Wheeled Mobility and Seating Equipment

Seated Surfaces

The seat cushion in a wheelchair has many roles depending on the individual’s unique needs. Primarily, the cushion’s role is, to contribute to a functional and balanced posture and redistributing pressure away from the critical areas of the IT and the sacrum and redistributing pressure over a larger contact area to reduce overall and peak pressures (Eitzen 2004). Bogie et al. (1995) stated that 47% of pressure ulcers occur at the IT or sacrum and are therefore more likely to have been initiated while seated. Provision of a wheelchair cushion that redistributes pressure is an important prevention recommendation. Cushions should be evaluated based on postural support and stability provided, pressure redistribution capabilities, comfort, function temperature effects level of SCI, pressure redistribution abilities, transfer technique, and lifestyle (Garber 1985; Makhsous et al. 2007a; Fisher et al. 1978; Seymour & Lacefield 1985; Sprigle et al. 1990). Many of the studies reviewed for this section compare different cushions in an attempt to identify the “best” cushion. One study explored how the intensity of the load when sitting on a cushion influences blood flow, which is thought to influence pressure injury risk.

Author Year

Country

Research Design

Score
Total Sample Size

 Methods  Outcome
Crane et al. 2016

USA

RCT Crossover

PEDro=5

N=10

 Population: Mean age= N/R; Gender: males=9, females=1; Level of injury: N/R; Mean time since injury= 20 yr.

Intervention:  Comparison of interface pressure between an off-loading cushion in three conditions: fully off-loading (C0-off), addition of the top well insert (C1-off), addition of both well inserts (C2-off) to a 10cm-high air flotation cushion (C3-float). The order of cushions was randomized for each participant with each trial being completed 5 times for 2 minutes each time. Risk of the pressure mat hammocking was accommodated. Sitting surface bony prominences were manually palpated and located in relation to the pressure readings.

Outcome Measures: Peak pressure index (PPI); Ischial tuberosity (IT) peak pressure; Dispersion Index; Contact Area; Average pressure using Interface Pressure Mapping.

 1.     PPI averaged values ranged from a low of 39±18mmHg (C0-off) to a high of 97±30mmHg (C3-float));(C1 – 61±19, C2 -78±30). Differences between all conditions was significant at P<.001.

2.     PPI , IT peak pressure, dispersion index, were all significantly lower in C0, C1 and C2 than C3 but significantly higher for contact area and average pressure
Sonenblum et al. 2018a

USA

RCT Crossover

PEDro=5

N=4

 Population: Mean age= 42.0 yr; Gender: males=1, females=3; Level of injury: T2-T12; Mean time since injury= 15.8 yr. All participants had significant muscle atrophy at their sitting surface therefore were considered high risk for developing pressure injuries.

Intervention: Participants buttocks’ were scanned sitting in a FONAR Upright MRI. Scans were collected with the individuals’ buttocks fully suspended without pelvic support and seated on 3 different wheelchair cushions: Enveloping cushions: Roho HP, Matrx Vi; Offloading cushion: Java.

Outcome Measures: Bulk tissue thickness, percent of gluteus coverage under the peak of the ischial tuberosity, muscle volume, tissue deformation, greater trochanter bulk tissue thickness measured using an MRI, sacro-coccygeal angle changes and Peak pressure Index using an IPM.

 1.     All participants had similar buttock anatomy with significant muscle atrophy (muscle volume avg: 265 cm3 ) and limited soft ticcue at the ischium (bulk tissue thickness ranged between 28 and 40 mm).

2.     Bulk tissue thicknesses at the ischium were reduced by more than 60% on Roho HP and Matrx Vi, and more variably (23–60%) on Java.

3.     Bulk tissue thickness under the greater trochanter was consistent acorss participants and cushions, ranging from 12-27mm in the loaded condition and displaced laterally in the loaded condition.

4.     Peak pressure indeces ranged varied across participants and cushions (50-290mmHg) – lowest PPIs seen with the Java and highest on the MatrixVi.

