knee arthrokinematics

Question 1

what assists with the discrepancy in size of the femoral condyles and the size of the tibial plateaus

Answer 1

presence of the menisci

Question 2

what do when the knee flexes/extends

Answer 2

will deform to maintain joint congruency throughout ROM

Question 3

in an open kinetic chain

Answer 3

concave tibia moving on the convex femur

BM, roll and glide –> same direction

Question 4

flexion OKC first 25 degrees of motion

Answer 4

minimal gliding

Question 5

flexion OKC from 25 to full extension

Answer 5

posterior glide of the tibia –> maintain contact b/w tibia and femoral condyles

Question 6

extension OKC

Answer 6

anterior gliding of the tibia on the femur throughout ROM

Question 7

closed kinetic chain

Answer 7

convex femur is moving on concave tibia

BM and roll –> same

glide –> opposite

Question 8

CKC flexion (stand to sit)

Answer 8

BM and roll –> posterior

glide –> anterior

occurs throughout ROM

Question 9

forces that induce posterior glide

Answer 9

PCL

anterior aspect of menisci

Question 10

force of femoral condyle on the meniscus

Answer 10

tends to cause posterior movement of the menisci

Question 11

screw home mechanism

Answer 11

automatic IR of the femur on the tibia (closed chain)

OR

automatic ER of the tibia on the femur (open chain)

during end range knee extension

Question 12

what is the screw home mechanism d/t

Answer 12

larger medial femoral condyle and knee joint ligs

Question 13

when does the 20 degrees of rotation occur –> screw home

Answer 13

occurs during the last 30 degrees of knee extension motion

especially the last 5 degrees (terminal knee extension)

Question 14

OKC –> screw home

Answer 14

during end range knee extension –> lateral tibial plateau will complete its slide along the lateral femoral condyle

this occurs while the medial tibial plateau continues to glide anteriorly on the femur
–> causing the tib to ER on the femur (vertical axis is the lateral femoral condyle)

Question 15

CKC –> screw home

Answer 15

during end range knee extension –> the lateral femoral condyle will complete its slide along the lateral tibial plateau

this occurs while the medial femoral condyles continues to glide posteriorly on the tibia (b/c it is longer/larger)
–> causes the femur to IR on the tibia (vertical axis is the lateral femoral condyle)

Question 16

what happens after the screw home mechanism

Answer 16

knee has some osseous stability

closed packed position of the knee

Question 17

unlocking the knee from full extension (“unscrewing”)

Answer 17

initial phase of flexion starts the unlocking

CKC: requires ER of the femur

OKC: requires IR of the tibia

Question 18

what can cause unlocking of the knee

Answer 18

LOG being posterior to the knee joint or by the popliteus muscle

CKC: popliteus will ER the femur on the tib –> unlocking it

OKC –> popliteus will IR the tib –> unlocking knee