Knee Joint Flashcards
Knee Joint
largest and most complex joint
most stability comes from soft tissue, not bone
provides mobility for foot in space
What are the two distinct articulations of the knee joint?
patellofemoral and tibiofemoral
Net forces in knee joint during dynamic activities?
2 -3 x BW in normal gait
5 - 6 x BW in running and stair climbing
10 x BW in single leg standing in basketball
Mechanical Axis
connection between hip and knee joint centers
line of action runs between hip and knee
shape defines which stresses the structure experiences
Bowing out = compression medially and tension laterally
norm = 3 degrees from vertical
The bigger the difference between the mechanical and anatomical axes ______ ???
the more compressive and tensile forces. if there is no difference between the two, the force will only be compressive.
Anatomical axis
runs along the shaft of the femur
normal = 6 degrees
lateral to the mechanical axis!!
Which ligament is very broad and is connected to the joint capsule?
MCL
Femur condyles (ovoid)
medial condyle larger and projects farther down, making the femur oriented laterally (femoral shaft obliquity) (anatomical axis)
which condyle experiences more load?
medial femoral condyle
which condyle is more in line with the shaft of the femur?
lateral
patellar surface
saddle shaped groove
lateral patellar surface is longer
when are the MCL and LCL taut?
taut in extension, slack in flexion
tight ligaments = more joint stability
Tibial plateaus
Medial condyle/tibal plateau is 50% larger than the right and the cartilage is 3x thicker than the right.
Due to the mechanical axis, the medial condyle takes on more force than the lateral.
Patellomeniscal ligaments
enlargements of the joint capsule
transverse ligament
located anteriorly, connects the menisci
Medial meniscus attaches to ___ and ____
MCL and semimembranosus
lateral meniscus attaches to ___ and ____
PCL and popliteus
coronary ligaments
connect meniscus to tibia underneath
lateral vs medial meniscus shape
lateral = almost a complete circle medial = C shaped
menisci withstand ____
tension! resist stretch! do not withstand compression
Function of menisci
- stabilize the joint - deepen articular surfaces
- shock absorption - improved congruency of joint surfaces
- force distribution within the joint
removing the menisci
increases contact area by 50%
coefficient of friction increases by 20% intrajoint
menisci = asymmetrical wedge-shaped
menisci vascularization
avascular structures, so they get their vascularization from the synovial membrane and joint capsule
meniscus has a free end (unattached) inside the joint, which helps synovial fluid move between the joint and decreases friction
Role of menisci during flexion
move/deform posteriorly with flexion
role of menisci during extension
move/deform anteriorly with extension
Role of menisci in a normal knee during extension
Path of instantaneous center of rotation (ICOR):
- moves posteriorly and then anteriorly
- moves superiorly
which way does the path of ICOR move with flexion?
inferiorly
Knee without meniscus (ICOR)
ICOR is variable
more glide in AP direction
early degeneration of cartilage
A loss of the patella results in:
18-20% loss of motion
48-50% loss of effectiveness of quads in extension
What does it mean that the patella is the least congruent joint in the body?
it has a large articular surface but the contact area is very limited during motion in different positions
Patella
anatomic pulley - friction reduction
largest sesamoid bone in the body
least congruent joint in the body
improves mechanical advantage of quads
The odd facet makes up what percentage of the posterior aspect of the patella?
30%
Articular facets
slightly convex
angle between medial and lateral facets is 138 degrees
lateral facet larger than medial facet
At what angle of knee flexion is there the most congruency with respect to the articular surface of the patella and the femoral groove?
90 degrees knee flexion
Patella Tendon Moment Arm (PTMA)
largest MA of patellar tendon is at 45 degree angle
the best ability of the quads to produce torque is when the knee is at a 45 degree angle
Patella Alta
patella rides too high on femoral condyles
patellar groove is shallow and patella has a tendency to dislocate in lateral direction
Patella Baja
patella rides too low on femoral condyles
due to patellar tendon shortening after surgery or injury
MA and effectiveness of quads decreases
Which aspects of the facets are in contact with the femoral condyles in patella baja?
lateral part of lateral facet and odd facet. the result of this is that the forces are concentrated in a smaller area
Genu valgum
abnormal angulation of tibia away from midline
leg mechanical axis is displaced laterally
medial structures = tensile stress
lateral structures = compressive stress
Knock kneed
genu valgum
Describe the load on the lateral compartment of the knee in genu valgum
more load on lateral compartment of knee between lateral condyle of femur and lateral tibial plateau
articular cartilage is already thinner laterally, and thins due to compressive stress, increasing risk for OA
Genu varum
medial structure = compressive stress
lateral structures = tensile stress
abnormal angulation of tibia towards the midline
leg mechanical axis is displaced medially
MCL = slack
LCL = tension
bow legged
genu varum
Genu recurvatum
tibia is tilted in the anterior direction
tibial plateaus are not horizontal, so the load from the femur is on the anterior aspect of the tibia
flexors of the knee are constantly active to control the passive load
Genu recurvatum
abnormal angulation of tibia anteriorly
leg mechanical axis is displaced anterioly
anterior structures = compression
posterior structures = tension
excessive strain/torque on which structures in genu recurvatum?
