous cable-like cords called ligaments. Bones also serve as attachment points for muscles through tough bands of connective tissue called tendons. Bony variations support other structures such as nerves and blood vessels as well. The femur or thigh bone, for example, contains a coarse ridge-like surface on the posterior or back portion called the linea aspera.
The linea aspera of the femur is a pronounced longitudinal elevation referred to as a ridge or crest present in the midsection of the bone. This gives the thigh bone a lip-like edge on the medial and lateral surfaces with a thin line through the center that is uneven and rough. It is along this line that certain muscles of the lower leg attach to the bone; it is also these muscles that are responsible for creating the ridge formations on either side of the line, which results from the tension generated by pulling on the bone when it tightens or contracts.
On the medial ridged aspect of the linea aspera, the muscle vastus medialis attaches to the femur. This muscle, often referred to as the teardrop muscle, is one of the four muscles of the group called the quadriceps. The main job of the vastus medialis on the inner thigh is to control the amount of extension of the knee joint. The lateral crest of the linea aspera contains the vastus lateralis, the muscle of the quadriceps group located on the outside of the thigh. This muscle also aids in the extension of the knee.
The ridge-like line known as the linea aspera is also the insertion point for a muscle called the adductor magnus. This large triangular muscle is positioned medially and is responsible for moving the leg back towards the midline or middle of the body. The portion of the adductor magnus that attaches directly to the linea aspera is also a key component in the legs' ability to laterally rotate, that is, to turn away from the midline of the body.
Between the vastus lateralis and the adductor magnus muscles, and the adductor magnus and vastus medialis attached to the linea aspera, there are several muscles that aid in the movement of the leg, knee, and hip. The adductor longus and brevis, for example allow the leg to return towards the midline or middle of the body when extended outward laterally. They also aid in movements such as rotation of the leg and hip flexion. The biceps femoris, part of the hamstrings, aids in the ability of the knee to flex or bend.