The Knee Joint: Bones, Ligaments, and Stability

Overview

The knee is the largest and one of the most complex synovial joints in the body. It is primarily a hinge joint that allows flexion and extension, with a small degree of rotation when flexed.

Bony Components

Three bones meet at the knee:

• Femur – the rounded condyles form the upper articular surface.
• Tibia – its flat plateau receives the femoral condyles.
• Patella – the kneecap, a sesamoid bone within the quadriceps tendon that improves leverage.

The fibula does not take part in the knee joint itself.

Menisci

Two C-shaped fibrocartilage pads, the medial and lateral menisci, sit between the femur and tibia. They deepen the joint surface, absorb shock, and distribute load across the plateau.

The Four Key Ligaments

• Anterior cruciate ligament (ACL): prevents the tibia from sliding forward.
• Posterior cruciate ligament (PCL): prevents the tibia from sliding backward.
• Medial collateral ligament (MCL): resists inward (valgus) force.
• Lateral collateral ligament (LCL): resists outward (varus) force.

Clinical Significance

The ACL is among the most commonly injured ligaments in sport, often torn during sudden pivoting. The combination of ACL tear, MCL tear, and medial meniscus injury is so frequent it is known as the "unhappy triad."

Summary

The knee balances mobility and stability through an interplay of bones, menisci, and ligaments. Each ligament resists a specific direction of stress, which is why knee injuries follow recognizable patterns.

For educational purposes only; not a substitute for medical advice.