The knee is one of the most fascinating parts of the human body. You’d probably expect us to say that – but it’s true! The knee isn’t merely the largest and most powerful of our joints, it’s also the most complicated: an intricate meeting point of bone and tissue that provides flexion and balance under duress. Because of that, it’s also one of the most easily-injured areas of our body. Understanding how the whole thing fits together can be helpful if you have an issue with your knee – an injury, a condition, an unexplained pain. Here, then, is a simple starter-guide to the knee (with quick-links for more detail on our website).
Your knee is structured around four key bones. The uppermost one is the femur (thighbone). Below it is the tibia (shinbone); alongside the tibia is the thinner fibula (calf bone). Front and centre of your knee is the patella (kneecap), which provides hard-impact protection to the joint (the word patella means ‘small plate’).
The meniscus is a tough, rubbery pad of ‘fibrocartilage’ that sits between the femur and tibia. In fact it’s really two pads: a C-shaped inner segment, called the medial meniscus, and a U-shaped outer one (lateral meniscus). The menisci are like shock absorbers for the knee, spreading load across your joint. The most common injury to the menisci is a tear, either through injury or gradual deterioration.
Remember those four knee bones? The end of each bone is covered in a smooth substance called chondral (or articular) cartilage. This important material allows the bones to slide smoothly against each other. Unlike the menisci, however, chondral cartilage can begin to wear away with time and age (or, alternatively, after an acute injury). We call this degeneration osteoarthritis.
The knee bones are connected by ligaments. These are like guy ropes, binding the bones tightly together to keep the whole unit stable. There are two key ligament pairs in the knee. The collateral ligaments run on the outside of the joint and control sideways movement – these are the MCL and LCL. The cruciate ligaments cross over each other in the middle of the joint to control back-and-forth movement – these are the ACL and PCL.
Tendons are the thick cords that connect bones to muscles. The key ones in the knee are the quadriceps tendon, which links the thigh muscles to the kneecap and helps the joint to straighten and extend, and the patellar tendon, which connects the shin to the kneecap. Various injuries and conditions can affect your knee tendons; common ones include tendonitis, Osgood-Schlatter disease and tendon tears.
Less firm than tendons but more pliable, muscles provide the nuanced range of movements, stability and control that we expect from our knees. They include the hamstrings (which provide flexion), the hip abductors (stability), and the iliotibial band, which runs down the outside of the thigh between the hip and the knee.