Influence of sacral sitting in a wheelchair on the distribution of contact pressure on the buttocks and back and shear force on the ischial region.

[Purpose] The purpose of this study was to investigate the influence of sacral sitting in a wheelchair on contact pressure on the buttocks and back, and shear force on the ischial region. [Subjects and Methods] Twenty-six healthy adults assumed two postures while seated in a wheelchair: a basic sitting posture, and sacral sitting with the pelvis tilted posteriorly and the ischium slid forward by 5 cm relative to its position in the basic sitting posture. The inclination angle of the sagittal pelvic line, contact pressures and contact areas on the buttocks and back, and the shear force generated by sliding the ischial region forward were measured. [Results] Posterior pelvic tilt was significantly greater during sacral sitting. Maximum contact pressures on the buttocks and ischial region were significantly lower during sacral than during basic sitting. However, maximum contact pressure on the back, the contact areas of the buttocks and back, and the shear force generated by sliding the ischial region forward were significantly greater during sacral sitting. [Conclusion] Sacral sitting in a wheelchair increases the maximum contact pressure on the back, contact areas of the buttocks and back, and the shear force generated by sliding the ischial region forward.