Accepted Manuscript Orthotic-style off-loading wheelchair seat cushion reduces interface pressure under ischial tuberosities and sacrococcygeal regions Barbara Crane, PhD, Michael Wininger, PhD, Evan Call, MS PII: S0003-9993(16)30080-6 DOI: 10.1016/j.apmr.2016.04.004 Reference: YAPMR 56527 To appear in: ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION Received Date: 19 October 2015 Revised Date: 7 April 2016 Accepted Date: 8 April 2016 Please cite this article as: Crane B, Wininger M, Call E, Orthotic-style off-loading wheelchair seat cushion reduces interface pressure under ischial tuberosities and sacrococcygeal regions, ARCHIVES OF PHYSICAL MEDICINE AND REHABILITATION (2016), doi: 10.1016/j.apmr.2016.04.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. ACCEPTED MANUSCRIPT Ms. Ref. No.: ARCHIVES-PMR-D-15-01345 Running head: Off-loading cushion interface pressures RI PT Title: Orthotic-style off-loading wheelchair seat cushion reduces interface pressure under ischial tuberosities and sacrococcygeal regions. Authors (with highest academic degree): Barbara Crane PhD,1 Michael Wininger PhD,1,2,3 and Evan Call MS4 SC Location where study performed: This study was performed at EC Services in Centerville, Utah and directed through the Department of Microbiology, Weber State University, Ogden, M AN U Utah 84408 Author affiliations: 1 Department of Rehabilitation Sciences, University of Hartford, West Hartford, CT 06117 2 Department of Veterans Affairs, Cooperative Studies Program, West Haven, CT 06516 3 4 TE D Department of Biostatistics, Yale School of Public Health, Yale University, New Haven, CT 06510 Department of Microbiology, Weber State University, Ogden, Utah 84408 EP Presentation of material: Preliminary findings from this research were presented during a 15 minute platform presentation AC C at the International Seating Symposium in Nashville, TN on February 27, 2015. Acknowledgement of financial support: Disclosure of interests and acknowledgement of study support: support for this study was provided by Ride Designs, Denver, Colorado – provided Java cushion materials for testing, provided funding for subject reimbursement and support for EC Services staff during testing – and support provided by Joan Padgitt, PT, ATP who assisted with data collection. ACCEPTED MANUSCRIPT Conflicts of interest: The authors assert there are no conflicts of interest related to the presented work. RI PT Corresponding Author: Barbara Crane, Ph.D.; University of Hartford, 200 Bloomfield, Avenue, West Hartford, CT, USA 06117; bcrane@hartford.edu; Phone: 860-768-5371 Reprints are not available. AC C EP TE D M AN U SC Clinical trial registration number: There is no clinical trial registration number for this study. ACCEPTED MANUSCRIPT 1 Title: Orthotic-style off-loading wheelchair seat cushion reduces interface pressure under ischial 2 tuberosities and sacrococcygeal regions. 3 Abstract (structured) – 225 words 5 Main text – 3,042 words 6 Tables – 4 7 Figures – 5 8 References - 38 SC RI PT 4 AC C EP TE D M AN U 9 1 ACCEPTED MANUSCRIPT Title: Orthotic-style off-loading wheelchair seat cushion reduces interface pressure under ischial 11 tuberosities and sacrococcygeal regions. 12 Abstract: 13 Objective: To assess the efficacy of an off-loading wheelchair seat cushion in removing pressure 14 from high-risk ischial tuberosities and coccyx/sacrum in wheelchair sitting. 15 Design: Repeated measures design 16 Setting: Private research laboratory 17 Participants: Manual wheelchair users with chronic spinal cord injuries (N=10) 18 Interventions: Three configurations of an off-loading wheelchair seat cushion compared with a 19 flotation style (4” air inflation) wheelchair seat cushion. 20 Outcome Measures: Outcome measures included peak pressure index (PPI), ischial tuberosity 21 peak pressures and the “dispersion index” or ratio of pressures under the ischial and sacral 22 regions to the total of all pressures recorded. 23 Results: PPI and IT Peak Pressure ranged from a low of 39 ± 18 and 68 ± 46 mmHg in the fully 24 off loaded cushion to a high of 97 ± 30 and 106 ± 34 mmHg, respectively for the flotation style 25 cushion (two-way ANOVA main effect across four conditions p < .001). Dispersion Index 26 ranged from a low of 8 ± 3% in the fully off loaded cushion, to a high of 16 ± 3% in the flotation 27 style cushion. Pair-wise comparisons yielded significance in all cushion-pair analyses (P<0.05 28 after multiple corrections). 