Lecture 15: Wearable Walking Assist Systems for Foot Drop Flashcards
foot drop
* what muscles are paralyzed, overactive, and weak?
* what is the movement pattern observed during gait?
* why is it problematic?
* what atrophy may be seen?
one side of body is paralyzed due to hemiplegia.
Flexors are paralyzed in one leg, extensors may be overactive (spastic and contractures). weak hip and knee flexors,
leg will be lifted, swung forward and in an arc. the individual will also lean on the uninjured side. this pattern is because the foot cant dorsiflex
unreliable, slow, requires a lot of energy
Shin muscles may atrophy due to disuse
What diseases is foot drop a consequence of?
stroke, tbi, ms, cp
Treatment options for foot drop
- ankle foot orthrosis (AFO)
- neuromuscular stimulation (therapeutic and function)
What are the pros and cons of AFOs
pros
- allows toe clearance for walking
- non invasive
- inexpensive
cons
- uncomfortable, can be heavy, hot
- promotes muscle disuse atrophy
- metabolic cost is still high
- not always available
- requires donning and doffing
- cosmetically objectionable
- can cause pressure sores
- can cause peroneal nerve palsy (compression)
- no therapeutic effect
What are the objectives of functional electrical stimulation for foot drop?
orthotic effects (benefits that occur during FES)
- stimulate dorsiflexors to elevate foot
- synergistic activation of weak hip and knee flexor
therapeutic effects (benefits that persist without stimulation)
- improvement in capacity of muscle and circuitry leading to increased ability to walk even without the FES
- increased force and endurance of disused muscle
- reduced extensor spasticity
person can still walk, without noticing the battery died. because there has been some improvement in the capacity of muscle and circuitry to drive walking
What are the objectives of therapeutic electrical stimulation for foot drop?
- Reverses disuse atrophy in paralyzed muscles
- Helps strengthen muscles, bones, circulation
Describe an external FES for foot drop
It is an event triggered state machine that monitors for heel strike and toe lift.
The foot switch within patient’s shoe (often in the heel cushion) senses and relays Heel Strike and Toe lift events to control unit. Control unit monitors sensed information and provides electrical stimulation when detecting gait events. This makes the system a closed loop. The control switch is set to autonomic cyclic stimulation
Surface stimulation electrodes are placed on the skin distal to the knee, near where the peroneal nerve courses. Battery powered external unit is connected to the foot switch and electrodes and stimulates the peroneal nerve to cause dorsiflexion of the ankle during swing phase.
- The stimulation amplitude is slowly increased until the foot is lifted.
closed loop because it has sensory input (sensing stance phase) that modulates activity.
Describe the importance of proper electrode positioning for external FES system?
Describe the issues with the following and how it can be corrected by repositioning the electrodes: the foot turns in and out during walking
It is often necessary to adjust the positioning of electrodes until it causes a straight lift of the foot and only the heel touches down first.
Incorrect pulling of the ankle joint may result in swelling and pain.
Foot turning in: causes unsteady gait as only the outer side of the foot will touch the ground during walking. Must move the upper electrode more lateral to the side of the leg.
Foot turning out: unsteady gait and ankle joint strain as only the inner side of the foot will touch the ground during walking. move the upper electrode more medial on the lower limb.
must balance the recruitment of peroneal branches so that inverter and evertor muscle is balanced.
Why must another heel cushion be placed in the shoe of the uninvolved side?
Another heel cushion (without a heel switch) is placed in the other shoe to prevent uneven back strain
In an external FES with felt cushion electrodes, what are the specific operating instructions.
moisten electrodes with saline solution to conduct electricity.
problematic if it dries. now they’re replaced with metal electrodes
What are you stimulating in an FES?
not clear what you’re stimulating, but most likely what you’re stimulating is a nerve, in its course to the muscle, not the muscle itself
that is why you should place the electrodes so that it overlies and stimulates the nerve.
