Simply put, the knee works in a similar fashion to a modified hinge on a door. It not only bends back and forth like a hinge, but it also has a complex rotational component that occurs whenever we bend (this is called “flexion”) as well as when we straighten it (this is referred to as “extension”). It is a major weight-bearing joint that is held together by muscles, ligaments and soft tissue. Cartilage can be found inside the joint and provides shock absorption which comes into play whenever we walk, run, lift, climb stairs and pretty much any other impact activity you can name. See the below illustration for more on the components of the knee.
Your knee is comprised of four main components:
Bones of the knee
Your knee is made up of the thighbone (femur), the shinbone (tibia) and the kneecap (patella). So how do these bones work together? The thighbone and shinbone come together to form a hinge with the kneecap in front of them, which provides protection for the joint. All the while, the kneecap moves in a sliding action up and down in a groove in the thighbone. This groove is called the femoral groove and the sliding occurs whenever we bend or straighten our knees.
Ligaments of the knee
The job of the ligaments is to assure that the components of the knee are held together and kept stable. The medial (inner) collateral ligament (MCL) and lateral (outer) collateral ligament (LCL) limit sideways motion of the knee. All the while, the posterior and anterior cruciate ligaments (PCL and ACL) limit forward motion of the knee bones, thus keeping them stable.
Cartilage of the knee
Each knee has two cartilage structures called menisci, which sit between the thighbone and the shinbone. These act as shock absorbers. Oftentimes, a torn meniscus is called “torn cartilage.” The menisci are one of two types of cartilage in the knee. The second type, articular cartilage, is a smooth and very slick material which covers the end of the thighbone, the femoral groove, top of the shinbone and the underside of the kneecap. All of these enable the knee and its bones to move smoothly.
Tendons of the knee
The job of tendons is to connect muscle to the knee. The quadriceps muscles on the front of the thigh are connected to the top of the kneecap by the quadriceps tendon, which covers the kneecap and becomes the patellar tendon. The patellar tendon then attaches to the front of the shinbone. The hamstring muscles in the back of the leg attach to the shinbone at the back of the knee. The quadriceps muscles straighten the knee while it’s the job of the hamstring muscle to provide the knee’s bending motion.
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