knee articulation Flashcards
primary function
functional lengthening and shortening of the lower limb
stability function
supports the body during both static and dynamic activities
the knee joint is also called
tibiofemoral joint
tibiofemoral joint
articulation b/w the condyles of the femur proximally and the tibial plateaus distally
what kind of joint is the knee joint
modified hinge joint
2 degrees of freedom
motions that the knee joint allows
flexion and extension
ER and IR
ABD and ADD
femoral condyles
the distal femur flares into 2 condyles
separated posteriorly by an intercondylar notch or fossa
femoral condyles anteriorly
blend to form the concave trochlear groove
articulating surface for the patella
what shape are the femoral condyles
biconvex
convex in the frontal and sagittal planes
in which direction are the femoral condyles longer
anteroposterior direction > mediolateral direction
lateral lip of the lateral femoral condyle
approximately 7 mm more anterior than the medial femoral condyle
gives osseous stability for the patella
which femoral condyle is larger and longer
medial femoral condyle
despite asymmetry of the femoral condyles
condyles are horizontal d/t angulation of the femoral shaft
tibial plateaus
proximal end of the tibia flares into a plateau that has a medial and lateral section
what are the tibial plateaus separated by
prominent tibial spine
will articulate w/ femoral intercondylar notch
what shape are the tibial plateaus in the frontal plane
concave
what shape is the medial tibial plateau in the sagittal plane
concave
the total surface area is larger than that of the lateral tibial plateau
–> accommodates the larger medial femoral condyle
lateral tibial plateau shape in the sagittal plane
convex
will create a convex on convex in the sagittal plane –> incongruency that is assisted by the menisci
the presence of the fibrocartilaginous menisci on the tibial plateaus creates
trough for the femoral condyles
menisci are concave –> create congruency
description of the knee joint
modified hinge joint w/ 2 degrees of freedom
motions the knee joint allows
flexion/extension (sagittal plane)
IR and ER (transverse plane)
small amount of automatic ABD and ADD in the frontal plane
extension ROM
actively = 0
passively = 5-10 degrees beyond 0 is considered hyperextension
what could affect extension ROM
passive insufficiency of hamstrings when the hip is flexed
what is hyperextension also called in the knee
genurecurvatum
flexion ROM
passively = 0-130 or 140
what is flexion limited by
soft tissue approximation
also dependent on position of the hip
–> passive insufficiency of the rectus femoris when the hip is extended
rotation ROM
passive only
greatest when knee is flexed to 90 degrees (ligaments are lax)
least extension occurs w/ knee in full flexion –> screw home mechanism
ER ROM
0-40
IR ROM
0-30
axis of motion
axis for flexion/extension is through the femoral condyles
oblique
why is the axis of motion oblique
medial femoral condyle is larger and longer
how is the axis oriented
medially and inferiorly
relative to the transverse plane
allows for accessory motions
accessory motion with flexion
ADD
accessory motion with extension
ABD
concept of “instantaneous axis” of motion
femoral condyles are longer than the tibial plateaus
–> femur must glide to maintain contact
—> changes the axis of motion
—-> as you flex, the axis moves superiorly and posteriorly
angles of the knee
medial tibiofemoral angle
Q angle
medial tibiofemoral angle
medial angle formed by the femoral and tibial shaft axes
why isnt the formal shaft axis included in the medial tibiofemoral angle
since the femoral head over hangs the femoral shaft
–> the axis of the femoral shaft doesn’t coincide with that of the leg
—-> but forms an obtuse angle
normal medial tibiofemoral angle
185-190 degrees
physiologic valgus (genuvalgum)
frontal plane angle
when does the medial tibiofemoral angle become pathological
when it is increased of decreased from normal
medial tibiofemoral angle is increased
greater than 195 degrees
genuvalgum
knock knees
could be influenced by coxa vera
medial tibiofemoral angle is decreased
less than 180 degrees
genuvarum
bow legs
coxavalga could influence this
what could genuvalgum/genuvarum cause
can lead to asymmetrical loading of the knee and cause arthritic changes
–> wear out one compartment of the knee
q angle
angle formed by the intersection of a line drawn from the ASIS to the mid-patella and a line drawn from mid-patella to the tibial tubercle
what is the q angle intended to represent
the force vector of the quadriceps femoris muscle
normal q angle
15 degrees
may be greater in women and less in men
when is the q angle considered abnormal
greater than 20 degrees
will lead to changes in patellar tracking
