Biomechanics Knee Flashcards
articulations in a common knee capsule
medial tibiofemoral
lateral tibiofemoral
patellofemoral
knee alignment: what are the values for
- genu varum
- normal
- excessive genu valgum
varum: >180
normal: 170-180
valgum: <170
anterior joint capsule reinforcements of the knee
CT
-patellar retinacular fibers (medial and lateral)
quad muscle/tendon
-patellar tendon
lateral joint capsule reinforcements of the knee
CT -LCL -lateral patellar retinaculum -IT band -lateral coronary ligaments biceps femoris popliteus
posterior joint capsule reinforcements of the knee
CT -oblique popliteal -arcuate popliteal gastroc hamstrings popliteus
medial joint capsule reinforcements of the knee
CT -medial patellar retinaculum -MCL -medial coronary ligaments pes anserine muscles
fat pads of knee
- associated with…
- function
associated with bursae
provide protection and lubrication between femur and patella
fat pads of knee
- associated with…
- function
associated with bursae
provide protection and lubrication
knee alignment: what are the values for
- genu varum
- normal
- excessive genu valgum
varum: >180
normal: 170-180
valgum: <170
menisci
- composition
- function
- anchored to tibia by…
- other meniscal attachments
fibrocartilage convert flat tibial plateaus to slightly concave sockets anchored to tibia by -ant/post meniscal horns -coronary ligaments (meniscotibial) transverse ligament links anterior horns posterior meniscofemoral ligament
lateral joint capsule reinforcements of the knee
CT -LCL -lateral patellar retinaculum -IT band -lateral coronary ligaments biceps femoris popliteus
posterior joint capsule reinforcements of the knee
CT -oblique popliteal -arcuate popliteal gastroc hamstrings popliteus
medial joint capsule reinforcements of the knee
CT -medial patellar retinaculum -MCL -medial coronary ligaments pes anserine muscles
synovial capsule of knee
- inside…
- name of “outpouchings” that minimize friction
- which ligaments are outside this capsule
inside fibrous capsule
outpouchings are called bursae
cruciate ligaments outside synovial capsule
fat pads of knee
- associated with…
- function
associated with bursae
provide protection and lubrication
plicae
- what are they
- why do we care?
synovial folds
-remnant of compartmental septa
can become large and fibrous in some people, leading to pain
tibiofemoral joint
- type of joint
- how well do they fit together?
bicondyloid joint (medial and lateral) minimal bony congruency
menisci
- composition
- function
- anchored to tibia by…
fibrocartilage convert flat tibial plateaus to slightly concave sockets anchored to tibia by -ant/post meniscal horns -coronary ligaments (meniscotibial) transverse ligament links anterior horns
effect of muscles on meniscus
quad and semimebranosus can pull meniscus anterior or posterior
meniscus vascularity and innervation
vascularity -outer 1/3: red (high) -middle 1/3: red-white (medium) -inner 1/3: white (avascular) innervation -aneural except at meniscal horns
medial meniscus
- shape
- attachments
- mobility compared to lateral
- -why?
C-shaped attachments -deep MCL -semimembranosus -quadriceps less mobile than lateral meniscus -MCL attachment -coronary ligaments
lateral meniscus
- shape
- attachments
- mobility
- -why?
O-shaped attachments -popliteus -semimembranosus -quad -no LCL attachment greater mobility than MCL -can move A/P and M/L easier -no LCL attachment -less dense coronary ligaments
meniscal functions
contribute to joint stability -deepen socket lubrication guide knee motion distribute load in weight bearing
of the cruciate ligaments, how do you determine which is the ACL and which is the PCL
by tibial attachment
meniscus injury MOI
rotation over weightbearing knee
-shear forces
MCL and LCL
-capsular or non-capsular
medial: capsular
lateral: non-capsular
MCL functions
primary -resists external valgus force secondary -taut with knee extension -taut with extremes of medial and lateral tibial rotation
which structures resist valgus force
MCL
medial capsule
medial muscles
ACL
LCL functions
primary -resists varus stress secondary -taut with knee extension -resists extremes of medial and lateral tibial rotation when knee flexed
what structures resist varus force
LCL
lateral capsule
IT band
ACL
anterolateral ligament (ALL) function
stabilizer for tibial internal rotation
of the cruciate ligaments, how do you determine which is the ACL and which is the PCL
by tibial attachment
cruciate ligaments
- location in relation to capsules
- blood supply from…
intraarticular but extrasynovial
blood supply from synovial capsule
cruciate ligaments
-functions
important in control of knee arthrokinematics
mechanoreceptors present
ACL
-portions
portions
- posterolateral
- -main component; tightest in extension
- anteromedial
- -tightest in flexion
voluntary axial rotation of the knee (transverse plane)
- motion greatest at…
- controlled by…
- resisted by…
greatest motion at 90 flexion
controlled by posterior musculature (horse reins)
resisted by capsuloligamentous tension
relationship between ACL and quads
quad is ACL antagonist
quad contraction: anterior glide of tibia
effect becomes greater towards full extension
must be careful with ACL surgical rehab towards full extension
ACL MOI
usually non-contact -rotation of trunk over planted foot -deceleration with knee hyperextension contact injury -valgus/varus force -hyperextension force
PCL
- strength vs. ACL
- location
- portions
shorter and stronger than ACL
location
-posterior tibia below plateau
-lateral aspect of medial femoral condyle
portions
-anterolateral: larger bundle, more taut in flexion
-posteromedial: more taut in extension
PCL functions
resists
- anterior translation of femur on tibia
- posterior translation of tibia on femur
- end range flexion
- extremes of varus, valgus, and rotation
what is the PCL antagonist
hamstrings
PCL MOI
fall on a flexed knee
knee axis of rotation during flexion/extension
- what is the axis
- location of axis
- influenced by…
medial-lateral
not fixed: migrates with ROM
influenced by contour of condyles
voluntary axial rotation of the knee (transverse plane)
- motion greatest at…
- controlled by…
- resisted by…
greatest motion at 90 flexion
controlled by posterior musculature (horse reins)
resisted by capsuloligamentous tension
automatic rotation of knee (transverse plane)
- aka _____
- when does it occur?
