Quantification of Forces Associated with Episodic Full-Body Extensor Spasticity in Children

D. Brown, MS, PT, ATP; A. Zeltwanger, BS; G. Bertocci, PE, PhD.; R. Burdett, PhD., PT; S. Fitzgerald, PhD.; E. Trefler, MEd., OTR, FAOTA, ATP

Slide 1
Quantification of Forces Associated with Episodic Full-Body Extensor Spasticity in Children

D. Brown, MS, PT, ATP; A. Zeltwanger, BS; G. Bertocci, PE, PhD.; R. Burdett, PhD., PT; S. Fitzgerald, PhD.; E. Trefler, MEd., OTR, FAOTA, ATP

Slide 2
Background

Match of device with characteristics of individual and environment

Atypical muscle tone

Altered muscle activation pattern

Poor force control

Delays in initiation

Inappropriate termination of movement

When it is determined that an individual will benefit from the use of assistive technology,the characteristics of the device must be matched to those of the individual and the environments in which it will be used. The human-technology interface of individuals whose muscle tone fluctuates in extreme ranges can be a difficult match to achieve. Their poor control of force produced during muscle contraction effects the timing, sequencing and coordination of muscle activation and de-activation which results in dyskinetic movement patterns. Characteristics associated with dyskinetic movement patterns include movements in extreme ranges with fluctuation in muscle tone; difficulty sustaining movement; inappropriate termination of movement and decreased co-activation. Bodily injury has been attributed to the action-reaction forces associated with inappropriate termination of movement. Bruising of the pelvis and abdominal area have been reported from individuals thrusting into and

Slide 3
Background
Consequences of Poor Match

Bodily injury

Equipment breakage

Loss of postural alignment

Physical discomfort

Slide 4
Objectives

To investigate the force generated in episodic increases in extensor spasticity

Specify properties of resistive elements needed to modify a static seating system into a dynamic system

Slide 5
Research Questions

What are the force characteristics associated with episodic full-body extension?

How are these characteristics affected by the introduction of controlled movement?

Slide 6
Methodology

Determine force characteristics associated with intermittent extension episodes

Quantify forces

Design dynamic prototype Test Wheelchair

Define, model, design, fabricate and validate prototype Test Wheelchair

Slide 7
Force Quantification
Subject Demographics

N= 18

10 males, 8 females

Age ranges: 5 yrs - 16 yrs

(mean 10.5 ± 2.6 yrs)

Primary Dx: CP (15), Lesch-Nyhan Syndrome (2), Glutaric Aciduria (1)

Slide 8
Force Quantification
Protocol

Weigh subject

Chair measurements

Seated anthropometric measurements

Use FSA Mat to measure seat back force for 30 minute data collection period

Stimulus to facilitate extension

Auditory: prerecorded sounds,

conversation

Visual: video, toys

Graphic Description:

Slide 9
Force Quantification
FSA Mat

Graphic Description:

Slide 10
Force Quantification
FSA Grid

The FSA software gave us information on the average pressure, the standard deviation, variation coefficient and the number of sensors included in that measurement for each frame of data. It also gave information of the maximum pressure and the location of the center of pressure. We used the average pressure data to calculate the total force. From the total force data we found the peak force that each subject achieved. 30 minutes of data collection resulted in ~13206 frames of information.

Graphic Description:

Slide 11
Force Quantification

Graphic Description:

Slide 12
Dynamic Prototype Test Chair

Input seatback force data from subjects into a rigid body model developed in Working Model 3D

Vary design parameters of the resistive elements to:

Investigate their influence on the seat system response

Design aid for a laboratory dynamic seating system

Slide 13
Dynamic Prototype Test Chair
Model Parameters

LaBac MRC used as model

Replace manual recline mechanism with a spring element.

Spring Constants: 100 to 1,000 lb/in.

Graphic Description:

Slide 14
Sample Model & Output

On the left is how the LaBac wheelchair was modeled and on the right is a sample output from one of our subjects. Information provided by Working model was the length in inches of the resistive element, the seatback angle in angles and the tension in pounds of force, as they all changed over approximately 3 to 4 seconds.

Graphic Description:

Slide 15
Dynamic Prototype Test Chair

Graphic Description:

Slide 16
Discussion

No definition of extensor thrust

Homogeneity of subjects

Eliciting extensor thrust

FSA limitations

Slide 17
Conclusion

Preliminary information regarding forces exerted on back panel

Ranges for resistive elements

Modeling of human-assistive technology interface

Slide 18
Acknowledgements

Funding was provided by the National Institute on Disability Rehabilitation and Research to the RERC on Wheeled Mobility at the University of Pittsburgh.

Assistance with recruitment of subjects and data collection was provided by The Children’s Institute.

Slide 19
Thank You!

Return to Slide Series

Updated: March 12, 2002