Evaluation of Titanium Ultralight Manual Wheelchairs Using ANSI/RESNA Standards

Article excerpt

INTRODUCTION

Choice of a suitable wheelchair requires serious consideration. The U.S. Food and Drug Administration recommends testing wheelchairs using American National Standards Institute (ANSI)/Rehabilitation Engineering and Assistive Technology Society of North America (RESNA) testing standards [1] to assess performance and safety and estimate life expectancy of a wheelchair. Results from ANSI/RESNA standard tests are a source of information about technical quality and performance and allow comparison of results across devices. The content of the standard tests covers many aspects that affect wheelchair usage and selection, such as dimensions, static stability, braking effectiveness, strength, and durability.

Dimensions, weight, and turning radius clue consumers in to whether a wheelchair will fit in their homes, working environments, and transportation means. Wheelchair performance in the static stability tests reveals the estimated behavior of the wheelchair on an incline. The results indicate how the stability of the wheelchair is affected by adjustment of the axle and other components. Determining wheelchair strength and durability from retail advertisements and user manuals is difficult. Although medical insurers' prescription guidelines typically require 3 to 5 years before a replacement wheelchair will be covered, previous research has shown that the predicted life expectancy of some wheelchairs is significantly less [2-7]. Premature wheelchair failure could potentially injure the users and may require them to pay for replacements, which can cost several thousand dollars. According to Smith et al., wheelchair users expect wheelchairs to improve their quality of life and help them maintain or achieve a desired level of mobility [8]. Users expect their wheelchairs to be comfortable, easy to propel, safe, and attractive [8]. In a survey of wheelchair users with amyotrophic lateral sclerosis, the most desirable features of manual wheelchairs were a lightweight frame and a small turning radius [9]. Comfortable propulsion and support, light weight, and small dimensions are very important features, especially for active manual wheelchair users [10-11]. A lighter wheelchair has lower rolling resistance, which reduces the force required to propel it. Thus, lighter wheelchairs are suggested for preserving upper-limb function of manual wheelchair users [12]. Developing a lighter and more functional wheelchair is a goal for the design of many manual wheelchairs. The titanium wheelchair is a product in response to this goal.

ANSI/RESNA standard tests provide specific testing protocols to evaluate the performance and durability of wheelchairs and serve as a universal platform for data collection and comparison. Reports using ANSI/RESNA standards evaluated aluminum ultralight and steel lightweight wheelchairs. Ultralight wheelchairs lasted more than five times as long as lightweight wheelchairs before failures occurred during fatigue tests [2-3]. However, ultralight wheelchairs experienced more repairable component failures, such as bolt or caster-stem failures and screws loosening. Although repairable component failures do not damage frame integrity, multiple component failures require frequent maintenance and may place the user in hazardous situations.

Many ultralight wheelchairs have titanium frames and/or components. Since titanium has a higher strength-to-weight ratio than aluminum, if engineered correctly, it could preserve the strength of the wheelchair frame while lowering the weight. Conventional wisdom in our wheelchair clinic has been that people who use titanium chairs benefit from their highly durable and lightweight properties, although no standards testing results of titanium wheelchairs have been reported in the literature. Our goal in this study, similar to prior works in this area, was to test a series of commercially available titanium rigid-frame wheelchairs using ANSI/RESNA testing procedures. …