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
Medialfemoralcondyle
Larger
Does not lie directly below the femoralhead
Lateral femoral condyle
Lies more directly below the femoralshaft
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
Medialtibialplateau
Longer in the AP direction
Thinner articular cartilage
Lateraltibialplateau
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
Genuvalgum ("knockknees")
Medial tibiofemoral angle is greater than 185°
Genuvarum ("bowlegs")
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
Medialmeniscus
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
Lateralmeniscus
Four fifths of a circle
Covers a greater percentage of the smaller lateraltibialsurface
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 posteriorhorns - open anterior and posterior ends of the menisci each of which is firmly attached to the tibia below
Transverseligament - connects both menisci anteriorly
Patellomeniscalligaments - anterior capsular thickenings connecting the menisci to the patella
Coronaryligaments - fibers from the knee joint capsule connecting the menisci and the tibial condyle peripherally
Medial Meniscal Attachments
Medialmeniscus has greater ligamentous and capsular restraints, limiting translation to a greater extent than the lateralmeniscus
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 anteriorcruciateligament (ACL) and posteriorcruciateligament (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 meniscofemoralligaments
The tendon of the popliteus muscle attaches to the lateral meniscus which helps restrain or control the motion of the lateralmeniscus
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 seventimes on the tibial plateau
The increase in joint stress may contribute to degenerativechanges
Meniscal Nutrition and Innervation
In firstyear 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 jointcapsule and the synovialmembrane
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 muscularcontractions
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 (ruffinicorpuscles,paciniancorpuscles, and golgitendonorgans)
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 synovialfluid 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 intercondylarnotch and distally to the posterior tibialcondyle
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 lateralpatellarretinaculum or together as the extensor retinaculum
Reinforcement of joint capsule
Medially, laterally, and posteriorly by capsular ligaments
SynovialLayer of the Joint Capsule
Forms the innerlining 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 anteriorcruciateligament and the posteriorcruciateligament
Relationship of cruciate ligaments to joint capsule
Both the anterior cruciate ligament and the posterior cruciate ligament are contained within the fibrouscapsule (intracapsular) but lie outside of the synovialsheath (extrasynovial)
Synovial lining location
Posterolaterally, the synovial lining is between the popliteus muscle and lateralfemoralcondyle; posteromedially it invaginates between the semimembranosus tendon, medial head of the gastrocnemius muscle, and medialfemoralcondyle
Fat pads in knee joint
The anterior and posterior suprapatellar fat pads lie posterior to the quadricepstendon and anterior to the distalfemoralepiphysis, respectively. The infrapatellar (Hoffa's) fat pad lies deep to the patellartendon.
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 femoralcondyles as the knee flexes and extends
The most frequent locations for the plicae, in descending order of incidence: 1. Inferior (infrapatellarplica)/ligamentummucosum, 2. Superior (suprapatellarplica), 3. Medial (mediopatellarplica), 4. Lateralplica