RERC: Research R-1

R-1: Investigation of Dynamic Seating for Children with Extensor Thrust

Task Leader: Gina Bertocci, PhD, PE (bio/mechanical engineer)

Co-investigators: Elaine Trefler, MEd, OTR (seating clinician); Raymond Burdett, PhD (physical therapist/mechanical engineer); Shirley Fitzgerald, PhD (research design specialist); Clifford Brubaker, PhD (design consultant); Dalthea Brown, PT (doctoral student)

Duration/Staging of Task: This 48 month research task will be conducted in months 1-48 of the 60 month RERC cycle.

Rationale/Task Summary
This task is designed to test the effectiveness of dynamic seating in those individuals exhibiting full body extensor thrust. Should it be determined that the dynamic seating concept is a useful therapeutic measure, the target population will benefit in the following ways:
1. Improved seated posture management leading to increased function following an extensor thrust event;
2. Increased independence following an extensor thrust event since intervention may no longer be needed to restore posture;
3. Reduced wheelchair component, seating system and assistive technology breakage often associated with extensor thrust, and a corresponding reduced potential for injury.
This task will also provide evidence-based findings that will guide rehabilitation service providers and clinicians in seating prescriptions for those clients experiencing extensor thrust events.

Specific objectives
This task will test the following hypotheses related to the provision of dynamic seating to children with CP exhibiting torso extensor thrust (ET) events as a result of muscle spasticity.
Hypothesis 1. Dynamic seating will result in decreases in the duration of ET events.
Hypothesis 2. Dynamic seating will decrease changes between pre- and post-ET event Seat Postural Control Measure Scores.
Hypothesis 3. Dynamic seating will result in decreases in angular impulse imparted to the
seating system by children during ET events.
The objectives of this study, met through testing the above hypotheses, are as follows. Each objective is focused on children with CP and associated muscle spasticity presenting as ET events.

Investigate the influence of dynamic seating on ET event descriptors (i.e., duration).
Investigate the influence of dynamic seating on seated posture management following an ET event.
Assess whether dynamic seating can reduce the likelihood of wheelchair component breakage and potential injury associated with ET events.

Progress Report (12/31/99)

We have received IRB approval for the first phase of subject evaluation, which entails measurement of seat back forces generated by children during extensor thrust events. We have developed a test protocol which utilizes a force sensing matrix placed between the subject and their seat back to capture forces during an extensor thrust event. To date we have evaluated 10 children fitting our inclusion criteria. We are currently analyzing preliminary data and plan to evaluate 8 additional subjects following this protocol.

Concurrently we have developed a rigid body model to aid in the design of a laboratory dynamic seating assessment system. With the model we are evaluating the influence of various seating parameters (such as seat back stiffness and energy absorption) on response of the seating system given force time histories measured in our extensor thrust force assessments described above. With this information we will identify a range of resistive elements to be incorporated into our laboratory dynamic seating system. We have procured a commercial wheelchair and seating system, which will lend itself to easy modification for use in the laboratory assessment phase of our study.

Progress Report (12/31/01)

We have completed Phase One of our study which entailed preliminary characterization of seat back forces associated with extensor thrusting or high torso muscle tone in children. This data was used to develop a computer model of a prototype dynamic seating system which aided in the selection of appropriate instrumentation and resistive components for a laboratory dynamic seating system. Results of this phase of the project were captured in two abstracts submitted to the Resna 2001 Conference, Quantification of Forces Associated with Episodic Full Body Extensor Spasticity in Children and Utilizing Computer Modeling in the Development of a Dynamic Seating System.

We have received IRB approval for Phase Two of our project. This phase of our project consists of evaluating approximately 20 children during extensor thrust events using an instrumented laboratory dynamic seating system. The seating system can be operated in both a static or dynamic mode. This specialized instrumented wheelchair seating system will be capable of measuring seat back forces during extensor thrusting events. We are currently in the process of mounting resistive elements and measurement instrumentation on the laboratory seating system. Subjects will also be equipped with EMG electrodes in an effort to characterize muscle activity during extensor events. We expect to begin testing subjects within the coming month.

Expected Outcomes

Assuming it is determined that dynamic seating is of value, this project will provide additional research foundation for clinical guidelines, as well as criteria for the manufacture of dynamic seating products. A unique laboratory measurement seating system (LMSS) will also result from this task and will be available for future dynamic seating studies. Additionally, through the execution of this task, two graduate students will receive research training. One of these students (Ms. Brown) will base her PhD dissertation research on this task.

Publications/Reports

Zeltwanger, AP, Brown, D, Bertocci, GE. Utilizing computer modeling in the development of a dynamic seating system. RESNA Annual Conference 2001, Reno, NV paper submitted

Brown, D, Zeltwanger, A, Bertocci, G, Burdett, R, Trefler, E, Fitzgerald, S. Quantification of forces associated with episodic full body extensor spasticity in children. RESNA Annual Conference 2001, Reno, NV, paper submitted

Contact Person: Gina Bertocci