Structural diversity of the vastus intermedius origin revealed by analysis of isolated muscle specimens.

The quadriceps femoris (QF), a major extensor of the knee joint, plays an important role in human movement. However, descriptions of the three vastus muscles of the QF in anatomy textbooks remain confusing. We analyzed 33 QFs by a novel approach, using isolated muscle specimens to clarify the structures of the vastus lateralis (VL), vastus medialis (VM), and vastus intermedius (VI) origins. The origins of the VL and VM were quite constant in shape and location, but the VI was much more structurally diverse. In typical cases (23 of 33), the origin of the VI attached muscularly to the anterior and lateral surface of the femoral shaft. It adjoined the origin of the VL at the lateral lip (LL) of the linea aspera to form a common origin. In some cases (10 of 33), the muscle belly and origin of the VI were much smaller than those in the typical cases; the origin of the VI attached only to the anterior surface of the femur and did not contact the LL. In addition, the muscle belly of the VI was narrow and almost corresponded to the width of the femoral shaft. The isolated muscle specimen is a useful tool for analyzing individual muscle structures, which can be difficult to observe by routine dissection. Using this method, it became clear that the VI is more structurally diverse in its origin than the VL and VM. Clin. Anat. 30:98-105, 2017. © 2016 Wiley Periodicals, Inc.