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Knee Pain Overview

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Introduction to Knee Pain

Knee pain is the most common musculoskeletal complaint that brings people to their doctor. With today's increasingly active society, the number of knee problems is increasing. Knee pain has a wide variety of specific causes and treatments.

Anatomy of the Knee

The knee joint's main function is to bend, straighten, and bear the weight of the body along with the ankles and hips. The knee, more than just a simple hinged joint, however, also twists and rotates. In order to perform all of these actions and to support the entire body while doing so, the knee relies on a number of structures including bones, ligaments, tendons, and cartilage.


  • The knee joint involves 4 bones.
  • The thighbone or femur comprises the top portion of the joint.
  • One of the bones in the lower leg (or calf area), the tibia, provides the bottom weight-bearing portion of the joint.
  • The kneecap or patella rides along the front of the femur.
  • The remaining bone in the calf, the fibula, is not involved in the weight-bearing portion of the knee joint but provides ligament attachments for stability.


  • Ligaments are dense fibrous bands that connect bones to each other.
  • The knee includes 4 important ligaments, all of which connect the femur to the tibia:
  • The anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) provide front and back (anterior and posterior) and rotational stability to the knee.
  • The medial collateral ligament (MCL) and lateral collateral ligament (LCL) located along the inner (medial) and outer (lateral) sides of the knee provide medial and lateral stability to the knee.


  • Tendons are fibrous bands similar to ligaments.
  • Instead of connecting bones to other bones as ligaments do, tendons connect muscles to bones.
  • The 2 important tendons in the knee are (1) the quadriceps tendon connecting the quadriceps muscle, which lies on the front of the thigh, to the patella and (2) the patellar tendon connecting the patella to the tibia (technically this is a ligament because it connects 2 bones).
  • The quadriceps and patellar tendons are sometimes called the extensor mechanism, and together with the quadriceps muscle they facilitate leg extension (straightening).
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