gait

definition

·      repeated performance of sequence of movements by lower limbs that achieves

·      forward progression

·      stance stability

·      energy conservation

Normal gait

Gait cycle

·      consists of

·      stance (60%)

·      swing (40%)

·      during stance

·      1st 10% and last 10% are double stance

·      middle 40% are single stance (ie. other leg in swing)

·      with increase in speed, stance phase decreases

·      only 30% in running

Functional elements
Progression

·      due to two factors

1.   forward fall in terminal stance

·      body weight is anterior to ankle joint

·      starts when ankle dorsiflexes beyond neutral

·      accelerates with heel rise

2.   contralateral swing

·      starts with onset of single limb support

·      momentum preserved at heel strike of next stance phase

·      heel, ankle and forefoot sequentially provide rocker

·      allow body to advance over foot

Standing stability

·      body divided into 2 units

·      passenger unit

·      locomotor unit

Passenger unit

·      head, arms and trunk

·      carried rather than contributing to walking

·      little posture change occurs

·      muscle action in spine serves only to maintain neutral vertebral alignment

·      arm swing is passive reaction to momentum and is not required

Locomotor unit

·      little passive stability

·      stability achieved by selective muscle control

Energy conservation

·      reduction of muscular effort required achieved by

Optimum use of momentum

·      occurs at person’s natural gait velocity

·      more energy used at both slower and faster pace

Minimisation of body displacement from line of progression

·      achieved by co-ordinating pelvic, hip, knee and ankle motion to keep limb length fairly constant throughout stance

Joint motion
Flexion-extension

Ankle

·      two phases of plantar and dorsi flexion

·      at onset of stance ankle at 90o

·      as heel loaded foot drops into 10o plantarflexion

·      as body weight moves over ankle, reverses and reaches 10o dorsiflexion

·      then plantarflexion starts again

·      reaches 20o by end of stance phase

·      with toe off ankle raised to plantigrade

·      maintained throughout swing

Knee

·      two phases of flexion and extension

·      at onset of stance is extended (flexed 5o)

·      flexes to 15o and extends again (to 5o flexion)

·      begins to flex with onset of double stance phase

·      flexion continues through swing phase

·      reaches maximum of 70o

·      then extends again

Hip

·      single phase of flexion and extension

·      at start of stance phase, hip flexed 30o

·      progressive extension throughout stance

·      reaches 10o extension at start of double stance

·      flexion begins at start of swing phase

·      reaches 30o and remains until stance phase

Rotation

·      entire lower segment rotates during gait

·      at heel strike, foot slightly internally rotated

·      increases progressively until midstance (opposite toe off)

·      external rotation begins and continues until toe off

Subtalar joint

·      at heel strike, heel everts at subtalar joint because of body weight

·      result is internal rotation of tibia

·      as opposite leg swings forward, pelvis externally rotates

·      result is that femur and tibia externally rotate

·      translated to inversion of heel at subtalar joint

·      inversion continues until toe off

Phases
Stance

Heel strike

·      heel strikes at 25o dorsiflexion

·      ankle plantarflexed few degrees

·      knee flexed few degrees

·      hip flexed 30o

Loading response

·      period of dual stance

Ankle

·      foot drops into 10o plantarflexion as body weight moves over foot

·      plantarflexion controlled by pretibial muscles

Knee

·      heel rocker causes knee flexion of 15o

·      flexion controlled by quadriceps

Hip

·      hip extends

Midstance

·      other foot lifted for swing

·      body advances over stationary foot

Ankle

·      progresses from 5o plantarflexion to 5o dorsiflexion

·      dorsiflexion controlled by soleus

Knee

·      extends as femur advances over tibia

Hip

·      continues to extend as body progresses

·      at start of single stance, pelvis drops

·      halted at 4o and then overcorrected by hip abductor contraction

Terminal stance

·      swinging leg passes stance leg

·      body falls forward over area of support

·      limb is like spoke of wheel

Ankle

·      dorsiflexion becomes maximal to 10o

Foot

·      heel rises

·      hallux MTP jt flexes 20o

Knee

·      passively extends to few degrees flexion

Hip

·      passively extends to 10o extension

Preswing

·      other foot in contact with ground (terminal dual stance)

