Effects of rear-wheel camber on wheelchair stability

Objectives: To evaluate how using a wheelchair with rear-wheel camber (when the bottoms of the wheels are farther apart than the lops) is associated with the risk of instability incidents, and to determine the effect of camber on wheelchair stability. Design, Setting, Patients: Epidemiologic data were analyzed from a sample of 576 users of manually propelled wheelchairs in Nova Scotia. A controlled trial was performed using a representative wheelchair occupied by an anthropomorphic test dummy, altering the camber in 5°increments from -15°to +15°. Main Outcome Measures: For the epidemiologic study, univariate and multivariate analyses were used. To measure the static stability, a tilting platform was used according to the guidelines of the International Organization for Standardization. Results: Camber users reported significantly more instability incidents; of these incidents, more were in the rear direction (40% vs 27%) and fewer in the lateral direction [17% vs 28%) (p < .01). When controlling for other factors, camber was associated with a 3.91-fold increased risk of sustaining an instability incident (p < .001). With increases in camber angle in the laboratory, lateral and forward stability increased and rear stability decreased (with the wheels unlocked and locked) (p < .001). Conclusion: Camber use is negatively associated with instability incidents in the lateral direction and positively associated with incidents in the backward direction, probably due in part to the effects of camber on lateral and rear stability.