STJ axis location and rotational equilibrium

Question 1

What is a MOMENT/torque/moment of force

Answer 1

the turning effect produced by a force acting at some distance from an axis
vector - has a direction

Question 2

Sum of moments

Answer 2

not in equilibrium induce a change in rotational velocityy

Question 2

Rotational equilibrium

Answer 2

if the sum of moments = 0Nm = object will continue in its state of rotational motion (ROTATIONAL EQUILIBRIUM)

Question 3

STATIC ROTATIONAL EQUILIBRIUM

Answer 3

if object is not rotating and moments are in rotational equilibrium =

Question 4

what allows joints to rotate

Answer 4

Moments generated by the forces acting around an axis is a force:
muscle forces
ligaments
interosseous compression forces
GRFs

Question 5

What is rotational equilibirum dependent on

Answer 5

STJ axis location

Question 6

Origins - for STJ to reach equilibrium:

Answer 6

Sum of the STJ pronation moments must exactly equal sum of stj supination moments

Question 7

pathological foot types in relation to position of stj axis:

Answer 7

medially deviated stj axis
laterally deviated stj axis

Question 8

interally generated forces - stj roational equilbrium

Answer 8

ligamentous and tendon tensile forces
joint compression forces

Question 9

externally generated forces - stj roational equilbrium

Answer 9

GRF
orthosis and footwear reaction forces

Question 10

what happens the longer the distance between the forces and the stj axis

Answer 10

= the greater the moment

Question 11

Effect of forces - grf and orthotics

Answer 11

those that act medial to stj will exert stj supination moment

those that act lateral to stj will exert stj pronation moment

Question 12

effect of forces - muscle and lig tensile forces

Answer 12

• force medial = stj supination
  lateral = stj pronation

Question 13

effect of forces - interosseous compression forces

Answer 13

lateral = stj supination moment
medial = stj pronation moment

Question 14

Moment arm of forces - in laterally deviated stj, short moment arm 5th mtpj

Answer 14

low pronation moment

Question 15

moment arm of forces - in medially deviated stj, large moment arm 5th mtpj

Answer 15

high pronation moment

Question 16

moment arm of forces - in laterally deviated stj, lays medial to the axis 1st mtpj

Answer 16

supination moment

Question 17

moment arm of forces - in medially deviated stj, lays lateral to the axis 1st mtpj

Answer 17

pronation moment

Question 18

Medially deviated stj axis

Answer 18

talar head and neck are positioned medially in relation to plantar surface

During relaxed stance:
1. medial border of foot will demonstrate a convex shape
2. ST contour of the talar head and neck at anterior ankle will be more medially positioned and internally rotated in relation to calc
from post: increase in convexity in the medial midfoot, just anterior and inferior to the med mall

Question 19

Laterally deviated stj axis

Answer 19

less common than medially deviated
talar head and neck postioned more laterally in relation to the plantar foot
increased magnitudes of stj supination moments and decreased stj

Question 20

Laterally deviated stj axis have increased frequency of:

Answer 20

lateral ankle sprains
peroneal tendinopathy

Question 21

Medially deviated stj and orthotic prescription

Answer 21

• induce modifications that will apply supination moments/ move grf medially
• medial heel skive, blake inverted device

Question 22

laterally deviated stj + orthotic prescription

Answer 22

modifications that will apply a pronation moment/grf laterally
- lateral heel skive
- everted balancing techniques
- valgus wedge

Question 23

RF structure and STJ on normal foot

Answer 23

• positioned lateral to the plantar WB area of the calc (medial tubercle)
• grf on medial tubercle = supination moment
• magnitude of the supination moment dependent on length of the lever arm and magnitude

Question 24

RF structure and stj - RF varus

Answer 24

medial calc tubercle more medially positioned relative to stj axis
increase stj supination
clinically:
- higher degrees of RFVR have lateral instability - common to see have stj pronation during gait

Question 25

RF and stj - RFVL

Answer 25

medial tubercl is more laterally in relation to stj axis
increase in pronation moment
CLinically:
usually maximally pronated at stj stance (WB) - no sufficient supination moment to counterbrace the prontion moments

Question 26

RF position and motion and STJ axis

Answer 26

position of stj alters relative position of medial calc tubercle and stj axis