Anatomy of the Knee
The largest joint in the human body, the knee joint connects the femur to the tibia. Three bones articulate at the knee joint; the femur, the tibia, and the patella. Some may believe that the fibula also helps compose the knee joint. The fibula does not articulate with the knee joint, therefore the fibula plays no role in the knee. A hinge joint, the knee allows the leg to flex and extend without the need for rotation or medial-lateral movement.
Muscles of the knee
The quadriceps muscles, hamstrings, and the muscles of the lower leg play a vital role in the functionality of the knee. These muscle groups provide strength and stability to the knee joint and must remain flexible for prime optimization. If muscle groups do not receive adequate exercise, they may atrophy. To atrophy means that the muscle degenerates and loses strength. When one muscle group does not do its part, other muscles may try to compensate and get injured from overcompensation.
Cartilage of the knee
A strong, flexible, and slippery form of cartilage, articular cartilage covers the surfaces of the bones where they articulate. Articular cartilage allows the bones to glide, allowing the joint to move freely. Articular cartilage also absorbs shock when the bones touch each other. When individuals suffer from arthritis of the knee or any other joint, the arthritis occurs from this articular cartilage wearing down from age or injury. Bone spurs, or small growths on the surface of a bone, can form which creates additional friction and lead to osteoarthritis.
Along with articular cartilage, the knee has thick bands of cartilage on each side between the tibia and the femur. Singularly called a meniscus, each knee has two menisci; The medial meniscus and the lateral meniscus. The medial meniscus lays on the inside of the knee with the lateral meniscus positioned on the outside. Comparable to articular cartilage, the menisci aim to reduce shock within the knee joint. The menisci take things one step further than the articular cartilage and aid in stabilization and mobilization of the knee.
Ligaments of the knee
In addition to the menisci, each knee has a group of ligaments to stabilize the knee. Do not confuse with tendons, ligaments connect bone to bone. Each knee has four main ligaments connecting the femur and tibia. The four main ligaments of the knee include the anterior cruciate ligament, the posterior cruciate ligament, the medial collateral ligament, and the lateral collateral ligament. Many physicians may refer to the ligaments of the knee using their acronyms; ACL, PCL, MCL, and LCL. The two cruciate ligaments prevent the tibia from moving out of anterior and posterior alignment while the two collateral ligaments prevent medial and lateral movement of the knee. A large tendon also plays an important role in the knee. Originating at the quadriceps muscles and inserting at the front of the tibia, the patellar tendon connects the quad muscles to the tibia. This allows the knee to flex and extend.
Membrane of the knee
A thin membrane covers the entirety of the knee joint, called the synovial membrane. Filled with synovial fluid, the synovial membrane allows for lubrication of the joint. If inflammation occurs within the synovial membrane, physicians call it synovitis.
Bursa of the knee
Sandwiched between the bones and soft tissues of the knee lays sacs of bursae. Lubricated, fluid-filled sacs, bursae reduce friction within the knee and allow for free movement. Injury and overuse may cause irritation to the bursae. When a bursa or bursae become irritated and inflamed, physicians call the condition bursitis.