Load Redistribution in Variable Position Wheelchairs in People With Spinal Cord Injury

Abstract

Background/Objective: Tilt and recline variable position seating systems are most commonly used for pressure relief to decrease potential for skin breakdown. This study provides quantitative information on the magnitudes of loading on the seat and back during phases of tilt, recline, and standing. The objective of this study was to show that the amount of force reduction at the seat would differ across these 3 methods within their respective clinical ranges. Participants: Six able-bodied (AB) subjects (2 men, 4 women) with a median age of 25 years, and 10 subjects (8 men, 2 women) with spinal cord injury (SCI) with a median age of 35.5 years. Methods: Subjects sat on a power wheelchair with Tekscan pressure mats placed underneath a foam backrest and cushion. Data were collected at 5 positions for each method. Order of position and method tested were randomized. Linear regressions were used to calculate the relationships of normalized seat and backrest forces to seat and backrest angles for each chair configuration. Results: Normalized seat loads had strong linear relationships with the angles of change in tilt, recline, and standing for both groups. Maximum decreases in seat load occurred at full standing and full recline in the SCI subjects and in full standing in the AB subjects. Loads linearly increased on the back during tilt and recline and linearly decreased during standing for both groups. Conclusions: Standing and recline offered similar seat load reductions at their respective terminal positions. Standing also reduced loading on the backrest. Recognizing that each method had clinical benefits and drawbacks, the results of this study indicate that tilt, recline, and standing systems should be considered as a means of weight shifting for wheelchair users.

The impact of tilting on blood flow and localized tissue loading

“…A 55 tilt may decrease the pressure under the ischial tuberosities somewhere between 30 and 50%. A recent study that measured the change in seated forces with tilt found a greater decrease in force (approximately 55% at 55 tilt) than this study found in pressure [19]. Because the change in load is distributed beneath the entire buttocks and thighs, the decrease in load is not necessarily evenly distributed.…”

Use of tilt-in-space in seating systems for adults with physical disabilities

“…Sonenblum and Sprigle 17 randomized the sequence of tilts used in their study. Similarly, Sprigle et al 18 randomized the order of position and method (tilt, recline, or stand) that was tested. In contrast, MacDonald et al 14 stated that wheelchair sequence was randomized, but did not describe the method used for this.…”

“…7 Jan et al 12 15,16 were experimental in design, with some evidence of randomization in the 2002 study, 16 whereby the order of the intervention (TIS and recline) was randomized. Sonenblum and Sprigle 17 and Sprigle et al 18 both used cross-over designs, randomizing either the order of the sequence of tilts, or the order of data collection across the range of positions to be tested. Fu et al 11 used similar randomization methods.…”

“…There was a range of study designs adopted by the researchers, with eight being quantitative in design, [11][12][13][14][15][16][17][18] two descriptive, 1,8 and two mixed methods. 9,10 Lacoste et al 1 utilized a cross-sectional design.…”

“…Twelve studies 1,[8][9][10][11][12][13][14][15][16][17][18] were published during the 11-year period, 2001-2012. The studies focused on three broad themes: (1) the effect of TIS and back recline upon sliding, pressure/force redistribution, propulsion, and skin perfusion over the ischial tuberosities; 11,12,[15][16][17] (2) the reasons for usage of TIS and back recline; 1,8-10 and (3) comparing TIS with the use of a new rear anti-tip device.…”