Towards a Standard for the Definition and Measurement of Wheelchair-seated Posture

Douglas Hobson, Ph.D & Barbara Crane, RPT
RERC
University of Pittsburgh

Slide 1
Towards a Standard for the Definition and Measurement of Wheelchair-seated Posture

Douglas Hobson, Ph.D & Barbara Crane, RPT
RERC
University of Pittsburgh

Slide 2
Approach to Date

1) Establish national/international working groups (ANSI/RESNA-ISO).

2) Obtain agreement on:
what postural quantification is required,
standard method for describing w/c seated posture that is:
consistent with current clinical practice,
results in standard terms and definitions.

3) integration into standardization process.

4) research validation and clinical tool development

Slide 3
Standard methodology-same way every time!

Clinical convention

3-D positions of the body

Limited to 2-D projections

Graphic Description: This black and white drawing illustrates the anatomical reference position and the seated anatomical reference position. There are two pictures of a man – one standing and one sitting. Both of these are side views of the person’s right side. Superimposed on these pictures are the three planes one divides the person into top and bottom halves, one divides the person into left and right halves and the third divides the person into front and back halves. These are the reference planes used in describing movement.

Slide 4
Body Measurement: Same way every time?

First, a little high school math

3-D positions of the body

The selected axis convention

How it works

2D coordinate system

Graphic Description: This is a graph of a simple two-dimensional coordinate system with a vertical and a horizontal axis. These axes intersect each other and the point of intersection is labeled with a zero. The axes are then numbered from 1 – 6 upward and to the right and from negative 1 to 6 downward and to the left.

Slide 5
Standard methodology-same way every time!

Standard axis convention required

Three orthogonal planes (3D)

2-D projections

Graphic Description: This drawing illustrates a three dimensional axis system with three axes superimposed on a cube shaped object that shows the three planes. The three planes are identified with different colors.

Slide 6
Standard methodology-same way every time!

The possible axis conventions

No one standard exists

Graphic Description: A line drawing of a persons right hand with the thumb, first and second fingers extended fully. These three fingers are at 90 degree angles to each other with the thumb pointing upward and the X, Y, and Z axes are superimposed on the fingers in the three possible combinations: on the left the X axis is along the thumb, the Y axis along the first finger, and the Z axis along the second finger, in the middle frame, the Z axis is along the thumb, the X axis along the first finger and the Y axis is along the second finger, in the right most frame, the Y axis is along the thumb, the Z axis is along the first finger and the X axis is along the second finger. This illustrates that all three of these configurations are possibilities.

Slide 7
Selected Axis Convention!

Graphic Description: There are three pictures on this slide. The picture in the upper left corner is one of the hands from the last slide with the Z axis along the thumb, the X axis along the first finger and the Y axis along the second finger. Below this is a picture of the left hand of a person with the fingers flexed around a line indicating the axis and with the thumb extended upward away from the hand. The axis is labeled positive Z and there is an arrow indicating that the direction of rotation is in the same direction as the persons fingers are bending. The third picture on this slide is a large picture of three hands and three silhouette images of a person seated on it. The body and hands are viewed from the front, side and top and the axis system is superimposed on both the hands and the bodies for illustration. The positive Z axis extends from the center of the persons hips up through the center of the head, the positive Y axis extends from the center of the hips forward to a point between the persons knees, and the positive X axis extends from the center of the hips to the right of the person at a ninety degree angle.

Slide 8
Three main components of all W/c seating

1) The wheelchair,

2) The person's support surfaces in the W/C--i.e. the seat plus postural accessories),

3) the person.

*Must be able to measure and record data on all three components relative to some known reference system(s)

Slide 9
Axis Convention is then used to define:

a) Wheelchair Axis System (WAS)--

b) Support Surface Axis System (SSAS)

c) Support Surface Reference Position (SSRP)

d) Seated Anatomical Axis System (SAAS)

e) Seated Reference Position (SRP)

Let's briefly review each of the above!

