Effects of Wheelchair Seat Sagging on Seat Interface Pressure and Shear, and Its Relationship with Changes in Sitting Posture

Objectives: Wheelchair seat sagging is hypothesized to increase pressure and shear forces, potentially leading to pressure injuries. The objective of this study was to assess the impact of correcting wheelchair seat sagging on ischial pressure, shear force, and posture in a population of healthy adults. Methods: A total of twenty-two participants who met the study requirements were included in the study. Participants were evaluated under two conditions: with seat base correction (With Correction) and without it (No Correction). Correction was achieved using insert panels. Ischial pressure was measured using a pressure-mapping system (CONFORMat), shear force with a specialized sensor (iShear), and posture with accelerometers (TSND151). The primary analysis compared peak pressure index (PPI), shear force, slide, and postural changes between conditions. The subgroup analysis was conducted as an exploratory approach to assess potential variation among participants with elevated shear forces. Results: There was no statistically significant difference in ischial pressure between the No Correction and With Correction conditions (p = 0.37). However, shear force and slide were significantly reduced when seat sagging was corrected (p < 0.05). Accelerometer data showed no significant difference in postural changes between conditions (p ≥ 0.05), although the With Correction condition displayed a slight trend toward greater positional variability over time. Conclusions: These findings indicate that correcting seat sagging can reduce shear force and slide, potentially lowering the risk of pressure injuries. However, because this study targeted healthy adults, further research involving older or at-risk populations is necessary. Addressing seat sagging could be an important component of comprehensive pressure injury prevention strategies.