Dynamic instability during obstacle crossing following traumatic brain injury
Introduction
Traumatic brain injury (TBI) is one of the most challenging problems faced by the medical community. It is estimated that 5.3 million Americans, a little more than 2% of the US population, currently live with disabilities resulting from TBI [1]. Each year over one million people are treated for TBI and released from hospital emergency rooms. The cost of TBI in the US is estimated to be US$ 48.3 billion annually. After one traumatic brain injury, the risk for a second injury is three times greater, and after the second injury, the risk for a third injury increases by a factor of eight [1]. Therefore, the ability to identify any functional impairment that may affect safety after a TBI is critical to prevention of re-injury. The utility of neuropsychometric testing in evaluating cognitive impairment resulting from TBI is well established [2], [3], [4], [5], [6]. However, comparatively little information is available on the performance of dynamic motor tasks following TBI.
Many individuals with a mild or moderate TBI complain of symptoms long after their injury, even though their clinical examinations and measurable cognitive deficits are small [7], [8]. Approximately one third of these patients complain of sensorimotor problems, in particular, poor balance and poor coordination [9], [10]. These balance and coordination complaints may not be surprising since effective coordination and balance involves a complex interaction of the sensory, motor programming and musculoskeletal systems. Sensory systems monitor the location of the whole body center of mass (COM) relative to the base of support, provide information about vertical orientation, and supply environmental information, particularly regarding the support surface. Appropriate motor responses include an appropriate latency of onset as well as measured and coordinated force generation in activated muscles [11].
Biomechanical studies of individuals with TBI have, for the most part, been limited to postural sway during quiet standing or during standing with altered sensory inputs [12], [13], [14], [15], [16], [17], [18], [19]. Subjects with TBI exhibit an increased reliance on visual input and are not able to use their vestibular systems as effectively as uninjured subjects to resolve conflicts in information from the visual and somatosensory systems [16]. Geurts et al. [16] reported that subjects who had sustained a TBI (mild, n=13; moderate, n=2; and severe n=5) exhibited at least 50% more static anterior–posterior (A–P) and lateral sway than healthy controls at 6 months following injury. These same subjects showed no sensorimotor impairments in a standard neurological examination. Guskiewicz [20], on the other hand, reported little relationship between symptoms and measures of cognitive function and static postural stability during the first 2 days following a concussion. These data suggest that motor function may recover more slowly than cognitive function or may not be closely related to standard neuropsychological assessments.
Many studies have used the whole body COM motion and its interaction with the center of pressure (COP) as indicators to examine an individual’s dynamic stability. It has been demonstrated that COM motion is tightly regulated to move between the alternating COP of each supporting foot [21], [22], [23], [24], [25]. Furthermore, our previous studies demonstrated that elderly adults complaining of “dizziness” or “unsteadiness” displayed significantly greater and faster medio-lateral (M-L) COM motion than the healthy elderly while negotiating obstacles of different heights [26], [27]. Therefore, COM motion in the frontal plane could be a functional indicator of balance maintenance during walking, and with the addition of the obstacle it could be a more sensitive measurement of dynamic stability.
Given that most falls appear to stem from tripping over objects [28], [29], [30], [31], it is important to determine the influence of pre-existing brain injury on an individual’s balance control while interacting with environmental hazards, such as stepping over an obstacle during walking. Therefore, the purpose of this study was to quantitatively assess dynamic stability of individuals who have complaints of “instability” or “imbalance” following TBI despite having an apparently normal gait on clinical examination. We hypothesized that patients with TBI would demonstrate less stability, as indicated by greater and faster M-L motion of the whole body COM, when stepping over progressively higher obstacles than subjects without a similar injury.
Section snippets
Methods
Ten patients (six men and four women) with a TBI were recruited by physician referral from the National Institute on Disability and Rehabilitation Research (NIDRR) sponsored Mayo Clinic Traumatic Brain Injury Model Center. The diagnosis of a TBI was based on their history and medical records (e.g., a decreased Glasgow Coma Score (GCS) within 24 h following initial admission and documented loss of consciousness). Based on the initial GCS obtained from their medical records, four of the subjects
Results
Eight of the subjects with TBI were able to consistently perform all testing trails with either their right or left limb leading (five right and three left leading). All control subjects except for one selected their left limb as the leading limb. No incidents of tripping occurred for any of the obstacle height conditions in either subject group. Post-TBI subjects adopted a gait pattern with a significantly slower walking speed (P=0.02) and shorter stride length (P=0.018) than controls during
Discussion
Subjects with TBI often complain of “dizziness” or “unsteadiness” despite what appears to be a clinically normal gait. The results of this study clearly demonstrate that these individual do have gait abnormalities based on objective testing. Specifically, the subjects with a history of TBI adopted a gait pattern with a significantly slower speed, a shorter stride length and an increase in the M-L COM motion. These individuals also maintained a significantly greater separation distance between
Acknowledgements
This study was supported by the Mayo Foundation. The assistance of Brian Kotajarvi, Chris Hughes, Denny Padgett and Diana Hansen in data collection and reduction is greatly appreciated.
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