Slide 10
Wheelchair Axis System (WAS)

Global Coordinate Reference

• serves as the constant over time
• defines the origin for absolute reference: 0,0,0
  

Slide 11
The Global Reference (WAS)

Graphic Descrpition: an outline view of a manual wheelchair shown from three sides – the right side view, the front view and the top view. The axis system described in slide seven is superimposed on the wheelchair. The 0,0.0 center point is midway between the large rear wheels of the chair but on the floor. The Z axis is vertical upwards from this point, the Y axis extends out the front of the chair and the X axis extends to the right side of the chair at a ninety degree angle from the Y axis.

Slide 12
Support Surface Axis System (SSAS)

defines the coordinate conventions used to define the support surface reference position (SSRP)

Graphic Description: a schematic view of a support surface system – basically a seating system – viewed from the right side. There are blocks illustrating several seating supports including a seat support, three back supports, lateral supports, arm supports, and leg supports. They are set up as they might be on a wheelchair, but the wheelchair is not visible. The 0,0 origin for this system is marked with a yellow dot at the point of intersection of the seat with the back. The Z and Y axes are illustrated – Z pointing upwards and Y pointing forward.

Slide 13
Support Surface Reference Position (SSRP)

The SSRP defines a hypothetical reference position for the support surfaces to which all other positions can be referenced

Slide 14
Seated Anatomical Axis System (SAAS)

defines the geometric measures needed to define and record the actual positions of a person's body segments relative to the seated reference position (SRP)

Slide 15
Seated Reference Position (SRP)

defines a fixed hypothetical neutral baseline of seated posture to which other postures may be referenced

Graphic Description: an outline of a seated person viewed from the right side with the axis system superimposed and several points labeled with letters of the alphabet. There are lines drawn connecting these points which represent segment lines that divide the body into articulating segments.

Slide 16
Integrated Measurement System (IMS)

Graphic Description: the three previous pictures combined on one slide – all are right side views, they include the view of the wheelchair, the view of the seating system and the view of the person with addition signs in between to indicate that we are combining these three systems into one integrated system.

Slide 17
IMS Concept:

all components use same axis convention,

all components measured, recorded and communicated in std.way,

integrates the three key components and produces the ongoing clinical record of the person's seated posture,

allows automated measurement and recording,

facilitates integration of future research.

Slide 18
Support Surface Measures

The support surfaces

orientation of support surfaces

• in space
• to each other
• in three views

location in space

dimensions of support surfaces

Graphic Description: a black and white line drawing type of picture of a person, viewed from the right side and in a sitting position. The persons back is leaned backward and the legs are tipped up from the horizontal position. Several angles are indicated with different types of shading. This picture illustrates the complexity of describing the seated posture.

Slide 19
Support Surface Measures

How it works:

• support surface reference planes
• the geometric center of a support surface--centroid

Graphic Description: a front view of a black and white drawing of a support surface system with back supports, a head support, arm supports, lateral supports, and leg supports. Each support has a circle with a horizontal and vertical line through it that indicates which surface is designed to contact a person sitting in the system.

Slide 20
Support Surface Measures

The support surfaces

orientation of support surfaces

• in space
• to each other
• in three views
  

location in space

length of support surfaces

Graphic Description: the same support surface system as described in the previous slide, slide 19, but with several vertical lines added to indicate measurement of the supports away from the 0,0 axis of the system

Slide 21
Support Surface Measures

The support surfaces

orientation of support surfaces

• in space
• to each other
• in three views

location in space

dimensions of support surfaces

Graphic Description: is the same support surface system, but with horizontal lines indicating measurement along the X axis away from the center point.

Slide 22
An example for support surface measures

Graphic Description: a diagram of the side view of a support surface system with the system tilted backwards in space – removing the support surfaces from their original horizontal or vertical orientations. Each support surface is labeled and the angles to be measured are indicated and measured. There is a table that indicates what the relationship is between the relative measurements and the absolute measurements.

