Lecture 8: Knee kinematics Flashcards
the capsule encloses what joints
medial and lateral tibiofemoral joints and patellofemoral joint
anterior reinforcement of knee
patella and tendon
connective tissue is reinforced by medial and lateral retinacular fibers (extensions of ITB, vastus lateralis and medialis, and connections to femur, tibia, patella, quads, patellar tendon, collateral ligaments, and menisci)
muscular reinforcement via quads
lateral reinforcemenrt of knee
connective tissue reinforcement via LCL, lateral patellar retinacular fibers, and ITB
muscular reinforcement via biceps femoris, tendon of popliteus, and lateral head of gastroc
posterior reinforcement of knee
connective tissue: oblique popliteal ligament, arcuate popliteal ligament
muscular: popliteus, gastrocs, hamstrings (especially semimembranosus)
posterior lateral reinforcement of knee
connective tissue: arcuate popliteal lig, LCL, popliteofibular lig
muscular: tendon of popliteus
what is the fabella
sesamoid bone in posterolateral capsule of human knee joint
presence is variable
located in posterior aspect where lines of tensile strength intersect
medial reinforcement of knee
from patellar tendon to posterior capsule medial side
connective:
-anterior 1/3 = thin fascial layer; medial patellar retinacular fibers
-middle 1/3 = medial patellar retinacular fibers, superficial and deep MCL
-posterior 1/3 = thick; starts near adductor tubercle blends with SM tendinous expansion and post capsule and post oblique lig; pes anserines reinforces
musclular = semimembranosus, SGT? - pes anserines
the internal capsule is lined with what
synovial membrane
how many bursae in knee
14 at inter tissue junctions that encounter friction with motion
some are extensions of synovial membrane, some are external to capsule
what are the fat pads present in the knee
suprapatellar and deep infrapatellar
describe the TF joint
large convex femoral condyles and flat, smaller, tibial plateaus
describe motion of TF joint/how injuries occur
excessive motion present but soft tissue provides stability
means injury can involve many structures
menisci acts as gasket to form seats for femoral condyles
describe how the menisci lay
anchored to intercondylar region of tibia at anterior and posterior horns
external edge of each is attached to tibia at capsule bu coroncary ligaments (meniscotibial) - allows pivoting
2 menisci connected anteriorly by transverse lig
what muscles have secondary attachments to menisci that help stabilize
quads (both menisci)
semimembranosus (both)
popliteus (lateral)
describe the differences between the 2 menisci
medial is oval shape and attaches to MCL and adj capsule
lateral is circular and only attaches to lateral capsule
where does popliteus run
passes between LCL and lateral meniscus
describe the blood supply to the menisci
peripheral is 1/3 from direct genicular arteries (off popliteal) = the red zone
inner 2/3 is avascular = white zone
nutrition is from synovial fluid
primary functional consideration for tibiofemoral joint
decrease compressive forces (triple joint contact area to decrease pressire on articular cartilage)
WB is axial; meniscus deforms peripherally = tensile stress
describe compressive forces at knee while walking
2.5-3x body weigth at knee and > 4x with stairs
weight bearing at knee with cycling
1.2x BW
complete lateral meniscectomy increases contact pressure by how much
230%
how much load goes through the medial and lateral compartmetns of the knee
70% load goes through lateral
50% of that in the medial goes through the meniscus
secondary functional considerations for tibiofemoral joint
stabilizing through joint motion
lubricating articular cartilage
providing proprioception
help guide arthrokinematics
common mechanisms of injury for meniscus
often associated with forceful, axial RT of femoral condyles over flexed WB knee (can pinch/dislodge meniscus)
a dislodged or folded flap (bucket handle) can mechanically block knee
medial is injured 2x as frequently via valgus force (large stress on MCL/post-med capsule)
risk increases with lig laxity (esp ACL) and malalignment
loss of hoop stress capacity with meniscal tear (especially with tear at medial posterior horn)
osteokinematics if flexion and extension of knee
2 deg of freedom
knee slightly flexed for RT to occur
frontal plane is passive only (6-7 deg)
with flex/ext IAR moves
130-150 flex and 5-10 hyperext
what are the biomechanical implications of the IAR or evolute
lengthens the moment arm of the flexor and extensor musculature
brace might piston; need to align to the average axis the lateral epicondyle
osteokinematics of IR and ER
longitudinal axis through tibia (influened by sagittal plane motion) little in ext
at 90 deg flex: 40-45 deg axial RT
ER 2:1 exceeds IR
RT is named by position of tibial tuberosity relative to the ant distal femur
describe arthrokinematics of tibio on femoral ext
tibia rolls and slides anteriorly on femur
meniscus is pulled anteriorly by quads
femoral on tibial ext arthrokinematics
femoral condyles roll anteriorly and slide posteriorly on tibia