5.     The gluteus maximus displaced superiorly and laterally on the Roho cushion, superiorly and laterally on the MatriVi, and was most similar to the unloaded condition on the Java, with the gluteau maximus not being loaded whiel sittign on the Java cushion.
Gil-Agudo et al. 2009

Spain

RCT

PEDro=5

N=48

 Population: Mean age: 42 yr; Gender: males=38, females=10; Mean weight: 67.6 kg; Mean BMI: 23.3 kg/m2; Level of injury: cervical=13, thoracic=35; Severity of injury: AIS A.

Intervention: Use of interface pressure mapping to determine its utility in cushion selection. Comparison of cushions: 1) single compartment low profile air cushion; 2) single compartment, high profile air cushion; 3) dual compartment air cushion; 4) gel and firm foam cushion. Wheelchair set-up was normalized (hips, knees and ankles at 90°, seat parallel to floor, back perpendicular or tilted up to 10 °); air cushions all individually adjusted at set-up for each trial based on manufacturer instructions.

Outcome Measures: Pressure mapping using the Xsensor to compare distribution of pressure (peak maximum pressure of entire map and peak pressure at ischial tuberosities (IT)) and contact surface (total contact area with readings greater than 60mmHg and less than 60mmHg) from a 1.5 min reading.

 1.    The interface pressure mapping system was useful for assessing the mechanical characteristics of this sample of cushions.

2.    The dual compartment air cushion had significantly lower peak maximum pressure across the mapping surface, and lower peak pressure in the area of the IT than other cushions evaluated in this study.

3.    The gel and firm foam cushion had the highest mean pressure values (p<0.05 versus low-profile air, high-profile air, dual compartment air) but had significantly lower peak pressure values at the ITs over the single compartment, low profile air cushion; there were no statistically significant differences (p<0.05) in any variable between the single compartment air cushions – low and high profile.

4.    For surface variable measurements, the dual compartment air cushion had the largest total contact surface (p<0.05) compared to the three other cushions; the dual compartment air cushion had the lowest percentage of the total contact surface with pressure readings over 60mmHg (p<0.05) compared to the other three cushions); the dual compartment air cushion had the lowest contact surface with pressure readings over 60 mmHg (p<0.05) except for the low profile single compartment air cushion (p=0.11).

5.    The cushion with the least favorable total contact surface was the single compartment low profile air cushion (p<0.05) compared to the other three cushions.

6.    The cushion with the largest surface area above the 60 mmHg threshold was the gel and firm foam cushion (p<0.05) compared to the other cushions.
Burns & Betz 1999

USA

Prospective Controlled Trial

N=16

 Population: Mean age: 46 yr; Gender: males=16, females=0; Level of injury: tetraplegia=16; Severity of injury: AIS A=7, B=9.

Intervention: Two static wheelchair cushions (dry flotation and gel) upright and at 45° tilt, compared to a dynamic cushion that was composed of two air bladders (H and IT) that alternated between inflation and deflation.

Outcome Measures: Interface pressure at ischial tuberosities (IT) was assessed with Clinseat seating interface pressure sensor.

 1.     When compared in the high-pressure condition, all cushions were significant (p<0.001), with means of 111 mmHg (dry flotation), 128 mmHg (gel), and 157 mmHg (dynamic).

2.     When compared in the low-pressure condition, only gel flotation (86 mmHg), and the dynamic cushion (71 mmHg), were significant (p<0.05).

3.     The IT had a significantly higher mean during IT bladder inflation of the dynamic cushion than the high-pressure position in the static cushions (p<0.01), with the dry flotation having significantly lower pressure than the gel cushion (p<0.01).

4.     The IT had significantly lower mean in the lower pressure position only for the dynamic cushion as compared to the gel cushion (p<0.01).
Garber 1985

USA

Prospective Controlled Trial

N=251

 

 Population: Gender: males=207, females=44; Injury etiology: SCI=251.

Intervention: Assessment of pressure distribution for seven cushions.

Outcome Measures: Seated pressure distribution.

 No statistical results reported.

1.     The air-filled cushion (ROHO which was 1 of 2 used) produced the greatest pressure reduction in 51% of the subjects.

2.     A foam cushion (the stainless comfy hard cushion) was effective for only 18% of the subjects even though it was the second most frequently prescribed cushion.

