RESNA 27th International Annual Confence

Technology & Disability: Research, Design, Practice & Policy

June 18 to June 22, 2004
Orlando, Florida

Investigation of Power Wheelchair Reliability

Michelle L Tolerico, BS, Shirley G Fitzgerald, PhD,
Rory A Cooper, PhD, Stephanie G Martin, BS
University of Pittsburgh, Dept. Rehabilitation Science and Technology
VA Pittsburgh Healthcare System


Failure of a powered mobility device can have a major impact on an individual's ability to complete daily tasks. A pilot study was designed to determine if reliability differs among classes of electric powered wheelchairs. Ten power wheelchair users, six of which used K0011 wheelchairs and four used K0014s, answered an initial demographic questionnaire and four follow-up questionnaires over an 18-month period. The questionnaires contained questions pertaining to the type of wheelchair used, the number of repairs needed over the previous three-month period, and average amount of time spent in wheelchair each day. A borderline significance was found between the number of repairs needed to the class K0011 and K0014 wheelchairs, suggesting K0014 wheelchairs are less reliable than K0011s. No relationship was found between wheelchair usage and the number of repairs reported.


Electric powered wheelchairs; reliability; repairs


Electric powered wheelchairs (EPWs) enable individuals with mobility impairments to function independently and move within their environment with relative ease. Given that EPWs are usually the primary means of mobility for the individuals who use them, it is essential for these devices to be reliable and durable. When failures occur to a wheelchair, the individual's capacity to complete daily activities is greatly impacted as well the risk of injury is considerably increased. Gaal et al. interviewed 109 wheelchair users who had sustained injuries while using their mobility device. Of the 253 incidents reported over a five-year period, fifty three percent of them occurred while using an EPW (1). Component failure occurred twice as many times among EPWs when compared to manual wheelchairs (1).

ANSI/RESNA and ISO have established a set of voluntary wheelchair standards and testing procedures in an effort to improve the overall quality of products made available to consumers (2). Within these sets of standards, safety, durability, and reliability are tested (2). However, since most of the testing procedures are conducted in a laboratory setting, it is unclear if this is a realistic interpretation of a real world situation. This pilot study was designed to achieve a more accurate depiction of the reliability among the different types of EPWs that are available on the market.


Hypothesis 1: K0014 electric powered wheelchairs are less reliable as defined by the number of repairs than K0011 wheelchairs.

Hypothesis 2: A relationship exists between wheelchair usage and the number of repairs needed to the wheelchair.


A longitudinal study of EPW users was conducted to determine the number of repairs needed to their wheelchairs over an eighteen-month period. Of the ten EPWs in the study, six of them fell under Medicare's classification code K0011 and four were class K0014. Class K0011 wheelchairs are standard weight/frame EPWs, with programmable control parameters. Class K0014 wheelchairs are customized wheelchair bases that are designed with special features that are not readily available in other models (3).

The participants of the study, who had first given written consent, completed an initial demographic questionnaire followed by a series of follow-up questionnaires. The follow-up questionnaires were completed every three months via mail or phone interview. They contained a variety of questions pertaining to the participant's wheelchair such as the type of wheelchair used, the number of repairs needed over the three month period, type of repairs necessary, and average amount of time spent in wheelchair each day.

Since the obtained data illustrated that variables were normally distributed and continuous, an independent t-test with significance level of p<0.05 was completed to compare the number of repairs reported between the Class K0011 and K0014 EPWs. A correlation test was completed to determine if a relationship exists between EPW usage and repairs.


There were ten participants enrolled in this study, of which 8 were male and 2 female. Six of these individuals reported having spinal cord injuries and four with other conditions such as multiple sclerosis, cerebral palsy, etc. Using the demographic information obtained from the initial questionnaire, it was determined that the K0011 wheelchairs on average were older than the K0014s. Also, when the two groups were compared, individuals using K0011 wheelchairs have been mobility impaired for a longer period of time than those using K0014s. However, participants using K0014 wheelchairs were older in age than those with K0011 wheelchairs.

Table 1: Comparison of class K0011 and K0014 power wheelchairs




Std. Deviation

Age of wheelchair










Age of Individual










Years of Disability










*Difference in sample size due to missing response on questionnaire

A total of 64 repairs were reported over the eighteen-month period. Results show that the mean number of repairs needed to K0014 wheelchairs was 9.00 ± 2.94 compared to the 4.67 ± 2.94 needed by K0011 wheelchair users. Analysis found a borderline statistical significance (p= 0.047) between the number of repairs needed to the class K0011 and K0014 EPWs. When comparing the average amount of time each group spent in the wheelchair each day, it was found that participants who used K0014s spent approximately 12.51 ± 1.81 hours and K0011s 11.31 ± 3.87 hours in their wheelchair. In testing hypothesis 2, no relationship was found between wheelchair usage and the number of repairs reported.


Our findings in this pilot study provide some evidence that wheelchair reliability differs between classes of EPWs. Specifically, the results suggest that K0014 wheelchairs are less reliable than K0011 wheelchairs. This was found even though the average age of the K0011 wheelchairs was older than the K0014s. One possible reason for K0014 wheelchairs being less reliable is that these wheelchairs are custom designed to fit the needs of the individual that cannot be satisfied with a standard power wheelchair. Greater complexity typically leads to decreased reliability (2). Therefore, consumers who purchase this type of wheelchair usually require special features, which increase the complexity of the wheelchair and the number of parts. These factors can potentially increase the risk of component failure, resulting in additional costs incurred by the K0014 EPW user.

There was no correlation found between wheelchair usage and the number of repairs needed to an individual's wheelchair. The question used to gather information about wheelchair usage inquired about the average amount of time spent in the wheelchair each day. The results could have been altered due to the fact that just because the individual is in his or her wheelchair does not mean that the wheelchair is moving.

This study was limited by the small sample size, which consisted primarily of males. Also, missing responses on the questionnaire pertaining to the number of repairs needed to the wheelchair and hours an individual spends in their wheelchair was another limiting factor. Regular maintenance to the wheelchair was not considered when determining reliability, which could have also influenced our results. Future research should be conducted on a larger and more diverse sample to validate the results obtained from this study. Also, in order to obtain more accurate depiction of wheelchair usage future studies could use a device such as a datalogger to track the individual's movement.


  1. Gaal RP, Rebholtz N, Hotchkiss RD, Pfaelzer PF. Wheelchair rider injuries: causes and consequences for wheelchair design and selection. J Rehabil Res Dev 1997; 34(1): 58-71.
  2. Cooper RA. Wheelchairs: a guide to selection and configuration. New York: Demos Medical; 1998.
  3. Health Care Financing Administration United Healthcare, Region A DMERC. Rehab specialties/wheelchair documentation, continuing education workshop. 1998; Fall.


This pilot work was funded by the RR&D Center of Excellence for Wheelchairs and Related Technology (Award # F2181C)

Michelle Tolerico
Human Engineering Research Laboratories (151-R1),
7180 Highland Drive
Pittsburgh, PA 15206-1297
(412) 365-4945

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