29 Conclusions: We conclude that the force-removal approach of this orthotic off-loading cushion 30 design effectively reduces a known extrinsic risk factor for pressure ulcers – interface pressure – 31 in the high-risk ischial tuberosity and sacral/coccygeal regions of the buttocks. AC C EP TE D M AN U SC RI PT 10 2 ACCEPTED MANUSCRIPT Key Words (MeSH terms): Pressure ulcer; wheelchairs; preventive measures; spinal cord injuries 33 Introduction 34 Pressure ulcers remain one of the most challenging problems faced by wheelchair users.1 For 35 many wheelchair users, pressure ulcer risk can be substantially reduced by the selection of an 36 optimal seat cushion.2-5 Wheelchair seat cushion selection is particularly important for its impact 37 on two factors: tissue interface pressure3 and sitting posture6,7; in addition to the implications of 38 body posture on musculoskeletal health and upper extremity mobility, posture itself has indirect 39 influence on interface pressure.6,8-10 M AN U 40 SC RI PT 32 Cushion technologies that rely on a flotation principle11 minimize interface pressures under bony 42 prominences by distributing pressure as evenly as possible over the largest contact area possible, 43 thereby reducing peak pressures under the bony prominences of the pelvis, particularly the 44 ischial tuberosities.12,13 While these cushions are useful in reducing pressures under these bony 45 prominences,14-16 pressures in these areas may remain unacceptably high.17,18 Thus, it may be 46 necessary to completely off-load these high-risk areas of the anatomy to effectively reduce the 47 risk of pressure ulcers in these critical regions.17,19,20 EP AC C 48 TE D 41 49 While the off-loading concept is not completely novel,18 there has been limited inquiry into the 50 impact of an off-loading design on seating interface pressures.19,20 Additionally, this body of 51 work is not recent, and pre-dates the characterization of interface pressure parameters currently 52 used in cushion assessment, including Peak Pressure Index (PPI) and Dispersion Index (DI), both 53 of which are used in this study. Nevertheless, there is indication that a previously-tested off- 3 ACCEPTED MANUSCRIPT 54 loading cushion design has also yielded significantly lower interface pressures in the area of the 55 ischial tuberosities.18 56 In this study, we test the ability of an off-loading cushion design to reduce external pressures in 58 key areas of the pelvic anatomy. This wheelchair seat cushiona is designed using orthotic 59 principles to intentionally and completely off-load high risk bony prominences. By re- 60 distributing contact pressure away from the ischial tuberosities, sacrum/coccyx and greater 61 trochanters, and towards the posterior gluteal muscles and proximal femurs (distal to the greater 62 trochanters), this cushion system is designed to significantly decrease peak pressures 63 immediately under these highly sensitive bony regions of the pelvis. Our main objective was to 64 measure the interface pressure characteristics of this off-loading cushion and compare them to 65 the flotation style seat cushion that is commonly used for pressure ulcer prevention in wheelchair 66 users.2,16,21 TE D 67 M AN U SC RI PT 57 Methods 69 Subjects 70 All study procedures were approved by the Institutional Review Board prior to recruitment or 71 testing and all subjects provided informed consent. Subjects included ten adults with chronic 72 spinal cord injury (3 to 42 years post injury – average 20 years). Exclusion criteria were: 73 presence of a pressure ulcer or subject hip width wider than 48 cm. Subjects were all tested in a 74 laboratory environment using their own wheelchairs or a suitable surrogate. AC C EP 68 4 ACCEPTED MANUSCRIPT 75 Materials 77 All testing was completed using a properly inflated (according to the manufacturer’s 78 instructions) 4” high air flotation cushionb and a newly developed off-loading cushion. The air 79 flotation cushion is comprised of a grid of interconnected air chambers, each 4” in height with a 80 single valve provided for adjusting the air inflation level. This system is designed to allow the 81 buttocks to “immerse” into the cushion and for the cushion to “envelop” the bony regions of the 82 pelvis.12 This cushion is commonly used to manage interface pressure in persons with chronic 83 spinal cord injury and has demonstrated effectiveness in interface pressure reduction, particularly 84 under the bony prominences of the pelvis.16,22-25 The off-loading cushion used employs a firm, 85 generically-shaped closed cell