quads direct the roll and stabilizes the meniscus vs posterior shear of femur
describe the screw home mechanism
full ext requires 10 deg ER during last 30 deg of ext (conjuct RT is linked; not independent motion)
increases joint congruency/stability
open chain = tibia ER
closed chain = femur IR
screw home is driven by
shape of femoral condyle (tibial follows medial condyle and creates ER)
passive tension in ACL
slight lateral pull of quads
how does screw home mechanism occur with flx
unlocking IR happens first
driven by popliteus (can RT femur or tibia)
arthrokinematics of IR and ER at knee
knee must be flexed
spin between menisci and articular surfaces of tibia and femur
axial RT of femur over tibia causes menisci to deform/compress
popliteus and SM help stabilize
describe the MCL
flat and broad; has superficial and deep parts
superficial = well defined parallel fibers at 10 cm med epicondyle to medial patellar retinaculum fibers to medial proximal tibia (just post to pes anserine)
deep = slightly post and distal; shorter and oblique attaches to capsule/medial meniscus/SM tendon
describe the LCL
short cord like
runs vertical from lateral epicondyle of femur to head of fibula
doesnt attach to adj meniscus (popliteus runs between)
blends distally with biceps femoris tendon
primary functional consideration for MCL and LCL
they function to limit motion in frontal plane
MCL vs valgus force and LCL vs varus
secondary function of MCL and LCL
provide general stabilizing tension (especially walking near ext and loading)
protect against RT extremes (MCL at extreme of ER); i.e. planting R foot and body cut L
describe the ACL and PCL
cross within intercondylar notch
intracapsular
covered by extensive synovial membrane
poor blood supply
named for attachment on tibia
thick/strong
ACL in youth can withstand how much force
405 lb or 1800 N
what do the ACL and PCL restrict
resist all extremes of motion
primarily AP shear forces between tibia and femur
cutting in sagittal plane motions
help guide arthrokinematics and provide proprioceptive feedback
describe the ACL
anterior tibia
runs posterior and superior and laterally toward the medial side of the lateral condyle
collagen fibers twist on each other (2 sets; ant med and post lat)
at any given point some fibers are taut in flex but increasingly taut as they reach ext
specifically the post lat bundle along with the post capsule, knee flexor muscles, and parts of the collateral lig)
describe what happens with the ACL during the last 50-60 deg ext
force of quads pulls tibia ant and thus tension in ACL limits slidegl
what is the ant drawer test
leg in 90 deg
pull proximal tibia ant
ACL is 85% of passive resistance to ant glide
8mm or 1/3in greater translation than contralateral LE = possible tear
HS spasm may prevent a good test
common mechanisms of injury for ACL
highly vulnerable if tensioned in extremes of motion; especially those with high velocity
factors
-speed/direction of GRF
-amount/direction of compressive and shear forces
-control/timing of muscular forces
-integrity and stength of tissues
-alignment of trunk and lower limb
transient sublux with secondary trauma (menisci, cartilgage, MCL, etc)
chronic instability and further degeneration
hyperext
limited ER and ABD
most frequently ruptured ligament in knee
ACL
half in ages 15-25 with high velocity sports
what does it mean that 70% of sports related ACL injuries are non contact
landing, decelerating, cutting, pivoting over single limb
how is strong quad activation related to ACL injury
valgus collapse
excessive ER (femur is internally rotated)
describe the PCL
slightly thicker than ACL
post tibia to lateral medial femur
2 primary bundles
twists and changes length and orientation with flexion
some fibers taut in flx and ext but the majority of PCL becomes increasingly taut with greater flex (90-120)
slack in 30/40 into ext
posterior glide - tibia partially limited by PCL
describe the post drawer test
proximal end of tibia posterior
knees in 90 flex
limits ant translation of femur
rapid descent into deep squat
sag at 90/90
common mechanisms of injury with PCL
high energy trauma
rare; 2-10% all knee injuries
falling onto a fully flexed knee “dashboard injury”
kinematics of the patallofemoral joint
articular side of patella and trochlear notch
stabilizer = quads
Can cause chronic anterior knee pain/degeneration
tibial on femoral = patella slides relative to fixed trochlear groove (patella pulled toward tibia)
femoral on tibial (squat) = trochlear groove slides relative to fixed patella (held by eccentric quads and patellar tendon)
desribe patellofemoral contact at 135 deg flexion
superior pole below the groove at the lateral and odd facets
patellofemoral contact at 90-60 flexion
in trochlear groove
contact area greates (still only 1/3 area)
patellofemoral contact at 20-30 deg flexion
contact at inf pole
lost much of the mechanical engagement with groove (45% of that 60 deg)
patellofemoral contact with full ext
rests completely prox to groove on suprapatellar fat pad
if quads are relaxed patella moves freely
