What is Knee Anatomy?

The knee is one of the largest and most complex joints in the body. A hinge-type joint, the knee is responsible for bearing the body’s full weight and providing movement essential for everyday activities, such as walking, running, sitting or standing. The bones that make up the knee include:

  • Lower shin bone (tibia) and the adjacent smaller bone (fibula)
  • Upper thigh bone (femur)
  • Kneecap (patella)

The lower end of the femur and the top end of the tibia bone create a hinge joint. The ends of these bones are covered with a coating cartilage layer, called articular cartilage. This cartilage allows the joint smooth, fluid motion. To help protect the coating cartilage layers at the ends of the femur and tibia, there are two shock absorbing meniscus cartilages that sit on top of the tibia, one on the inside of the knee (medial meniscus) and one on the outside of the knee (lateral meniscus). Together the articular cartilage and the menisci are responsible for absorbing impact.

Muscles and tendons work in conjunction to create movement across a joint. A muscle is attached to a tendon and it is the tendon portion that attaches to bone.  When a muscle contracts, its tendon is pulled and the force is transmitted to bone and motion across a joint occurs. Two main muscle groups activate movement of the knee:

  • The quadriceps muscles–above and in front of the knee–straightens the knee (extension)
  • The hamstring muscles–behind and above the knee–bends the knee (flexion)

What Ligaments and Tendons Make Up the Knee?

Ligaments within the knee provide stability. There are four main ligaments in the knee:

  • Anterior Cruciate Ligament (ACL): Located in the center of the knee, the ACL prevents excessive forward motion and excessive rotation of the tibia in relation to the femur.
  • Posterior Cruciate Ligament (PCL): Located in the center of the knee, the PCL prevents excessive backward motion of the tibia in relation to the femur.
  • Medial Collateral Ligament (MCL): Gives stability to the inner part of the knee.
  • Lateral Collateral Ligament (LCL): Gives stability to the outer part of the knee.

There are two major tendons in the knee: (1) the quadriceps tendon, located just above the patella and connecting the quadriceps muscle to the patella and (2) the patellar tendon, located just below the patella and connecting the patella to the front of the tibia.

What is the Anatomy of the Back of the Knee?

The anatomy of the back of the knee is distinct in design and function. The major nerves, artery and vein to the lower leg are located in the back of the knee in an area called the popliteal fossa. The hamstring tendons and calf muscles attach at the back of the knee. Most commonly pain in the back of the knee is caused by arthritis or meniscus tears in the back of the knee. Fluid from arthritis can create a popliteal cyst in the back of the knee and cause pain. Tendonitis of the hamstrings or tears of the calf muscle can also cause pain in the back of the knee.

Knee Anatomy on MRI or X-ray

In addition to a good physical exam of the knee by a knee specialist, a simple xray or an MRI can help diagnose a wide range of conditions in the knee. X-rays show the bones. Although x-rays do not show cartilage, a decreased space between the femur and tibia indicates articular cartilage wear and loss. This is arthritis. An x-ray may also show bone spurs, cysts and other deformities.

When the soft tissues of the knee, such as the meniscus or ligaments, need to be visualized, then an MRI may be ordered. This diagnostic tool provides a more comprehensive evaluation of damaged cartilage, torn ligaments, or inflamed tendons.

What are the Common Causes of Knee Pain?

Due to the complexity of the knee joint, there are numerous conditions which cause knee pain including:

  • Knee Arthritis: Knee osteoarthritis, or “wear and tear” arthritis is a common cause of knee pain. Less common forms of arthritis include rheumatoid arthritis, an autoimmune disease; septic arthritis, caused by an infection; crystalline deposition diseases such as gout or pseudogout.
  • Ligament Injuries: These most commonly occurring during sports activities. Ligament injuries are often due to suddenly decelerating or twisting and pivoting on the knee. Although any of the four ligaments in the knee may be injured, the most common ligaments to tear are the anterior cruciate ligament (ACL) and the medial collateral ligament (MCL).
  • Cartilage Tears: The menisci can tear as a result of “wear and tear” over time or as a result of a traumatic injury. Surgical repair of a torn meniscus is one of the most common surgical treatments performed in the knee by Dr Cunningham.
  • Tendonitis: Tendons surrounding the knee are prone to developing inflammation. This inflammation creates pain, both during rest and activity. This condition may also cause tenderness in and around the knee.

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When Should You Have Surgery for Knee Pain?

Treatment for knee pain begins with an accurate diagnosis by an orthopedic knee specialist. Depending on the diagnosis, many knee conditions can be treated without surgery. Initial conservative treatments include:

  • RICE (rest, ice, compression, elevation)
  • Pain management and swelling reduction with anti-inflammatory medicines
  • Partial weight bearing with crutches
  • Knee Bracing to provide stability or restrict certain knee motions
  • Physical therapy

Some knee injuries do not heal properly without surgical repair. Dr Cunningham is able to repair most knee injuries arthroscopically or through a minimally invasive approach, which helps decrease recovery time.

Dr. Cunningham is a knee specialist at Vail Summit Orthopaedics and Neurosurgery. He is an expert at diagnosing and treating a variety of knee conditions for patients in the Vail, Summit County, Aspen, and Denver, CO areas.

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Dr. Cunningham specializes in the treatment of knee, shoulder, and sports injuries.

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