Slide 23
Seated Person Measures

orientation of body segments:

• in space
• to each other
• in three views (2-D)
• dimensions of body segments?

Graphic Description: a black and white line drawing of a person in a seated position, viewed from the right side with their upper body reclined and the legs tilted up from the horizontal.

Slide 24
Seated person measures-cont.

orientation of body segments:

• in space
• to each other
• in three views (3-D)

dimensions of body segments

Graphic Description: a black and white silhouette of a person sitting with the axis system superimposed and several vertical lines indicating possible measurements of the persons body that relate to the measurements needed for a seating system.

Slide 25
Seated Person Measures-cont.

How many body segments?

• min. to define define seated posture
• these are:
  • head, neck,
  • upper arm, forearm
  • trunk, pelvis
  • thigh, lower leg
  • foot
• represent each segment by a line (body segment line)
• segment line defined by body landmarks
• repeat in all three views

Graphic Description: the same silhouette of the person seated, viewed from the right side, with several points indicated and labeled with letters of the alphabet and with lines connecting these points indicating body segments.

Slide 26
The Seated Person Measures-cont.

repeat in all three views

frontal

Graphic Description: This is the same image with points and lines, but a front view instead of a side view.

Slide 27
The Seated Person Measures-cont.

repeat in all three views

transverse

Graphic Description: The same image – but a top view.

Slide 28
Seated Person Measures-cont.

Body landmarks used to define body segments in the three planes?
These are: in sagittal plane

• Head- Tragion, Eye Corner (a-b)
• Neck- upper , lower centers
• Trunk- lower neck center, hip center (c-d)
• Pelvis- ASIS, PSIS ( k-l)
• Thigh- hip center, lateral condyle (m-n)
• Leg- lateral condyle, lateral malleolus (n-o)
• Plus a few others
• Several joint centers located by calculation (hip, upper and lower neck,shoulder. (Reid et al)
  

saggital view

Graphic Description: This is a right side view of a skeleton in a seated position. Several bony prominences are labeled with letters. The same segments are identified as in slide 25.

Slide 29
Person Measures-cont.-landmarks/body segments-

frontal

transverse

Graphic Description: the skeleton view from the top and the front with the anatomical points and segment lines identified.

Slide 30
The Seated Person Measures-cont.

pelvis landmarks

segment lines

Graphic Description: front, top and side views of the pelvis with the body segments associated with pelvic landmarks identified and labeled.

Slide 31 Development Plan

ANSI/RESNA, ISO combined resources-(done)

1st stage(CD) ISO voting-Spring 2001-(done)

Research validation-starts (01/2002

Completed std.- 2003

Education materials-2003

Automated measurement tools -2004

Slide 32
Utilization Plan-US

ANSI/RESNA-ISO seating standards (ISO 16840-Part 1) Body and Seat Measures

Continuing education forums,

WWW-based self instruction guidelines,

Grant (SBIR) support for automated tool development,

Refinement of standard over time.?

Slide 33 Future Research Contributions

Accuracy Analysis (ex. repeatability)

True 3-D measures

Spinal segment measures

Measurement methodologies

Demonstration measurement tools

Automated data capture and display

Computerized recording-keeping tools

Technology transfer

Slide 34
Summary:

A measurement system that:

• extends/facilitates quantification of clinical practice,
• defines postural measurement terms,
• supports communication of clinical research,
• positioned to be adopted as a universal standard.
• facilitates tech. transfer and dev. of automated clinical tools over time,
  

Slide 35
How to keep tuned in!!

http://www.wheelchairstandards.pitt.edu/

• Scroll to ISO WG-11: 16840, Part 1
• Minutes and draft standards--.pdf format??

Presentation Download:

• http://www.wheelchairnet.org
  • Go to: Wheelchair University, Continuing Education, Slide lecture series on---,seating biomechanics?
    

Slide 36
THE END

Thank you !!

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Updated: March 12, 2002