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Department of Orthopaedics
UB Orthopaedics & Sports Medicine
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Knee Basics
The knee has the difficult task of transferring the load of the body, while at the same time having the freedom to allow rapid change of direction and speed.
This necessary twisting and rotating adds to the stress the joint endures. With certain activities, the knee is subjected to nearly ten times body weight. (another reason to keep body weight optimal)
The knee joint is made up of three bones, two different types of cartilage and four major ligament groups. The bones in the knee are:
Femur (thigh bone): At the knee joint there are two separate promineces called condyles. Touching your knees together brings the inside condyles closer together—the medial femoral condyles. The outer condyle is the lateral femoral condyle.
Tibia (shin bone): Meets the femur at the knee with two areas on which the two femoral condyles “ride.” These are the medial and lateral tibial plateaus.
Patella (knee cap) - Rides in a shallow groove (or sulcus) over the front part of the femur called the trochlea.
The ends of these bones at the joint are covered by articular cartilage. This glistening white substance has somewhat the consistency of firm rubber but is actually a mixture of collagen and special large sponge-like molecules, all maintained by living cells (chondrocytes). With normal joint fluid, the surface is more slippery than water on ice. This allows the normal smooth and easy joint motion.
The other type of knee cartilage is the meniscal cartilage. These C-shaped pads are located between the thigh bone and shin bone. There is one meniscus on each side of the knee.
The medial meniscus resides on the inner thigh aspect and lateral meniscus on the outer side. These menisci are attached predominantly to the tibial plateaus. They serve as shock absorbers for the articular cartilage and transfer joint force. They accomplish this by distributing joint forces over a larger area of the joint, transferring force from the curved femoral condylar margins to the flatter tibial plateaus.
Injury to either type of cartilage can upset the normal loading of the joint. This “injury” is not limited to trauma; it may occur with normal daily activities. Once the delicate balance of the knee is upset, the resulting abnormal loads then lead to “overload damage”. Over time, initially small defects in the articular cartilage, or tears in the meniscal cartilage can progress. This gradual deterioration can lead to degenerative joint disease. (osteoarthritis)
Ligaments are rope-like structures which connect two bones. There are four main ligaments in the knee: two inner cruciate (cross) and two outer collateral (side) ligaments. The main function of the knee ligaments is to stabilize the knee joint, and to protect the articular cartilage and menisci from injury.