By Dr Tarun Arora, Dr Alison Oates and Dr Kristin Musselman
After someone has injured their spinal cord, the communication between their brain and body is disrupted, which can make movement challenging. In more than half of spinal cord injuries (SCI), the spinal cord is not completely damaged (i.e., an “incomplete” injury ). The majority of individuals with an incomplete SCI (iSCI) are able to walk. Unfortunately, about three-quarters of people with an iSCI report at least one fall per year. This risk of falling is similar or even higher than other populations who are prone to falls such as older adults (33%) or those living with stroke (73%) and Parkinson’s disease (68%). Research shows that individuals with iSCI walk slower, take shorter steps, and spend more time in double support which improves their mechanical stability. Thus, they are less likely to lose their balance during walking, but can they recover once their balance is perturbed? Our research studied reactive responses to an unexpected slip perturbation in people with an iSCI.
We brought 20 individuals with iSCI and 15 age-and-sex matched individuals without SCI (niSCI) to the Biomechanics of Balance and Movement Lab at the University of Saskatchewan. A slip device embedded into the floor becomes highly slippery (comparable to that of clean ice at 0 deg. celsius!) when unlocked (Figure 1). Without knowing when the slip device will be unlocked, participants walked for several “normal walking” trials. Then we unlocked the slip device for an “unexpected slip”without telling them (click here for videos). The velocity of the slipping heel was used to categorize the severity of the slip as hazardous (>1m/s) or non-hazardous. Using 3-D motion capture, we measured stability at the first compensatory step after the slip. We also measured when and how much the muscles in the leg activated in reaction to slip.
Both groups had similar proportions of hazardous and non-hazardous slips suggesting a comparable slip severity. The iSCI group could not regain as much stability as the niSCI group using a compensatory step. Also, the iSCI group demonstrated lower calf muscle activation compared to the niSCI group.
Using the unexpected slip paradigm, we demonstrated some important limitations in the reactive balance of individuals with iSCI. This research highlights the importance of evaluating reactive balance during clinical balance evaluations in individuals with iSCI. Clinicians should consider evaluating reactive balance evaluation (e.g., mini-BESTest) in their practice.
Figure 1. Slip device and schematic lab setup for data collection (modified from Arora T et al., PM&R 2019)
Note: this study was a part of a larger research project that was funded by the Saskatchewan Health Research Foundation (awarded to AO and KEM).
Arora T, Musselman KE, Lanovaz JL, Linassi G, Arnold C, Milosavljevic S, Oates A. (2020) Reactive balance responses to an unexpected slip perturbation in individuals with incomplete spinal cord injury. Clin Biomech (Bristol, Avon), 78:105099. https//doi.org/10.1016/j.clinbiomech.2020.105099
About the Author
Tarun Arora, BPT MSc PhD
Department of Biomedical Engineering, Lerner Research Institute, Cleveland Clinic Foundation
Tarun is a postdoctoral fellow at the Cleveland Clinic. He studies non-invasive ways of neuromodulation for motor recovery in individuals with neurological impairments.
College of Kinesiology, University of Saskatchewan
Alison is the co-director of the Biomechanics of Balance and Movement Lab and Associate Professor in the College of Kinesiology at the University of Saskatchewan. She studies sensorimotor control of balance during standing and walking.
Kristin Musselman PT, PhD
Department of Physical Therapy, Temerty Faculty of Medicine, University of Toronto; KITE, Toronto Rehabilitation Institute-University Health Network
Kristin is a physical therapist and Assistant Professor at the University of Toronto. She leads the SCI Mobility Lab, which aims to develop innovative, clinically feasible approaches to restore movement, function and participation for individuals living with complex neurological disease across the lifespan.