What is the Knee Complex?

The knee is the largest and one of the most complex joints in the human body.  It consists of 4 bones, multiple ligaments, muscles and tendons, cartilage and soft tissue.  The knee is a modified hinge joint allowing primary motions of knee flexion and extension.  The knee has some slight internal and external rotation as well.  The joint and its components function together to provide stability and power for activities of daily living and athletic movements.  However, any of these structures can be injured or damaged requiring treatment as easy as bracing, rest and therapy to as complex as surgery to correct.  Regardless, either treatment will typically allow a full return to activity or sports without additional complications.

Boney structures of the knee consist of the patella (knee cap), Femur (thigh bone), Tibia and Fibula (lower leg bones).

Ligaments

Ligaments of the knee are classified as cruciate and collateral ligaments. Ligaments connect bone to bone.  The major ligaments of the knee consist of the ACL (anterior cruciate ligament, PCL (posterior cruciate ligament), MCL (medial collateral ligament) and LCL (lateral collateral ligament).  

  • Cruciate ligaments are within the knee joint.  They prevent anterior (forward) and posterior (backward) translation of the femur from the tibia.  
  • Collateral ligaments are outside the knee joint and prevent medial (inside) and lateral (outside) instability.