quadriceps The full name quadriceps femoris, or commonly ‘quads’, refers to the mass of muscle with four ‘heads’, partly surrounding the femur in the front of the thigh. This is the muscle that primarily extends the leg, straightening and stabilizing the knee by virtue of its strong attachments around the front and sides of the joint and to the tibia below it. Also, because part of it spans the front of the hip joint, it assists other muscles around the hip in maintaining an erect posture. The quads are thus essential simply for standing and for rising to standing, as well as for walking and running. The four components are partly distinct muscles with individual names: the vastus lateralis, the largest, lies mainly on the outer side, covering the deeper vastus intermedius; the vastus medialis lies on the inner side; the fourth muscle is attached to the pelvic bone above the hip and thence runs a straight course down the thigh — hence its name, rectus femoris — to end in a tendon that continues into the common quadriceps tendon in the front above the knee. The vastus muscles are attached above to the femur itself. Above the knee they curve in from the sides, accounting for the fleshy masses on either side just above the kneecap (patella), to be linked by fibrous sheets to the sides of the patella and to join the quadriceps tendon. This thick tendon is attached to the top of the patella, but also its strong fibrous extensions carry on downwards, embedding the patella within them, and linking up with the patellar tendon below it (the one that is tapped to elicit a knee-jerk reflex). This in turn is attached to the top of the tibia.

Sheila Jennett

quadriceps A group of extensor muscles that cover the anterior surface and sides of the mammalian femur. These muscles join at the base and are connected to the tibia by a single tendon. Muscle spindles in the quadriceps are responsible for the knee-jerk reflex (see stretch reflex).

quad·ri·ceps / ˈkwädrəˌseps/ • n. (pl. same) Anat. the large muscle at the front of the thigh, which is divided into four distinct portions and acts to extend the leg.

quadriceps (kwod-ri-seps) n. one of the great extensor muscles of the legs. It is situated in the thigh and is subdivided into four distinct portions: the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.