Effect of Wheelchair Seat Deflection on Seat Pressure and Shear, and Its Relationship to Sitting Postural Sway

KIYO SASAKI, Yoshiyuki Yoshikawa, Kyoko Nagayoshi, Kenta Nagai, Koudai Yamasaki, Koji Ikeda, Yasutomo Jono, Noriaki Maeshige, Hiroto Terashi
Purpose:

This study aimed to assess the impact of rectifying wheelchair seat deflection on seat pressure, shear forces, and postural sway.This study aimed to assess the impact of rectifying wheelchair seat deflection on seat pressure, shear forces, and postural sway.

Methods:

Twenty-two healthy adults (11 males, 11 females) participated in the study. An adjustable wheelchair (Revo; LAC Healthcare Ltd., Osaka) was employed with and without seat deflection correction (Kiso; Tatsuno Cork Kogyo Co., Ltd., Hyogo). Urethane cushions (Moderate cushion; LAC Healthcare Ltd., Osaka) were used in both conditions. Seat pressure was measured using the CONFORMat system (Nitta Corp., Osaka), and shear forces were assessed using the iShear device (LAC Healthcare Ltd., Osaka). Sitting posture at the head, chest, and iliac crests was evaluated via the TSND151 accelerometer (ATR-Promotions Inc., Kyoto). The order of testing was randomized, and the wheelchair was adjusted to the individual participant’s body configuration. Each measurement session lasted for 10 minutes. Seat pressure was calculated as the mean of four cells surrounding the maximum pressure point (PPI: peak pressure index), while shear force was determined by dividing the peak recorded value by a reference. Postural changes were quantified by variations observed during the measurement period. Statistical analyses were conducted using paired t-tests and Wilcoxon signed-rank tests, with correlations examined for significant data. A significance threshold of 5% was applied to all analyses.

Results:

The PPI on the seat was 65.4 ± 39.9 mmHg without correction and 68.1 ± 38.4 mmHg with correction, indicating no statistically significant difference between the two conditions. Shear force was 22.6 ± 28.3 N without correction and 13.0 ± 16.7 N with correction, showing a significant reduction in shear force in the corrected condition (p 0.05). No significant correlations were identified between shear force and variables such as height, weight, or BMI. Postural changes at the head, chest, and iliac crests exhibited no significant differences between conditions, although greater postural variation tended to occur with correction.



Conclusion(s):

Correcting the deflection of wheelchair sling seats reduces shear forces, although it does not appear to have a direct effect on pressure relief. Moreover, correction seems to facilitate postural adjustments, potentially aiding in pressure redistribution. 

Implications:

For the prevention of pressure injuries in wheelchair users, it is essential to address pressure distribution and shear force reduction. This study suggests that correcting seat deflection can help mitigate shear forces, thereby contributing to more effective pressure injury prevention strategies.

Funding acknowledgements:
This research was funded by Nara Gakuen University Grant, 2023.
Keywords:
Pressure injury prevention
Wheelchair
Sling seat
Primary topic:
Disability and rehabilitation
Did this work require ethics approval?:
Yes
Name the institution and ethics committee that approved your work:
Institution: Graduate School of Rehabilitation Sciences Naragakuen University Committee: Graduate School of Rehabilitation Sciences Naragakuen University
Provide the ethics approval number:
5-R002
Has any of this material been/due to be published or presented at another national or international conference prior to the World Physiotherapy Congress 2025?:
No

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