Bones LO11

11. Identify the major joint and associated ligaments in the knee region. Explain what kind of movements occur at the joints and other pertinent information.

Movement Video

The knee joint is a modified hinge joint which is capable of a small degree of medial and lateral rotation, particularly from a flexed position. The knee joint is actually a complex of 3 articulations: patellofemoral and lateral & medial tibiofemoral joints. When observing the articular surfaces of the medial and lateral condyles of the femur and tibia, one can observe the notable incongruence of the articulation structures. Due to this incongruence, accessory structures are vital to the structural integrity of this joint.

Accessory structures of knee joint:

  • Muscles and muscle tendons are more important in structural integrity of the knee joint than ligaments. Muscle conditioning can prevent numerous injuries in this area.
    • Most important set of muscles is the quadriceps femoris mm., particularly vastus lateralis and vastus medialis mm. These muscles and associated patellar ligament are the main source of stability for the anterior portion of this joint.
    • The semimembranosus and popliteus mm. play an important roles as well for the posterior portions of the joint.
  • Ligaments of knee joint
    • Patellar ligament: distal expansion [apex of patella to tibial tuberosity] of the quadriceps femoris tendon
      • Forms the anterior portion of the joint capsule
    • Fibular [lateral] collateral ligament (FCL/LCL) is an extracapsular ligament separated from the articular capsule by the tendon of the popliteus m. Similar to the tibial collateral ligament, the FCL checks hyperextension and is relaxed in flexion.
    • Tibial [medial] collateral ligament (TCL/MCL) is a substantial thickening of the medial articular capsule (capsular ligament).
      • The TCL and medial meniscus are attached and are often damaged in unison due to this connection.
      • This ligament also plays the role of check ligament for excessive lateral rotation.
  • Intra-articular structures of knee joint (i.e. located within articular capsule)
    • Cruciate ligaments: important in checking lateral & medial rotation of the knee joint
      • Anterior cruciate ligament (ACL) limits hyperextension of the knee as well as prevention of femoral posterior displacement
        • This cruciate ligament is the weaker and more commonly injured of the two.
          • If ruptured and anterior tibial displacement allowed: anterior drawer sign
      • Posterior cruciate ligament (PCL) limits hyperflexion of the knee as well as prevention of femoral anterior displacement
        • In actions such as walking down stairs, the PCL plays a major role in femoral stabilization.
        • If ruptured and tibial posterior displacement allowed: posterior drawer sign
    • The menisci of the knee are fibrocartilaginous structures that deepen the articular surfaces and play a role in shock absorption.
      • Medial meniscus is the less mobile of the menisci, and there is considerable attachments to surrounding structures, including the TCL.
      • Lateral meniscus is smaller and more mobile than the medial meniscus.
  • Bursae
    • There are approximately 12 bursae associated with the knee joint or surrounding regions.
    • There are 4 bursae that directly communicate with the joint cavity.
      • Suprapatellar bursa is the most clinically relevant of these bursa due to its very large size and is a common site of infection that may lead into the synovial cavity. This bursa serves to reduce friction between the quadriceps femoris tendon and femur.
      • Anserine bursa is located between the tendons of gracilis, sartorius, and semitendinosus at pes anserinus and TCL.
      • Gastrocnemius bursa is located between gastrocnemius, medial head and femur.
      • Popliteus bursa is located between the rope-like popliteus tendon and lateral condyle of tibia.
    • There are various infrapatellar bursae that help facilitate smooth movement of the patella and rest of knee joint.
  • Clinical significance:
    • "Unhappy (terrible) triad" is a term used for knee injuries that involve the anterior cruciate ligament, medial meniscus, and tibial (medial) collateral ligament. Recall that the tibial collateral ligament has a strong attachment to the medial meniscus. The medial meniscus has a smaller attachment to the anterior cruciate ligament; thus, when there is injury to one of these structures, it may affect the others.
      • These types of injuries are more common in contact sports, and in cases of direct blows to lateral knee region during extension or excessive lateral twisting of a knee in flexion.