The knee is one of the largest and most complex joints in the body. It plays a crucial role in movement related to walking, running, and jumping. The knee joint is made up of bones, ligaments, tendons, cartilage, muscles, and other structures.
The knee’s structure allows it to withstand great pressure from activities like running and jumping. It is, however, prone to injury and wear-and-tear, which can lead to conditions like osteoarthritis.
Bones: The knee joint involves three bones. The lower end of the femur (thighbone) meets the top of the tibia (shinbone) to form the main joint. This joint has two compartments: the medial compartment (inside of the knee) and the lateral compartment (outside of the knee). The patella (kneecap) sits in front of the joint to provide some protection.
Muscles: There are two primary muscle groups responsible for knee motion: the quadriceps and the hamstrings.
The popliteus muscle, located at the back of the knee, helps in unlocking the knee from the extended position.
Cartilage: Two types of cartilage are found in the knee. The menisci are tough, rubbery cartilage that sit between the femur and tibia to cushion and stabilize the joint. Articular cartilage is a smooth, slippery substance that covers the ends of the bones and helps reduce friction in the knee.
Ligaments: The knee joint is stabilized by several ligaments:
Tendons: Tendons are fibrous tissues that connect muscle to bone. The quadriceps tendon connects the muscles at the front of the thigh to the patella, and the patellar tendon connects the patella to the tibia.
Synovial Membrane: This is a thin lining that covers the knee joint. It produces synovial fluid, which lubricates the knee, reducing friction and allowing smooth movement.
Blood Vessels: The knee receives blood from the genicular arteries, which are branches of the popliteal artery.
Nerves: The knee is innervated by the femoral, tibial, and common fibular nerves.
Fascial Compartments: The thigh is divided into three fascial compartments: anterior, posterior, and medial.
Joint Anatomy: The knee is a hinge joint that primarily allows for flexion and extension, but it also allows a small degree of rotation and lateral and medial displacement. The articulating surfaces of the femur, tibia, and patella are covered with hyaline cartilage, reducing friction and wear. Two fibrocartilaginous discs, the medial and lateral menisci, sit on the tibial plateau and provide shock absorption.
Bursa Sacs: There are approximately 14 bursae around the knee joint that help reduce friction. Some of the main ones include:
Kinesiology: The primary movements of the knee joint are flexion and extension:
A small amount of medial and lateral rotation can also occur when the knee is flexed. The knee also plays a key role in shock absorption during activities such as walking and running.