Anatomy of the Knee
Did you know that not only is your knee amazingly complex, it’s the largest joint in your body? Unfortunately, it’s not the most stable joint and it’s prone to injury.
Your Knee Anatomy
Your knee is strong—it has more ligaments than any other joint—but its complexity can also be its downfall. The network of ligaments is so intricate that sometimes they don’t always work together as designed. The result can be instability, misalignment, and injury.
Take a Closer Look at Knee Joint Anatomy
The knee is a type of a hinge joint, responsible primarily for flexing (bending) and extending (straightening) movements—but the knee also has the ability to slightly rotate internally and externally. Our knees enable us to sit, stand, walk, run, jump, squat, and more.
Within the knee, bones, muscles, tendons, ligaments, and nerves all work together to keep your knee in motion. They are fed by an intricate vasculature providing nutrient-rich blood.
Bones of the Knee
Your knee joint capsule holds three bones in place, and it has two layers specially designed to help it do so. The outer layer is thick connective tissue and the inner layer is comprised of the synovium, a membrane which releases a gel (synovial fluid) that lubricates the joint.
The three bones that meet in the knee capsule include:
- Femur: the thigh bone and the largest bone in the body
- Patella: the kneecap, a triangular bone that “caps” the other two bones at the front of the knee
- Tibia: the shin bone
The ends of the bones are coated with slick, elastic cartilage that acts as a shock absorber as it enables bones to glide fluidly during movement. The following describes the cartilage in your knee:
Two crescent-shaped segments of cartilage cushion the space between the tibia and femur bone in each knee. They keep the bones moving against each other smoothly and help distribute body weight across the knee joint. They are:
- Lateral meniscus at the outside of the knee
- Medial meniscus at the inside of the knee
- Articular Cartilage
This cartilage covers the head of the femur and the end of the tibia.
- Muscles of the Knee
Several of the muscles of the knee serve double-duty as “hip movers” as well. The two major muscle groups that control knee movements include:
- Hamstrings: muscles located at the back of the thigh, extending from the hip to just below the knee
- Quadriceps: four muscles located at the front of the thigh, extending from the hip to the knee
Ligaments are critical in guiding the knee’s movements and keeping its components in alignment.
- Medial & Lateral Collateral Ligaments
The collateral ligaments are located on each side of the knee joint:
- Medial collateral ligament, on the inside of the knee, maintains knee stability during inward rotation
- Lateral collateral ligament, on the outside of the knee, provides lateral stability to the knee during outward rotation
- Cruciate Ligaments
The cruciate ligaments connect the tibia and femur within the knee joint and prevent overextension. The cruciate ligaments include:
- Anterior cruciate ligament (ACL) aids knee rotation and deceleration while preventing forward overextension of the knee
- Posterior cruciate ligament (PCL) helps to prevent backward overextension of the knee
- Collateral Ligaments
The collateral ligaments maintain control of the sideways motion of your knee and play a key role in its stabilization:
- Medial collateral ligament (MCL) provides stability to the inside of the knee
- Lateral collateral ligament (LCL) provides stability to the outside of the knee
- Medial & Lateral Collateral Ligaments
The knee’s tendons are tough and strong connectors of bone to muscle and help the joint to move while shielding it from injury. The two main tendons of the knee are as follows:
Quadriceps tendon: Runs from the kneecap up to the quadricep’s muscles
Patellar tendon: A continuation of the quadricep’s tendon, and runs down from the kneecap to the tibia
The knee has more than 20 bursae, making it the joint with the most bursae of any in the body. Filled will naturally lubricating synovial fluid, the bursae help to minimize friction between the structures in the knee joint. Related: Bursitis