Quantifying seated buttock tissue response to commercial wheelchair cushions through MRI and pressure mapping analyses.

OBJECTIVE To describe how different wheelchair cushion designs impact interface pressure and buttock tissue deformation during sitting.

MATERIALS & METHODS 43 chronic full-time wheelchair users at high risk for pressure injuries were studied in an unloaded/suspended condition and on the Acta-Embrace, HR45, Jay J2 Deep Contour, Java, Matrx Vi, and/or the Roho HP cushions in randomized order. FONAR Upright MRI scans were used to measure seated soft tissue anatomy, and interface pressure mapping was used to measure peak pressure index (PPI) and pressure gradient.

RESULTS Median unloaded bulk tissue thickness beneath the ischium was 36.0 mm, decreasing by 53% when loaded. Tissue thickness under the ischium varied significantly between the Java (an off-loading design) and other pressure redistributing cushions (HR45, J2 Deep Contour, Matrx Vi) during upright sitting. Greater bulk tissue thickness correlated with increased proximal thigh thickness and reduced deformation under the ischium. Average PPI and pressure gradient were 116.2 ± 44.8 mmHg and 26.1 ± 17.8 mmHg, respectively. Matrx Vi exhibited significantly higher PPIs and gradients despite comparable deformation. Both PPI and gradient showed weak inverse correlations with tissue thickness (r = -0.276, p = 0.002; r = -0.321, p < 0.001). Both were associated with greater immersion on most cushions.

CONCLUSION The wheelchair cushions investigated showed comparable tissue deformation and PPI, though individuals with greater tissue thickness experienced less deformation. While participants experienced similar maximal tissue deformation across cushions, pressure gradients provided a more reliable representation of internal tissue response than PPI. Different cushion designs influenced load distribution uniquely despite similar overall tissue response, with notable differences between off-loading and pressure redistribution approaches. Regular skin checks remain essential for all wheelchair users.