Muscles around the knee joint | The human musculature

Muscles around the knee joint

The knee is the largest joint in the human body and is exposed to enormous stress during the course of life, which is why complaints in the knee area almost always occur in old age. The knee itself has no muscles of its own to guide it, but many muscles in the area of the knee start or rise from here and pull further down towards the foot. First there is the gracilis muscle.

This originates in the area of the pubic bone (Os pubis) and from here it moves along the inside of the thigh to the upper part of the lower leg, beyond the knee. When tensed (contraction), this muscle ensures that we can bend the knee (flexion) and also rotate it inwards. The next muscle is the sartorius muscle.

This originates in the area of the hip shovel (spina iliaca anterior superior) and from here also pulls on the inside of the knee joint, running superficially along the thigh. Tension of this muscle results in flexion and internal rotation of the knee. The next large muscle affecting the knee is the quadriceps femoris muscle, which has four heads and originates in the hip area and forms the relief of the thigh from the front.

From the hip, the muscle then extends to the knee and ends in the patellar tendon (patella tendon). This four-headed muscle is thus the only muscle that can stretch the knee straight again when tensed, as is always the case in normal standing. The biceps femoris muscle, the semimembranosus muscle and the semitendinosus muscle run along the back of the thigh.

These all originate in the area of the buttocks and pull from here from behind to the knee. Thus, when these muscles are tensed, a flexion of the knee occurs. Since the biceps femoris muscle is located on the outside of the knee, it can also rotate the knee outwards when tensed.

Since the semitendinosus and semimembranosus muscles are located on the inner side of the knee, they rotate the knee inward when tensed. In addition, there is a very small muscle that pulls on the back in the hollow of the knee from the upper edge of the hollow of the knee to the lower edge of the hollow of the knee. This muscle (Musculus popliteus) provides a slight flexion and internal rotation in the knee and stabilizes the knee minimally.

Finally, there is the calf muscle, which originates above the knee on the back of the knee, pulls down over the hollow of the knee and then starts at the heel bone. If the superficial calf muscles contract, this results in flexion of the knee.The lower leg is significantly narrower than the thigh, so it is assumed that the lower leg also contains less muscle. However, this is not the case, which is probably due to the fact that our ancestors used their feet for much more delicate work than just walking.

Therefore, several small muscles had to perform more precise work, while the thigh muscles were used exclusively for posture. The lower leg muscles are divided into extensor muscles, muscles in the fibula and flexor muscles. The extensor muscles are located in the frontal area of the lower leg between the knee and the toes.

There are three muscles in the lower leg, which belong to the extensor muscles in the upper ankle joint: the muscle tibialis anterior, the muscle extensor digitorium longum and the muscle extensor hallucis longus. All three muscles originate below the knee on the outside and from here they move towards the foot. When this group of muscles is tensed, the ankle joint is stretched, which is very useful when standing on the heel, for example.

In addition, the extensor group can be used to tilt the foot inwards and outwards (supination and pronation). The next group of the lower leg muscles is the so-called fibularis group. A distinction is made between a Musculus fibularis longus and a Musculus fibularis brevis.

Both muscles originate on the outside of the lower leg at the fibula and from here they run under the foot to the underside of the foot at the big toe. In the upper ankle joint, they ensure that we can stand on our toes (flexion), while in the lower ankle joint they ensure that we can turn the foot outwards. The last group of the lower leg muscles is the flexor group (flexors).

Here we distinguish between the superficial flexors and the deep flexors. The superficial flexors form the calf. They include the triceps surae muscle, which consists of the soleus muscle and the gastrocnemic muscles.

The three-part muscle originates in the area of the knee on the back and then extends to the heel. The tendon is also called the Achilles tendon here because it is particularly stable. The deep flexors include the muscle tibialis posterior, the muscle flexor digitorum longum and the muscle hallucis longus. Common to all flexors is that they ensure that the foot can be pulled backwards, which is of enormous importance in ballet, for example, when standing on your toes.