Wear in Wheelchair Cushions 2.0

Hello all!

In May 2012, I wrote an article for my Clinical Corner blog, titled "Wear in Wheelchair Cushions". I continue to receive questions on how to determine when a wheelchair cushion requires replacement so I thought it would be a good idea to revisit this topic. This month, I will update the discussion on wear in wheelchair cushions by reviewing research that has been published since my blog article was posted.

As I indicated in my previous article on wear in wheelchair cushions, visual inspection of both the cushion cover and the cushion itself is required to identify signs of wear. In a study published in 2013, visual inspection was conducted on 202 wheelchair cushions after everyday use by community-dwelling participants recruited from a rehabilitation hospital¹. The wheelchair cushions were categorized based on their primary and secondary materials, including foam, elastomer, viscous fluid, air and other materials. For example, a cushion in which a fluid insert sits in a foam base was classified as fluid being the primary material and foam being the secondary material. All of the cushions met the American criteria to be either for skin protection or skin protection and positioning.

The study was conducted over a period of time, which allowed for some cushions to be inspected approximately every 6 months to see changes in the cushion over time. Researchers performed visual inspections on the cushion covers, evaluating the condition of seams, fabric, zipper, pocket and attachment. Cushion covers were removed, if possible, and the cushion was inspected for the following:

• Condition of bladder
• Condition of valve
• Condition of internal seams, sewn, or welded structure
• Visible tears, breaks, or fractures of any component
• Amount of interior component discoloration
• Compression set or permanent deformation of foam
• Presence of granulation or brittleness of foam^{1 (p. 177)}

In addition to demographic information, information related to cushion use was gathered from the participants. In order to compare wheelchair cushions based on the duration of use, rather than calendar age, CushionAge was determined by multiplying the calendar age of the cushion (in days) by the average daily use by the participant (in hours). CushionAge then was used to categorize the cushions in the study, from being less than 12 months old, between 12 and 36 months old, and over 36 months old. For example, a CushionAge of 12 months was "defined as 4,320 hours of use based on 12 hours/day for 12 months and using 30 days/month"^{1 (p. 177)}. Twelve hours per day was the average length of time that participants used the cushions each day.

The findings of the study showed that cushion covers demonstrated the greatest amount of wear or damage, with torn seams and damaged fabric being the most prevalent signs. As the CushionAge increased, so too did the percentage of findings of damage to the cushion cover.¹

In terms of the cushions themselves, foam cushions were found to have more visible signs of wear than fluid or air cushions.¹ Over 60% of foam cushions that were 12 months or less old (based on 12 hours per day of daily use) showed compression set, granulation or changes in stiffness. This figure increased to 84% when the CushionAge was 36 months or more. Cushions that had foam components in addition to other materials showed these same signs of wear in the foam; however, at 12 months or less and at over 36 months of average use, the percentages of cushions showing wear in the foam components was 42% and 61%, respectively.¹

Data for visual inspections of air cushions showed that 12% of the inspections (recall that cushions could be inspected multiple times over the course of the study) showed damage to the air bladder, 3.5% showed damage to the valve, and 3.5 showed damage to the seams or welded components.¹ The data was not broken down by CushionAge.

Data for visual inspection of fluid cushions showed that 5% of the inspections revealed damage to the fluid bladder seams or welded components and 14% of the inspected bladders showed visible tears or breaks. Again, the data was not stratified by CushionAge.¹

The material itself may be one of the reasons for the difference in visible wear between foam, fluid and air cushions. By its nature, foam compresses when a load is on it. Fluid and air displace under a load. Therefore, the materials are experiencing different forces when loaded. In addition, when an air or fluid cushion shows damage, it is to the structure that contains the medium. If an air or fluid cushion develops a leak, the bladder is either repaired or the cushion is replaced if it cannot be repaired. For a foam cushion, it is the supportive material itself that may show structural changes; however, the person using a foam cushion may continue to use the foam cushion, despite it showing signs of wear or fatigue.¹

This study showed signs of wear on cushions that full-time wheelchair users, using skin protection or skin protection and positioning cushions, may see; however, as the author states, the study does not correlate signs of wear in wheelchair cushions to changes in performance in the cushions.

A study published in 2014 aimed to identify the most important factors in predicting degradation in wheelchair cushions. Using a sample drawn from the seating clinic of a rehabilitation hospital, researchers gathered information about the wheelchair user, the cushion (e.g., material, age and daily use, and condition of cover and cushion), and wheelchair usage (e.g., transfer technique and frequency, environmental exposures, and stressful activities, such as curb jumping).²

Wheelchair cushion performance was measured via pressure mapping using a rigid buttocks model to measure load distribution over the cushion's surface.² Cushions were measured multiple times, approximately every 6 months.

What this study found was that the AgeHours of a cushion, defined as the product of the cushion age in days and the daily use of the cushion in hours per day, was not a predictor of performance.² The way in which the cushion was used and the characteristics of the user had more influence on the pressure distribution than age of the cushion. Factors that caused more stress to the cushions included "the number of daily transfers, factors resulting from user activities, such as curb jumps, sports, and high vibration activities, and environmental exposures, such as moisture and high or low temperatures. Based upon the coding of wheelchair type, manual wheelchair users appear to induce these stressors more than power wheelchair users."^{2 (p. 67)}. The authors noted that because the sample was from a rehabilitation hospital, the majority of the cushions were fluid and air and therefore, the results may not be generalizable to all cushions.

What we can see from these two studies is that age is not a predictor of when a wheelchair cushion requires replacement. Visual inspection will provide information on the condition of the cushion cover, which may need replacement before the cushion itself, and on the cushion and its components. How a person uses a cushion, in what environments and for what activities, will influence its performance over time. Therefore, it is important to have an understanding also of how the cushion is used in considering the need for a replacement cushion.

References

1. Sprigle, S. (2013). Visual inspections of wheelchair cushions after everyday use. Assistive Technology, 25, 176-180.
2. Sprigle, S. & Delaune, W. (2014). Factors that influence changes in wheelchair cushion performance over time. Assistive Technology, 26, 61-68.