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Biomechanics > Subtalar Joint > Flashcards

Subtalar Joint Flashcards

1
Q

What is the STJ?

A

articulation between talus and calcaneus

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2
Q

what is the function of the STJ?

A

allows for shock absorption during gait

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3
Q

what is the function of interosseous talocalcaneal ligament?

A

limits inversion and eversion (but mostly eversion)

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4
Q

which ligament limits inversion? which ligament limits eversion?

A

cervical ligament- limits inversion

interosseous ligament- limits eversion

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5
Q

what is the STJ axis?

A

42 degrees from transverse plane

16 degrees from sagittal plane

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6
Q

what is the primary motion of STJ?

A

almost equal ratio of inversion- eversion to abduction: adduction (because there is equal movements for frontal and transverse planes)
*very little sagittal plane motion (dorsiflexion/plantarflexion)

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7
Q

what is the ratio for transverse and frontal: sagittal plane motion for STJ?

A

3:1 ratio

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8
Q

in OKC, describe what is happening in supination

A

inversion, plantarflexion and adduction

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9
Q

in OKC, describe what is happening in pronation.

A

eversion, dorsiflexion, and abduction

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10
Q

what is the STJ doing during 1st half of OKC?

A

STJ pronates during 1st half of OKC. this allows for ground clearance

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11
Q

what is the STJ doing during the last half of OKC?

A

STJ starts to supinate

just before heel strike though, the STJ is in neutral

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12
Q

at heel strike, what is the STJ doing?

A

STJ is supinated (but moving towards pronation)

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13
Q

in CKC, what is happening in supination? (in terms of calcaneus, talus, and tibia)

A

calcaneus inverting
talar head is abducted and dorsiflexed
tibia is externally rotating

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14
Q

in CKC, what is happening in pronation? (in terms of calcaneus, talus, and tibia)

A

calcaneal eversion
talar head adduction and plantarflexion
tibia internal rotation

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15
Q

what relationship does talus have to the leg?

A

talus acts as an extension fo the leg and will follow its motion
Ex. internal leg rotation- talar adduction
Ex. external leg rotation- talar abduction

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16
Q

what relationship does talus and leg have to the calcaneus?

A

because talus and leg are proximal to axis, will act in OPPOSITE motion of the calcaneus

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17
Q

in CKC, what happens to STJ at heel strike?

A

at heel strike, STJ is supinated but quickly starts to pronate. (which unlocks the rest of the joints in the foot)This allows foot to become a “mobile adaptor” and allows for shock absorption.

18
Q

in CKC, during midstance, what happens to STJ?

A

during midstance, STJ starts to supinate to allow for heel-off . Foot becomes a rigid lever.

19
Q

in CKC, what is STJ pronation good for?

A

shock absorption (esp when foot strikes the ground)

20
Q

in CKC, what is STJ supination good for?

A

allows foot to become a rigid lever to propulse off the ground

21
Q

what is the STJ total ROM?

A

(30 degrees total ROM)

2:1 ratio of supination (calcaneal inversion) to pronation (calcaneal eversion)

22
Q

what is the max. degrees of STJ inversion/ eversion?

A

(2:1 ratio)
inversion- 20 degrees
eversion- 10 degrees

23
Q

how do you calculate STJ neutral thru ROM?

A

max. eversion - (inversion + eversion/3)

* determine which direction (varus/valgus) based on the normal STJ ROM (inversion- 20, eversion- 10)

24
Q

how do you measure STJ neutral?

A
  1. place patient in prone position
  2. bisect calcaneus and lower leg
  3. place patient in STJ neutral and measure angle
25
Q

what is the Kirby method used for?

A

to map out deviated STJ axis

26
Q

where does the normal STJ axis pass through in the foot?

A

posterior-lateral heel posteriorly and thru the 1st intermetatarsal space of the plantar foot anteriorly

27
Q

if the STJ axis is deviated medially, what does this indicate?

A

STJ pronation

28
Q

if the STJ axis is deviated laterally, what does this indicate?

A

STJ supination

29
Q

what happens when you apply thumb pressure medial to the STJ axis?

A

STJ supination

30
Q

what happens when you apply thumb pressure lateral to the STJ axis?

A

STJ pronation

31
Q

what is RCSP?

A

(relaxed calcaneal stance position) - is the position of STJ (calcaneus) when patient is fully compensated in midstance

32
Q

how do you measure RCSP?

A
  1. bisect calcaneus
  2. have patient stand and march in place to get them into angle and base of gait
  3. mesure calcaneal bisection in relation to WB surface
33
Q

what is normal RCSP?

A

2 degrees varus to 2 degress valgus

34
Q

how would you compensate for a rearfoot varus (inversion)?

A

calcaneus will be vertical if fully compensated

35
Q

how would you compensate for a rearfoot valgus (eversion)?

A
  • if neutral position >2 but <10 degrees, the foot will pronate to max. ROM
  • if over 10 degrees, then talar head hits ground and prevents further pronation
36
Q

what is NCSP?

A

(neutral calcaneal stance position)- position fo the STJ when patient is placed in neutral posiiton while standing

37
Q

how would you measure NCSP?

A
  1. bisect calcaneus
  2. place patient in angle and base of gait.
  3. have patient slowly invert/evert foot until neutral talus is palpated.
  4. have patient hold position
  5. measure calcaneal bisection in relation to WB surface
38
Q

what is the normal tibial influence?

A

0-4 degrees of varus

*valgus is very unusual unless trauma or congenital abnormality

39
Q

what is tibial influence (tibial stance position)?

A

bisection of lower leg (tibia) in relation to the ground while in NCSP

40
Q

how could you calculate NCSP?

A

add amt of tibial influence + STJ neutral

Biomechanics (14 decks)

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