excessive knee hyperextension
excessive strain on ACL
excessive extension torque during standing
typical Q angle
15 degrees
abnormal = >20
what is the Q angle influenced by?
location of patella
knee joint alignment on frontal plane
femoral and tibial torsions
Q angle in valgus
> 15 (greater Q angle = increased likelihood for patellar dislocation in lateral direction)
Q angle in varus
Patellar ligament
a continuation of the quad tendon
Bowstring effect
draw patella laterally
causes chondromalacia from chronic stress
Chondromalacia
type of OA
inflammation and softening of cartilage
involves bony structures
knee movements on sagittal plane
flexion and extension
knee movements on frontal plane
valgus and varus (about 5 degrees in each direction)
knee movements on transverse plane
IR/ER with knee at 90 degrees flexion
function of articularis genu muscle
moves bursa out of the way during knee extension
the synovial membrane gives rise to _______ and wraps around the ____ and ____
gives rise to multiple bursal structures and wraps around the ACL and PCL
cruciate ligaments are outside the synovial membrane but inside the joint capsule
MCL
longer, wider, and closer to the capsule than the LCL
tight in extension, slack in flexion
two parts of MCL
anterior and posterior
anterior portion is tight in flexion
location of MCL
runs from medial femoral epicondyle to the tibia
location of LCL
from lateral femoral epicondyle to fibular head
function of LCL
resists varus stress/force and ER of tibia
tight in extension
function of MCL
resists valgus stress/force
resists ER and IR of tibia
resists anterior translation of tibia along with ACL
the MCL connects to which two structures?
medial meniscus and capsule
3 bands of the ACL
anteromedial
intermediate
posterolateral
origin/insertion of ACL
anterior intercondylar eminence of tibia to posterior part of the medial aspect of the lateral femoral condyle
functions of ACL
resists anterior tibial translation, hyperextension, and tibial IR
resists anterior movement of the tibia on the femur (or posterior movement of the femur on the tibia)
when is the ACL tight?
in extension
when is the PCL tight?
in flexion
location of PCL
posterior intercondylar eminence to lateral aspect of medial femoral condyle
name the two bands of the PCL
anterolateral
posteromedial
functions of PCL
resists posterior tibial translation (posterior motion of tibia on femur)
also resists flexion
common symptom after ACL injury
quad weakness
knee flexion is a protective mechanism for fear of reaching extension position by using quads
PCL and PTT
PCL resists PTT up to 90 degrees of knee flexion, and diminishes after that
PCL effect on PTT
PCL limits PTT until 90 degrees of flexion, and then decreases at higher flexion angles (does not help limit flexion in deep squat position)
Which ligaments limit hyperextension?
Arcuate popliteal, oblique popliteal, ACL
function of arcuate popliteal ligament
reinforces posterolateral capsule
resists varus stress/impact
helps LCL
limits hyperextension
function of oblique popliteal ligament
reinforces posteromedial capsule
resists valgus stress
limits ER
limits hyperextension
function of medial and lateral retinaculum
controls movement of the patella in the medial and lateral direction
ITB attachments
Iliopatellar band (causes lateral pull on patella) lateral tibial tubercle (Gerdy's tubercle) (assists ACL in resisting anterior translation of tibia on femur) (resists varus stress)
Which structures pull the patella laterally?
lateral retinaculum, ITB, iliopatellar band
Knee function stability
no bony stops to motion joint geometry change of menisci (1) passive restraint from ligaments (2) active muscles (3) compressive load ( more compressive load = more joint stability?)
motion of femur on tibia during closed kinetic chain
proximal on distal
convex on concave
roll and glide in opposite directions
motion of tibia on femur during open kinetic chain
distal on proximal
concave on convex
roll and glide in same direction
roll and glide during closed kinetic fhain
flexion: roll posteriorly and glide anteriorly
extension: roll anterior and glide posterior
menisci responsible for translation/glide that occurs during rolling
screw-home mechanism
15 degrees of tibial rotation occurs during final 30 degrees of knee extension. most of this rotation occurs during final 5 degrees of knee extension because of bony asymmetry (medial condyle projects farther than lateral condyle, creating IR) and because of ligament tension
open chain screw home mechanism
during terminal extension, ER of the tibia on the femur occurs
closed chain screw home mechanism
during terminal extension, IR of the femur on the tibia occurs
peak ability of muscles to do IR/ER of knee is when?
at 30-45 degrees of knee flexion. decreases beyond 45 degrees due to decreased muscle length
ER of knee
biceps femoris
IR of knee
semi ten and mem, sartorius, gracilis, popliteus
when do the quads produce maximum torque?
45 degrees of knee flexion (due to muscle length and muscle MA)
