surgical biomechanics Flashcards
Biomechanical abnormalities can lead to…
Development of foot and ankle pathologies that
often require surgical intervention
* Developmental abnormalities in pediatric patients
GAIT CYCLE REVIEW
Stance Phase 65
Swing Phase 35
CONTACT PERIOD
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
MIDSTANCE PERIOD
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
PROPULSIVE PERIOD
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
SWING PHASE
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
PEDOBAROGRAPHS
Met primus elevatus
Structural vs. functional elevation of 1st met
* First met DF leading to dorsal jamming of MPJ
* Results in hallux limitus/rigidus
* Ineffective propulsion
Met primus equinus
Structural vs. functional PF of 1st met
* If fixed, can lead to STJ supination and lateral weight
transfer during gait, lateral ankle sprains
FLEXIBLE FLATFOOT
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
FLEXIBLE FLATFOOT
* Clinical Findings
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
RIGID FLATFOOT
~10% of deformities
* Structural, alignment related
* Coalition leading to Peroneal spasticity
Congenital vertical talus
* Traumatic
flatfoot deformity: Radiographically
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
Radiographically: cavus foot
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
SURGICAL INTERVENTION - REARFOOT
Ankle Arthrodesis
STJ Fusion
Ankle Arthrodesis
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
STJ Fusion
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
SURGICAL INTERVENTION - MIDFOOT
TNJ/CCJ Fusion
Intertarsal, TMTJ Fusion
Tendon Transfers
TNJ/CCJ Fusion
Essentially eliminates STJ motion, foot must be held in
plantigrade position
* If foot supinated, forefoot rigid and inverted, lateral
stress
Intertarsal, TMTJ Fusion
Minimal loss of function, little to no motion
* Consider lateral TMTJ – most motion, try to spare
Tendon Transfers
Phasicity
SURGICAL INTERVENTION - FOREFOOT
Keller
McKeever
Lapidus
Cotton
Keller
removal of PP base yields instability, disruption of
Windlass mechanism causing decreased WB on 1st ray and
lateral transfer
McKeever
10-15 abduction and dorsiflexion, still allows
efficient propulsion, but increased stress on IPJ
