Knee 1

• Knee Complex


  • Works in conjunction with the hip and ankle joints to support the body's weight in static and dynamic activities
  • 2 distinct articulations within a single joint capsule
• Articulations within the knee complex

  • Tibiofemoral joint
  • Patellofemoral joint
  • Tibiofibular joint?
• The combined bony architecture of the somewhat convex tibial plateaus and convex femoral condyles does not bode well for joint stability
• Because of the lack of bony stability, accessory joint structures (menisci) are necessary to improve joint congruency
• Tibiofemoral Joint


  • Double condyloid joint with three degrees of freedom of angular (rotary) motion
  • Flexion/extension
  • Medial/lateral rotation-through the lateral side of the medial tibial condyle
  • Abduction/adduction
• Proximal Articular Surface


  • Medial and lateral femoral condyles
  • More convex in shape in the sagittal plane than the frontal plane
  • Separated inferiorly by the intercondylar notch/fossa
  • Joined anteriorly by an asymmetrical, shallow groove called the femoral sulcus/patellar groove/patellar surface
• Medial femoral condyle


  • Larger
  • Does not lie directly below the femoral head
• Lateral femoral condyle


  • Lies more directly below the femoral shaft
  • Shifted more anteriorly
  • Shorter tibial articulation
• Distal Articular Surface


  • Medial and lateral tibial plateaus/condyle
  • Predominantly flat, with a slight convexity at the anterior and posterior margins
  • Proximal tibia is larger than the shaft and overhangs it posteriorly at 7° to 10°
  • Separated by a roughened area and two bony spines called the intercondylar tubercles/eminence that lodge into the intercondylar notch of the femur during knee extension
• Medial tibial plateau


  • Longer in the AP direction
  • Thinner articular cartilage
• Lateral tibial plateau


  • Shorter in the AP direction
  • Thicker articular cartilage
• Tibiofemoral Alignment and Weight-Bearing Forces

  • Anatomical (longitudinal) axis of the femur is oblique, directed inferiorly and medially from its proximal to distal end
  • Anatomical axis of the tibia is directed almost vertically
  • Femoral and tibial longitudinal axes normally form an angle medially at the knee joint of 180° to 185°
  • Femur is angled 5° off vertical, creating a slight physiological (normal) valgus angle at the knee
• Genu valgum ("knock knees")


  Medial tibiofemoral angle is greater than 185°
• Genu varum ("bow legs")


  Medial tibiofemoral angle is 175° or less
• Genu valgum or genu varum


  Alters the compressive and tensile stresses on the medial and lateral compartments of the knee
• Mechanical axis/weight-bearing line


  A line drawn on a radiograph from the center of the femoral head to the center of the head of the talus, passing through the center of the joint between the intercondylar tubercles
• Mechanical axis/weight-bearing line


  • Simplification of the ground reaction force as it travels up the lower extremity
  • In bilateral stance, the weight-bearing stresses on the knee joint are equally distributed between the medial and lateral condyles
  • In unilateral stance (ex. During gait), the weight-bearing line shifts toward the medial compartment and increases its compressive forces
• Menisci


  Fibrocartilaginous discs with a semicircular shape, located on top of the tibial condyles, covering one half to two thirds of the articular surface of the tibial plateau, open toward the intercondylar tubercles, thick peripherally and thin centrally
• Functions of menisci


  • Improves the relative tibiofemoral incongruence
  • Distributing weight-bearing forces
  • Reduces friction between the tibia and the femur
  • Serving as shock absorbers
• Medial meniscus


  • C-shaped
  • Covers a lesser percentage of the larger medial tibial surface-medial condyle is more susceptible to injury from the relatively greater compressive loads
• Lateral meniscus


  • Four fifths of a circle
  • Covers a greater percentage of the smaller lateral tibial surface
• Compressive forces in the knee

  • Gait and stair climbing-one to two times the body weight
  • Running-three to four times body weight (mens assuming 50% to 70% of this imposed load)
• These loads can be influenced by the presence of frontal plane malalignment (ex. Genu varum/valgum)
• Meniscal Attachments

  • Anterior and posterior horns - open anterior and posterior ends of the menisci each of which is firmly attached to the tibia below
  • Transverse ligament - connects both menisci anteriorly
  • Patellomeniscal ligaments - anterior capsular thickenings connecting the menisci to the patella
  • Coronary ligaments - fibers from the knee joint capsule connecting the menisci and the tibial condyle peripherally
• Medial Meniscal Attachments

