âA D is not a Dâ: Identifying sources of neuromuscular and functional heterogeneity within an AIS D population.
1Atkinson D, 2Schmidt Read M, 3Tefertiller C, 2watson E, 4Oakley A, 3Joyce M, 5Forrest G, 5Wojceihowski B, 6basso D, 7Sisto S, 1Harkema S, 1Behrman A
1University of Louisville, louisville, KY, United states; 2Magee Rehabilitation Hospital, Philadelphia, PA, United states; 3Craig Hospital, Denver, Colorado, United states; 4Frazier Rehab Institute, Louisville, Kentucky, United states; 5Kessler Rehab Institute, West Orange, New jersey, United states; 6The Ohio State University, Columbus, Ohio, United states; 7Stony Brook University, Stony Brook, New york, United states
Background: Spinal cord injury (SCI) may result in highly variable sensorimotor and autonomic deficits depending on the location and severity of injury, resulting in a wide range of functional abilities (1). The International Standards for the Neurological Classification of Spinal Cord Injury (ISNCSCI) exam is the most widely utilized clinical measure of neuromuscular function after SCI; its classification system is designed to stratify SCI into more homogenous sub-groups (i.e. A-E) (2). However, within an ISNCSCI classification, there remains variability in functional capacity (3). The purpose of this study is to describe the interactions between neuromuscular capacity and functional ability within a sample of people with an AIS D classification.
Methods: We evaluated demographic factors, balance and gait performance, and neuromuscular capacity in individuals with chronic SCI classified as AIS D (n=344), who participated in standardized activity- based therapy at out-patient clinical sites within the Christopher and Dana Reeve Foundation NeuroRecovery Network (NRN). Impairment was assessed using the ISNCSCI examination and neuromuscular capacity was assessed by the ISNCSCI examination and the Neuromuscular Recovery Scale (NRS), while functional abilities were assessed by the Berg Balance Scale, 6-minute-walk test (6MW), and the 10-meter-walk test (10MWT).We further examined whether demographic and neuromuscular capacity measures predicted baseline ambulatory status (Yes/No) using a random forest methodology.
Results: Ambulatory capacity among the 256 individuals able to walk was highly varied. The10MWT speeds ranged from .01-2.69m/s and the 6MW distances ranged from 4-616m. Similarly, Berg balance scale scores ranged from 0 to 56, and were highly correlated was with walking speeds and distances (Spearman correlation coefficients .84 and .83, respectively) among ambulators. Device usage at enrollment included 123 (48%) individuals who used a walker to ambulate, 81 (32%) who used cane(s) or crutch(es), and 52 (20%) who did not use a device.
Significant differences were observed for NRS and ISNCSCI subscale scores across these ambulatory device subgroups (p<.05), with the NRS being the better predictor of ambulatory status. Interestingly, although the task of walking is directly assessed by the NRS, analysis of the relative importance of individual NRS Items items in the prediction of ambulation found that the walking subscore was only 6th out of 13, while 4 NRS items (trunk extension in sitting, sit, sit- to- stand, and stand) – which all entail elements of intrinsic trunk control - were top predictors.
Conclusions: These results highlight the difficulty in functionally stratifying SCI by neuromuscular impairment; as evidenced by the distinct ambulatory groups described and the variable performance across items in the NRS. Our results indicate that measurement of the axial musculature can improve sensitivity in the evaluation of neuromuscular capacity after incomplete SCI.
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