Lecture 3: Gait Assessment Technologies
Be able to identify the phases of Contact/Propulsive and Recovery during wheelchair use.
- Hand initially strikes the push rim (initial contact) - Early push phase before 12 o'clock - After it gets past 12 o'clock it is the late push phase
What is the Push frequency (Hz) basic variable in wheelchair research?
- "Cadence" - Number of contacts/cycles per unit time - Typically 1 cycle per second (1 Hz) - Involves both the propulsion and recovery phase for one cycle
What is the Push/stroke angle (degrees) basic variable in wheelchair research?
- "Step length" - Angular distance traveled by the hand during the contact phase - Distance over which force is applied to the push rim
How many cameras for 3D motion capture systems is used for gait analysis?
- 10-12 cameras for gait analysis across larger area - System is calibrated prior to trials
How many cameras for 3D motion capture systems is used for unilateral analysis?
- 5 cameras - System is calibrated prior to trials
What are the statistics for Wheelchair use?
- 65 million people worldwide - 3.3 million in U.S. - 1.8 million > 65 y.o.
How many footfalls are allowed on a force plate?
- Has to be a single foot fall from a single foot on a force plate - If there is a partial foot or two footsteps on one plate, you cannot use that data
What are the Clinical Practice Guidelines recommendations for wheelchair users?
- Adjust rear axle as far forward as possible without comprising the stability of the user - Position the rear axle so that when the hand is placed at the top dead center position on the push rim, the angle between the upper arm and forearm is between 100-120 degrees; assuming the patient has full 180 degrees (at the elbow) Educate the patient to: - Use long, smooth strokes that limit high impact on the pushrim - Allow the hand to drift down naturally, keeping it below the push rim when not in actual contact with that part of the wheelchair - The more forward the big rear wheels are, the easier it is to propel themselves forward because the COM is closer; however, it is easier to tip backwards - The more forward the rear wheels are, the closer they are to the COM, the easier it will be for the user to propel forward and tip backwards
Describe the Propulsive Phase of Wheelchair use.
- Begins with initial contact on push rim - Ends with release of hand contact from pushrim
Describe the Recovery Phase of Wheelchair use.
- Begins with release of hand contact from pushrim - Ends with initial hand contact with push rim
What are the basic parts of a wheelchair?
- Camber: tilt of the wheel itself - 5th wheel: help with anti-tipping - Push rim: outer part of the wheel
How do you avoid "targeting" foot fall in force plate collection with subjects?
- Camouflaged plates - Subject looks straight ahead
What are some diagnoses that may require wheelchair use?
- Cerebral Palsy - Muscular Dystrophy - Spina Bifida - SCI - CVA - Amputation - ALS - TBI - MS, etc., - CVA, TBI, Elderly, Peds: may use 2 feet propulsion or 1 hand + one foot propulsion
Define the kinematics of wheelchair stroke pattern.
- Contact is characterized by: - Shoulder flexion - Elbow flexion --> elbow extension - Wrist radial deviation --> ulnar deviation - Core variable is stroke pattern (path of the hand during recovery) - Four classic stroke patterns: Semicircular, Arc, Single loop over, Double loop over
What are imbedded force plates?
- Contain piezoelectric or strain gauge transducers (this is what calculates the force that we are putting into the force plates/ground) - Pit/recessed into walkway or platform - Practical - Minimizes noise - Typically 2+ - "Stand-alone" outcome measure (get the force graphs right from the force plates)
How is data from 3D motion capture transmitted?
- Data from markers is transmitted directly to computer and given a 3-dimensional location; translated into digital motion data by software for analyzing
What are Wearable insoles?
- Detect CoP excursion - Portable - Use array of pressure sensors, strain gauges, etc. - Each sensor records an independent vertical force allowing localization of pressure (force/area of sensor) - Can be expensive - Robust? (aren't really robust; some only last 40 steps and die after) - Soft insoles that slide into the shoes; are super thin and can be cut to fit the patient's shoe size - Can be used to analyze skiers (where they are shifting their CoP)
What is the Lokomat?
- Developed in response to the difficulties of manual gait training on a treadmill - Provides data - Endurance training - Neuroplasticity (retrain walking patterns in the brain of patient's who have difficulty) - Might see it in a university based hospital
What are some factors influencing marker data (reflective markers)?