3.     More subjects with tetraplegia received the ROHOs than subjects with paraplegia (55% versus 45%) while more paraplegic subjects were prescribed the Jay cushion (a combination of foam and flotation materials (19% versus 7%).
Makhsous et al. 2007b

USA

Cohort

N=60

 Population: Mean age: 37 yr; Gender: males=45, females=15; Level of injury: paraplegia=20, tetraplegia=20, and able-bodied=20.

Intervention: Two 1-hr protocols. 1) Alternative-sitting position was altered every 10 min between normal and WO-BPS (partially removed ischial support and lumbar support). 2) Normal-normal posture and push-ups every 20 min.

Outcome Measures: XSensor pressure mapping system measuring Interface pressure measures of total contact area, average pressure and peak pressure on backrest and anterior middle and posterior sections of the seat.

 1.     Those with tetraplegia had a larger contact area at the anterior portion of the cushion, as compared to the other groups.

2.     The mean pressure over the whole cushion was significantly different for each group (p<0.001).

3.     Those with tetraplegia had the highest mean pressure during the WO-BPS posture, as compared to the other groups (p<0.001).

4.     The contact area of the posterior portion of the cushion and the peak interface pressure decreased in all groups, with the largest decrease in those with tetraplegia for the latter. The mean pressure on the anterior and middle portions of the cushion increased in all groups.

5.     At the posterior portion of the seat where ischial tuberosities are usually positioned, average pressure was higher for those with paraplegia (88.9 mmHg).

6.     Average push up time was 49 sec for those with paraplegia.
Seymour & Lacefield 1985

USA

Case Control

N=20

 Population: Age range: 16-35 yr; Weight range: 40.6-72.5 kg; Injury etiology: SCI=10, healty control=10.

Intervention: Seven commercially available cushions and one experimental cushion were evaluated for each subject.

Outcome Measures: Temperature and pressure effects for each cushion. Subjects were asked to rate each cushion as to cosmesis, handling and suitability for purchase.

 

 1.       Greatest pressure was seen under the soft tissue areas of most subjects; no significant differences between the cases and controls.

2.       Temperatures were lowest for gel, water and air cushions and highest for alternating pressure and foam cushions.

3.       SCI group – Greatest pressure under a bony area occurred most often with the Spenco cushion (90.10 mmHg); controls – it occurred most often with the Tri-pad (89.20 mmHg) indicating that these cushions did not compare favorably to others.

4.       There was wide variability in pressure measurements in individual subjects (SD=12.21 mmHg). However, air filled (Bye Bye Decubiti) had the best pressure readings.

5.       Cosmesis (83%) and handling (73%) were related to purchase decisions.
Vilchis-Aranguren et al. 2015

Mexico

Pre-Post

N=16

 Population: Mean age: 31.8 yr; Gender: males=9, females=7.

Intervention: Participants were administered a prototype wheelchair cushion designed to adjust the anthropometry of the user’s ischio-gluteal area and prevent pressure ulcer formation. Participants were assessed at baseline and at 2 mo.

Outcome Measures: Functional independence measure (FIM), Modified ashworth scale (MAS), Pressure distributions, Balance performance; Perceived satisfaction.

 1.     No significant differences were found between the previous cushion and after using the prototype cushion for: transfer capacity indicated by FIM scores (p>0.05); MAS scores (p>0.05).

2.     Pressure distributions decreased significantly after using the prototype cushion (p=0.012).

3.     There were no statistical differences in balance performance using the prototype cushion (p>0.05).

4.     Participants reported higher perceived satisfaction with the prototype cushion in performing activities of daily living (p=0.006).
Hamanami et al. 2004

Japan

Pre-Post

N=36

 Population: Mean age: 40.1 yr; Gender: males=28, females=8; Level of injury: paraplegia=36; Severity of injury: AIS A=35, B=1.

Intervention: ROHO High Profile multi-cell air cushion.
Outcome Measures: Tekscan pressure measurement system measuring total seat surface area, maximum pressure and area of high concentration.

 1.      In all subjects, the highest pressure points were at the ischial areas.

2.      The maximum surface pressure was related to the ratio of high concentration areas to seating surface area at the point of minimum pressure (r=0.466, p=0.0042).

3.      A significant relationship between point of minimum pressure and maximum interface pressure or body weight was not found.

