Structure and Motion of the Knee PT 706

What planes does tibiofemoral joint work in?

sagittal and transverse plane

Normal angle at the tibiofemoral joint?

valgus angle, about 5 degrees

genu varum (varum)

decreased medial angle

genu valgum (valgus)

increased medial angle

Forces during varus

medial is compressed, lateral tensile force (on stretch)

forces during valgus

lateral is compressed, medial tensile forces (on stretch)

which femoral condyle is longer in the anterior/posterior direction

medial is longer in anterior/posterior direction

medial menisci shape

C shape

lateral menisci shape

O shape

how much of the load does the menisci absorb

50-70 percent

medial meniscus attaches to

MCL, semimembranosis

lateral meniscus attaches to

popliteus

menisci horns

anchor menisci to intercondylar region of tibia (anterior and posterior horns)

coronary ligament menisci

attach menisci to tibia condyles

vascularization of meniscus

only periphery is vascularized, red and white zone (clinically important so surgeon can decide to do a repair), you need blood flow to region so it can heal

What bone does the menisci move/distort with

femoral condyles of femur. Even though they are on the tibia, they move with the femur

medial collateral ligament

primary resist to valgus

ER of tibia

anterior tibial translation

when is MCL taut

extension

when is optimal force resistance at for MCL

25 degrees of flexion (we care about this for testing the integrity of the ligament)

lateral collateral ligament

primarily resists varus forces

limits ER of tibia

When is LCL ligament taut

extension

What is optimal force resistance at for LCL?

35 degrees of flexion

anterior cruciate ligament

Limits anterior tibial translation

Hyperextension

Varus/valgus

Rotation

Max anterior translation occurs for ACL

30 degrees of flexion

Bands in ACL

anterior/medial band and posterior/lateral band

anterior medial band of ACL

becomes more slack at knee extension

posterior medial band of ACL

becomes more slack at knee flexion

Why we do the ACL test at 30 degrees?

Neither bands of the ACL are particularly taut

synergist with ACL

Hamstrings

(because they attach posteriorly to the tibia, and can pull the tibia posteriorly (resisting anterior tibial translation))

posterior cruciate ligament

*Primarily limits posterior tibial translation

Resists varus and valgus

Resists rotation

synergist with PCL

quads because they pull the tibia anteriorly

iliotibial band

thickened fascia

inserts on lateral tubercle of tibia (gerdys tubercle)

reinforces lateral knee= stability

some fibers attach to patella= lateral pull

AAOS knee flexion

135 degrees

AAOS knee extension

10 degrees

genu recurvatum

excessive extension

posterior tilt on tibia

plantar flexion of ankle

compression on the anterior side of tibiofemoral joint and length on the posterior side of tibiofemoral joint

axis of motion of knee

migrating axis due to incongruent surfaces, this is why we measure at lateral epicondyle (average of migrating axis that occurs)

when is there the greatest amount of axial rotation

90 degrees of flexion at the knee

ER to IR ratio of axial rotation

2:1

maximal restriction of axial rotation is when knee is in

full extension

Screw Home Mechanism

closed chain extension

IR of femur on fixed tibia

Screw home mechanism

open chain extension

ER of tibia on fixed femur

screw home mechanism

closed chain flexion

ER of femur occurs

screw home mechanism

open chain flexion

IR of tiba occurs

why does screw home mechanism occur

shape of medial femoral condyle, passive tension in ACL, slight lateral pull of quadriceps

open chain extension of knee

tibia rolls and glides anteriorly

open chain flexion of knee

tibia rolls and glides posteriorly

closed chain flexion of knee

femur rolls posteriorly and slides anteriorly

open chain extension of knee

femur rolls anteriorly and glides posteriorly

closed packed position of knee

full extension

resting position of knee

about 25 degrees of flexion

what way does the menisci roll

menisci rolls with the direction of roll

anterior deformation

during closed kinetic chain, the femur rolls anteriorly causing deformation on anterior menisci

posterior deformation

during closed kinetic chain, the femur rolls posteriorly causing deformation of posterior menisci

patella

largest sesamoid bone in the body, sits in a tendon and acts as a lever

covered with cartilage

joint of incongruency

Synovial joint

base of patella

superior surface

apex of patella

pointy inferior surface

which facet of the patella is the largest?

lateral facet

what helps prevent patellar dislocations

lateral ridge of femur

135 degrees of flexion

primary contact: superior pole

inferior to inter condylar groove

facets in contact: lateral edge of lateral facet and odd facet

90 degrees flexion

primary contact: starts to migrate towards inferior pole

engaged within the intercondylar groove from 90-60 flexion

facets in contact: medial and lateral facets

20 degrees flexion

priamary contact: inferior pole

superior to intercondylar groove

facets in contact: medial and lateral facets

external torque demands are greatest

open chain knee extension

and closed chain knee flexion

why do we not extend our knee all the way during knee extension exercise?

decreased the moment arm, but you are still working the quads effectively, this way you can avoid the high external moment arm

what is the role of the patella?

increases internal moment arm of knee extensor mechanism (making knee extension easier for us)

joint reaction forces are influenced by

the angle of knee flexion, force within the quad muscle

patella femoral joint reaction forces (PFJRF)

The deeper you go into a squat the compressive force into a joint goes higher, the contact area is higher from 60-90 degrees so it can help distribute this force

Q angle

ASIS to center of patella

tibial tuberosity to center of patella

normal Q angle

10-15 degrees, larger in females due to wider pelvis

Is there more medial or lateral pull of the patella?

More lateral

This is why people dislocate more lateral, because we have more forces pulling laterally than medially.

Clinically, you want to have a more equal pull to prevent dislocatiom.

If you have a larger Q angle, you can have more lateral pull

patella movements

- tilited medially and laterally

- rotated medial and lateral based on ifnerior pole

- glide medial and lateral

- superior and inferior glide