Category Archives: Anatomy

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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The Knee: Anatomy and Function Part 2 – Ligaments and Joint Capsule

Continuing where we left of in the last post! Hope the pictures are of some help for part 2, this is a tough one! WARNING: Big words ahead!

*Menisci – Fibrocartilaginous structures that has a crescent half moon shape. Their shape has also given them the alternative name of semilunar (halfmoon) cartilages. The functions of the menisci are mainly shock absorption (landing after a jump) and helps accomodate movement of the bones of the joint . You have both a medial and lateral meniscus that both attach at the central intercondylar region together with the ACL (on anterior side) and PCL (on posterior side).  The medial meniscus is attached medially to the tibial/medial collateral ligament and to the capsule of the joint of the knee,  while the lateral meniscus is attached to neither. This causes the lateral meniscus to become more mobile (and sadly more easy to tear).

*Transverse ligaments – Serves to connect the two menisci.

*Medial/tibial collateral ligament – proximal attachment of medial epicondyle of femur, distal attachment medially on tibia – more specifically a little bit above the tendonous insertion attachment points of the following muscles: Sartorius, gracilis and semitendinosus.

*Lateral/fibular collateral ligament – Proximal attachment point at lateral epicondyla of femur, distal attachment point on lateral head of fibula.

*Cruciate Ligaments – Fun fact: called cruciate because they cross over each other. The PCL crosses over the ACL from the medial wall of the intercondylar fossa (of the femur) to attach on the posterior side of the knee and the ACL crosses under the PCL from the lateral wall of the femurs intercondylar fossa to attach more on the anterior side of the knee (both attaches at the intercondylar region of the tibia)

*ACL – Prevents tibia from sliding forward.

*PCL – Prevents tibia from sliding backwards.

*Patella ligament – continuous of the femoris/quadriceps tendon which attaches at the proximal side of the patella, and becomes the tibial tuberosity at its distal side (point that sticks out of the upper anterior side of the tibia). Just behind and a little distal to the ligament we also have a small piece of fat called the infrapatellar fat pad which separates the ligament and the synovial membrane of the joint capsule.

Now that is mostly it for the ligaments and all that stuff, now onto the joint capsule which is a bit more tricky to explain. The joint surfaces (or articulate surfaces to just to make it a bit more fancy) is covered by hyaline cartilage.

*Joint capsule of the knee fibrous membrane medial and anterior support – Fibrous joint capsule of the knee. The fibrous membrane is reinforced by ligaments, namely the MCL (medially), medial meniscus (one of two reasons why it is not very mobile) and the patella ligament (anteriorly) where it blends with the quadriceps muscle fibers of the vastus medialis and vastus lateralis at the margins of the patella. This strengthens the capsule anteriorly.

*Joint capsule of the knee fibrous membrane lateral support – On the lateral side of the knee the fibrous membrane is not reinforced by its respective collateral ligament as it is separated from the joint capsule by the fibular bursa which is located underneath the LCL. However, the capsule is supported laterally by the iliotibial tract which is located more medially towards the patellar ligament and runs downward alongside it.

*Joint capsule of the knee fibrous membrane posterior support – Posteriorly the fibrous capsule is supported by the oblique popliteal ligament, which is an extension from the semimembranosus tendon which attaches onto the tibia.

*Joint capsule synovial membrane – The synovial membrane lines the fibrous membrane which attaches to the margins of the articulate surfaces and the outer aspects of the menisci (the membrane does not enclose the cruciate membrane as they are not actually contained within the articular cavity.

*Synovial membrane bursas – The synovial membrane folds in various places to form bursa (gaps). These are the following: Suprapatella bursa (above patellar ligament behind patellar/quadriceps femoral tendon), Subpopliteal recess (lies between lateral meniscus and popliteus tendon), infrapatellar fat pad (see patellar ligament), deep and superficial infrapatella bursa (inside and outside of the patellar tendon respectivelly) prepatella bursa (subcutaneous at patella, which just means under the skin).

Next up is muscles, saved the best for last! Part 3 here we come!

The Knee: Anatomy and Function Part 1 – Knee Joint Fundamentals

Knees are one the more troublesome joints of the body especially for athletes or elderly whose knee has been subject to a lot of wear and tear. Having personally torn an ACL (anterior cruciate ligament) and meniscus, the knee is probably my least favorite joint and I catch myself saying ****ing knees a bit too much… However this has also motivated me to learn a lot more about how the knees work, and the reason why this is the first of many musculoskeletal system anatomy articles.

The knee is classified as a hinge joint which are formed between two or more bones and is limited to movement along one axis (flexion or extension). Fun fact: The knee is the largest and most complex synovial joint of the body (hinge is a common synovial joint class). However because of the complexity of the knee joint it may also be referred to as a “modified” hinge, bicondylar as well as biaxial joint. It might a good idea to check with your lecturer if you are at university.

The joint articulates between the femur and the tibia as well as the femur and patella. Flexion of the knee pulls the tibia posteriorly and extension pushes it anteriorly. Now this is where the complexity of the knee comes in, as during flexion the knee may rotate both laterally and medially, and during extension (standing position) the femur will rotate the knee medially to lock the knee into position (you can see this very well if you hyperextend your knee, but no over-hyperextension experiments please as that is painful). To unlock the knee the femur will rotate it laterally.

Now that the basics of the knee joint itself has been covered let us take a closer look at the landmarks of the knee and their functions:

*Femoral condyles at the articulate surfaces (posterior side of knee)- One medial, one lateral. The femoral condyles have an intercondylar fossa that separates them, which is home to the proximal attachment points of the anterior and posterior cruciate ligaments (ACL and PCL)

*Epicondyles – upper portion of the femoral condyles. These are home to the proximal attachment of the lateral and medial collateral (NOTE: NOT CRUCIATE) ligaments (LCL and MCL). The MCL (medial) is of course on the medial condyle 🙂 These bad boy ligaments are also known as fibular and tibial according which side they are on. The lateral collateral is for example on the same side as the fibula as the fibula is the most lateral of the fibula and tibia (yay, easypiecy).

*Tibial Plateu – Superior proximal surface of the tibia. Has a couple tibial condyles (medial and lateral) at the articulate surfaces. These condyles also has an intercondylar region between them which is where the cartilage of the menisci as well as the ACL and PCL.

*Intercondylar eminence – The point thing that sticks out of the superior surface of the tibia. The point thing also has two other pointy things, which are the lateral and medial intercondylar tubercle.

Continued in Part 2…