4.      The cushion air pressure was significantly related to body weight (r=0.495, p=0.0021).
Gilsdorf et al. 1991

USA

Post-Test

N=17

 Population: Paraplegia (N=6): Mean weight: 83 kg; Tetraplegia (N=5): Mean weight: 66 kg; Able-bodied controls (N=6): Mean weight: 76 kg.

Intervention: 30 min sitting intervals, on different surfaces [Jay cushion; ROHO cushion; hard surface (controls only)] in a wheelchair that had a force plate attached to it.

Outcome Measures: Normal and shear seating forces; Armrest forces; Centre of mass location.

 1.    On Jay cushion, those with tetraplegia had higher amplitude lateral movements and those with paraplegia had more lateral zero-crossings, when compared to ROHO cushion.

2.    Larger arm force variation was found among those with paraplegia.

3.    On the ROHO cushion, all subjects had larger normal and shear forces and an anterior centre of mass.

4.    Those with paraplegia had more variation, while those with tetraplegia had less, on static force factors between cushion types.

5.    SCI groups had higher force measurements than control group.

6.    Armrest forces applied by those with paraplegia were larger than those applied by those with tetraplegia (8-9% versus 5%, p<0.11).
Trewartha & Stiller 2011

Australia

Case Series

N=3

 Population: Age range: 27-48 yr; Gender: males=3, females=0; Injury etiology: traumatic SCI=3; Level of injury: paraplegia=1, tetraplegia=2; Mean time since injury: 7.0 mo.

Intervention: Xsensor pressure mapping system used to measure interface pressure of two cushions (Roho Quadtro Select HP versus Vicair Academy Adjuster) in two phases (both mapped daily x7 days and 3x/d for an additional 3 d with the cushion that demonstrated the lowest pressure in phase 1).

Outcome Measures: Number of cells with pressure >100 mmHg, and 60-99 mmHg, compared between the two cushions.

 1.    The number of cells with pressure >100 mmHg was consistently lower on the Roho Quadtro Select HP cushion compared to the Vicair Academy Adjuster cushion (p<0.001; 95% confidence interval 1.86 Vicair, 5.58 for Roho).

2.    There was variability across participants in the number of cells within the 60-99 mmHg range for each cushion type (no significant difference between the cushions; p=0.32).
Takechi & Tokuhiro 1998

Japan

Case Series

N=6

 Population: Age range:18-48 yr; Gender: males=6, females=0; Level of injury: paraplegia=6; Severity of injury: complete=6.

Intervention: Five different cushions (air cushion, contour cushion, polyurethane foam cushion, Cubicushion, silicone gel cushion).

Outcome Measures: Tekscan BigMat pressure mapping system measuring peak pressures and area of total contact.

 1.     If the area of contact was more widespread, the peak pressure was found to be lower.

2.     The air cushion had the largest area of pressure distribution and the lowest peak pressure (257-87g/cm2). The silicone cushion had the second lowest (292-129g/cm2) peak pressure.
Effects of Different Sitting Surface Loading on Blood Flow and Tissue Displacement
Sonenblum & Sprigle. 2018b

USA

Pre-Post

Ninitial=34

Ninitial=28

 Population: Age range= 18-40 yr; Gender: males=28, females=0; Level of injury: N/R; Time since injury >2 yr.

Intervention: The seated buttock was unloaded, and loaded at lower (40–60 mmHg) and high (>200 mmHg) loads.

Outcome Measures: Blood flow at the ischial tuberosity; tissue compliance using the Myotonometer measuring buttock tissue displacement at ischial tuberosity and ratio of displacement; risk factors of level fo injury, body mass index, blood pressure, smoking status, hematocrit, serum albumin, and lymphopenia.

 1.     Tissue compliance varied widely with on BMI being related to the amount of buttock tissue displacement (beta=0.229, 95% CI [0.106, 0.492).

2.     Ratio of displacement was associated with the smoking staus risk factor only (beta=0.070, 95% CI [0,018, 0.122].

3.     Blood flow was significantly reduced at high loads (p<0.05), while no significant changes were found at lower loads (p>0.05).

4.     Blood lfow at lower loads differed according to having a history of pressure injuries, with those no history having a greater blood flow (mean(SD) – 1.5(0.7), p=0.006, 95%CI for difference =[0.2, 1.2].

