Pathologic Gait & Orthotic Management: Ankle Foot Orthoses Flashcards
What are the 4 basic functions of normal gait
- Weight bearing stability
- Stance limb progression
- Shock absorption
- Energy conservation
What happens to alignment when the knee is slightly flexed
- Body weight vector falls slightly behind knee, anterior to hip, & through the ankle
- Now requiring active contraction of hip extensors, knee extensors, & ankle plantar flexers to stay upright
Describe normal gait according to Elaine Owen
- The shank is not vertical at midstance
- There is no place in the gait cycle when both the shank & thigh are vertical
Describe causes of the shank being vertical to the ankle during midstance
- 10-12º inclined position of the shank places the knee joint center over the center of the foot during mid-stance
- Creates a stable distal support mechanism
- Angular velocity of the thigh increases at the time that the angular velocity of the shank decreases
- Stability in stance is one of the 5 attributes of normal walking & is vital in MST
What dictates proximal segment kinematics & GRF (ground reaction force) alignment
- Shank kinematics
What are the different rockers during stance
- Heel: initial contact and loading response
- Ankle: mid stance
- Forefoot: terminal stance
- Toe: terminal stance
What are the critical events during stance
- Loading: heel rocker forward progression of body onto foot, shock absorption
- Single limb stance: tibial stability, ankle rocker, progression of passenger unit in front of foot over stable tibia
- Critical players in stance: tibia & ankle
What are the critical tasks during stance at the ankle
- Stance: to provide a stable tibia over which the passenger unit can progress
- Muscle activity: 2 groups of muscles act at the ankle during stance -> pretibials during loading & plantar flexors during SLS
What are the critical tasks during stance at the knee
- Stance: secondary shock absorber during loading as we transfer weight onto the stance limb
- Muscle activity: after initial activity during loading, quads are quiet during stance
What are the critical tasks during stance at the hip
- During loading: provide stability for the passenger until body vector aligns for stability (mid stance)
- Muscle activity: hip extensors active during loading; after loading (given proper alignment), hip extensors are quiet, hip ABD active
What are the critical events of the swing phases
- Initial swing: knee flexion to clear a slightly PF foot with thigh flexion to advance limb forward
- Mid swing: hip flexion continues, with knee starting to extend
- Terminal swing: knee extension creates step length & prepares limb for heel contact
- Knee & hip are main players
Common characteristics of hemiplegic gait
- Poor control of flexor muscles during swing
- Spasticity of extensor muscles
- Equinovarus deformity
- Abnormal initial contact onto lateral edge of foot/forefoot
- Stiff knee that hyperextends
- Contralateral step meets the position of the paralyzed limb instead of advancing normally
- Absent rhythmic reciprocal swing of arm with stance phase
- Pt may drag toe of the affected leg during swing or adopt abnormal movements to clear limb
Characteristics of a slow extender walker
- AKA circumduction
- ~11% normal walking speed
- Quads too weak to support the knee during stance
- Glute Max retracts femur into knee hyperextension for stance limb support
- Ankle OF spasticity
- Hip hike & circumduction occur for foot clearance
- Usually require an assistive device (AD)
Characteristics of a moderate walker
- ~21% normal walking speed
- Weakness of PF
- Weakness in hip extensors (glute max) & knee extensors (quads)
- Greater knee flexion in mid stance
What are we trying to improve in post-stroke gait
- Biomechanics: consider long term viability of gait pattern (risk of overuse injury)
- Energetics (efficiency vs energy cost)
- Endurance
- Speed
- Independence
- Safety
- Level of Physical Activity
What are the main functions of an AFO for foot drop
- Provide moderate resistance during loading response to prevent foot drop: AFOs assist eccentric contraction of the DF during loading response
- Allow free dF in stance
- Provide large resistance in swing to inhibit foot drop
