The semimembranosus, semitendinosus, medial gastrocnemius, sartorius, and gracilis work to bend or flex the knee.Each of the muscles attaching near the medial compartment helps move the knee in one or multiple directions.The meniscus helps improve the congruency of the joint and, along with the articular cartilage, assists in absorbing the stresses that are placed through the bones as you go about your day.As a result of these joint movements, the knee is able to fully bend and straighten as you move.

The rounded end of the medial femoral condyle sits on the relatively flat tibial plateau, which allows the two bones to roll, slide, and rotate slightly on one another.It inserts below the knee joint on the posterior (back) and posteromedial (back and inside) portions of the tibia. Semimembranosus: One of the three hamstring muscles, this structure originates from just below the buttocks and runs down the back of the leg.This fluid-filled sac separates the muscle tendons from the tibia bone and helps to reduce friction in the area. Pes anserine bursa: On the anteromedial (front and inside) portion of the tibia, three muscles (from top to bottom: the sartorius, the gracilis, and the semitendinosus) insert one above the next and form the outer border of the pes anserine bursa.Vastus medialis oblique (VMO): One of the four quadriceps muscles, the VMO runs down the leg on the inner part of the thigh and eventually joins the quadriceps tendon to insert into the superomedial (top and inside) border of the kneecap.Medial gastrocnemius muscle: This calf muscle travels up the lower leg from the Achilles tendon to a boney prominence below and slightly behind the adductor tubercle.Adductor magnus muscle: This muscle runs along the side of the leg and inserts near a boney bump called the adductor tubercle on the medial femoral condyle.

Compartments of lower leg