Quadriceps

Structure

Parts

The quadriceps femoris muscle is subdivided into four separate muscles (the 'heads'), with the first superficial to the other three over the femur (from the trochanters to the condyles):

• The rectus femoris muscle occupies the middle of the thigh, covering most of the other three quadriceps muscles. It originates on the ilium. It is named for its straight course.
• The vastus lateralis muscle is on the lateral side of the femur (i.e., on the outer side of the thigh).
• The vastus medialis muscle is on the medial side of the femur (i.e., on the inner side of the thigh).
• The vastus intermedius muscle lies between vastus lateralis and vastus medialis on the front of the femur (i.e., on the top or front of the thigh), but deep to the rectus femoris muscle. Typically, it cannot be seen without dissection of the rectus femoris.

Attachments

The rectus femoris arises from the anterior inferior iliac spine and from the superior edge of the acetabulum. It is thus a biarticular muscle. The other parts of the quadriceps arise from the surface of the femur. All four parts of the quadriceps muscle ultimately insert into the tuberosity of the tibia via the patella, where the quadriceps tendon becomes the patellar tendon.

Other muscles

There is a small fifth muscle of the quadriceps complex—the articularis genus muscle—that is not often included.

In addition, cadaver studies have confirmed the presence of a sixth muscle, the tensor vastus intermedius. While this muscle has a variable presentation, it consistently originates at the proximal femur, runs between the vastus lateralis and vastus intermedius muscles, and inserts distally at the medial aspect of the patellar base. Historically considered a part of the vastus lateralis muscle, the tensor vastus intermedius muscle is innervated by an independent branch of the femoral nerve and its tendinous belly can be separated from the vasti lateralis and intermedius muscles in most cases.

Innervation

The quadriceps femoris is innervated by the femoral nerve, which originates from L2, L3, L4.