Measuring the effect of incremental angles of wheelchair tilt on interface pressure among individuals with spinal cord injury

Spinal Cord (2011) 49, 827–831 & 2011 International Spinal Cord Society All rights reserved 1362-4393/11 $32.00 www.nature.com/sc ORIGINAL ARTICLE Measuring the effect of incremental angles of wheelchair tilt on interface pressure among individuals with spinal cord injury EM Giesbrecht1, KD Ethans2 and D Staley3 1 Department of Occupational Therapy, University of Manitoba, Winnipeg, Manitoba, Canada; 2Department of Medicine, University of Manitoba, Winnipeg, Manitoba, Canada and 3Office of Clinical Research, St Boniface General Hospital, Winnipeg, Manitoba, Canada Study design: This study was a repeated measures study. Objectives: The objective was to systematically measure the relative reduction in interface pressure (IP) at the ischial tuberosities (IT) and sacrum through 101 increments of tilt in a manual wheelchair among individuals with motor complete spinal cord injury (SCI). Setting: This study was carried out in Manitoba, Canada. Methods: A total of 18 adults with ASIA A or B level of injury were recruited through an out-patient SCI clinic. Using a standardized protocol, participants were tilted in 101 increments between 01 and 501, and IP readings were obtained at the IT and sacrum using pressure mapping technology. Relative pressure reduction from baseline was calculated and compared between tilt angles. Results: Tilt angle had a highly significant effect on pressure reduction at the IT (P ¼ 0.000) and the cosine relationship between these variables was expressed as quadratic. Reduction in sacral pressure did not occur until 301 tilt, with increased loading at smaller tilt angles. Pressure reduction at the IT and sacrum was not significantly different for tetraplegic and paraplegic participants. Conclusion: Small tilt angles are more suitable for postural control than pressure management. A minimum tilt of 301 is required to initiate unloading the sacrum and to achieve a clinically important reduction in pressure at the IT. Larger tilt angles resulted in more substantial pressure reduction than previously reported. Tilt-in-space appears to have similar benefits for individuals with paraplegia and tetraplegia. Spinal Cord (2011) 49, 827–831; doi:10.1038/sc.2010.194; published online 18 January 2011 Keywords: tilt-in-space; wheelchairs; interface pressure; pressure ulcers; pressure mapping; spinal cord injury Introduction Pressure ulcers are a significant and costly problem for individuals with a spinal cord injury (SCI), who use a wheelchair. Prolonged sitting, without intermittent weightshifting and pressure relief, creates a high risk for ischemia.1 Sensory and motor impairment can impede anticipation of pressure and independent performance of repositioning. Tilt-in-space (TIS) wheelchairs are used as one strategy to address the risk of pressure damage. With a TIS configuration, the entire seating system rotates backwards within the wheelchair frame, while keeping the seat-to-backrest angle fixed. By changing the orientation of the individual relative to gravity, the normal force between the seat cushion and buttocks is reduced. Reducing the intensity of pressure at the Correspondence: Assistant Professor, EM Giesbrecht, Department of Occupational Therapy, University of Manitoba, R214–771 McDermot Avenue, Winnipeg, Manitoba, Canada R3E 0T6. E-mail: Received 20 September 2010; revised 11 December 2010; accepted 13 December 2010; published online 18 January 2011 human–seat interface is expected to extend the duration of time before ischemia occurs.2 Tilting the wheelchair backwards allows the user to assume a more recumbent position, taking the pressure off of the buttocks. While TIS wheelchairs are regularly employed to address issues of pressure redistribution, there are also other indications for their use. Research and clinical evidence suggest that TIS may address changes in body structure and function to enable outcomes, such as improved postural control and stability, comfort, pain relief, digestion and biomechanical efficiency of propulsion.3–5 However, TIS has also been reported to impede upper extremity function, elicit abnormal reflexes and limit accessibility.5,6 Wheelchairs configured for TIS are typically larger, heavier and more expensive than traditional wheelchairs.7 Furthermore, specific models of wheelchairs are required to achieve large angles of tilt. For example, over 15% of the funding-approved TIS wheelchairs in Ontario do not tilt to 301; 40% do not tilt to 401 and 85% do not reach 501. Given these accessibility, functional and Pressure reduction with wheelchair tilt EM Giesbrecht et al 828 economic implications, the effectiveness of these wheelchairs must be demonstrated in order to justify their prescription. Currently, there is limited empirical evidence to inform clinicians about the relative benefit in interface pressure (IP) reduction obtained as tilt angle increases. Previous studies have employed small sample sizes and explored a few select angles of tilt, often in conjunction with other interventions such as recline. Hobson8 explored nine different combinations of sitting posture, tilt and recline, reporting an 11% reduction in peak IP at 201 of tilt. Vaisbuch et al.9 found a 22% reduction in peak pressure at the ischial tuberosities (IT) when children with paraplegia were tilted to 251. Burns and Betz10 combined three different cushions in a horizontal and 451 tilt position, with the latter resulting in a 33% reduction in peak IP, whereas Henderson et al.11 compared tilt at 351 and 651 and found 27% and 47% reductions, respectively. Comparisons between these results are challenging owing to differences in study design and measurement tools. Intuitively, larger angles of tilt are expected to result in greater reduction of IP and should be more effective in addressing the risk of pressure ulcers. Clinicians often prescribe TIS wheelchairs and specific tilt angles based on clinical experience; additional empirical evidence would inform their professional reasoning. Therefore, the purpose of this study was to systematically measure the relative reduction in IP at the IT and sacrum through 101 increments of tilt in a manual wheelchair among individuals with motor complete SCI. Specific objectives included establishing the nature of the relationship between tilt angle and relative pressure reduction and identifying clinically significant differences between angles of tilt. In addition, we compared the effect of TIS between paraplegic and tetraplegic participants. Materials and methods Study design and participants A repeated measures design was used, allowing each participant to act as his/her own control. Participants were exposed to a reference position (01 tilt, seat-to-backrest angle 1001), followed by five conditions of the TIS intervention (101 increments of tilt from 101–501). Differences in IP between tilt angles were compared within individuals. In all, 18 participants were recruited through the out-patient SC (...truncated)