661 biomechanics 1 and 2

normal hip alignment

170 - 175

Load bearing axis (LBA)

ground reaction force passes vertically through LBA with no external moments for any of the joints

if the LBA off-set through genu varum, same GRF result in external moments at the knee, what kind of moments would it be?

external varus movement

tibiofemoral joint

largest synovial joint, structural stability necessary for function (accomplished primarily through soft tissue)

two articulations of TF joint

medial femoral condyle-medial tibial plateau and lateral femoral condyle-lateral tibial plateau

osteology of the femur

two convex condyles, force transmission functions

why does it matter that the medial condyles project more distally on the femur

to account for the slope of the femur so the connection is flatter making the tibia hit the ground vertically

what attaches at the intercodylar fossa/notch

cruciate ligaments

medial tibial plateau

larger and slighly concave

lateral tibial plateau

smaller flat/slightly convex

intercondylar tubercles

two bony spines, attachment of cruciate ligaments

osteokinematics at the TF joint

flexion/extension, abduction/adduction, internal/external rotation

joint angle of flexion/extension

relative orientation of distal segment relative to the proximal segment in the sagittal plane

what is the segment long axis

the line from the hip to the knee

healthy knee flex/ext values

flexion = 130-150 extension = 5-10 (hyperextension)

what does modified hinge mean

four-bar linkage (roll and slide is possible)

what mechanical advantage do we get from having the four-bar linkage in our knee

high stability and clearance during walking (being able to lift leg higher with lower energy expenditure)

the axis of rotation lines up with the

femoral epicondyles

closed chain arthrokinematics flexing vs extending

extending = velocity, the femoral condyles roll anteriorly and slide posteriorly flexing = femoral condyles roll posteriorly and slide anteriorly

open chain arthrokinematics extending vs flexing

extending = tibial plateau, roll anteriorly and slide anteriorly flexing = tibial plateaus roll posteriorly and slide posteriorly

closed packed position: max congruency

full extension creates maximal bony congruence, ligamentous tautness and natural stability

screw home mechanism

provides stability and reduces effort when standing (extension of knee paired with external rotation)

loose packed position

25 degrees of flexion (not suggested because minimal bony congruence, ligaments are lax, and low pressure)

if the hips are flexed what does that do to the hamstrings

lengthens

what happens if the hips are extended

the rectus femoris lengthens

varus/valgus position

relative orientation of distal segment to the proximal segment in the frontal plane (using the midlines of each segment)

conservative ways to reduce internal valgus moments

lateral wedging, valgus bracing, gait modifiction

intenal rotation/external rotation position

relative orientation of distal segment to the proximal segment in the transverse plane (axis is medial tibial intercondylar tubercle)

why does minimal rotation occur with extended knee

close packed position and screw home mechanism

how to unlock the knee

activation of popliteus to internally rotate the tibia (relative to the femur)

how to the menisci effect the TF joint

enhance stability and congruency

functions of the meniscus

compressive load management, joint stabilization, lubrication, proprioception, guiding knee arthrokinematics

which meniscus is more restricted

medial because of greater ligamentous and capsular restraints

what are the secondary attachments to the meniscus

semimembranosus and popliteus

blood supply to the meniscus

outer 3rd gets blood supply (red zone) inner zone requires cyclic motion

hyaline cartilage

decreases friction, assists with shock absorbtion, resists wear

articular cartilage deforms

22-30%

articular cartilage focal lesions

traumatic in origin, focused on site of injury

articular cartilage degenerative lesions (OA)

repetitive movements/aging and peripheral tissues affected

ACL and PCL stabilize against

horizontal translation/shear loads

MCL and LCL stabilize against

valgus/varus and lateral translation

do cruciate ligaments have good blood supply

no

true/false the cruciate ligaments are intra-articular but extrasynovial

true

ACL is made of what 2 bundles of collagen fiber

anteromedial (flexion) and posterolateral bundles (extension)

why do graft cycling post surgery

need to train quads right after surgery to avoid atrophy and find baseline intergrity of the ACL

ACLs secondary restraints

tibial internal rotation and external valgus/varus forces

should expect if leg is at 30 degrees of flexion (loose packed position)

there would be anterior tibial translation of 5-8 mm

ACL injury mechanisms

quad activation, knee near full extension, dynamic valgus, tibial torsion

PCL injuries typically come from

trauma

2 bands of the PCL

anterolateral - tight in flexion postereomedial - tight in extension

medial/lateral collateral ligaments stabilize

against valgus/varus and lateral translation

MCL two laters separated by bursa, superficial vs deep

superficial - medial femoral epi. to medial proximal tibia deep - continuous with joint capsule and medial femoral condyle to medial tibial plateau

MCL is taught in

full knee extension

function of MCL

resist external valgus moment/force, resist hyperextension, resist rotation, resist tibial anterior translation

function of the medial capsule

stabilize against external valgus moments

is the LCL intra- or extra- capsular

extracapsular

functions of LCL

resist external varus moments/forces, resist hyperextension, resist rotation

IT band

anterolateral support to the knee - as become more flexed the line of action can change

function of the posterior lateral capsule

resist external varus moment, external rotation, posterior translation

posterior capsule

resists excessive hyperextension (genu recurvatum >10 degrees)

what are the stabilizers of the patella

quadriceps tendon, patellar tendon, quadriceps muscles, IT band, patellar retinacular fibers

what does the knee extension moment depend on

internal moment arm (patella position maximizes) and muscle length-tenion ratio

where is the patella point of contact when the knee is flexed

superior

where is the patella point of contact when your knee is in extension

inferior

if someone has PF joint pain, do you want to train with maximum patellar contact or low patellar contact

maximum (at 60 and 90 degrees)

the patella is most mobile when the quadriceps are

relaxed in full extension

what generates internal knee extensor mometns

knee extensors (quadriceps)

what generates knee internal knee flexor moments

hamstrings (also some from gastroc, popliteus, sartorius, gracilis, plantaris)

what influences patella tracking

limb positioning, anatomy, muscle contraction

what muscle pull the patella posteriorly

vastus medialis

what is the Q-angle based on

patella mid point to ASIS and patellas long axis (supposed to approximate how much lateral pull there is)

what are the lateral directed forces

IT band, bowstringing force on the patella, lateral patellar retinacular fibers

what are the medial directed forces

vastus medialis (oblique) raised lateral facet of the trochlear groove, medial patellar retinacular fibers

what are the global factors

netural alignment and excessive knee external rotation and valgus

when will patella contact force be highests

in a deep squat (a larger arrow pointing posteriorly)

what is the most common form of knee pain

patellofemoral pain syndrome (PFPS)

what are the categorical causes of PFPS

overuse without impairment, strength deficits, coordination deficits, mobility impairments

what would the intervention be for overuse without impairment PFPS

activity modification and load management, homeostasis between load and capacity

biomedical considerations of strengthening

increased exteneral moment, muscle force, and joint reaction forces

lack of flexibility in what muscles can cause PF pain

hamstring, gastroc, soleus, IT band, quadriceps lengths

what is the ideal way to land from a jump

feet in front of you, bend in the knees and bend at the hip

rehabilitation principles of QT and PT

load management, gradual loading

less flexion: PT load

more flexion: QT load

what are the progression of tendon loading

activity modification (stop doing things that hurt), slow and heavy resistance (isometric/isotonic, increasing creep), progression of energy storage/return to sport