The Knee: Anatomy and Function Part 3 – Muscles

Here is a short and sweet list of all the muscles that produce movement of the knee joint. Of course their origin and insertion (WARNING: lots of fancy big words), specific function if necessary and easy-to-understand pictures of location are also included 🙂

The knee is able to produce three different kinds of movements, these movements being flexion, extension and rotation. Flexion is pulling you leg towards your buttocks, extension is pushing your leg forward, assisting during kicking, and helps lock and unlock the knee joint which  is important for knee stability. If you ever wanted strong, bad-ass knees these are the primary muscles that need to be strengthened and conditioned for whatever physical activity you plan to impose on them.

Muscles that produce extension (all located on the anterior side of the body)

*Quadriceps: Consists of the 4 following muscles:

-Rectus femoris – The prime mover and also a flexor of the hip. Origin: Anterior-inferior iliac spine of ilum. Insertion: Top of patella and patellar ligament.

-Vastus lateralis: Origin: Lateral lip/side of linea aspera. Insertion: Lateral half of upper patella + Patella ligament + Anterior tibial tuberosity

-Vastus medialis: Medial side of the linea aspera + internal condyloid ridge. Insertion: Medial half of upper patella and patellar ligament

-Vastus intermedius (underneath rectus femoris): Origin: Two thirds of the upper anterior surface of femur. Insertion: Upper patella and patellar ligament

Muscle that produce flexion

*The hamstring group consists of 3 different muscles. The semitendinosus and semimembranosus is on the medial side, while the biceps femoris is on the lateral side. They can also assist hip extension.

-Semitendinosus: Origin: Ischial tuberosity. Insertion: Anterior medial tibial surface. Also does internal rotation of knee.

-Semimembranosus: Same origin and insertion as semitendinosus, but lies deeper. Also does internal rotation of the knee.

-Biceps femori – Crosses over medially to laterally on posterior side. Long head origin: Ischial Tuberosity. Short head origin: lower half of linea aspera. Insertion of both: Head of fibula. Also does external rotation of the knee.

*Pes anserinus – The collective name of the muscles:
Sartorius, gracilis and semitendinosus (mate, both Pes and Hammy group? This guy has a lot of friends). The group also for some not fully clear to me has been called the “Goose Foot”, but I am guessing it has something to with the anatomical look when they all inserts at the same place.

-Gracilis – Origin: Pubis crest. Insertion: Antertior medial surface of tibia.

-Sartorius – Origin: Anterior-superior spine of ilium. Insertion. Anterior medial surface of tibia (note that as many as 4 flexor inserts here)

*Popliteus – lies on the back of the knee. Origin: Lateral condyle of femur. Insertion: On proximal third of posterior tibia. Also does internal rotation.

*Gastrocnemius, the “calf” muscle – Origin: Posterior Surface of the medial and lateral femoral condyles. Insertion: The calcaneus (this is at the ankle) through the Achilles tendon.

Flexors that are not commonly included:

*Plantaris – Origin: Lateral supracondylar ridge of femur. Insertion: Calcaneus, medial and deep to gastrocnemius.

*Tensor fascia latae – the muscle itself does not fully cross the knee but it crosses the iliotibial band does can minorly act upon the knee (IT band can become really tight so important to stretch. The muscle is more related to hip function but it is a key to maintain strong knees so I decided to throw it in here.

Quick overview of the muscles which act in rotation, which consist of no new muscles that we have not yet discussed (yey!)

Internal/medial rotation:
Popliteus, Semiteninosus and Semimembranosus

Exertnal/lateral rotation
Biceps femoris and Sartorius

That is it for knee anatomy! Next up for knees is getting into prevention of injuries and strengthening. Finally something that about knees that is going to be an easy read ey?


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