- Difference between actual anatomical landmark and marker position - Skin and soft tissue movement - Bowstringing of tendons, muscle contractions - Skin wobble during limb acceleration - Excessive adipose tissue - Try to put markers where there is little tissue over the tendon; can keep on a bony landmark as well. For example, instead of putting a marker on the front of the quad, we tend to put it at the distal TFL because there is very little tissue over the tendon
Describe the research behind instrumented treadmills with a split belt going at different speeds.
- Examined how able-bodied subjects' dynamic stability (MOS) and step symmetry responded to changes in velocity of one leg - Started with one belt moving at 0.5 mph then other belt abruptly moving at 1.5 mph for 15 minutes - Walking became highly asymmetric initially but improved towards baseline over time; larger changes occurred in fast limb step length - Stride width didn't change - High level TTAs accommodated the same way as able-bodied individuals
Describe instrumented treadmills.
- Force plate technology - Optional split belt - Optional incline - Optional pressure sensing - Customization - Data may require post processing (need to know someone who knows the software to be able to analyze the data); not immediately available - $100,000+
What are the advantages of 3D motion capture?
- Gold standard - 3D analysis
What do 3D motion capture systems measure?
- Measures magnitude and timing of individual joint motions at multiple joints simultaneously - Movement is easy to observe, hard to measure
What are the pros of a single camera recording?
- Most convenient - Least costly - From all 4 views ideal - Provides a visual history of person's gait - An example is a phone camera - Specific to the setting you're working in (videoing a person's gait)
What are the disadvantages of 3D motion capture?
- Non-portable - Costly - Can't measure force (directly); only force plates can measure force directly - Intensive user training
What is the Semi-circular (SC) propulsion style corresponded with?
- Reduced stroke frequency - More time spent on rim (increased length) - Increased efficiency
Describe Marker placement for 3D motion capture systems.
- Reflective markers - Adequate space between markers to prevent overlapping of bright areas - Other reflective materials in the room can interfere (ex: tennis shoes or certain clothing can have reflective materials) - Placement over body segments to prevent artifact - Segments= 2 markers - Complex/3D= multiple markers (might put cluster of markers) - Operator will label the markers to coordinating body locations - Attach directly to skin or very close-fitting clothing - Placed on locations that most accurately represent actions of underlying joints - Two main objectives for marker placement: (1) accurately represent motion of limb segments; (2) define centers of joint rotation for joint force calculations - No consistent guidelines for placement - Often software provides predefined anatomically based marker sets (e.g. Helen Hayes or Plug-in Gait marker systems) - Placement at the discretion of the investigator
Define kinetic stroke angle.
- Resultant force: mimics heel strike, the hand hits the rim and the force starts - Propulsion moment: may include or exclude braking moment
What propulsion style is the most common?
- Single loop over (SLOP) is the most common (45%) followed by DLOP, SC, and ARC
How do you properly track limb motion through space?
- To properly track limb motion through space a minimum of 2 camera are required - Amount of out-of-plane motion can affect perception of ROM - Sagittal plane motions could be underestimated - At least 60 Hz for walking; higher rates for faster activities (we walk at about 1 Hz/sec, so anything lower than that you would be losing data) - In the image, both knees are flexed to 60 degrees, but because of IR rotation of the tibia and foot, it gives the illusion that it is less than 60 degrees of knee flexion in the sagittal plane
What is the Seat Angle (Dump)?
- Used to help stabilize the pelvis and trunk - May make transfers more difficult - Seat is set more downwards - With a larger dump, they are usually more stable and stronger to bring themselves out of their wheelchair during a transfer (more active high-level user)
Is there a large variance in cost for 3D motion capture systems?
- Yes, large variance in cost of systems - Usually at places such as universities
What are some intervention opportunities for wheelchair use?
1) User - Weight loss (Want them to be at a healthy weight for wheel chair use (especially for SCI patients); must be able to lift legs out of chair to transfer; lighter they are, the easier it is for them to get in and out of the wheelchair) - Propulsion technique (stroke pattern) 2) Wheelchair - Light, ultralight - Wheel size (front and rear) - Tire type, tread, pressure - Center of gravity; position of seat wheel to acromion 3) User-wheelchair interface - Seat height/shoulder-axle distance (vertical distance between shoulder and axle)
What are the Basic Variables in Wheelchair Research?
1. External power out (watts) 2. Velocity (m/s) 3. Push frequency (Hz) 4. Push angle (degrees) 5. Resultant force (N) 6. Propulsion moment (Nm) 7. Push power output (watts) 1 &2 provide context for 3-7
What effects External PO?