·      weight transferred to the other limb

Knee

·      rapid passive flexion to 45o

Hip

·      flexes from extension to neutral

Ankle and foot

·      rapid ankle plantarflexion to 20o

Rockers

·      1st rocker is heel

·      2nd rocker is ankle

·      3rd rocker is forefoot

Swing

Initial swing

·      recovery from trailing posture

Hip

·      rapidly flexes to 20o

·      iliacus contracts

Knee

·      flexes to 70o

·      required for toe clearance

Ankle

·      dorsiflexes to 10o plantarflexion

Midswing

·      limb advancement

Hip

·      maximum flexion to 30o

Knee

·      extends passively to 30o

·      means tibia is vertical

Ankle

·      dorsiflexes to neutral

Terminal swing

·      limb prepared for stance

Hip

·      30o flexion maintained

Knee

·      extends to neutral

Ankle

·      neutral dorsiflexion

Abnormal gait

contractures
Plantarflexion contracture

·      to place body weight over ankle and achieve stability, substitutive postures required

·      hyperextension of knee

·      hip flexion and forward lean of trunk (with cane to support body weight if hip extensors weak)

·      effects on gait

·      flat foot or toe strike initial contact

·      as body weight dropped onto foot, tibia driven posteriorly

Weakness of ankle dorsiflexors

·      role of ankle dorsiflexors is

·      dorsiflex ankle during swing phase for toe clearance

·      control plantarflexion during loading response

·      weakness causes dropfoot

·      foot drops into plantarflexion during midswing

·      requires increased hip and knee flexion for toe clearance

·      if sufficient dorsiflexion cannot be achieved, toe clearance possible by circumducting the entire limb

·      initial contact may be

1.   low heel strike

2.   toe strike

·      with increased knee flexion

3.   normal heel strike but foot slap

·      enough strength to support foot weight

·      not enough to control forefoot drop

Weakness of ankle plantarflexors

·      role of ankle plantarflexors is

·      control forward motion of tibia over foot

·      weakness causes excessive tibial advancement

·      leads to

·      excessive dorsiflexion in midstance

·      lack of heel rise during terminal stance

·      result is persistently flexed knee

·      substitution is avoidance of knee flexion during loading response

·      heel strike minimised

·      knee locked prematurely

Weak quadriceps

·      role of quadriceps is to

·      stabilise knee during heel strike

·      control flexion during loading response

·      causes total flexion collapse of knee

·      if mild, avoided by avoiding normal loading response knee flexion

·      low heel strike

·      restrained tibial advancement

·      if severe, avoided by leaning body forward so weight anterior to knee joint

·      result is

·      straight knee

·      excessive plantarflexion, hip flexion, forward trunk

Weak hip abductors

·      role of hip abductors is

·      elevate contralateral pelvis during stance phase

·      weakness causes contralateral pelvic drop at onset of midstance

·      trunk falls to same side if not restrained

·      preservation by trunk lean over stance limb before swing

·      called Trendlenburg lurch

·      if iliotibial band tight, excessive pelvic drop avoided

·      called Trendelenburg gait

Biomechanics of running

·      running is natural extension of walking

·      critical velocity at which walking changes to running for normal adults is 2.5 m/s

·      function of leg length

·      running differentiated from walking by percentage of stance (ground contact) in gait cycle

·       in walking, always contact in ground

·      during single stride, there are two periods of double and single support

·      in running, there are times when there is no contact with the ground

·      these times called double float

stride parameters

·      in walking, stance:swing is 60:40

·      in running, stance:swing is 45:55

Stance phase

·      in walking, stance phase divided into five periods

·      initial contact, loading response, midstance, terminal stance and preswing

·      in running, stance phase divided into two phases

·      absorption and propulsion

·      during absorption, knee and ankle joints of supporting legs flex

·      during propulsion, all joints of supporting limb are extending

Swing phase

·      in walking, divided into three phases

·      initial swing, mid-swing and terminal swing

·      in running, divided into two phases

·      initial swing and terminal swing

·      initial swing starts at initiation of first double-float

·      terminal swing terminates at end of second double-float

kinematics

·      ankle is major power generator

·      hip is secondary power generator

·      knee is primary power absorber