What are the given instructions for electrode application
- Clean leg with water
- With the involved leg straight, find the head of the fibula
- place the first electrode just under the head of the fibula (this overlies where peroneal branches into common and deep branches - helps with balancing activation of inverters and evertors)
- place second electrode over tibialis anterior
Why did a study show FES compliance decrease after one year? Why did some patients stop before 18 weeks had elapsed?
some of the patients could have died or could have gotten worse (another stroke –> limiting walking completely) to the point where they can’t walk even with FES
- 3 lost to follow up
- 2 unable to find electrode positions
- 2 non-related medical problems
- 1 cognitive problems
- 1 chose not to use the device
What are the main reasons patients choose to continue to external FES system
- Reduced effort of walking
- Increased confidence when walking
- Reduced trips and falls
What is the orthotic effect and carry over effect (training) of external FES systems found in the Odstock trial. Explain its significance as well.
total orthotic effect: changes during walking
* 27% increase in speed in walking (normal pace is 1.2 m/s. you need .70m/s speed to cross the street before the light changes.)
* physiological cost index: efficiency. 31% decrease (more efficient)
carry over effect: capacity to walk without the system (therapeutic effect)
* 14% increase in speed
* 19% decrease in PCI
better than AFO because there is no therapeutic affect with AFO
Describe the external FES system used for someone with bilateral foot drop
Use a two channel stimulator system to independently activate 2 independent muscle groups. Only 1 foot switch is needed.
When weight is taken off foot switch (toe rise/heel rise - during end of stance phase), channel 1 is activated and common peroneal nerve 1 is stimulated. This causes ankle dorsiflexion during the swing phase of leg 1. Stimulation amplitude slowly rises over 100-200ms until it plateaus. Stimulation amplitude decreases gradually upon heel strike of leg 1. Stimulation is decreased gradually as opposed to ceased immediately upon heel strike to slow the foot in making full contact with the ground. Otherwise, the foot would slap onto the ground harshly. This also causes coactivation of ankle flexors and extensors during weight transfer between legs, increasing ankle joint stiffness and thus balance during transfer.
Theres a delay between stimulation of common peroneal nerve of other leg, allowing time for weight transfer to first leg for slow walkers
Describe the external FES system used for someone with foot drop and weak hip extension
Use a two channel stimulator system to independently activate 2 independent muscle groups. Only 1 foot switch is needed.
Foot switch will sense the heel-rise / toe rise (end of stance phase) and signal for the stimulation of common peroneal nerve 1 (channel 1). This causes ankle dorsiflexion during the swing phase of the leg. Stimulation amplitude slowly rises over 100-200ms until it plateaus. Stimulation amplitude decreases gradually upon heel strike of the same leg. Stimulation is decreased gradually as opposed to ceased immediately upon heel strike to slow the foot in making full contact with the ground. Otherwise, the foot would slap onto the ground harshly. This also causes coactivation of ankle flexors and extensors during weight transfer between legs, increasing ankle joint stiffness and thus balance during transfer.
channel 2: To extend the hip, gluteal muscles are stimulated through the stance phase (heel strike to toe off).
To increase abduction, one electrode can also be placed over the gluteus medialis.
Describe the external FES system used for someone with foot drop and knee hyperextension during stance phase
Use a two channel stimulator system to independently activate 2 independent muscle groups. Only 1 foot switch is needed.
Foot switch will sense the heel-rise / toe rise (end of stance phase) and signal for the stimulation of common peroneal nerve 1. This causes ankle dorsiflexion during the swing phase of the leg. Stimulation amplitude slowly rises over 100-200ms until it plateaus. Stimulation amplitude decreases gradually upon heel strike of the same leg. Stimulation is decreased gradually as opposed to ceased immediately upon heel strike to slow the foot in making full contact with the ground. Otherwise, the foot would slap onto the ground harshly. This also causes coactivation of ankle flexors and extensors during weight transfer between legs, increasing ankle joint stiffness and thus balance during transfer.