foam base, a 2” molded soft polyurethane foam overlay, and a 86 moisture wicking outer cover. Wedges can be selectively inserted into the posterior-lateral 87 support structures (i.e. cantles) of the cushion to correct postural asymmetries and/or increase the 88 amount of ischial off-loading (Figure 1). Though complete off-loading of the bony prominences 89 is the primary intended use of this cushion, optional reticulated foam “well inserts” can be added 90 to provide increased ischial contact and reduce the sensation of rapid transitions from supportive 91 contours to off-loaded tissue if desired by the clinician or wheelchair-user. EP TE D M AN U SC RI PT 76 AC C 92 93 [insert figure 1 here] 94 Study Design 95 In order to assess the potential effectiveness of the off-loading design, we compared this design 96 against the flotation style cushion, which is believed to minimize extrinsic risk factors for 97 pressure ulceration and is commonly used in wheelchair seating among a high-risk population 5 ACCEPTED MANUSCRIPT 98 like individuals with chronic SCI.3,11,14,16,23 Because the off-loading cushion can be re-configured 99 to allow for two semi-loading conditions, we tested three configurations, each with different loading characteristics: fully off-loading (C0-off), which was determined through clinical 101 evaluation which included or excluded posterolateral wedges according to the manufacturer 102 instructions26; addition of the top well insert (C1-off); and addition of both well inserts (C2-off). 103 The comparator condition (flotation-style cushion) was labeled C3-float. RI PT 100 SC 104 Instrumentation 106 Seat pressure measurement was conducted using the Xsensorc interface pressure mapping 107 system. The system consisted of a flexible mat (46 cm X 46 cm) containing an array of 1,296 108 pressure sensors (36 X 36 array of 1 cm2 sensors). The mat was placed between the cushion 109 being tested and the seated person. The mat electrical output was connected to a laptop computer 110 for data reduction. The system incorporates software for mapping of pressure distributions and 111 export of data. 112 TE D M AN U 105 Protocol 114 The Xsensor mat was calibrated and validated according to the IPM system manufacturer’s 115 instructions and to a standard range of 0 – 220 mmHg. The manufacturer’s recommended 116 validation procedure was used at the start of each testing day and if the calibration was not found 117 to be adequate (i.e. outside the validation range recommended by the system manufacturer), the 118 mat was re-calibrated. Special care was taken to assure that the sensing mat was not 119 “suspended” on any of the cushion configurations tested, which would create a hammocking 120 effect and interfere with the accuracy of the interface pressure readings. AC C EP 113 6 ACCEPTED MANUSCRIPT 121 Subjects sat in the same wheelchair (either their own wheelchair or a comparable substitute on 123 which a solid back support had been installed) under all four conditions in a randomized order. 124 For each condition, subjects sat for 2 minutes after visual verification by the researcher of proper 125 sensor mat placement and adequate functioning of all sensors.27,28 Pressure data were recorded 126 at a sampling rate of 1 Hz for 2 minutes, collecting a minimum of 120 frames of data per trial. 127 Subjects completed five trials for each condition, performing a complete pressure relief 128 maneuver (i.e. wheelchair “push up”) to un-weight the cushion fully between trials. SC RI PT 122 M AN U 129 When each subject was initially seated on each cushion, the locations of both ischial tuberosities 131 (IT), both greater trochanters, and the sacrococcygeal region were verified via palpation by an 132 experienced physical therapist. The sensor locations of the IT’s and the sacrum were recorded 133 for use in data processing and the IT and sacrococcygeal regions were selected on the pressure 134 map image using the appropriate Xsensor software feature. Region size was standardized across 135 all subjects and all conditions, selecting a 3 X 3 sensor region for each of the IT’s and for the 136 sacroccygeal region.28 The region of the mat encompassing the two ischial tuberosities and the 137 sacral regions was used in the calculation of the “dispersion index” as described by Sprigle, 138 Dunlop and Press28; we note that while Sprigle is the first to have reported on the Dispersion 139 Index, the DI was developed by ISO TC173 SC1 WG11(ca. 2002) during the development of the 140 ISO 16840 standards. This region was identified based on the palpated locations of the ischial 141 tuberosities and the sacrum/coccyx. This region was also standardized in size across cushion 142 configurations so that it contained the same number of sensors for each configuration tested. For 143 this reason the region used (area B in Figure 2) did not necessarily contain all sensors under the AC C EP TE D 130 7 ACCEPTED MANUSCRIPT 144 ischial tuberosities and the sacrum, however it was necessary to standardize the size of the region 145 for fair comparisons. 