  • Medial meniscus has greater ligamentous and capsular restraints, limiting translation to a greater extent than the lateral meniscus
  • Medial meniscus is firmly attached to the joint capsule through medial thickening that extends distally from the femur to the tibia
  • Through capsular connections, the semimembranosus muscle connects to the medial meniscus
  • Anterior and posterior horns of the medial meniscus are attached to the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL), respectively
• Lateral Meniscal Attachments

  • Anterior horn of the lateral meniscus and the anterior cruciate ligament share a tibial insertion site
  • Posterior horn of the lateral meniscus attaches to the posterior cruciate ligament and the medial femoral condyle through the meniscofemoral ligaments
  • The tendon of the popliteus muscle attaches to the lateral meniscus which helps restrain or control the motion of the lateral meniscus
• Role of the Menisci

  • Allowing for greater contact area between the tibia and the femur
  • Removal of the menisci nearly doubles the articular cartilage stress on the femur and multiplies the forces by six or seven times on the tibial plateau
  • The increase in joint stress may contribute to degenerative changes
• Meniscal Nutrition and Innervation

  • In first year of life, blood vessels are contained throughout the meniscal body
  • Once weight-bearing is initiated, vascularity begins to diminish until only the outer 25% to 33% is vascularized by capillaries from the joint capsule and the synovial membrane
  • After 50 years of age, only the periphery of the meniscal body is vascularized
• Nutrition of central portion of meniscus

  1. Relies on the diffusion of synovial fluid

  2. Requires intermittent loading of the meniscus by either weight-bearing or muscular contractions

  3. During prolonged periods of immobilization or conditions of non-weight-bearing, the meniscus may not receive appropriate nutrition
• Innervation of menisci

  • The horns of the menisci and the peripheral vascularized portion of the meniscal bodies are well innervated with free nerve endings (nociceptors) and three different mechanoreceptors (ruffini corpuscles, pacinian corpuscles, and golgi tendon organs)
• Joint Capsule

  • A large and lax capsule that encloses the tibiofemoral and patellofemoral joints
  • Critical in restricting excessive joint motions to maintain joint integrity and normal function
  • Responsible for providing a tight seal for keeping the lubricating synovial fluid within the joint space
  • Grossly composed of a superficial fibrous layer and a thinner deep synovial layer
• Posterior portion of joint capsule

  • Attached proximally to the posterior margins of the femoral condyles and intercondylar notch and distally to the posterior tibial condyle
• Anterior portion of joint capsule

  • The patella, the tendon of the quadriceps muscles superiorly, and the patellar tendon inferiorly complete the anterior portion of the joint capsule
• Anteromedial and anterolateral portions of capsule

  • Often separately identified as the medial and lateral patellar retinaculum or together as the extensor retinaculum
• Reinforcement of joint capsule

  • Medially, laterally, and posteriorly by capsular ligaments
• Synovial Layer of the Joint Capsule


  • Forms the inner lining in much of the knee joint capsule
  • Secrete and absorb synovial fluid into the joint for lubrication and to provide nutrition to avascular structures, such as the menisci
  • Invaginated synovium adheres to the anterior aspect and sides of the anterior cruciate ligament and the posterior cruciate ligament
• Relationship of cruciate ligaments to joint capsule

  • Both the anterior cruciate ligament and the posterior cruciate ligament are contained within the fibrous capsule (intracapsular) but lie outside of the synovial sheath (extrasynovial)
• Synovial lining location

  • Posterolaterally, the synovial lining is between the popliteus muscle and lateral femoral condyle; posteromedially it invaginates between the semimembranosus tendon, medial head of the gastrocnemius muscle, and medial femoral condyle
• Fat pads in knee joint

  • The anterior and posterior suprapatellar fat pads lie posterior to the quadriceps tendon and anterior to the distal femoral epiphysis, respectively. The infrapatellar (Hoffa's) fat pad lies deep to the patellar tendon.
  • Fat pads are also intracapsular but extrasynovial
• Patellar Plicae


  • Composed of loose, pliant, and elastic fibrous connective tissue that easily passes back and forth over the femoral condyles as the knee flexes and extends
  • The most frequent locations for the plicae, in descending order of incidence: 1. Inferior (infrapatellar plica)/ligamentum mucosum, 2. Superior (suprapatellar plica), 3. Medial (mediopatellar plica), 4. Lateral plica