Unsupervised clustering reveals multiple personal and clinical determinants of wheelchair propulsion strategies in SCI

STUDY DESIGN: Cross-sectional observational study. OBJECTIVE: To address the substantial heterogeneity among SCI manual wheelchair users, this study aimed to identify distinct subgroups based on demographic-clinical characteristics and propulsion pattern, and to examine whether these subgroups exhibit different biomechanical propulsion characteristics. SETTING: Department of Orthopedic Surgery, Klinikum Bayreuth GmbH, Germany. METHODS: Ninety SCI manual wheelchair users were included. Wheelchair propulsion was recorded using a 3D marker-based motion capture system. Unsupervised two-step cluster analysis was performed using demographic and clinical variables alongside propulsion pattern. To examine the differences between the clusters, an ANOVA was performed for continuous variables, and Fisher's exact test was used for categorical variables. RESULTS: Three distinct clusters were identified. Cluster 1 comprised older, recreationally active participants with shorter time since injury, most frequently exhibiting the arc pattern. Cluster 2 consisted of younger, highly active participants with the longest time since injury, most frequently showing the under-rim pattern alongside significantly higher velocities and larger push angles. Cluster 3 comprised recreationally active participants with intermediate time since injury, showing predominantly arc and single loop patterns with propulsion characteristics similar to Cluster 1. CONCLUSION: Unsupervised clustering revealed distinct subgroups of SCI manual wheelchair users with differing propulsion strategies and biomechanics. Higher velocities and larger push angles were observed only in Cluster 2 including individuals with complete C4-C8 motor lesions. These findings indicate that propulsion characteristics recommended by clinical guidelines are not determined by neurological injury classification alone, but may also be influenced by time since injury and physical activity level.