Glenohumeral contact forces and muscle forces evaluated in wheelchair-related activities of daily living in able-bodied subjects versus subjects with paraplegia and tetraplegia

Objective: To estimate the differences in glenohumeral contact forces and shoulder muscle forces between able-bodied subjects and subjects with paraplegia and tetraplegia during wheelchair-related activities of daily living (ADLs).
Design: Kinematics and external forces were measured during wheelchair ADLs (level propulsion, weight-relief lifting, reaching) and processed by using an inverse dynamics 3-dimensional biomechanical model.
Setting: Biomechanics laboratory.
Participants: Five able-bodied subjects, 8 subjects with paraplegia, and 4 subjects with tetraplegia (N=17).
Interventions: Not applicable.
Main Outcome Measures: Glenohumeral contact forces and shoulder muscle forces.
Results: Peak contact forces were significantly higher for weight-relief lifting compared with reaching and level propulsion (P<.001). High relative muscle force of the rotator cuff was seen, apparently needed to stabilize the joint. For weight-relief lifting, total relative muscle force was significantly higher for the tetraplegia group than for the able-bodied group (P=.022).
Conclusions: Glenohumeral contact forces were significantly higher for weight-relief lifting and highest over the 3 tasks for the tetraplegia group. Without taking paralysis into account, more muscle force was estimated for the subjects with tetraplegia during weight-relief lifting.