Lecture 8 Knee pt 1

why is the knee frequently injured

located between two of longest bones, large forces, limited protection, contact injuries, not made for frontal plane movement

what bones form the knee joint

femur, tibia, and patella

t or f: the fibula is not directly part of the knee joint

t

what are the three articulations of the knee joint

medial tibiofemoral articulation, lateral tibiofemoral articulation, patellofemoral articulation

how is the knee joint classified

double condyloid joint

why is the knee more complex than a simple hinge joint

requires significant arthrokinematics motion, rolling and sliding not just flexion and extension

the best knee braces have how many hinge points

2

what is the intercondylar eminence

a raised bony region between medial and lateral tibial plateaus

the patella is embedded where

within the quadraceps tendon

what connects the patella to the tibia

patellar tendon

what is the quadriceps tendon

tendon connecting the quadriceps muscles to the patella

what movements occur at the knee

flexion/extension, in/external rotation

what is ROM for knee flexion

140

what limits knee flexion

soft tissue interference

what is normal ROM for knee extension

0 degrees

how much hyperextension (negative extension) does the knee have

-3 to -5

what limits hyperextension

ligaments

How much external rotation can the tibia perform non-weight bearing

50

how much internal rotation can the tibia perform non-weight bearing

25

what happens during closed chain knee extension

femur rotates internally, screw home mechanism

what are menisci

circular rims of fibrocartilage

what are the purpose of the menisci

motion control, stability, depth, lubricate, transmit forces and weightbearing, deepen articulation/increase congruency

what is the shape of the medial menisci

c shape

what is the shape of the lateral menisci

round, incomplete circle

describe the thickness and structure of the menisci

thick peripheral borders that taper toward thin inner edges

what are the vascular zones of the menisci

red, pink, and white

red and pink zones of the menisci can heal and have vascular supply t or f

t

describe the medial menisci

larger, moves 6 mm anteriorly/posteriorly, attaches to the MCL

if you tear your MCL you are most likely tearing you

medial menisci

is the medial or lateral menisci damaged more often

medial

the medial meniscus slides more to the

medial side

describe the lateral meniscus

more freedom of movement, less atttachments, moves 12 mm in anteror/posterior

what is the primary function of the medial collateral ligament (MCL)

resists valgus stress, force from outside

what is the primary function of the Lateral collateral ligament

resists varus stress, force from inside

how is the MCL shaped

longer, flatter, broader

how is the LCL shaped

shorter and cord like

what do the collateral ligaments prevent

rotation of tibia on femur when knee is extended since they are taunt

when the knee if flexed the collateral ligaments are

laxed and allow greater frontal plane motion

what structures provide medial knee stability

pes anserine tendons (sartorius, gracilis, semitendinosus)

what structures provide lateral knee stability

IT band attached to Gerd'y’s tubercle

where does the PCL run

most posterior runs anteriorly to attach on medial femoral condyle

where does the ACL run

runs from anterior tibia to lateral femoral condyle

what is the function of the ACL

prevents anterior translation of tibia on the femur and excessive rotation of tibia

what is the function of the PCL

prevents posterior translation of tibia on femur and hyperextension

t or f: the PCL is injured less often than the ACL

t

what ligament is secondary support to varus and valgus forces

ACL

what muscle group should be avoided or used with caution during early rehab of a PCL injury

hamstrings

what muscle group is focused on during ACL rehab

hamstrings

what muscle group should you avoids with a ACL injury

quads

what muscle group should be worked during rehab of a PCL

quads

cruciate become more taunt in internal tibial rotation/external femoral rotation because

cruciate ligaments become more taunt since they twist around and rub against each other

cruciate become more lax in external tibial rotation/internal femoral rotation because

cruciate ligaments become more lax since they untwist

when does peak stress on the ACL occur

open chain knee extension between 28 and 14 degrees

why does closed-chain exercise decrease stress on the ACL compared to open-chain knee extension

promote hamstring co-contraction which helps reduce anterior tibial shear forces and stress on ACL

Does co-contraction during open-chain knee extension significantly decrease anterior shear forces?

No although it may help but has not been proven

what are the main functions of the knee

lengthening/shortening, support/stability, shock absorption

the knee is the middle link of the kinetic chain and relies on what for stability

ligaments and menisci

what is normal genu valgum

2-5 degrees

excessive valgus stresses what structures

medial structures, MCL

varus stresses what structures

lateral structures, LCL

how is genu valum measured

x-rays, middle of hip, middle of knee, and middle of ankle

how is the q angle measured

asis to middle of knee to middle of ankle

what is the normal q angle for males and females

males: 10-15, females: 15-20

why do women have a greater q angle

pelvis is wider

genu valgum creates

knocked knee more than 15 or 20

genu varum creates

bow-legged, less than 10 degrees

with an increased q angle you are more likely to have

valgus collapse, patellar subluxation/dislocation

what is the screw-home mechanism (terminal locking mechanism)

occurs during final degrees of extension in closed chain position

how does SHM happen

femur internally rotates on tibia, rotation looks the knee into a stable position

with SHM what muscle group is relxed

quadriceps

what structures help maintain the knee’s locked position

acl, hip extension, line of gravity

what happens to the line of gravity during SHM

movers anterior

how is the knee unlocked during closed-chain movement

hip flexion, activation of popliteus muscle

the patella is what kind of bone

sesamoid bone

the patella acts like a what at the knee

pulley

the patella improves the

line of pull and force arm length of quads

why does the last 15 of knee extension require quadriceps strength

quads lose mechanical advantage as the knee approaches full extension, requiring approximately tice the quad strength

the patella glides how much

5-7 cm total

what causes improper patellar tracking

increased q angle, weak glute med, pronated feet, increase external tibial rotation, imbalance/poor timing of quads, patellar tilting/decreased mobility

proper patella tracking depends on

complex of interaction of muscle forces, structure, and biomechanical considerations

where does poor tracking of the patella occur

laterally in the groove

good congruence means

patella fits properly in the femoral groove, smooth tracking and greater stability