- Assist push-off function by providing PF moment
What are the Rancho ROADMAP pre-requisites for AFOs
- Sufficient ROM in LE joints to align segments
- Ability (including cognition) & desire to meet ambulation goals
- Adequate cardiovascular endurance & adequate UE & LE strength for the intended activity
- Sufficient strength to advance the limb
What are the effects of AFOs on motion control
- Foot relative to tibia
- Tibia relative to foot
- Ankle joint: achieved by stopping, assisting, or resisting various ankle joint motions
- Subtalar joint
What motions does an AFO influence
- Knee & hip joints
What AFOs have a fixed ankle position
- Rigid polypropelyne AFO
- Metal AFO with double adjustable ankle joint (DAAJ) & poly footplate, locked
- Metal AFO with DAAJ, locked
Describe a double action ankle joint
- Anterior compartment: a pin is utilized to control tibial advancement (DF stop0 in stance for a knee extension moment at heel off
- Posterior compartment: either a spring or pin is effective to aid in foot clearance during swing; pin limits PF (stop) and spring limits PF through a DF assist
Describe the mechanics of a solid ankle AFO (SAFO)
- PF stop ad DF stop
- Influences knee stability
- Triplanar control is based on trim lines (if plastic)
Indications for a SAFO
- Weakness of dorsiflexors and plantarflexors
- Quadriceps weakness
- Excessive ankle/foot pronation
- Helps restore normal stance phase shank and knee kinematics
Contraindications for a SAFO
- Isolated swing phase deficits without stance phase deficits
- Isolated dorsiflexor weakness
- If there is sufficient plantarflexor length AND strength to allow free dorsiflexion and still achieve maximum knee extension at mid-stance and a stiff ankle in late stance
How will a SAFO impact progression through stance phase of gait
- Biomechanically interferes with transitions through all 3 rockers of gait in stance phase bc of the fixed ankle position inherent in the design
- Prevents controlled lowering of the foot that usually occurs in the ankle/1st rocker
What AFOs have a dorsiflexion stop
- Polyarticulating AFO with DF stop
- Metal AFO with DAAJ & poly footplate, DF stop
- Metal AFO with DAAJ, DF stop
Describe a DF stop/free PF
- Use of an articulating (joint) & a “stop” to permit only one of the sagittal plane motions
- Facilitates knee extension & stiff ankle in late stance
Indications for a limited motion articulated ankle DF stop/free pf
- Weakness of the PF
- Weakness of the quads
Contraindications for a limited motion articulated ankle DF stop/free pf
- DF weakness
- Knee hyperextension
Which rocker of gait would be most affected by an AFO with DF stop
- 3rd rocker
How could the AFO/footwear combination be modified to help normalize 3rd rocker?
- Rocker sole
- Rounded toe rocker vs point loading toe rocker
What AFOs have a dorsiflexion assist (primarily for swing limb clearance)
- Leaf spring AFO
- Polyarticulating AFO with DF assist
- Metal AFO with DAAJ & poly footplate, DF assist
- Metal AFO with DAAJ, DF assist (spring in posterior channel)
Describe the mechanics of a DF assist AFO
- Assists with toe clearance during swing
- Allows for controlled foot flat from initial contact to loading response
What are the indications and contraindications of a DF assist AFO
- Indications: DF weakness
- Contraindications: abnormal shank & knee kinematics; moderate to severe tone/spasticity
Describe the mechanics of a posterior leaf spring DF assist AFO
- Least bulky
- Provides some dF assist but limits PF
Indications & contraindications for a posterior leaf spring DF assist AFO
- Indications: DF weakness with minimal need to control stance phase kinematics; Primarily facilitate swing limb clearance
- Contraindications: need to control stance kinematics, medial/lateral ankle instability, knee instability, & moderate to severe tone/spasticity
What AFOs have a plantar flexion stop (helps with swing limb clearance & decreasing knee hyperextension in early stance)
- Polyarticulating AFO with PF stop
- Metal AFO with DAAJ & poly footplate, Pf stop
- Metal AFO with DAAJ, PF stop
Describe the mechanics of a PF stop AFO
- Usually a limited. motion articulated ankle joint allowing ankle DF
- Facilitates knee flexion in early stance