146 Outcome Measures 148 Primary outcome measures used in this study included peak pressure index (PPI), ischial 149 tuberosity peak pressures (ITPP), and the dispersion index (DI).28 The DI characterizes the 150 percent of pressure distributed under the bony prominences (ischial tuberosities and 151 sacrococcygeal region) of the pelvis compared to the total pressure under all areas of the seat28; 152 this measure was selected for its unique ability to evaluate the effectiveness of the “off-loading” 153 properties of the wheelchair seat cushion. While the dispersion index is a newer measure and has 154 not yet been fully validated as an extrinsic pressure ulcer risk factor, the more commonly used 155 peak pressure index (PPI) and ischial tuberosity peak pressures and have been widely used to 156 assess interface pressure risks in a seated environment.18,27,29-32 Lastly, we included two 157 additional summary measures (contact area (CA), and average pressure (AVG)) with only modest 158 relevance to a focal study on pressure re-distribution, but whose reporting helps to provide 159 valuable context related to general efficacy of a pressure management seat cushion. All outcome 160 measures analyzed for this study are described in Table 1 and depicted in Figure 2. 162 163 164 SC M AN U TE D EP AC C 161 RI PT 147 [insert Table 1 here] [insert Figure 2 here] 165 166 167 Data Processing and Analysis 8 ACCEPTED MANUSCRIPT Data were extracted from frame # 120 of each trial, unless there was a visually obvious sensor 169 recording anomaly, in which case the frame nearest to frame number 120 was used and the frame 170 number was noted. Pressure matrix data were processed according to published standards, in the 171 following order: non-linear filtering with a 20% width two-dimensional Gaussian window, and 172 then two dimensionally triplicate interpolation with a cubic spline.33,34 A custom routine was 173 prepared in the Matlab numerical computation environment (Mathworks, Natick, MA) for all 174 data processing. RI PT 168 SC 175 Three configurations of the off-loading cushion were examined, along with the flotation cushion. 177 We tested the hypotheses that PPI, ischial tuberosity peak pressures, and dispersion index 178 variables (PPI, ITPP, DI, Table 1 and Figure 2) would show significant differences in the 4-way 179 cushion comparison, indicative of progressive reduction of interface pressures in these critical 180 regions and off-loading of the high risk areas of the pelvis; our null hypothesis was that there 181 was no significant difference among the four cushion configurations. TE D 182 M AN U 176 Due to the nature of the off-loading cushion, it was anticipated that contact area might be 184 reduced in the off-loading cushion, given that the off-loading is intentional and that whole mat 185 average pressure would be similar across all conditions. For each outcome measure, we tested 186 the hypothesis of significant difference among conditions via two-way ANOVA with condition 187 and subject ID as factors; p-values were reported for condition only. The multiple-comparison 188 analyses were corrected for multiple testing within condition-pair via Bonferroni correction. All 189 variables were computed via the Matlab data processing routine; all statistical analyses were AC C EP 183 9 ACCEPTED MANUSCRIPT 190 performed in the R statistical computing environment (The R Foundation for Statistical 191 Computing, Vienna, Austria).35 RI PT 192 Results 194 Demographics 195 Ten subjects (1 female, 9 male) with chronic spinal cord injuries completed all testing (Table 2). 196 Average height of the subjects was 179 cm (SD 9 cm), average weight was 80 kg (SD 10 kg) and 197 average hip width of the subjects was 41 cm (SD 4 cm). 198 [insert table 2 here] M AN U 199 200 Representative data samples are shown in Figure 3. [insert figure 3 here] 203 TE D 201 202 SC 193 Outcome measures 205 The average pressure (among non-zero sensors) ranged from 31±14 (C0-off) to 68±37 mmHg 206 (C3-float), and the contact area ranged from 2071±33 (C3-float) to 2091±25 (C0-off). 