 In this video, I will identify the muscles that move the tibiofemoral joint, commonly known as the knee joint, and list the origin, insertion, and action of the major muscles that move the tibiofemoral joint. We'll start here with a superficial view of the anterior femoral region, where the quadriceps muscle group is located. There are four muscles in the quadriceps group. They all have a common insertion and action to extend the tibiofemoral joint, and they insert onto the patella, and then from the patella down to the tibiotuberosity via the patella ligament. Here will be the insertion of the quadriceps femoris group on the tibiotuberosity, but the four muscles we can see in the quadriceps femoris group, there are three superficial that we can see from this view, and a fourth muscle located deep to the rectus femoris. The rectus femoris is found right along the midline, just anterior to the femur, then vastus lateralis is located just to the lateral side of rectus femoris, and vastus medialis is located just to the medial side of rectus femoris. The fourth muscle in the quadriceps group is vastus intermedius, and that's located deep to rectus femoris. The origin of rectus femoris is the anterior inferior iliac spine. The insertion for all the quadriceps femoris muscle group including rectus femoris is the tibiotuberosity, and the action of rectus femoris as well as all of the quadriceps femoris group includes extension of the tibiofemoral joint. Rectus femoris also crosses the acetabulofemoral joint, and therefore can also contribute to flexion of the acetabulofemoral joint. The primary action of rectus femoris is extension of the tibiofemoral joint. Vastus lateralis has its origin from the linea spera on the posterior of the femur, and inserts at the tibiotuberosity to perform the action of extension at the tibiofemoral joint. Vastus medialis also has its origin from the linea spera of the femur, its insertion on the tibiotuberosity, and performs the action of extension of the tibiofemoral joint. Vastus intermedius, located deep to rectus femoris, has its origin on the anterior diaphysis of the femur, inserts on the tibiotuberosity, and performs the action of extension of the tibiofemoral joint. Now moving to a posterior view of the femoral region, we have the hamstrings muscle group. There are semi-membranosis, and just superficial to semi-membranosis on the medial side is semi-tendinosis, and then on the lateral side is biceps femoris. And so, semi-membranosis, semi-tendinosis, and biceps femoris are the hamstrings muscle group that performs the action of flexion of the tibiofemoral joint. So flexion of the leg at the knee is the action of the hamstrings working as antagonists to the quadriceps femoris group. Biceps means two heads, and so biceps femoris, like biceps brachii, has two origins. The origin of the long head of biceps femoris is the ischial tuberosity. The insertion of biceps femoris, both the long head and the short head, insert onto the head of the fibula and the lateral condyle of the tibia, and the action is to flex the tibiofemoral joint. The origin of the short head of biceps femoris is on the femur at the linea aspera. Then the insertion is onto the head of the fibula and the lateral condyle of the tibia, and the action is to flex the tibiofemoral joint. Now the most superficial muscle in the hamstrings on the medial side is semitendinosis. Semi-tendinosis is both superficial and more narrow than semi-membrinosis. Semi-tendinosis has its origin from the ischial tuberosity, and it has its insertion on the medial condyle of the tibia to perform the action of flexion at the tibiofemoral joint. Then semi-membrinosis is located deep to semitendinosis. Also has an origin from the ischial tuberosity and insertion on the medial condyle of the tibia to perform the action of flexion at the tibiofemoral joint.