Knee Pain

Knee Pain Summary
The knee joint is composed of three compartments and ligaments which stabilize the joint. Causes of knee pain may include injury, degeneration, infrequently infection and rarely bone tumors. Although routine x-rays do not revel meniscus tears, they can be used to exclude other problems of the bones and tissues. The knee joint is the most commonly involved joint in rheumatic disease, as well as immune diseases that affect various tissues of the body.
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Knee pain facts

  • The knee joint has three compartments: medial, lateral, and patellofemoral.
  • Causes of knee pain include injury, degeneration, arthritis, infrequently infection, and rarely bone tumors.
  • Ligaments within the knee (cruciate ligaments) and on the inner and outer sides of the knee (collateral ligaments) stabilize the joint.
  • Surgical repair of ligament injury can involve suturing, grafting, and synthetic graft repair. Some patients require total knee replacement.
  • Routine X-rays do not reveal meniscus tears but can be used to exclude other problems of the bones and other tissues. Arthroscopy and MRI studies are used most frequently to diagnose knee ailments; occasionally, a needle aspiration of fluid is done.
  • The knee joint is one of the most commonly involved joints in rheumatic diseases (over 100 disease types). Rheumatic diseases are immune diseases that affect various tissues of the body, including the joints, by causing arthritis (pain, swelling, stiffness, and limited joint movements).

How is the knee designed, and what is its function?

It is important to understand the components of the knee because any of these tissues can become injured or diseased to cause pain in the knee.

The knee is a joint that has three compartments. This joint has an inner (medial) and an outer (lateral) compartment. The kneecap (patella) joins the femur to form a third compartment called the patellofemoral joint. The thighbone (femur) meets the large shinbone (tibia), forming the main knee joint.

The knee joint is surrounded by a joint capsule with ligaments strapping the inside and outside of the joint (medial and lateral collateral ligaments [MCL and LCL]) as well as crossing within the joint (cruciate ligaments). These ligaments provide stability and strength to the knee joint.

The meniscus is a thickened cartilage pad between the two joints formed by the femur and tibia. The meniscus acts as a smooth surface for motion and absorbs the load of the body above the knee when standing. The knee joint is surrounded by fluid-filled sacs called bursae, which serve as gliding surfaces that reduce friction of the tendons. The prepatellar bursa sits atop the kneecap while the anserine bursa is at the inner knee just below the knee joint.

Below the kneecap, there is a large tendon (patellar tendon) which attaches to the front of the tibia bone. There are large blood vessels passing through the area behind the knee (referred to as the popliteal space). The large muscles of the thigh move the knee. In the front of the thigh, the quadriceps muscles extend the knee joint. In the back of the thigh, the hamstring muscles flex the knee. The knee also rotates slightly under guidance of specific muscles of the thigh.

Picture of the knee joint
Picture of the knee joint

The knee functions to allow movement of the leg and is critical to normal walking. The knee flexes normally to a maximum of 135 degrees and extends to 0 degrees. The bursae, or fluid-filled sacs, serve as gliding surfaces for the tendons to reduce the force of friction as these tendons move. The knee is a weight-bearing joint. Each meniscus serves to evenly load the surface during weight-bearing and also aids in disbursing joint fluid for joint lubrication.

The goal of this article is to give the reader an overview of causes of knee pain. Most of the topics covered in this article are further expanded in detail as separate articles. For example, bursitis, types of arthritis, total knee replacement, and others are covered in articles devoted to knee pain-related topics that include specifics on diagnosis, tests, treatments, and other details.

Medically Reviewed by a Doctor on 9/11/2013

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