Recommendations on Standards for the Design of Medical Diagnostic Equipment for Adults with Disabilities, Advisory Committee Final Report

3. Buttock-Popliteal Length

For this study, an estimate of buttock-popliteal length was calculated as the horizontal distance from the proximal (rear) edge of the wheelchair seat cushion to the popliteal fossa (i.e., crease at the back of the knee) of the right leg. The median buttock-popliteal length provides an upper bound for the depth of a seating surface. If seat depth is increased beyond this length, it becomes difficult to engage the backrest as well as exerting pressure to the back of the knees. Figure 3 provides a box-plot showing the distribution for shoulder breadth stratified by gender and mobility device type. The median (50th percentile) values for buttock-popliteal length across the 6 sub-groups ranged from 18.5-19.5 in. Seat depths should preferably not exceed these values (see next section for more information).

Figure 3: Box-plot showing the distribution for approximate buttock-popliteal length stratified by gender and mobility device type. The horizontal line splitting the box depicts the median, the box length represents the inter-quartile (25th – 75th percentile) range, and the whiskers represent the minimum and maximum values. Extreme values are shown as dots and asterisks. The red dotted lines depict the observed range of 95th percentile values across sub-groups.