Summarized Level 5 Evidence Studies

The following level 5 evidence studies have been reviewed, and the overarching findings from the studies are highlighted in this section. As noted at the start of this chapter, these types of studies are not included in the discussion or in the conclusions.

Wu et al. (2016) provided participants with alternating pressure air cushions six times a week for two weeks, every three months for a total of 18 months. A high percentage of users were very satisfied with comfort and performance of these cushions. However, there were no measures of pressure or pressure ulcer incidences in relation to this trial therefore the full benefits of this type of cushion is not known.

Kovindha et al. (2015) surveyed chronic SCI wheelchair users in Thailand about their pressure ulcer prevalence, quality of life and health status. McClure et al. (2014) similarly surveyed a group of chronic SCI wheelchair users about their pressure ulcer prevalence and wheelchair cushion use. In both studies over half of the population had a pressure ulcer at some point. Common sites for current pressure ulcers were the IT, while that of healed pressure ulcers was the sacrococcygeal area. Kovindha et al. (2015), found those with current pressure ulcers were more depressed than those without current pressure ulcers. There was however no difference in health status between those with and without pressure ulcers. McClure et al. (2014) found that more than half of the participants used their wheelchair cushions when travelling in motor vehicles or airplanes.

Meaume et al. (2017) completed two observational studies exploring pressure ulcer incidence in recently spinal cord injured people who were at high risk for developing pressure injuries following a 35 day period of using an air-filled cushion; one study used a single compartment air-filled cushion (n=78) and the second using a multi-compartment air-filled cushion (n=74). They found an incidence of 2.6% for developing a pressure injury in the single compartment air-filled cushion group versus a 4% rate in the other group. The authors indicate that this rate is low, and therefore recommended the use of these types of cushions however, they do not reference support for this being a low incidence rate. They also did not account for any other variables that may have supported good pressure management strategies to reduce the risk of developing pressure injuries given the participants were newly admitted and in a very supportive environment. Additionally, the authors also declare an affiliation and funding support with the manufacturer of the air-filled cushions.

Sprigle and Delaune (2014), and Sprigle (2010) investigated the properties of cushions used by SCI wheelchair users at an adult inpatient rehabilitation center. Cushion type varied from air, foam and fluid cushions. The average cushion age was approximately 30 months, and the average cushion usage per day was 12 hours. The proportion of cushion damage from deformation, granulation, or stiffness to cushions was greater as cushions aged. Sumiya et al. 1997 reported similar findings with regards to frequency of replacement of cushions and types of cushions used.

Brienza et al. (2018) explored the effects ot tissue compositions (fat and muscle) and deformation under the ischial tuberosities of 6 participants (4 with SCI, 2 without), on 6 different seat cushions using Magnetic Resonance Imaging (MRI) and Interface Pressure Mapping (IPM). They found that no one cushion performed best for all participants. They also found a difference in tissue composition between SCI and non-SCI participants. Participants with SCI having higher tissue volume reductions when loaded (sitting). Higher IPM Peak pressure indexes were also associated with lower overall tissue thicknesses in the ischial tuberosity areas. These findings reinforce that cushion selection must be individualized and the need for a comprehensive assessment to support the prescription of individualized seating equipment. Individual anatomy composition and cushion type will affect deformation response (and therefore assumed pressure injury response). The authors identify limitations in this study such as the small number of participants and that findings are observational. However, the findings are similar to other findings in this section and throughout the chapter as well as the Pressure Ulcer chapter.

Discussion

Sonenblum et al. (2018b) identified clinical factors for consideration that influence buttock tissue response to loading. The study found that people with higher BMI experienced greater magnitude of deformation of the ischial tuberosity tissue and slightly increased blood flow at lower loads. They also found that buttock tissue reached maximum deformation (“bottomed out”) at a lower load for people who smoked compared to non-smokers. In regard to superficial blood flow, there was great variability across all participants, at both high (200+mmHg) and low loads (40-60mmHg). However, for people with a history of pressure injuries, there was a blood flow decrease even at low loads. These findings suggest that there are clinically related factors to consider during the process of determining the optimal seated surface for pressure management.