Anything that changes the resistance to rolling - Surface effect (rolling over carpet, dirt, or a regular floor) - Weight effect (wheelchair weight, user's weight) - Tire pressure (flatter tire has more resistance and absorbs energy and shows in the velocity that the person can push) - Rear wheel position (further the wheel is set from COM they're not going to be able to get the propulsion as well as if it were set forward) - Seat position (more dump decrease rolling resistance) - Accessories (air cushion, foldable, shocks all can absorb energy)
Where does the COM move to in sitting?
Between lower trunk and abdomen
What is the breaking moment?
Breaking moment when we get the hand on the wheel, as we come off the wheel there is more force and a propulsive moment at the end of contact with the wheel (circled area on the image)
How can you get appropriate foot fall on each force plate?
Can stagger the participant's start position to get the appropriate foot fall on each force plate
Describe Single loop over stroke pattern.
Contact the wheel then comes back on top and then contacts again
Describe Semicircular stroke pattern.
Contacts the wheel in the back, lets go, then swoops back down coming below the rim of the wheel and recaptures the wheel behind the body again
Why study wheelchair propulsion?
Demand: - Musculoskeletal - Metabolic Upper limb pain/injury: - High rates in shoulder and wrist Identify clinical interventions that: - Minimize demands (on wheelchair users) - Decrease stress (stress on joints and musculoskeletal system) - Increase mobility and delay/prevent injury
If we don't see the valley on the force graph, what could be happening at the knee?
Don't have full knee extension so their COM can't accelerate up high enough
Describe Double loop over stroke pattern.
Figure 8; Contact the wheel and then comes up and below the wheel
What are the gait parameters provided for Instrumented Walkways?
Gait parameters provided: - Gait cycle time - DLS time - Stance and swing time/% - Step and stride length and time - Velocity - Cadence - CoP - CoMe (estimated COM excursion); validate CoMe by using with a 3-D camera system and compare the measures - Etc.
What process has been applied to the EMG to make it look like the image?
Linear envelope detection: take the negative and makes them positive, take the absolute value of the signals, filter them, then apply the linear envelope detection
Most people with SCI are ______ and are between the ages of ________ y/o.
Men; 16-30
In 3D motion capture systems, in what plane do most joint motions occur in?
Most joint motions are in sagittal plane - Smaller arcs in frontal and coronal planes - Deviations from sagittal plane may present with greater clinical significance in pathological gait
Are SCI patients the most common wheelchair user?
Most w/c research is performed on adults with SCI, however they are not the most common user
What are portable force plates used for?
Portable force plates are more for static balance (usually the one square)
What is the Push frequency-stroke angle relationship?
Preference is for a longer stroke vs. increased frequency - Less upper limb stress Someone may take a smaller angle due to - Not using their full ROM - Fatigue and weakness - Lack physiologic capacity to maintain longer stroke
What are instrumented walkways? What are the pros?
Pressure sensing mats - Portable - Fairly quick set up - Provide temporal-spatial data (stride/step length, stride/step width, stance time, etc.); don't get joint angles or joint moments - Can provide pressure data, force?? (some can provide pressure and force data but those are the more customized matts. Can get M curves from these as well) - More commonly seen in PT clinics because they are not as expensive
Describe Arc stroke pattern.
Pushes the wheel and comes back over the top of the wheel
Define kinematic stroke angle.
Reflective marker placed on hand, decide when it contacts rim
What captures 3D motion capture?
Reflective markers; the more reflective markers the more ability to capture different moving parts
Which stroke pattern is recommended for optimal shoulder health?
Semicircular
What is the External power out (watts) basic variable in wheelchair research?
Sum of external forces that must be overcome to achieve or maintain a given speed
What muscle is usually examined often with wheelchair use?
Supraspinatus
What is the Computer Assisted Rehabilitation ENvironment (CAREN)?
Virtual reality stimulator (CAREN): motion capture, instrumented treadmill (can rotate in different direction and tip up and down); use of sensors as well
What are Inertial Measurement Units (IMU)?
What is an IMU? A small device typically containing two or three sensors that measure: - Acceleration (accelerometer): A-P, M-L, vertical directions - Angular rotation (gyroscope): data is "angular velocity"; rate at which an object is changing its angle in time (rate of rotation in space; can see how certain segments move in space); measured in Rad/sec - Compass heading (magnetometer); gives us directions compared to due north Provides "portable" gait lab: - Relatively low cost - Place anywhere on body Maybe an inch or so in diameter and height IMUs are good if not almost better than camera motion capture systems
