Knee Joint Anatomy

The knee is the largest hinge joint in the body, connecting the thigh bone to the shin bone. It's a complex structure of bones, cartilage, ligaments, tendons, and muscles that work together to provide stability and enable movement essential for walking, running, jumping, and daily activities.

Bones of the Knee

The knee consists of three main bones:

• Femur (Thighbone): The lower end has two rounded knobs called femoral condyles that form the upper part of the knee joint.
• Tibia (Shinbone): The flat upper surface (tibial plateau) has medial and lateral sides that articulate with the femoral condyles.
• Patella (Kneecap): A small, protective bone that sits in the patellofemoral groove and shields the joint from direct impact.
• Fibula: The smaller lower leg bone that forms a minor joint with the tibia but isn't part of the main knee joint.

Articular Cartilage and Menisci

Specialized cartilage structures provide cushioning and smooth movement:

• Articular Cartilage: Smooth, slippery tissue covering the ends of the femur, tibia, and back of the patella, reducing friction during movement.
• Menisci: Two C-shaped wedges of fibrocartilage (medial and lateral) that sit between the femur and tibia, distributing weight and absorbing shock.
• Synovial Fluid: Lubricating fluid produced by the joint lining that nourishes cartilage and enables smooth motion.

Ligaments of the Knee

Four major ligaments provide knee stability:

• Anterior Cruciate Ligament (ACL): Located inside the joint, controls forward motion and rotation of the tibia. One of the most commonly injured ligaments.
• Posterior Cruciate Ligament (PCL): Works with the ACL to control backward movement of the tibia and provide rotational stability.
• Medial Collateral Ligament (MCL): On the inner side of the knee, prevents inward bending and provides side-to-side stability.
• Lateral Collateral Ligament (LCL): On the outer side, prevents outward bending and adds lateral stability.

Muscles and Tendons

Powerful muscle groups control knee movement:

• Quadriceps Muscles: Four muscles on the front of the thigh that straighten the knee. They connect to the patella via the quadriceps tendon.
• Patellar Tendon: Connects the patella to the tibia, forming part of the knee extension mechanism.
• Hamstring Muscles: Three muscles on the back of the thigh that bend the knee and attach via the hamstring tendons.
• Calf Muscles: Gastrocnemius and other muscles that assist in knee flexion and ankle movement.

Common Knee Conditions

Knee Osteoarthritis

Degenerative condition where cartilage wears down over time, causing pain, stiffness, and swelling. Most common in older adults and those with previous injuries.

ACL Tear

Rupture of the anterior cruciate ligament, often occurring during sports with sudden stops, jumps, or direction changes. Causes instability and often requires surgical reconstruction.

Meniscus Tear

Tear in the C-shaped cartilage between the femur and tibia. Can result from twisting motions or gradual degeneration. Symptoms include pain, swelling, and catching sensations.

Patellar Tendinitis (Jumper's Knee)

Inflammation of the patellar tendon from overuse, especially in jumping sports. Causes pain below the kneecap that worsens with activity.

Patellofemoral Pain Syndrome

Pain around or behind the kneecap from improper tracking, muscle imbalance, or overuse. Common in runners and younger, active individuals.

MCL/LCL Sprains

Stretching or tearing of the collateral ligaments from direct impact or twisting. MCL injuries are more common and typically heal with conservative treatment.

Patellar Dislocation

Kneecap slips out of its groove, usually to the outside. More common in younger patients and those with anatomical variations.

Bursitis

Inflammation of fluid-filled sacs around the knee joint. Can occur in front of the patella or on the inner side of the knee below the joint.

IT Band Syndrome

Overuse injury causing pain on the outer knee where the iliotibial band rubs against bone. Common in distance runners and cyclists.