207 Mean values and standard deviations for all outcome measures are reported in Table 3. All 208 ANOVA results were found significant at the p < .001 level. The peak pressure index (PPI) 209 values ranged from a low of 39 ± 18 mmHg (C0-off) to a high of 97 ± 30 mmHg (C3-float); 210 average: 39 ± 18, 61 ± 19, 78 ± 30, and 97 ± 30 in C0 to C3, respectively. These differences were 211 significant at p < 0.001 (Figure 4). AC C EP 204 10 ACCEPTED MANUSCRIPT 212 213 [insert Table 3 here] 214 216 RI PT 215 [insert figure 4 here] 217 Where all hypothesis tests yielded significant differences, we report on pair-wise comparisons in 219 Table 4. 220 [insert Table 4 here] M AN U SC 218 221 We note that the peak pressure index (PPI) and dispersion index (DI) co-vary; although a linear 223 model is significant (p<0.001), the r-squared value is also low (R2=0.19), indicating a significant 224 trend of PPI with DI, albeit imprecise and non-deterministic (Figure 5). TE D 222 227 228 229 230 [insert figure 5 here] AC C 226 EP 225 Discussion Study Validity 11 ACCEPTED MANUSCRIPT Here, we hypothesized that the four cushion configurations would yield significantly different 232 results in a set of interface pressure outcome measures, including PPI which is the outcome 233 measure most closely linked with extrinsic pressure ulcer risk factors. While we considered a 234 more conventional comparative effectiveness study of a single representative off-loading 235 configuration, we elected instead to test all three configurations of this off-loading cushion for 236 two reasons: 1) it was unclear which single configuration would be most informative and 237 clinically relevant, and 2) there are no existing validation studies on the off-loading seat cushion 238 design tested, so the hypothesis that the three configurations yield different pressure parameters 239 has yet to be formally tested; we believed it to be important to incorporate this test into our study. SC RI PT 231 M AN U 240 This study incorporated a sufficiently large and diverse pool of outcome measures, either as a 242 direct variable of seat cushion performance, or as a measure for context. In particular: peak 243 pressure index (PPI), ischial tuberosity peak pressures, and dispersion index (a measure of how 244 much of the interface pressure is concentrated under the ischial tuberosities and sacral regions of 245 the pelvis). We also measured two parameters for context – the average of all non zero pressure 246 readings across the full mat (i.e. average pressure) and the full contact area - to identify 247 differences on these additional, commonly reported interface pressure measures associated with 248 determining clinical efficacy of various cushion designs.3,22,36 EP AC C 249 TE D 241 250 The performance of the off-loading cushion on the primary outcomes was as hypothesized. 251 Commonly used correlates of extrinsic pressure ulcer risk (i.e. PPI and peak pressures under the 252 ITs) were significantly higher with the flotation style cushion than with the various 253 configurations of the off-loading cushion. Additionally, the dispersion index, a measure of the 12 ACCEPTED MANUSCRIPT percent of total pressure distributed under the ischial and sacral regions, was significantly lower 255 for the off-loading cushion, which is indicative of the efficacy of this cushion in reducing 256 pressures in these highly sensitive anatomical regions. All parameters were compared against a 257 flotation style cushion, which is the most commonly used cushion for reduction in these very 258 critical interface pressure characteristics.37 The novel seating configurations studied here make it 259 difficult to compare these results with the existing body of literature, however, these values may 260 provide valuable context for understanding the interface pressure characteristics of this cushion 261 and comparing them to existing research. SC RI PT 254 M AN U 262 Results from the present study indicate that the off-loading cushion effectively reduced interface 264 pressures under the ischial tuberosities and sacrum of the pelvis, as indicated by a significant 265 difference in the PPI, ischial peak pressures, and dispersion index. This result is similar to the 266 findings of Rosenthal et al18 in their testing of a similarly designed wheelchair seat cushion. 