- caused by…
- purpose
aka "screw-home" mechanism mechanically involuntary coupled rotation that occurs in final 15 extension caused by -asymmetry of femoral articular surfaces -tension in ACL and PCL -lateral "pull" of quads "locks" the knee in full extension
how does screw-home mechanism occur during open chain actiion
motion of the lateral TF compartment stops before motion of the medial TF compartment
tibia laterally rotates on the femur as knee fully extends
ligaments and capsule tight, “screwing home” or “locking” the knee
relationship between tibiofemoral rotation and PF contact area
-implication
increased tibiofemoral rotation corresponded to decreased PF contact area in subjects with PFP
less contact = more PF stress
tibiofemoral arthrokinematics
- OKC extension
- CKC extension
OKC -concave on convex -anterior roll and glide -tibial lateral rotation CKC -convex on concave -anterior roll, posterior glide -femoral medial rotation
tibiofemoral arthrokinematics
- OKC flexion
- CKC flexion
OKC -tibia medially rotates on femur -posterior roll and glide CKC -femur laterally rotates -posterior roll, anterior glide
knee
- close packed position
- loose packed position
close
-full extension, lateral rotation of tibia on femur
loose
-25-30 degrees flexion
genu varum and valgum
-lead to leading of what compartments
varum
-medial compartment loading
valgum
-lateral compartment loading
genu recurvatum
- defined as…
- resisted by…
- may be result of…
- consequence
excessive (>10) knee hyperextension resisted by passive tension in posterior capsule may be result of -neuromuscular disease -postural habit worsens with age consequences -decreased blood supply down back of leg -places excessive stretch on posterior structures
muscle innervation (peripheral nerve)
- knee extensors
- knee flexors/rotators
extensors -femoral nerve ST, SM, BF long -tibial portion sciatic BF short -peroneal portion sciatic sartorius -femoral gracilis -obturator
PF joint
- when is contact area greatest
- when is stability greatest
contact area greatest in flexion
most stable in flexion
least stable in extension
PF movements
-name of movement and plane movement occurs in
tilt: transverse
spin: frontal
shift: medial-lateral translation
flexion/extension (sagittal)
patellar tracking in
-extension
-flexion 0-30
flexion >30
extension: slightly laterally shifted
flexion 0-30: shifts and tilts medially
flexion >30: shifts and tilts laterally
PF minimal movement
5 mm total shift
5 degrees total tilt
what is the Ratio of Insall and Salvati
-ranges
patellar tendon length / patellar height
normal: 0.8-1.2
patella alta: >1.2
patella infera (baja): <0.8
muscle innervation (root level)
- knee extensors
- knee flexors/rotators
extensors: L3, L4
flexors: S1, S2
muscle innervation (peripheral nerve)
- knee extensors
- knee flexors/rotators
extensors -femoral nerve ST, SM, BF long -tibial portion sciatic BF short -peroneal portion sciatic sartorius -femoral gracilis -obturator
%torque of extensors created by
- rectus femoris
- vasti group
rectus femoris: 20%
vasti: 80%
knee extensor synergist
- location
- function
articularis genu
inserts on suprapatellar bursa
pulls suprapatelar pouch out of the joint
knee extensor eccentric contraction examples
sitting down
stair descent
in the frontal plane, what is the direction of the overall pull of the quads
lateral
medial tibial rotators
SM ST gracilis sartorius popliteus
in a CKC, at what point in the ROM is the torque demand the greatest
in flexed position
-greatest moment arm
patellofemoral joint reaction force (sagittal plane) equals…
-compressive or tensile force
force of quadriceps + force of patellar tendon
compressive force
patellofemoral joint reaction force (frontal plane)
- direction
- due to…
lateral
due to net lateral quadriceps force
lateral pull of quadriceps on patella is resisted by…
-local factors
local
- vastus medialis
- intercondylar groove (lateral)
- medial patellar retinaculum (medial PF ligament)
lateral pull of quadriceps on patella is resisted by…
-global factors
tibiofemoral alignment
- frontal plane
- transverse plane
knee flexor synergists
sartorius, gracilis, and popliteus
-flex and IR tibia
popliteus
lateral tibial rotators
BF
TFL
how do knee flexors control OKC osteokinematics during gait
eccentric action in walking gait
concentric action in running gait
why are the knee flexors necessary for control of CKC osteokinematics
needed for simultaneous control of multiple degrees of freedom across hip and knee
control high velocity movements
poor control of knee flexors in CKC can lead to…
ACL tearing
knee flexion torque
- greatest torque at…
- greatest moment arm between…
torque greatest at 20 extension
moment arm greatest between 50-90 flexion
length vs. leverage in relation to force production in knee flexors
length-tension relationships more important in torque production than leverage
hamstrings produce greater torque in relatively elongated position
knee rotation torque
-at what angle do rotators have greatest MA?
90 degrees
popliteus has greatest moment arm for rotation torque at…
40 degrees flexion