To enable greater knee flexion and inhibit quadricep tone during midswing. Hamstring is stimulated after delay following heel strike. Stimulation amplitude slowly rises over 100-200ms until it peaks and plateaus during heel rise/toe rise. Stimulation amplitude decreases after heel rise and ceases at heel strike.
To instead discourage knee hyperextension at heel strike, the hamstrings can be stimulated at or just before heel strike.
Describe the external FES system used for someone with foot drop and weak quadriceps
Use a two channel stimulator system to independently activate 2 independent muscle groups. Only 1 foot switch is needed.
Foot switch will sense the heel-rise / toe rise (end of stance phase) and signal for the stimulation of common peroneal nerve 1. This causes ankle dorsiflexion during the swing phase of the leg. Stimulation amplitude slowly rises over 100-200ms until it plateaus. Stimulation amplitude decreases gradually upon heel strike of the same leg. Stimulation is decreased gradually as opposed to ceased immediately upon heel strike to slow the foot in making full contact with the ground. Otherwise, the foot would slap onto the ground harshly. This also causes coactivation of ankle flexors and extensors during weight transfer between legs, increasing ankle joint stiffness and thus balance during transfer.
The quadriceps (part of the antigravity muscles) are stimulated throughout the stance phase to allow weight bearing.
Describe the external FES system used for someone with foot drop and a weak calf
Use a two channel stimulator system to independently activate 2 independent muscle groups. Two foot switches are used: under the heel and under the 1st metatarsal head (detects toe rise and strike).
Foot switch will sense the heel-rise / toe rise (end of stance phase) and signal for the stimulation of common peroneal nerve 1. This causes ankle dorsiflexion during the swing phase of the leg. Stimulation amplitude slowly rises over 100-200ms until it plateaus. Stimulation amplitude decreases gradually upon heel strike of the same leg. Stimulation is decreased gradually as opposed to ceased immediately upon heel strike to slow the foot in making full contact with the ground. Otherwise, the foot would slap onto the ground harshly. This also causes coactivation of ankle flexors and extensors during weight transfer between legs, increasing ankle joint stiffness and thus balance during transfer.
Calf stimulation starts a short delay after flat foot during stance phase and continues until the toes leave
the ground. The stimulation of the calf promotes weightbearing and provides push off at the end of the stance phase. Ankle dorsiflexion begins at toe off and ends at heel strike after an extension.
What is Trendelenburg gait?
Why is it problematic?
Describe the external FES system used for someone with Trendelenburg gait
- Weak hip extension and abduction affects both sides and causes hips to drop when weight is taken through it.
- causes instability and sway during gait.
- 2 channel stimulator system to independently activate left and right gluteal muscles. 2 heel switches are used.
- When weight is on a switch (stance phase), the gluteal muscle on the same side is activated.
Describe the external FES system used for someone with foot drop and weak elbow extension. Why would we want to correct for weak elbow extension?
If the arms don’t extend during opposite leg’s stance phase, this will decrease balance and momentum generated. With a decrease in momentum, walking will be more laborous and less efficient.
Thus, the triceps brachii is stimulated when the same leg is in the swing phase.
How did the WalkAide differ from the other external FES systems at the time of production?
pros: no wire or foot switch, simpler to use to wear and safer with no wires
- has a tilt sensor inside the control box
The stimulation electrodes were attached under the strap of the control unit. A tilt sensor measures angle of the tibia in relation to gravity and starts stimulation.
One-piece design allows one-hand application, making the device accessible to incomplete SCI, stroke, and MS patients
The electrodes were placed inside the strap by the therapist after determining where it should go for each patient. Simplifies putting things on as patient doesn’t have to apply the electrodes in specific positions every time they wear the device.
Benefits of walkaide
increased speed
increased symmetry
decreased effort
