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Objectives: The objective of this pilot study was to investigate car-to-wheelchair transfer motion patterns as a risk factor for long bone fractures in the spinal cord injured (SCI) population. Fracture of the insensate osteopenic limb is a serious problem, with car-to-wheelchair transfers accounting for nearly 25% of lower limb fractures in this population.
Clinical Relevance: Accelerometric motion analysis may be a useful tool for reducing risk of lower limb fractures by optimizing safe transfer techniques, by providing feedback to transferees while learning transfer methods, and by identifying person- or vehicle-specific risk factors.
Methods: Experimentation was performed in a motion analysis lab, using six healthy non-SCI individuals. Due to time and safety concerns, non-SCI subjects simulated transfers between a fixed car seat and a wheelchair for this study, emulating videotaped performance by three SCI subjects. Video images and 3-axis accelerometric data were recorded at four locations along the left side of the subject's body. The following comparisons were made between transfer strategies: feet-first vs body-first, transfers involving multiple stages vs. one-movement transfers, and "safe" vs. "dangerous" transfers. The latter simulated inadvertent catching of the foot on the car door rim or wheelchair footrest. Comparisons were based on vector magnitude and body segment angle derived from accelerometric data. Tibial torsion load was estimated from the difference in axial rotation between proximal and distal tibial sensor sites.
Results: It was determined that transferring the body in multiple stages is safer than transferring in one movement, based on the criterion of minimum area under the peak acceleration magnitude curve (equivalent to velocity). Feet-first transfers have approximately the same peak accelerations and tibial torsion as body-first transfers, implying that feet-first transfers are as safe as body-first transfers. Catching or holding the foot during body transfer resulted in a torsional load on the tibia, which may put the transferee at increased risk for fracture. Differences in height between car seat and wheelchair of less than 4 inches had no effect on peak acceleration, but resulted in more small peaks due to additional shifting of weight prior to transfer and prolonged time to completion.
Conclusions: By gaining a greater appreciation for accelerations and torques that occur during car-to- wheelchair transfers, safety of various strategies may begin to be quantified. This preliminary study should be extended to include actual instead of simulated SCI subjects and vehicles.
Acknowledgments: Paralyzed Veterans of America, Bay Area and Western Chapter, PVA/SCI Summer Scholars award to Erin E. Butler; VA Rehabilitation R&D; project E601-3RA.