267 TE D 263 Study Limitations 269 This study is limited by the lack of a universally accepted interface pressure parameter directly 270 tied to pressure ulcer risk. While several measures were used here, each with wide use by the 271 community, and each with some support in the current literature for metric validity, there is 272 simply no “gold standard” measure definitively tied to pressure ulcer risk.21,30,32 Moreover, 273 many of the measures used to describe interface pressure do not inform the discussion of 274 pressure re-distribution, but are important for context and as free-standing measures to inform 275 the broader discussion on seating technology. Consequently, our study is somewhat diffuse. Our 276 primary outcome measure, PPI, is the metric most closely tied to extrinsic risks of developing AC C EP 268 13 ACCEPTED MANUSCRIPT pressure ulcers, however the newer Dispersion Index measure, first defined by Sprigle et. al in 278 200328, has also been incorporated into a number of studies over the past 10 years.29,31,38 Prior 279 to this, multiple studies also examined interface pressures under various defined “regions” – 280 particularly high risk regions such as those under the ischial tuberosities and the 281 sacrum/coccyx.17-20,27 As the applied research into interface pressure mapping matures, more 282 focal studies will be possible. RI PT 277 SC 283 Additionally, our study design was structured in such a way that the three off-loading cushion 285 configurations were considered three distinct seating systems, and compared along with the 286 flotation style cushion. It could be argued then that the significant differences seen could be 287 attributable to differences among the three off-loading cushions, and not due to differences 288 between the off-loading cushion and the flotation cushion. While this is a fair point, the 289 manufacturer makes the assertion that the off-loading cushion can be considered to be three 290 different cushions, depending on the particular cushion configuration selected and that the three 291 configurations provide quite different profiles in the degree of off-loading of the pelvic region. 292 Furthermore, our pair-wise comparisons show that each of the three off-loading cushions 293 consistently yield significant differences versus the flotation-style cushion. TE D EP AC C 294 M AN U 284 295 Whereas our sample size for this study was small, our findings, while certainly preliminary, 296 could well be argued as generalizable. While our study participant pool comprised a narrow 297 demographic (mostly male SCI patients), we study here only those variables related to interfacial 298 pressure; we have no evidence that the parameters measured here vary by diagnosis or sex. We 299 believe that the off-loading cushion paradigm would have potential utility in populations broader 14 ACCEPTED MANUSCRIPT than those subjects studied here, however more testing would be required to support this 301 conjecture. These are fair and valid characterizations: given the relative lack of literature base for 302 seating technologies like the off-loading cushion, this work will be inherently exploratory. 303 Nevertheless, despite the relatively small sample, we identified several parameters for which the 304 null hypothesis was rejected at P<0.001. Thus, we believe that our study design was appropriate 305 and adequate. Further investigation with other patient populations may also be warranted and we 306 made no effort in this study to quantify or assess seated posture characteristics (e.g. pelvic tilt in 307 the sagittal plane), however this may also be useful in the investigation of the potential benefits 308 of an off-loading seat cushion designed based on orthotic principles. SC RI PT 300 M AN U 309 Conclusion 311 All metrics indicated reduction in a key extrinsic risk factor for pressure ulceration – pressure at 312 the buttock-cushion interface. This was demonstrated through significant changes in PPI, 313 ischial region peak pressures, and the related parameter Dispersion Index. Additionally, the off- 314 loading cushion did not demonstrate reductions in contact area or increased overall average 315 pressure, further reinforcing its potential for mitigating likelihood of developing pressure ulcers 316 in the high risk population, chronic spinal cord injured population. 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AC C 385 Rehabilitation Research & Development. 2009;46(5):577-586. 32. Sprigle S, Sonenblum S. Assessing evidence supporting redistribution of pressure for pressure 391 ulcer prevention: A review. Journal of Rehabilitation Research & Development. 