Biomechanics of the knee Flashcards
Tibiofemoral joint type
double condyloid - prevent motion in the frontal plane
2° of freedom
Flexion extension in sagittal plane
medial lateral rotation in transverse plane
Tibiofemoral femoral articular surface
Large AP convexity
Small curvature Posterior
medial condyle is longer than lateral and extends further distally for the angled femur
tibiofemoral tibial articular surface
Medial and lateral tibial plateau- concave and slopes posterio inferiorly
medial tibial plateau is 50% larger, oval and long , and the articular cartilage is three times thicker than the lateral
Lateral plateau is more circular
meninsci Compensate for incongruency
Function of the meniscus
increases stability by deepening the tibial plateau
decreases the friction by 20%
Increases contact area by 70%
Enhances proprioception via mechano receptors
attenuates forces
medial meniscus
c shaped
Firm attachment to the deep layers of the MCL
Thick posteriorly
thicker on periphery thinner along inner margin
Lateral meniscus
o shaped
Loose attachment to the lateral capsule
Uniform thickness
thicker on periphery thin along inner margin
menisci transmit how much percent of imposed load at the knee
50 to 60%
after a complete menisectomy, the average load per unit area
two times on the femur
6 to 7 times on tibial condyle
Shock absorption capability is reduced by 20%
menisci vascularization
initially, well vascularized
Recedes to periphery by age 11
in adults, vascularized by capillaries from the joint capsule and synovial membranes
tibiofemoral ligaments control and resist
hyper extension
Varus valgus
AP displacement of tibia on femur
Medial lateral rotation of tibia on femur
Combination of AP and rotation
collateral ligaments
MCL
LCL
MCL
prevent abduction, valgus stress
attaches 7 to 10 cm below joint line
Assist in prevention of anterior tibial translation
Attaches to joint capsule and medial meniscus
MCL dynamic
all fibers taut in full extension
anterior fibers also taut in mid range flexion while posterior fibers are more on slack
LCL
prevents adduction, varus stress
No attachment to capsule or meniscus
Assist with internal rotation and external rotation restraint
Greater laxity than MCL
Pencil like band of tissue
LCL Dynamic
tight in knee extension
Loosen as knee flexes
Anterior cruciate ligament
Anterior aspect of tibial, posterior aspect of LFC
three bundles - anteromedial
posterolateral
Intermediate
33 mm in length
11 mm in diameter
ACL functions
prevent anterior tibial translation
checks hyperextension
works with the MCL to stabilize against valgus
With assistance from hamstrings
Posterior cruciate ligament
One of the strongest ligaments of the body
Shorter and less oblique than the ACL
Rarely injured
PCL functions
prevents posterior translation of the tibia on femur
primary restraint to posterior displacement
Minor restraint to varus and valgus
genu valgum
TF angle <165
Increased lateral compressive forces
genu varum
TF angle >180
increase medial compressive forces
Q angle
angle formed by the line drawn from ASIS to mid patella and line from mid patella to tibial tuberosity
Males 10 to 14°
Females 15 to 17°
knee flexion extension ROM
flexion- 130 to 140°
Extension - 5 to 10° of hyper extension
genu recurvatum
Excessive hyper extension of the knee
closed chain AROM related to ankle
decreased dorsiflexion- decreased knee flexion
Decrease plantarflexion- decreased knee extension
Gait ROM needed at knee
60 to 70°
On or off toilets, ROM
75°
stair climbing ROM
70-80°
in and out of bath ROM
90°
sit and rise in chair ROM
90°
Advanced function, ROM
115°
Full extension and rotation
Rotation restricted by interlocking of femoral and tibial condyles
90° of flexion and rotation
ER- 0 to 45°
IR - 0 to 30°
screw home mechanism
during the last 5° of extension
Lateral femoral condyle shorter
Medial tibial condyle continues to move on the femur
Lateral rotation of tibia on femur or internal rotation of femur
screw home mechanism augmented by
Tension on ACL
Lateral pull of quadriceps
flexion and screw home mechanism
Flexion requires unlocking
Femur laterally rotate on tibia
Tibia must mediately rotate
popliteus and screw home mechanism
OKC- moves tibia medial IR
CKC - moves femur lateral ER
patellofemoral joint
Posterior surface covered with thick hyaline cartilage
patella slides within trochlear groove
patellofemoral facets
medial- flat to slightly convex
Lateral - longer than med
Odd - medial angle
PF joint contacts
first consistent contact is between 10 to 20° of flexion
By 90° all aspects of facets have made contact except odd facet
At 135° contact is on odd and lateral facets
PF compression
As the angle of knee flexion increases so do compressive forces
Greatest PF compression force at 90° flexion
As Q angle increases so will lateral vector due to pull of the quads
PF joint reaction force
Fully contracted, quad and full extension produces little PF contact force
medial facet bears most force
PF forces
Foot strike knee flex 10 to 15°- 50% of body weight
60° knee flexion- 3.3 times bodyweight
130° knee flexion - 7.8 times bodyweight
transverse stabilizes for PF
medial and lateral reticulum
VMO and VL
MPFL
longitudinal stabilizers for PF
Quad tendon
patellar tendon
what else stabilizes pf
IT band
Lateral wall of femoral groove
