Knee Joint Biomechanics

Question 1

Name the 4 ligaments of the knee

Answer 1

ACL
PCL
MCL
LCL

Question 2

What happens if the ACL is absent?

Answer 2

the femur can slide excessively backwards over the tibia

Question 3

what happens if the PCL is absent?

Answer 3

the femur can slide excessively forwards over the tibia

Question 4

What is subluxation?

Answer 4

partial/complete dislocation

Question 5

What is interesting about the knee joint rotation?

Answer 5

it has a varying centre of rotation

Question 6

What is the point where the centre of rotation is at any point of movement?

Answer 6

the instantaneous centre of rotation

Question 7

Where does the centre of rotation move as the knee rotates?

Answer 7

posteriorly

Question 8

What is the 4 bar linkage mechanism and what does it function to do?

Answer 8

four bar linkage mechanism is made up of the cruciate ligaments and function so that there is a combination of rolling and sliding motion

Question 9

What two types of motion does rotation of the knee involve>?

Answer 9

rolling and sliding

Question 10

What type of loading is mainly experienced at the knee joint?

Answer 10

compression

Question 11

How many times bodyweight is the loading at the knee during normal activities?

Answer 11

2-6

Question 12

Which ligament prevents the shearing of the femur over the tibia when descending stairs?

Answer 12

PCL

Question 13

What muscle groups activate to contain excessive horizontal loadings?

Answer 13

quadriceps

hamstrings

Question 14

What happens to joint reaction force as a result of quadricep and hamstring recruitment?

Answer 14

increase

Question 15

What is required of a knee prosthesis is the collateral ligaments are lost?

Answer 15

the knee prosthesis must provide lateral stability - i.e a hinge prosthesis

Question 16

Which structures normally resist axial torsional stresses?

Answer 16

the menisci

Question 17

What two materials are knee prostheses commonly made from?

Answer 17

cobalt chrome femoral component

tibial HDP

Question 18

What are the minimum functional requirements of a knee prosthesis?

Answer 18

it should fully extend to 180 degrees at which point the patient should be able to stand normally

it should flex to 90 degrees so a patient can climb stairs

it should permit slight axial rotation as the knee extends to maintain normal ligament tension

Question 19

Why must the posterior capsule of the knee be fully dissected?

Answer 19

ensures that the replacement can fully extend

Question 20

how should ligaments be balanced?

Answer 20

in tension - so that there is no increase in medial/lateral opening

Question 21

how are ligaments balanced?

Answer 21

typically by lengthening tight ones to match slack ones, and the ensuing a thicker tibial component to stretch the gap

Question 22

Are cruciate ligaments always preserved?

Answer 22

no

Question 23

How many times more expensive are knees than hips?

Answer 23

5x