5.9 Concave Convex Rules

Question 1

What are the three key arthrokinematic principles?

Answer 1

Roll, glide (slide), and spin

Question 2

What are arthrokinematic movements necessary for?

Answer 2

They allow voluntary, full active motion of the joints

Question 3

What are other names for arthrokinematic movements?

Answer 3

Accessory movements, component movements, joint play

Question 4

Are arthrokinematic movements under conscious control?

Answer 4

No, but they are essential for normal physiologic motion

Question 5

What is rolling (rocking) in arthrokinematics?

Answer 5

A rotary/angular motion where new points on one surface meet new points on the opposite surface

Question 6

Example of rolling?

Answer 6

A ball rolling across the floor

Question 7

What is sliding (gliding) in arthrokinematics?

Answer 7

A linear motion where the same point on one surface contacts multiple new points on the opposite surface

Question 8

Example of sliding (gliding)?

Answer 8

A figure skater gliding across ice

Question 9

What is spinning in arthrokinematics?

Answer 9

Rotation where a single point on one surface rotates against a single fixed point on the other surface

Question 10

Example of spinning?

Answer 10

The femur spinning on the tibia

Question 11

Why must roll, glide, and spin work together?

Answer 11

Because only rolling would dislocate a joint, only sliding would eliminate angular motion, and only spinning would give limited motion

Question 12

What is the concave–convex principle?

Answer 12

A biomechanical rule predicting the direction of joint surface movement during rolling and sliding

Question 13

What happens when a convex surface moves on a fixed concave surface?

Answer 13

The convex bone rolls in the same direction as osteokinematic motion but slides in the opposite direction

Question 14

What happens when a concave surface moves on a fixed convex surface?

Answer 14

The concave bone rolls and slides in the same direction as osteokinematic motion

Question 15

Example of convex on concave?

Answer 15

Femoral head (convex) moving in the acetabulum (concave)

Question 16

Example of concave on convex?

Answer 16

Middle phalanx (concave) moving on the proximal phalanx (convex)

Question 17

In knee flexion (squat), what happens to femur on tibia?

Answer 17

Convex femur rolls backward and slides forward (opposite directions)

Question 18

In knee extension (seated kick), what happens to tibia on femur?

Answer 18

Concave tibia rolls and slides forward together (same direction)

Question 19

What is the key question to ask when applying the concave–convex rule?

Answer 19

Which surface is moving

Question 20

What is the memory trick for concave motion?

Answer 20

Concave has an “A,” which pairs with “same” (roll and slide are the same direction)

Question 21

Summary of convex vs concave movement rule?

Answer 21

Convex moving: roll and slide opposite; Concave moving: roll and slide same