Crane et al. (2016) sought to measure the interface pressure characteristics of an offloading cushion (Ride Java in 3 configuration – full offloading, and addition of 2 well inserts) compared to an air inflation cushion (single valve ROHO). Their findings suggest that the offloading cushion provided improved pressure management than the air inflation, however since their isn’t a universally accepted interface pressure parameter directly linked with pressure ulcer risk or development it is not known if these differences are enough to impact pressure ulcer incidence. Generalizability is also challenging due to limited information on participants, about their posture on the cushions and the small sample size.

Sonenblum et al. (2018a) also compared the Java in its offloading configuration with the 4” roho (single valve) as well as with the MatrixVi cushions. Their goal was to determine differences in tissue deformation using an MRI and Peak pressure index via IPM. The participants they chose had signficant atrophied sitting surface tissue as this was felt to be one of the most challenging individuals to seat safely. Their findings suggest that there is a relationship between the tissue thickness under the iscial tuberosities and interface pressure, where the thinner the tissue the higher the pressures. However, they also found that all cushions deformed tissue in some location, and that tissue responds individually to load in different locations, supporting the need for indivudalized assessment for identifying the optimal seat cushion for each person.

Vilchis-Aranguren et al. (2015) provided a wheelchair cushion personally customized to each participant’s ischiogluteal area. After using these custom cushions for two months, pressure distributions around the ischiastic tuberosity zone decreased and participants reported increased satisfaction in performing activities of daily living compared to their regular cushions. These findings support the need for consideration of the sitting surface anatomy during the individualized assessment for seating.

The following studies evaluated different cushions using different interface pressure mapping systems and different pressure mapping outcomes. Typically, the studies used very small numbers of participants and did not evaluate a range of contributing factors such as posture on the cushions evaluated. Since there isn’t an absolute pressure threshold identified related to pressure injury incidence, the findings from these studies provide data for consideration in clinical practice but should be used with clinical judgment for determining the optimal cushion in conjunction with the other seating components and configuration of the wheelchair frame. Trewartha and Stiller (2011) used pressure mapping to evaluate the Roho Quadtro and the Vicair Academy among three people with SCI. Findings indicated that the Roho Quadtro had significantly fewer cells in the greater than 100 mmHg range than the Vicair Academy but there was no significant difference in the 66-99mmHg range. The study did not examine the number of cells in the less than 65mmHg range. The location of the cells with greater than 100mmHg were not identified as being over bony prominences. Other pressure characteristics such as peak pressure gradient, area of distribution, or symmetry were not measured.

In the cushion comparison study by Gil-Agudo et al. (2009) the dual compartment air cushion exhibited the best mechanical performance with regard to the distribution of pressures and contact surface interface compared to the other three cushions studied (low profile air, high profile air, and gel and firm foam cushions). This study compared only four cushions, and based findings only on distribution of pressure and not any of the other factors that are required for cushion selection. The main finding was that using interface pressure mapping could augment cushion selection but is only part of the cushion selection process.

Makhsous et al. (2007b), compared the contact sitting surface areas in two different conditions; one where the ischial support was partially removed for 10 mintues periods and the other where push up were performed every 20 minutes. The investigators found that the anterior portion of the seat cushion had a larger contact area among those with tetraplegia with higher pressure in the anterior and middle portion of the cushion for the partially removed ischial support condition.The authosr suggest that the reducing the contact area at the posterior sitting surface can be achieved with increased contact at the middle and anterior areas, thereby reducing the pressure over the sittign surface bony prominences.

Hamanami et al. (2004) used a pressure mapping system to evaluate the pressures found on an air floatation cushion (high profile ROHO) with 36 subjects with SCI. The results indicated that the optimal reduction in interface pressure was just before bottoming out on the cushion. No reliable method was found for systematically determining the appropriate air pressure for a ROHO for participants with SCI (Hamanami et al. 2004). Takechi and Tokuhiro (1998) also found that the air cushion had the lowest peak pressure and the highest area of pressure distribution followed by the silicone (gel) cushion.

