Essentially the human knee is a hinge joint in the human leg connecting the tibia and fibula with the femur and protected in front by the patella. Within the knee itself a vast connection of muscles, cartilage, tendons and ligaments are surrounded by synovial fluid. The human knee is an important aspect of human anatomy in the sense that it is a staple component of locomotion that controls direction and stability, while at the same time providing ample shock absorption with ground reaction force that can be three times body weight.
Figure 1. Diagram of the human knee
Ligaments
In essence ligaments are a band of tough, fibrous dense regular connective tissue comprised of attenuated collagenous fibers that connects bones to other bones. Ligaments are crucial to the operation in different joints of the body but particularly important in the human knee joint. The human knee consists of eleven different types of ligaments each with it's own important aspect of providing stability and connection. These ligaments are classified either as being Intracapular (within the knee cap/patella) or Extracapular (outside of knee cap/patella)
Intracapular Ligaments
1. Anterior Cruciate Ligament: is a band of dense connective which courses the femur to the tibia in the center of the knee. It is important in limiting the rotation as well as backward motion of the tibia. A fun fact about the ACL is that its injury accounts for 40% of all sports injury.
Fig 2. Low Power View of cruciate ligament
Fig 3. Cross section of Ligament
2. Posterior Cruciate Ligament: it connects the femur and the tibia and limits the forward motion of the tibia in the center of the knee.
3. Transverse Ligament: this is a ligament of the knee that is responsible for connecting the anterior end of the medial meniscus to the anterior convex margin of the lateral meniscus
4. Posterior Meniscofemoral Ligament: is a small collagen fiber band in the knee joint. It attaches to the posterior area of the lateral meniscus and crosses superiorly and medially behind the Posterior cruciate ligament to attach to the medial condyle of the femur
5. Anterior Meniscofemoral Ligament: is a small fibrous band of the knee joint. It arises from the posterior aspect of the lateral meniscus and passes superiorly and medially in front of the posterior cruciate ligament to attach to the anterior cruciate ligament
6. Meniscotibial Ligament: is responsible for the periphery of the ibial plateus to connect to the inferior edges of the fibrocartilagenous menisci inside joint capsule
Extracapular Ligaments
1. Patellar Ligament: a strong flat ligamentous band that connects the patella to the tuberosity of the tibia
2. Medial Collateral Ligament: this ligament runs down the inside of knee joint and connects femur to the tibia and limits the sideways motion of the knee. It consists of three groups of fibers with one stretching between the two bones, and two fused with the medial meniscus.
3. Lateral Collateral Ligament: it runs on the outside of the knee and connects the lateral epicondyle of the femur to the head of fibula. It is responsible for limiting the sideways motion of the knee from inside bending force (Varus force).
4. Oblique Popliteal Ligament: located on the dorsal side of knee; it is a broad, flat fibrous band that connects upper margin of the intercondyloid fossa and posterior surface of the femur
5. Arcuate Popliteal Ligament: is a Y-shaped ligament that extends from the head of the
fibula into the capsule
Injury
The possibility of injury to a ligament of the knee increases as the level of activity rises. The tearing of ligaments is a common occurrence in sports. The most common of them all is that of a torn ACL which accounts for approximately one fifth of all sports knee injuries. Ligament tears are designated into three categories:
1. First degree tears are partial longitudinal tears of the tendon
2. Second degree tears which are also partial tears but are of a higher severity
3. Third degree tears which are complete tears of a ligament and result in higher complications and pain levels.
Fig 4: Normal ACL versus torn ACL
Stretching of ligaments is also an issue of concern especially for athletes. If a joint is dislocated and not inserted back in place then this can result in a stretching of the ligaments making individuals more susceptible to future dislocations of that particular joint. Some individuals have a higher level of elasticity than others in their ligaments and this results in what is referred to as hyperlaxity (Double Jointed).
References:
Mak-Ham, L., Fong, D., (2009), Knee stability assessment on anterior cruciate ligament injury: Clinical and biomechanical approaches, Sports Med Arthrosc Rehabil Ther Technol. doi: 10.1186/1758-2555-1-20
Figure 1: https://meded-portal.ucsd.edu/isp/2006/knee/images/Knee4.jpg
Figure 2: http://www.drbraceco.com/images/Collateral-Ligaments.jpg
Figure 3: http://neuromedia.neurobio.ucla.edu/campbell/connective_tissue/wp_images%5C142_ligament_TS.gif
Figure 4: http://www.ontheroadwithdavid.com/OnTheRoad/Knee/TornACL.jpg
