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: Twenty-four healthy adults, meeting specific anthropometric requirements for proper wheelchair fit, were recruited. 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, shear force was assessed with a specialized sensor, and posture was recorded via accelerometers. The primary analysis compared peak pressure index (PPI), shear force, slide, and postural changes between conditions. Subgroup analyses were conducted for participants who exhibited higher shear force values. Results: There was no statistically significant difference in ischial pressure between the No Correction and With Correction conditions. However, shear force and slide were significantly reduced when seat sagging was corrected. Accelerometer data showed no significant difference in postural changes between conditions, 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. Future studies should include older adults, who may experience additional musculoskeletal and skin changes, to confirm these results. Addressing seat sagging could be an important component of comprehensive pressure injury prevention strategies.