2011;48(3):203- 392 213. 18 ACCEPTED MANUSCRIPT 33. 394 application to the wheelchair-seating interface. Disabil Rehabil Assist Technol. Sep 9 2014(0):1-6. 34. 397 pressure arrays. Journal of Rehabilitation Research & Development. 2014;51(9):1365. 35. 398 399 Austria: R Foundation for Statistical Computing; 2015. 36. 400 401 404 Brienza D, Lin C, Karg PE. A method for custom-contoured cushion design using interface pressure measurements. Rehabilitation Engineering, IEEE Transactions on. 1999;7(1):99-108. 37. 402 403 R Development Core Team. R: A Language and Environment for Statistical Computing. Vienna, RI PT 396 Wininger M, Crane B. Effect of interpolation on parameters extracted from seating interface SC 395 Wininger M, Crane B. A comparison of strategies for imputing saturated pressure array data with Cullum N, Deeks J, Sheldon TA, Song F, Fletcher AW. Beds, mattresses and cushions for pressure sore prevention and treatment. The Cochrane Library. 2000. 38. M AN U 393 Maurer C, Sprigle S. Effect of seat inclination on seated pressures of individuals with spinal cord injury. Physical Therapy. 2004;84(3):255-261. 405 AC C EP TE D 406 19 ACCEPTED MANUSCRIPT 407 Suppliers: 408 a 409 b 410 c Ride Designs, 4211-G South Natches Court, Sheridan, CO 80110 Roho, 1501 S 74th St Belleville, IL62223-5900 RI PT XSENSOR Technology Corporation, 133 12 Avenue SE Calgary, AB, Canada 411 Figure legends: 413 414 Figure 1: The Ride Deigns JAVA cushion. Full system including wedges and two well inserts (Left), , and posterolateral wedge inserts (Right). 415 Figure 2: Outcome measures used in this study 416 417 Figure 3: Exemplars of data collected from two patients in four conditions (C0-off, Far Left; C1off, Left; C2-off, Right; C3-float, Far Right). 418 Figure 4: Peak Pressure Index (PPI) Results 419 Figure 5: Correlation of Peak Pressure Index (PPI) and Dispersion Index (DI) Results 423 424 425 426 427 428 M AN U TE D 422 EP 421 AC C 420 SC 412 20 ACCEPTED MANUSCRIPT Table 1: Outcome measures used in this study Descriptor Peak pressure index (PPI) Units Definition mmHg Average of 9 sensors in the neighborhood around the IT peak pressure m2 IT Peak pressure mmHg Maximum measured pressure across all sensors in the two ischial tuberosity regions m3 Dispersion index % Total pressure in the mat region containing the IT’s and Sacrum divided by the total pressures across the entire mat m4 Contact area*† mm2 Active sensors multiplied by the area of each sensor m5 Average pressure* mmHg Average of all active sensors * Indicates threshold of 5mmHg applied prior to calculation †Increased values of this measure indicate improvement Mat region used Ischial tuberosity regions Ischial tuberosity regions AC C EP TE D M AN U SC RI PT Metric m1 Sacral and both ischial regions compared to whole mat Whole mat Whole mat ACCEPTED MANUSCRIPT Table 2: Subject demographics AC C EP TE D M AN U SC RI PT Subject ID Gender Height (in) Height (cm) Weight (lbs) Weight (kg) Hip Width (cm) PM 01 M 71 180 160 73 38 PM 02 M 74 188 200 91 38 PM 03 M 74 188 210 95 45 PM 04 M 74 188 185 84 43 PM 05 M 70 178 200 91 48 PM 06 M 66 168 165 75 36 PM 07 M 70 178 180 82 40 PM 08 F 64 163 135 61 41 PM 09 M 70 178 165 75 43 PM 10 M 72 183 170 77 38 ACCEPTED MANUSCRIPT Flotation P value 97 ± 30 < .001 98 ± 43 106 ± 34 < .001 14 ± 3 2096 ± 16 54 ± 25 RI PT Off-loading condition 2 78 ± 30 EP TE D M AN U * indicates threshold of 5mmHg applied prior to calculation †Increased values of this measure indicate improvement AC C 16 ±3 < .001 2071 ± 33 < .001 68 ± 37 < .001 SC Table 3: Outcome measure results (mean ± SD) Metric Descriptor Off-loading Off-loading condition 0 condition 1 m1 Peak pressure 39 ± 18 61 ± 19 index (mmHg) m2 IT Peak pressure 68 ± 46 81 ± 34 (mmHg) m3 Dispersion Index 8±3 13 ± 3 (%) m4 2091 ±25 2094 ± 22 Contact area * † (cm2) m5 Average pressure* 31 ± 14 45 ± 18 (mmHg) ACCEPTED MANUSCRIPT Table 4: P-values for pair-wise comparisons between conditions for five outcome measures (P values corrected for multiple comparisons) C0-C2 P<0.001 P<0.001 P<0.001 P<0.001 P<0.001 C0-C3 P<0.001 P<0.001 P<0.001 P<0.001 P<0.001 C1-C2 P<0.05 P<0.05 P<0.01 P<0.01 P<0.05 C1-C3 P<0.001 P<0.001 P<0.001 P<0.001 P<0.001 M AN U TE D EP AC C C2-C3 P<0.001 P<0.001 P<0.01 P<0.01 P<0.001 RI PT C0-C1 P<0.001 P<0.001 P<0.001 P<0.001 P<0.001 SC Metric m1 m2 m3 m4 m5 AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT AC C EP TE D M AN U SC RI PT ACCEPTED MANUSCRIPT