Knee Anatomy Summary Questions

Knee Joint

The knee joint is the largest joint of the body.

• It actually consists of three articulations.
  • The femoropatellar joint is found between the patella and the distal femur.
  • The medial tibiofemoral joint and lateral tibiofemoral joint are located between the medial and lateral condyles of the femur and the medial and lateral condyles of the tibia.
• All of these articulations are enclosed within a single articular capsule.

The knee functions as a hinge joint, allowing flexion and extension of the leg.

• This action is generated by both rolling and gliding motions of the femur on the tibia.
• In addition, some rotation of the leg is available when the knee is flexed, but not when extended.

The knee is well constructed for weight bearing in its extended position, but is vulnerable to injuries associated with hyperextension, twisting, or blows to the medial or lateral side of the joint, particularly while weight bearing.

At the femoropatellar joint, the patella slides vertically within a groove on the distal femur.

• The patella is a sesamoid bone incorporated into the tendon of the quadriceps femoris muscle, the large muscle of the anterior thigh.
• The patella serves to protect the quadriceps tendon from friction against the distal femur.
• Continuing from the patella to the anterior tibia just below the knee is the patellar ligament.
• Acting via the patella and patellar ligament, the quadriceps femoris is a powerful muscle that acts to extend the leg at the knee.
  • It also serves as a “dynamic ligament” to provide very important support and stabilization for the knee joint.

The medial and lateral tibiofemoral joints are the articulations between the rounded condyles of the femur and the relatively flat condyles of the tibia.

• During flexion and extension motions, the condyles of the femur both roll and glide over the surfaces of the tibia.
• The rolling action produces flexion or extension, while the gliding action serves to maintain the femoral condyles centered over the tibial condyles, thus ensuring maximal bony, weight-bearing support for the femur in all knee positions.
• As the knee comes into full extension, the femur undergoes a slight medial rotation in relation to tibia.
  • The rotation results because the lateral condyle of the femur is slightly smaller than the medial condyle.
  • Thus, the lateral condyle finishes its rolling motion first, followed by the medial condyle.
  • The resulting small medial rotation of the femur serves to “lock” the knee into its fully extended and most stable position.
• Flexion of the knee is initiated by a slight lateral rotation of the femur on the tibia, which “unlocks” the knee. 00
  • This lateral rotation motion is produced by the popliteus muscle of the posterior leg.

Located between the articulating surfaces of the femur and tibia are two articular discs, the medial meniscus and lateral meniscus.

• Each is a C-shaped fibrocartilage structure that is thin along its inside margin and thick along the outer margin.
• They are attached to their tibial condyles, but do not attach to the femur.
  • While both menisci are free to move during knee motions, the medial meniscus shows less movement because it is anchored at its outer margin to the articular capsule and tibial collateral ligament.
• The menisci provide padding between the bones and help to fill the gap between the round femoral condyles and flattened tibial condyles.
• Some areas of each meniscus lack an arterial blood supply and thus these areas heal poorly if damaged.

The knee joint has multiple ligaments that provide support, particularly in the extended position.

• Outside of the articular capsule, located at the sides of the knee, are two extrinsic ligaments.
  • The fibular collateral ligament (lateral collateral ligament) is on the lateral side and spans from the lateral epicondyle of the femur to the head of the fibula.
  • The tibial collateral ligament (medial collateral ligament) of the medial knee runs from the medial epicondyle of the femur to the medial tibia.
• As it crosses the knee, the tibial collateral ligament is firmly attached on its deep side to the articular capsule and to the medial meniscus, an important factor when considerin000g knee injuries.
• In the fully extended knee position, both collateral ligaments are taut (tight), thus serving to stabilize and support the extended knee and preventing side-to-side or rotational motions between the femur and tibia.

The articular capsule of the posterior knee is thickened by intrinsic ligaments that help to resist knee hyperextension.

• Inside the knee are two intracapsular ligaments, the anterior cruciate ligament and posterior cruciate ligament.
• These ligaments are anchored inferiorly to the tibia at the intercondylar eminence, the roughened area between the tibial condyles.
• The cruciate ligaments are named for whether they are attached anteriorly or posteriorly to this tibial region.
  • Each ligament runs diagonally upward to attach to the inner aspect of a femoral condyle.
  • The cruciate ligaments are named for the X-shape formed as they pass each other (cruciate means “cross”).
• The posterior cruciate ligament is the stronger ligament.
  • It serves to support the knee when it is flexed and weight bearing, as when walking downhill.
  • In this position, the posterior cruciate ligament prevents the femur from sliding anteriorly off the top of the tibia.
• The anterior cruciate ligament becomes tight when the knee is extended, and thus resists hyperextension.

The knee joint is the largest joint of the body. It is supported by the tibial and fibular collateral ligaments located on the sides of the knee outside of the articular capsule, and the anterior and posterior cruciate ligaments found inside the capsule. The medial and lateral menisci provide padding and support between the femoral condyles and tibial condyles.

Joints

Injuries to the knee are common.

• Since this joint is primarily supported by muscles and ligaments, injuries to any of these structures will result in pain or knee instability.
• Injury to the posterior cruciate ligament occurs when the knee is flexed and the tibia is driven posteriorly, such as falling and landing on the tibial tuberosity or hitting the tibia on the dashboard when not wearing a seatbelt during an automobile accident.
• More commonly, injuries occur when forces are applied to the extended knee, particularly when the foot is planted and unable to move.
  • Anterior cruciate ligament injuries can result with a forceful blow to the anterior knee, producing hyperextension, or when a runner makes a quick change of direction that produces both twisting and hyperextension of the knee.

A worse combination of injuries can occur with a hit to the lateral side of the extended knee.

• A moderate blow to the lateral knee will cause the medial side of the joint to open, resulting in stretching or damage to the tibial collateral ligament.
• Because the medial meniscus is attached to the tibial collateral ligament, a stronger blow can tear the ligament and also damage the medial meniscus.
  • This is one reason that the medial meniscus is 20 times more likely to be injured than the lateral meniscus.
• A powerful blow to the lateral knee produces a “terrible triad” injury, in which there is a sequential injury to the tibial collateral ligament, medial meniscus, and anterior cruciate ligament.

Arthroscopic surgery has greatly improved the surgical treatment of knee injuries and reduced subsequent recovery times.

• This procedure involves a small incision and the insertion into the joint of an arthroscope, a pencil-thin instrument that allows for visualization of the joint interior.
  • Small surgical instruments are also inserted via additional incisions.
  • These tools allow a surgeon to remove or repair a torn meniscus or to reconstruct a ruptured cruciate ligament.
• The current method for anterior cruciate ligament replacement involves using a portion of the patellar ligament.
  • Holes are drilled into the cruciate ligament attachment points on the tibia and femur, and the patellar ligament graft, with small areas of attached bone still intact at each end, is inserted into these holes.
  • The bone-to-bone sites at each end of the graft heal rapidly and strongly, thus enabling a rapid recovery.

Knee Injury A strong blow to the lateral side of the extended knee will cause three injuries, in sequence: tearing of the tibial collateral ligament, damage to the medial meniscus, and rupture of the anterior cruciate ligament.

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