Indications for a PF stop AFO
- DF weakness
- Knee hyperextension in early stance (reclined shank)
Contraindications for a PF stop AFO
- Weak quads
- Gastroc spasticity
- Insufficient PF length & strength to allow free DF and achieve maximum knee extension at mid stance & stiff ankle in late stance
Is there anything that we could do to modify the AFO footwear combination to restore 1st rocker with a PF stop
- Cushion heel
- Rocker heel
Describe the mechanics of a ground reaction AFO (GRAFO)
- Rigid section over anterior proximal tibia provides an external extension moment at the knee
- Provides additional knee stability in late stance phase
- Often an attempt to avoid going towards long leg bracing
Indications for a GRAFO
- DF weakness
- PF weakness
- Quad weakness
Contraindications for a GRAFO
- If “less” control will suffice
- Knee hyperextension
- For prefabricated designs: any frontal/transverse plane ankle instability and/or if ankle angle other than 90º is required
What happens if your AFO is too stiff
- AFO will resist ankle PF at initial contact phase of gait & cause abrupt forward rotation of the tibia at initial contact causing the knee to be pushed forward, thereby increasing knee flexion at early stance & inducing gait instability
What happens if your AFO is less stiff
- PF resistive moment will not be sufficient to prevent the foot slapping of keep clearance during swing
CPG for use of AFO and FES post stroke
- An AFO customized to the individual is BEST
- An AFO may be better for slower walkers, FES for faster walkers
- More meaningful improvements observed when AFO/FES combined with skilled PT
- Consistent reassessments needed to meet changing needs
- AFO provision early in recovery enhances participation & leads to faster progress towards goals
- Wearing an AFO does NOT hinder muscle activation
- FES can improve muscle activation through a therapeutic effect
- No evidence that AFO or FES can decrease PF spasticity
- AFO that allows PF motion may lead to greater effects on gait speed
What should you consider when thinking about using an AFO on a patient
- Applying an AFO to someone who is dragging their foot will not necessarily improve limb clearance
- The primary benefit of the foot being at neutral is positioning the foot for heel contact in loading
Common deviations that go together during single limb stance (SLS)
- Excessive DF: increased knee flexion & hip flexion
- Excessive PF: knee hyperextension or extension thrust, forward lean at trunk, & backward rotation of pelvis
What is the mostly likely cause of excessive ankle DF in stance
- Weakness of plantar flexors not quads
- Most noticeable deviation to naked eye is walking in knee flexion
What is the solution to excessive ankle DF in stance
- AFO with a DF stop will prevent tibia from collapsing into DF, hence controlling the tibia & the alignment further up the chain
- The more you PF the AFO the more it will straighten the knee
Potential causes of extension thrust or hyperextension in loading response
- Forefoot contact (PF tone or contracture)
- Weak quads
- Quad tone
- Absent/impaired proprioception at knee 7 ankle
- Intentional to maintain limb stability
Potential causes of extension thrust or hyperextension in single limb support (SLS)
- Excessive PF: either due to lack of adequate DF ROM or PF tone
- Intentional to maintain limb stability in the absence of quads (polio)
What is the solution to excessive ankle PF in stance
- Dorsiflexing an AFO you can cause a plantar flexion stop, slowing the extensor thrust
- Can only be achieved with a PF stop AFO, either rigid or open DF
Possible causes of a step to gait (decreased stance limb stability) and solution
- cause: short step is due to the stance instability on the opposite side or not enough DF ROM
- Solution: AFO with either DF stop or locked ankle (fix the stance instability then step length increases)
Possible causes of increased double limb support time
- Patient has extremely shortened swing
- Instability on one or both sides
- Not enough DF ROM & instability to progress HAT (head, arms, & trunk) over the foot
Solution for increased double limb support time
- Provide tibial stability with DF stop
- DF/PF stop rigid AFO
- Compensate for lack of DF ROM
