surgical biomechanics

Question 1

Biomechanical abnormalities can lead to…

Answer 1

Development of foot and ankle pathologies that
often require surgical intervention
* Developmental abnormalities in pediatric patients

Question 2

GAIT CYCLE REVIEW

Answer 2

Stance Phase 65
Swing Phase 35

Question 3

CONTACT PERIOD

Answer 3

Heel strike of WB limb to toe-off of CL limb
* Prior to heel strike the limb is slightly internally rotated and
heel contacts 2-3 degrees inverted
* This leads to STJ pronation – calcaneal eversion of 4 degrees
past neutral

Question 4

MIDSTANCE PERIOD

Answer 4

egins with toe-off of CL limb to heel-off of WB limb
* Transition from “pronating, mobile adaptor” to “supinated,
rigid lever”
* STJ/OMTJ re-supinates, LMTJ pronates

Question 5

PROPULSIVE PERIOD

Answer 5

Heel-off to toe-off of WB limb
* Foot must have re-supinated in order to achieve optimal push-
off
* Body moves over leg, shifts weight to forefoot in lateral to
medial direction
* Hallux planted, 1st ray PF 65 degrees

Question 6

SWING PHASE

Answer 6

From toe-off to heel strike
* External rotation of leg ends after toe-off, begins internally rotating
to prep for heel strike
* STJ pronation at first to assist with clearance, then begins to supinate
for heel strike

Question 7

PEDOBAROGRAPHS

Answer 7

Question 8

Met primus elevatus

Answer 8

Structural vs. functional elevation of 1st met
* First met DF leading to dorsal jamming of MPJ
* Results in hallux limitus/rigidus
* Ineffective propulsion

Question 9

Met primus equinus

Answer 9

Structural vs. functional PF of 1st met
* If fixed, can lead to STJ supination and lateral weight
transfer during gait, lateral ankle sprains

Question 10

FLEXIBLE FLATFOOT

Answer 10

Onset early childhood
* Etiology – malinsertion, ligamentous laxity, forefoot/rearfoot
varus, hypermobile 1st ray, met primus elevatus, met adductus,
equinus, lateral column cavus
* Stretching, tearing of plantar medial structures

Question 11

FLEXIBLE FLATFOOT
* Clinical Findings

Answer 11

Partial vs. total arch collapse in WB
* Calcaneal eversion, medial ankle deviation
* PTTD – calcaneus won’t invert with heel raise
* Too many toes sign
* Rearfoot valgus
* Forefoot varus
* HAV
Heel/arch pain
* Ankle impingement/equinus

Question 12

RIGID FLATFOOT

Answer 12

~10% of deformities
* Structural, alignment related
* Coalition leading to Peroneal spasticity
Congenital vertical talus
* Traumatic

Question 13

flatfoot deformity: Radiographically

Answer 13

Decreased CIA, Increased TDA, abnormal Meary’s,
obliterated sinus tarsi, increased CAA, increased Kite’s, HAV,
talar head uncovering, so aka Unable to supinate throughout the gait cycle
* Unable to generate rigid platform on which to propel
* Apropulsive, peeling-off type gait, early heel off

Question 14

Radiographically: cavus foot

Answer 14

Increased Meary’s & CIA, bullet hole sinus tarsi, decreased
talar declination, retracted digits, met adductus, calcaneal
varus
If rigid, foot is unable to transition to pronating, mobile
adaptor
* Lateral column bears most weight if unable to compensate
* May not propel off the 1st ray
* May have difficulty with clearance during swing

Question 15

SURGICAL INTERVENTION - REARFOOT

Answer 15

Ankle Arthrodesis
STJ Fusion

Question 16

Ankle Arthrodesis

Answer 16

Internally rotated talus – increased stress on STJ, results in
proximal external rotation to compensate
* Externally rotated talus – medial foot collapse, HAV, medial
knee pain
* Varus positioning – lateral weightbearing with fixed
supinated foot
* If stiff STJ, need slight valgus positioning
* 90 degrees relative to leg
* If PF, creates LLD and genu recurvatum, midfoot stress
* If DF, heel bears brunt of force
* Patients develop increased sagittal plane motion in distal
joints

Question 17

STJ Fusion

Answer 17

Joints proximal and distal compensate
* If in varus, forefoot is supinated and semi-rigid, weight
passes laterally, roll over medial foot to pass forward
* Ideally slight valgus - ankle stability, slight pronation and
flexibility of forefoot, allows transfer of weight medially
* Dwyer & Evans – size of wedge
* Kouts – amount of slide
* Heel Cord Lengthening – appropriate level and
amoun

Question 18

SURGICAL INTERVENTION - MIDFOOT

Answer 18

TNJ/CCJ Fusion
Intertarsal, TMTJ Fusion
Tendon Transfers

Question 19

TNJ/CCJ Fusion

Answer 19

Essentially eliminates STJ motion, foot must be held in
plantigrade position
* If foot supinated, forefoot rigid and inverted, lateral
stress

Question 20

Intertarsal, TMTJ Fusion

Answer 20

Minimal loss of function, little to no motion
* Consider lateral TMTJ – most motion, try to spare

Question 21

Tendon Transfers

Answer 21

Phasicity

Question 22

SURGICAL INTERVENTION - FOREFOOT

Answer 22

Keller
McKeever
Lapidus
Cotton

Question 23

Keller

Answer 23

removal of PP base yields instability, disruption of
Windlass mechanism causing decreased WB on 1st ray and
lateral transfer

Question 24

McKeever

Answer 24

10-15 abduction and dorsiflexion, still allows
efficient propulsion, but increased stress on IPJ

Question 25

Lapidus

Answer 25

if fused in DF position, yields decreased 1st MPJ ROM
and decreased propulsion

Question 26

Cotton

Answer 26

if too large of a wedge, over PF 1st ray

Question 27

Hallux/Partial 1st Ray Amputation

Answer 27

No longer have main source of
propulsion
* Progression of gait/weight transfer
shifts laterally

Question 28

Transmetatarsal Amputation

Answer 28

Potential muscular imbalance
depending on how proximal
* GS complex at mechanical
advantage - TAL