In the study conducted by Burns and Betz (1999), three wheelchair cushions were tested: dry flotation (ROHO High Profile), gel (Jay 2), and dynamic (ErgoDynamic), the last consisting of two air-filled bladders (H-bladder, IT-bladder). These were compared to each other under high pressure conditions (upright sitting or IT-bladder inflated) and low-pressure conditions (seat tilted back 45° or H-bladder inflated). When analyzing the pressure placed on the IT, it was found that the pressure was higher during upright sitting than in the tilted back position for both the dry flotation and the gel cushion , with the dry flotation cushion providing more pressure redistribution than the gel cushion during upright sitting. Mean pressure with the IT-bladder-inflated cushion was greater than upright pressures for either the dry flotation or gel cushions.

Takechi and Tokuhiro (1998) studied the seated buttock pressure distribution in six patients with paraplegia using computerized pressure mapping. Five wheelchair cushions were evaluated (air cushion, contour cushion, polyurethane foam cushion, cubicushion, silicone gel cushion). Tests showed that if the area of contact was more widespread, the peak pressure was lower. The air cushion and the silicone cushion were found to have the lowest peak pressures.

Gilsdorf et al. (1991) studied subjects sitting on ROHO and Jay cushions. Normal force, shear force, centre of force, lateral weight shifts and amount of weight supported by armrests were studied under static and dynamic conditions. The ROHO cushion showed a tendency to carry a larger percentage of total body weight; have a more anterior centre of mass; and showed more forward shear force. There were more lateral weight shifts on the Jay cushion. Armrests supported a portion of body weight.

Seymour and Lacefield (1985) evaluated eight cushions for pressure, temperature effects and subjective factors influencing cushion purchase. While data indicated a wide variability in pressure measurements in individual subjects, the air-filled cushion (Bye Bye Decubiti) had the best pressure readings. The alternating pressure and foam cushions had consistently higher temperature readings across both groups.

Garber (1985) evaluated seven cushions based on amount of pressure reduction. The author also looked at how frequently each cushion was prescribed to subjects with quadriplegia and paraplegia. The ROHO cushion produced the greatest pressure reduction in the majority of subjects (51%) but was prescribed more often for subjects with quadriplegia versus paraplegia (55% versus 45%).

These studies demonstrate that there are individual variations in cushions needs inherent in those with SCI (e.g., paraplegia versus tetraplegia). Pressure mapping is a useful clinical tool to assist in determining pressure redistribution properties of cushions, but pressure is not the only factor to consider in cushion selection (Gil-Agudo et al. 2009). This is an important consideration as most of the studies reviewed have identified air inflation cushions as providing the lowest pressures but have not examined any other suitability factors. Objective findings together with the clinical knowledge of the prescriber, individual characteristics and the client’s subjective reports need to be considered when prescribing a wheelchair cushion to minimize pressure ulcer risk factors. None of these studies included direct evidence of pressure ulcer prevention associated with a particular cushion type.

Conclusion

There is level 2 evidence (three randomized controlled trials: Gil-Agudo et al. 2009; Crane et al. 2016, Sonenblum et al. 2018a, and one pre-post study: Vilchis-Aranguren et al. 2015) suggesting that cushions that envelope specific to the individual’s shape may have lower sitting surface pressures may have higher patient satisfaction than cushions that envelope less.

There is level 2 evidence (from one prospective controlled trial: Burns & Betz 1999, one randomized control study: Sonenblum et al. 2018a, and one cohort study: Makhsous et al. 2007) that cushions that reduce the pressure (e.g., dynamic versus static) or offload pressure in the ischial tuberosity region may be associated with potentially beneficial reduction in seating interface pressure and/or pressure injury risk factors.

There is level 4 evidence (from one pre-post test study: Sonenblum et al. 2018b) to suggest that the factors of body mass index, smoking status, and pressure injury history affect tissue response to different loads when seated on a cushion.

No one cushion is suitable for all individuals with SCI.

Cushion selection should be based on a combination of pressure mapping results, clinical knowledge of the prescriber, individual characteristics, tissue loading response, and preference.

More research is needed to see if decreasing ischial pressures or decreasing risk factors such as skin temperature via the use of specialty cushions will reduce pressure injury risk.

Pressure mapping is a useful tool for comparing pressure redistribution characteristics of cushions for an individual, but it needs to be a part of the full evaluation not the main part or only evaluation; further research is needed to explore the relationship with tissue deformation.

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