Knee

The knee is one of the most important joints in the human body and consists of the following:

• Bones and joints,
• Ligaments and tendons,
• Muscles,
• Nerves, and
• Blood vessels

Bones and Joints

The knee joint is a synovial joint. These are joints that are enclosed by a ligament capsule and contain fluid that lubricates the joint. It is the meeting place of two important bones in the leg, the femur (the thighbone) and the tibia (the shinbone). The patella (or kneecap, as it is commonly called) is made of bone and sits in front of the knee.

Ligaments and Tendons

Two important ligaments are found in either side of the knee joint. These are the medial collateral ligament (MCL) and the lateral collateral ligament (LCL). Inside the knee joint are the anterior cruciate ligament (LCL) in the front and the posterior cruciate ligament (PCL) in the back.

The MCL and the LCL prevent the knee from moving too far side to side, while the ACL and the PCL control the front to back motion of the knee joint.

Two special types of ligaments called menisci sit between the femur and the tibia. The two menisci of the knee are important for two reasons: (1) they work like a gasket to spread the force from the weight of the body over a larger area, and (2) they help the ligaments with stability of the knee.

Tendons attach muscles to bones. The largest tendon around the knee is the patellar tendon. This tendon connects the patella (kneecap) to the tibia. This tendon covers the patella and continues up the thigh.

Muscles

Muscles are the motor that drive the knee joint and allow us to walk. It sits in front of the knee joint and is made up of the patella, the patellar tendon, the quadriceps tendon, and the quadriceps muscles.

The four quadriceps muscles in front of the thigh are the muscles that attach to the quadriceps tendon. When these muscles contract, they straighten the knee joint, such as when you get up from a squatting position.

The hamstring muscles are the muscles in the back of the knee and thigh. When these muscles contract, the knee bends.

Nerves

The popliteal nerve in the back of the knee is the most important nerve around the knee. This large nerve travels to the lower leg and foot, supplying sensation and muscle control. The nerve splits just above the knee to form the tibial nerve and the peroneal nerve.

The tibial nerve continues down the back of the leg while the peroneal nerve travels around the outside of the knee and down the front of the leg to the foot. Both of these nerves can be damaged by injuries around the knee.

Blood Vessels

The popliteal artery and popliteal vein travel down the back of the leg and are the largest blood supply to the leg and foot. If the popliteal artery is damaged beyond repair, it is very likely the leg will not be able to survive. The popliteal artery carries blood to the leg and foot. The popliteal vein carries blood back to the heart.

Problems with Knees

Though the knee has a somewhat unstable design, it must support the body's full weight when standing, and much more than that during walking or running. This leads to knee problems that are a fairly common complaint among people of all ages.

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