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!

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