Elsevier

Medical Engineering & Physics

Volume 38, Issue 9, September 2016, Pages 999-1007
Medical Engineering & Physics

Identifying characteristic back shapes from anatomical scans of wheelchair users to improve seating design

https://doi.org/10.1016/j.medengphy.2016.06.017Get rights and content

Highlights

  • An array of back contours were distinguished using 3D laser scanning and classified using mathematical modeling.

Abstract

Spinal deformities are common in people who require the use of a wheelchair for mobility as a result of spinal cord injuries and other disabilities. Sitting positions vary between individuals with disabilities who use wheelchairs and individuals without disabilities. In individuals with spinal cord injury, spinal deformities can result in the development of back contours that deviate from the shape of standard rigid back support shells. The purpose of this study was to distinguish and classify various back contours of wheelchair users by utilizing digital anatomic scanning technology in order to inform the future development of back supports that would enhance postural support for those with spinal deformities. The three dimensional (3D) locations of bony landmarks were digitized when participants were in position, using a mechanical wand linked to the FastScantm system commonly used to measure surface contours. Raw FastScantm data were transformed according to bony landmarks. A total of 129 individuals participated in this study. A wide range of back contours were identified and categorized. Although participant characteristics (e.g., gender, diagnosis) were similar amongst the contour groups; no one characteristic explained the contours. Participants who were seated in a forward lean position had a higher amount of pelvic obliquity compared to those seated in an upright position; however, participants’ back contour was not correlated with pelvic obliquity. In conclusion, an array of different back shapes were classified in our cohort through 3D laser scanning technology. The methods and technology applied in this study could be replicated in future studies to categorize ranges of back shapes in larger populations of people with spinal cord injuries. Preliminary evidence indicates that customized postural support may be warranted to optimize positioning and posture when a standard rigid shell does not align with contours of a person's back. To optimize positioning, a range of contoured rigid backrests as well as height and angle adjustability are likely needed.

Section snippets

Background

Due to aging populations and the increased prevalence of disability, experts anticipate that the need for wheelchairs worldwide will surge [1], [2]. Consumer demand for wheelchairs that fit the personal needs, physical abilities, and functional requirements of current and expected wheelchair occupants has led to the application of sitting biomechanics and ergonomic design to the development of wheelchair components [3]. Preserving health by preventing secondary medical conditions (e.g.,

Methods

This study utilized the scanning technology known as the FastScan™ System (Polhemus, Colchester VT, USA), which features rapid recording of three-dimensional surfaces obtained by sweeping a hand-held laser scanner several times over a surface to cover the entire range of the object's surface [32]. Similar to the process of spray painting, multiple swipes are needed to measure slices of an entire surface area. This system has been used previously in clinical settings to measure the skin surface

Participants

A total of 129 individuals (average age 53.2 ± 12.0 years, and male: 109, female: 19) who used wheelchairs as their primary means of mobility participated in this study and had the following diagnoses (Table 1).

There were no significant differences between the two seated position groups based on age (p = 0.078), years of using wheelchair (p = 0.293), gender (p = 1.000), or disability (p = 0.580). For Hypothesis 1, back contour (p = 0.500) was not significantly different between the two groups. However, a

Discussion

For Hypothesis 1, although back contour was not significantly associated with sitting position, the forward lean position of participants resulted in significantly higher pelvic obliquity. Based on a sitting spinal model that was developed for the automotive industry to improve car seat design, reduction in the trunk to thigh angle led to posterior rotation of the pelvis and decrease in lumbar lordosis [36]. As the posterior buttocks and thigh muscles (e.g., gluteus maximus, hamstrings)

Study limitations

The main limitation of this study was that all participants were recruited from the National Disabled Veterans Winter Sports Clinic and the National Veterans Wheelchair Games. Participants were all active wheelchair users and may not represent the wheelchair user population. Although 18 bony landmarks were identified from the scans in this study, additional bony landmarks on the spine could have provided more detailed information about spine shapes. Moreover, in this study occupants’ backs were

Conclusion

This study established an efficient method of using digital anatomic laser scanning technology and mathematical modeling to distinguish and categorize back shapes that would be replicable with larger populations of wheelchair occupants. A range of back asymmetries were found in people who have SCI, amputation, MS, stroke, TBI, amputation and other complex disabilities. Preliminary evidence indicated that customized postural support may be warranted to optimize positioning and posture when a

Funding

Supported by The VA Center of Excellence for Wheelchairs and Associated Rehabilitation (Grant B6789C) and Paralyzed Veterans of America. The contents of this paper do not represent the views of the Department of Veterans Affairs or the United States Government.

Ethical approval

This study was approved by the VA Pittsburgh Healthcare System Institutional Review Board. Participants were recruited at the National Disabled Veterans Winter Sports Clinic and the National Veterans Wheelchair Games.

Conflicts of interest

None to declare.

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