A high prevalence of manual wheelchair rear-wheel misalignment could be leading to increased risk of repetitive strain injuries

Figures & data

Figure 1. RR free body diagram where F_t is the tangential force, V is the angular velocity and W is the load on the axle, F_RR is the RR force, M_ZFT is the moment due to the tangential force, M_ZFRR is the moment inducing the RR force.

Figure 2. RR force versus toe angle for rear wheels.

Figure 3. Toe angle free body diagram, V is velocity, F_t is the tangential force, F_tx is the tangential component in the x direction, F_ty is the tangential component in the y direction.

Table 1. Design specifications.

Need	Specification	Rationale
Portability	Overall size not bigger than 101 cm wide and 66 cm deep	It will be easily transported in most vehicles
Toe angle measurement	Reach the front and rear of a 61 cm (24″) wheel	61 cm (24″) wheel is a very common size
Slop measurement	Apply pressure with the rear-wheels unloaded	Force needs to be applied to take up tolerances in order to measure the amount of tolerance, which cannot be performed with the rear-wheels under load
Accuracy	1.5 mm or less	Equals less than a 0.25 degree of toe angle on a 61 cm (24-inch) wheel
Adjustability	Height of measurement from 25 to 35 cm	Will be able to adjust to axle height of 20 to 71 cm (28″) wheels
Device accommodation	Fit devices from 35 to 81 cm in width	Very few MWUs would have a device under 35 cm and 81 cm is the width of a standard doorway
User accommodation	Lifting capacity of 136 kg	Most standard MWC can accommodate 113 kg with a 20% factor of safety
Rigidity	Flex less than 0.63 cm across the system	Rigidity is important to mitigate flex which ensures accurate measurements
Speed of collection	Less than 10 min per person	Voluntary study where we did not want to detract from the events going on

Table 2. Manual wheelchair community-based study recruitment.

Recruitment event	N	(%)
Adaptive sports^a	164	(82)
Assisted living	14	(7.0)
Education and training	15	(7.5)
Research lab	5	(2.5)
Seating clinic	2	(1.0)

Total N = 200.

^aLost three participants.

Table 3. Manual wheelchair community-based study manufacturers.

Wheelchair make	N	(%)
Manufacturer A	91	(45.5)
Manufacturer B	40	(20.0)
Manufacturer C	25	(12.5)
Manufacturer D	21	(10.5)
Manufacturer E	9	(4.5)
Other	14	(7.0)

Total, N = 200.

Table 4. Manual wheelchair community-based study K codes.

Frame description	N	(%)
Wheelchair frame
Custom rigid (Former K0009)	171	(85.5)
K0005	13	(6.5)
Other/unknown	16	(8.0)

Total N = 200.

Table 5. Manual wheelchair community-based study age.

Wheelchair information	N	(%)
Approximately how many years have you had this wheelchair?
<1 year	27	(13.5)
1–2 years	42	(21.0)
3–4 years	50	(25.0)
>4 years	79	(39.5)
No response	2	(1.0)

Total, N = 200.

Table 6. Manual wheelchair community-based study use data.

Wheelchair use frequency	N	(%)
Approximately how many hours per day do you use your wheelchair?
<5 h	13	(6.5)
5–10 h	34	(17.0)
10–15 h	73	(36.5)
>15 h	77	(38.5)
No response	3	(1.5)
Approximately how many days per week do you use your wheelchair?
1 day	3	(1.5)
2–3 days	3	(1.5)
4–5 days	11	(5.5)
>5 days	181	(90.5)
No response	2	(1.0)

Total, N = 200.

Table 7. Manual wheelchair community-based study tire types.

Tires by type	N	(%)
High-pressure (689 kPa and over)	108	(54.0)
Low-pressure (under 689 kPa)	36	(18.0)
Solid or airless inserts	37	(18.5)
Unknown	19	(9.5)

Total N = 200.

Table 8. Manual wheelchair community-based study tire manufacturers.

Tires by manufacturer	N	(%)
Manufacturer A	79	(39.5)
Manufacturer B	70	(35.0)
Manufacturer C	15	(7.5)
Manufacturer D	8	(4.0)
Manufacturer E	6	(3.0)
Other	22	(11.0)

Total N = 200.

Table 9. Manual wheelchair community-based study wheel diameter.

Wheel measurements	N	(%)
Overall wheel and tire diameter
cm (\in.)
56 (22)	7	(3.5)
61 (24)	117	(58.5)
63.5 (25)	53	(26.5)
66 (26)	23	(11.5)

Total N = 200.

Table 10. Manual wheelchair community-based study wheel type.

Wheels by type	N	(%)
Performance	123	(61.5)
Lite spoke	56	(28.0)
Solid	14	(7.0)
Other	7	(3.5)

Total N = 200.

Figure 4. Toe angle and slop prevalence in the community.

Figure 5. Tire manufacturer versus slop.

Table 11. Slop across each tire manufacturer.

	Mfr. A	Mfr. B	Mfr. C	Mfr. D	Mfr. E	Other
Average (deg)	0.49	0.54	0.59	0.26	1.04	0.64
Std Dev (deg)	0.37	0.49	0.36	0.21	0.71	0.46
N (qty)	79	70	15	8	6	22

Figure 6. Wheel diameter versus slop.

Table 12. Wheel diameter versus slop.

	56 cm (22 inch)	61 cm (24 inch)	63.5 cm (25 inch)	66 cm (26 inch)
Average (deg)	1.14	0.49	0.54	0.64
Std Dev (deg)	0.75	0.37	0.40	0.59
N (qty)	7	117	53	23

Table 13. Average results from the community-based study.

Measurement	Average	Standard deviation	Perceived weight equivalent (kg)
Toe angle (mm)	9	12	11
Toe angle (deg)	0.9	1.4
Slop (mm)	6	8	2
Slop (deg)	0.6	0.8
Toe angle + slop	1.5	N/A	21
Camber (deg)	3.0	1.5	3
Tire pressure	40%	24%	9

Table A1. Device information to be collected.

Device make – categorical

Device model – categorical

Age of device – categorical

Hours used per day – categorical

Days per week – categorical

Tire type – categorical

Tire make – categorical

Wheel diameter – continuous

Wheel type – categorical

Figure A1. Measurement Device in Operation. Arrow represents applied force from force spring.

Figure B1. Laser measurement frame. (1) Frame, (2) linear slide, (3) spring with hook, (4) laser.

Figure B2. Rear View of Slop Measurements (3) Spring with Hook, (5) Jack.

Figure B3. Toe-out Slop Tensioner. (3) Spring with Hook.