Analysis of Body-Slip and Buttock Pressure Characteristics during Operation of a Double-Sliding Reclining Wheelchair in Patients with Spinal Cord Injury  
[PERSON]  
Correspondence: [EMAIL_ADDRESS]; Tel.: +82-32-509-5249  
[PERSON]  
Correspondence: [EMAIL_ADDRESS]; Tel.: +82-32-509-5249  
may increase the shear force on the back and the compression force on the buttock; this can lead to tissue destruction and pressure sores, and excessive body-slip increases the risk of falling in the wheelchair (Figure 1) [8]. To solve the body-slip problem, [PERSON] proposed \"the shear-reducing\" recline system, which reduces the shear forces through repositioning of the seat-to-back angle [9]. Thereafter, wheelchairs with a contoured seat back or a molded back (which maintain contact between the body and the seat) have been developed. Additionally, various studies have been conducted to derive optimal conditions by combining the tilt and recline angles of the wheelchair [7; 10; 11; 12; 13].  
Previous studies that have analyzed the biomechanical characteristics related to reclining wheelchairs have mainly focused on body-slip and changes in buttock pressure according to changes in the recline angle [7; 12; 13]. For body-slip, a change in the movement distance between a wheelchair marker and a body marker was measured using a three-dimensional motion analysis system [7]. Buttock pressure was measured by measuring the maximal pressure in the ischial tuberosity using a force sensor [14; 15], or by examining skin perfusion using laser doppler flowmetry [2; 13]. In most studies, the wheelchair angle at the point with the lowest buttock pressure was suggested as the optimal wheelchair angle, and guidelines for wheelchair use were presented based on this. In general, the maximum pressure develops on the ischial tuberosity in a wheelchair-sitting position. [PERSON] et al. reported a 14% reduction in peak pressure on the ischial tuberosity at a tilt angle of 20\({}^{\circ}\)[4], while other studies also reported that the ischial tuberosity pressure was reduced by 27% and 47% at posterior tilt angles of 35\({}^{\circ}\) and 65\({}^{\circ}\), respectively [16]. In addition, [PERSON] et al. reported that up to 40.2% of body weight shift occurred in a wheelchair tilted at 45\({}^{\circ}\) and inclined at 120\({}^{\circ}\), and acrom marker slip of up to 74 mm occurred upon repositioning at 120\({}^{\circ}\)[7].  
As stated above, special devices for minimizing body-slip in a reclining wheelchair have been developed. In particular, a powered wheelchair with a sliding backrest has been designed such that the backrest slides at a specific reclining angle and a wire or linear actuator is applied to the backrest to minimize body-slip [17]. Our institute also developed a reclining wheelchair with a sliding backrest function. It is a double-sliding system with a pre-sliding function that changes the sliding distance appropriately according to the user's body type before sliding. A previous study has confirmed that a double-sliding system reduces body-slip and buttock pressure compared to single- or non-sliding systems [14]. However, since the study was conducted in healthy people, additional research is required on disabled people who actually use wheelchairs. Since patients with SCI who have lost muscle tone may show different characteristics from healthy people when reclining and repositioning a wheelchair, research on actual users is essential for clinical application.  
Therefore, in this study, we aimed to verify the effect of the double-sliding system on patients with SCI by investigating the differences in body-slip and buttock pressure between the double-sliding system and general reclining systems during wheelchair reclining and  
Figure 1: Schematic of the problem caused by the use of a reclining wheelchair.  
repositioning. The results of this study are intended to provide basic data on prescriptions and guidelines for wheelchair selection in clinical practice and to aid in the development of wheelchairs.