5.5 Arthrokinematics

Question 1

What are arthrokinematics?

Answer 1

Small subtle motions that occur between joint surfaces

Question 2

What are the three basic types of arthrokinematic motions?

Answer 2

Rolling or rocking, sliding or gliding, and spinning

Question 3

Why do joints often combine rolling sliding and spinning?

Answer 3

To keep motion smooth and maintain proper contact between articular surfaces

Question 4

What is rolling in arthrokinematics?

Answer 4

A rotary motion where multiple points on one surface contact multiple points on another surface like a ball rolling on the floor

Question 5

What is an example of rolling in the body?

Answer 5

Articular surfaces of joints making new contact points during motion

Question 6

What is sliding in arthrokinematics?

Answer 6

A translatory motion where one point on one surface contacts multiple points on another surface like an ice skate gliding

Question 7

What is an example of sliding in the body?

Answer 7

One joint surface gliding across another to maintain contact

Question 8

What is spinning in arthrokinematics?

Answer 8

A rotary motion where one point on one surface rotates on one point of another surface like spinning a basketball on a finger

Question 9

What is an example of spinning in the body?

Answer 9

The radius spinning on the humerus during pronation and supination

Question 10

Why don’t rolling and sliding occur in isolation in the body?

Answer 10

Because rolling alone would cause dislocation so sliding occurs in the opposite direction to maintain congruency

Question 11

What happens at the knee joint when the femur extends on the tibia?

Answer 11

Rolling occurs in one direction and sliding occurs in the opposite direction to maintain surface contact

Question 12

Why are rolling and sliding important together?

Answer 12

They allow smooth motion maintain joint congruency and distribute forces safely across surfaces

Question 13

What is the instantaneous axis of rotation?

Answer 13

The shifting axis around which a joint rotates due to combined rolling and sliding

Question 14

Why is the instantaneous axis of rotation important clinically?

Answer 14

Because goniometric measurements are only approximations as the axis shifts during motion

Question 15

What is the evolute?

Answer 15

The path of the instantaneous axis of rotation as a joint moves

Question 16

What shape can the evolute take at the knee?

Answer 16

A backwards J shaped path

Question 17

Why are goniometric measurements always approximations?

Answer 17

Because the axis of rotation shifts with rolling and sliding

Question 18

How can clinicians improve reliability in goniometry?

Answer 18

By measuring consistently in the same way each time

Question 19

Why is understanding the evolute important in prosthetics and orthotics?

Answer 19

Because a fixed hinge axis may not match the body’s natural shifting axis