Arthrokinematics

Question 1

What is spin?

Answer 1

New parts of moving bone come into contact with some part of static bone (part of tibia contacting new parts of moving femur).

More common along long axis in rotation of femur or tibia.

Question 2

What is slide?

Answer 2

Same part of one bone comes into contact with new parts of another bone. (same part of femur touching different parts of tibia)

Question 3

What is roll?

Answer 3

New parts of both bones coming into contact with each other.
Bones rolling across surface of other.

Question 4

What does every knee movement involve?

Answer 4

a combination of roll and slide

Question 5

What does the knee locking mechanism involve?

Answer 5

when spin, roll and slide are involved

Question 6

How does the screw home mechanism work when the knee extends when weight bearing?

Answer 6

The femur simultaneously:
- rolls forwards
- slides backwards
- spins medially on the tibial plateau
- menisci pushed forwards - increases area of contact

As lateral condyle ends before extension completed (it is shorter than medial condyle) this is why medial rotation occurs in the last 15-20 degrees of extension.

Question 7

What is the close pack position of the knee?

Answer 7

extension

as it has congruency, compression, contact and thus stability.

Question 8

What are the arthrokinematics of the knee when it flexes when weight bearing?

Answer 8

Femur simultaneously:
- rolls backwards
- slides forwards
- spins laterally

Question 9

How does the screw home mechanism work when the knee is extended when non-weight bearing?

Answer 9

Tibia simultaneously:
- rolls forwards
- slides forwards
- lateral spin of femoral condyles

The continued movement of the medial condyles will be accompanied by conjunct lateral rotation of the tibia on the femur to “lock” the joint.

Question 10

What are the arthrokinematic of the knee when it flexes when non-weight bearing?

Answer 10

Tibia simultaneously:
- rolls backwards
- slides backwards
- medial spin of femoral condyles