The Effects of Balanced Seating Pressure on Pelvic Asymmetry in Under-Buttocks Pressure, Spinal Alignment, and Lower Back Pain: A Pilot Study

Trial Design This study is designed as a randomized, double-blind, placebo-controlled, two-period crossover trial to be conducted at the Department of Rehabilitation, Taoyuan Chang Gung Memorial Hospital. A total of 24 participants will be screened, with an estimated 20 completing the full protocol. Participants will be randomly assigned to one of two treatment sequences: Group A will receive the DaSuit® cushion followed by the placebo cushion; Group B will receive the placebo cushion followed by the DaSuit® cushion. Each intervention period will last approximately 10 minutes, separated by a 10-minute washout interval to minimize potential carry-over effects. The crossover design is chosen to reduce between-subject variability, as each participant will serve as their own control.

Participants The study will not involve patients or the public in the design, conduct, reporting, or dissemination.

Inclusion criteria are as follows: (1) adults aged 20 to 50 years; (2) experiencing non-specific low back pain exacerbated by sitting, with a VAS score between 3 and 7; (3) height between 150-180 cm; (4) BMI between 18.5-24; and (5) radiographically verified hemi-pelvic height discrepancy ≥ 0.5 cm in a seated posture.

Exclusion criteria include: (1) inability to sit for 20 minutes; (2) MMSE < 24; (3) significant spinal or pelvic disorders (e.g., fractures, prior surgeries, herniated discs with nerve compression); (4) diagnosed scoliosis with a Cobb angle ≥ 20°; (5) recent use of analgesics or muscle relaxants; (6) pregnancy; and (7) skin conditions affecting sitting tolerance. All participants will provide written informed consent following clinical pelvic examination confirming asymmetry.

Interventions Each participant will undergo both intervention conditions in a randomized order. In each session, the participant will sit for 10 minutes on either the DaSuit® cushion or the placebo cushion, placed on a standardized 40×40×40 cm wooden chair. A pressure sensor mat will be placed on the cushion surface to measure under-buttock pressure. Following the sitting period, pain intensity will be assessed using the VAS, and an anterior-posterior full-spine X-ray will be taken. After a 10-minute washout period-during which the participant will be instructed to walk-the alternate cushion condition will be administered.