Midtarsal Joint

Question 1

What does the midtarsal joint consist of?

Answer 1

calcaneocuboid joint + talonavicular joint

Question 2

what is midtarsal joint aka?

Answer 2

Chopart’s joint

Question 3

the midtarsal joint has a longitudinal axis and an oblique axis. what is the longitudinal axis?

Answer 3

(runs proximal, plantar and lateral to distal, dorsal and medial)
-is 15 degrees from transverse plane and 9 degrees from sagittal plane

Question 4

what is the primary motion about the longitudinal axis of MTJ?

Answer 4

frontal plane motion (inversion/eversion)

Question 5

describe the oblique axis of the MTJ.

Answer 5

(runs proximal, plantar and lateral to distal, dorsal and medial)
-is 52 degrees from transverse plane and 57 degrees from sagittal plane

Question 6

what is the primary motion about the oblique axis of MTJ.

Answer 6

There is equal motions about the transverse plane (abduction/adduction) and sagittal plane (dorsiflexion/plantarflexion)
*PADs/DABs

Question 7

what does the longitudinal axis of MTJ allow the foot to do?

Answer 7

allows foot to adapt to subtalar joint variations and allows foot to remain plantargrade
Ex. forefoot can:
-invert on everted rearfoot
-evert on inverted rearfoot

Question 8

what is the purpose of the oblique axis of the MTJ?

Answer 8

“secondary ankle joint”- oblique axis can compensate for lack of ankle dorsiflexion

Question 9

in which position is the “unlocked” MTJ?

Answer 9

STJ pronation

Question 10

what happens in STJ pronation?

Answer 10

MTJ axes become more parallel –> unlocks MTJ –> allows foot to become mobile adaptor

Question 11

what happens in STJ supination?

Answer 11

MTJ axes cross –> locks MTJ –> foot becomes rigid lever and decreases ROM

Question 12

in which position is the “locked” MTJ and rigid lever?

Answer 12

STJ supination

Question 13

in which position are the MTJ axes crossed? paralle?

Answer 13

STJ pronation = MTJ axes parallel

STJ supination = MTJ axes crossed

Question 14

which position of STJ is more stable?

Answer 14

STJ supination (axes crossed = rigid lever)

Question 15

which position of MTJ is more stable?

Answer 15

MTJ pronation

as STJ supinates- which is more stable, MTJ pronates

Question 16

which position of MTJ is unstable?

Answer 16

MTJ supination

Question 17

what happens to calcaneocuboid joint when MTJ pronates?

Answer 17

calcaneocuboid joint dorsiflexes (cuboid rotates up into dorsolateral overhang on the calcaneus)
*ligaments also tighten, preventing excessive motion

Question 18

what happens to bones and ligaments when MTJ supinates?

Answer 18

ligaments will also tighten

bones, however, are not tightly packed (osseous locking not present)

Question 19

how do you “lock” MTJ?

Answer 19

place STJ in neutral. then push up on 4th and 5th metatarsal heads to simulate WB.

Question 20

what happens during contact period of gait? (in regards to OA, LA, STJ)?

Answer 20

OA- pronated (EDL and peroneus tertius activated –> allows dorsiflexion and abduction)
LA- supinated (anterior tibialis muscle contracted –> inversion)
STJ pronated to allow for shock absorption

Question 21

what hapens during midstance?

Answer 21

STJ- supinated to prepare for propulsion
LA- pronated to help lock the MTJ to become a rigid lever
OA- pronated (dorsiflexed and abducted)

Question 22

what happens during propulsion?

Answer 22

STJ is supinated
LA- pronated (locking still present at CC joint)
OA- supinated (windlass mechanism- big toe dorsiflexes and pulls on plantar fascia to help contract intrinsic muscles and the arch height increases)

Question 23

MTJ ROM is controlled by what?

Answer 23

passively control by the position of STJ
STJ supination - causes decrease in MTJ ROM - “locked axes”
STJ pronation- causes increase in MTJ ROM

Question 24

MTJ position is controlled by what?

Answer 24

GRF during stance phase of gait and by surrounding muscles during other phases

Question 25

which muscle inverts the longitudinal axis?

Answer 25

tibialis anterior

Question 26

which muscles pronate the oblique axis?

Answer 26

peroneus tertius
extensor digitorum longus
*also helps to shift weight from lateral to medial

Question 27

which muscles help to decelerate the foot at heel strike to prevent foot slap?

Answer 27

anterior tibial
peroneus tertius
EDL

Question 28

how do you measure forefoot to rearfoot relationship?

Answer 28

1. place patient in prone position
2. place patient in STJ neutral
3. lock MTJ
4. look straight down and elavuate if plantar heel is parallel with met head

Question 29

what is the ideal compensation for a forefoot varus?

Answer 29

calcaneus ideally everts to same degree of forefoot varus

Question 30

what happens in uncompensated forefoot varus?

Answer 30

forefoot varus > calcaneal eversion available

*bc calcaneus is unable to evert pass netural

Question 31

what happens in partially compensated forefoot varus?

Answer 31

forefoot varus > calcaneal eversion available

• calcaneus is able to evert pass neutral but not to same degree of FF varus
• additional compensation gained thru oblique axis of MTJ and 1st ray

Question 32

what happens in compensated forefoot varus?

Answer 32

forefoot varus >= calcaneal eversion

Question 33

how do you compensate for a forefoot valgus?

Answer 33

LASOS

1. LA supination
2. subtalar supination
3. OA supination
4. further subtalar supination

Question 34

what is a flexible deformity?

Answer 34

if only LA compensation

-heel remains vertical but foot is unstable in midstance due to midfoot supination