Knee Flexors

Original Editor - Lucinda hampton

Top Contributors - Lucinda hampton  

Introduction

The knee flexors include the set of hamstrings, gracilis, sartorius, gastrocnemius, plantaris, and popliteus. Most of these knee flexors also internally or externally rotate the knee.

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Hamstrings Group

The semitendinosus, semimembranosus, and biceps femoris (long and short heads) make up the hamstring group.

Spanning the posterior thigh, the hamstring muscles are the primary knee flexors. The hamstrings also perform hip extension, except short head biceps femoris.

As the three of the four hamstrings cross the hip, as well as the knee, the position of the hip (and knee) can significantly affect the functional length of these muscles. As such, both the extensibility and the maximal force generated by the hamstrings are highly dependent on the position of the hip.

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10,11,12. Tendons of sartorias, gracilis, and semi-tendinosus

The gracilis and sartorius flex and internally rotate the knee and play an important role in providing stability to the medial side of the knee. They also have roles at the hip. These muscles attach proximally at the hip.

Distally these muscles course posterior to the medial-lateral axis of rotation of the knee, and with semitendinosus form a collective insertion on the proximal-medial tibia, commonly known as the pes anserinus. These three muscles all perform three common functions at the knee: Flexion of the knee; Internal rotation of the knee; Dynamic support of the medial collateral ligament, providing medial stability to the knee

Gastrocnemius and Plantaris

The gastrocnemius produces a large plantar flexion torques across the ankle, and as muscle crosses the posterior aspect of the knee, it is also a knee flexor. The relatively small plantaris, which also crosses the posterior knee, so is a flexor of the knee.

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