Untangling biomechanical differences in perturbation-induced stepping strategies for lateral balance stability in older individuals.

When recovering balance from a lateral perturbation, younger adults tend to stabilize balance with a single lateral sidestep while older adults often take multistep responses. Using multiple steps to recover balance is consistently associated with increased fall risk, altered body center of mass (CoM) control and instability. The aim of this study was to compare the spatio-temporal stepping characteristics and the margin of stability (MoS) of single lateral sidesteps (LSS1) with the first and second steps of a two-step protective step sequence. Two-step sequences begin with either a cross-over step to the front or back, or a medial step followed by a lateral sidestep. Seventy-one older adults received random lateral waist-pull perturbations to either side. We hypothesized that LSS1 would be more stable (larger MoS) than either step in a two-step sequence. With some exceptions, utilizing a two-step sequence was associated with a reduced CoM velocity and distance between the base of support and CoM and decreased stability in the frontal plane following limb loading of the first and second step. There were no differences in the time available to arrest the extrapolated CoM at the end of a single lateral sidestep or the final step of a two-step sequence. Two-step sequences involving a cross-over step include more complex stepping trajectories and also challeng stability in the sagittal plane requiring a multidimensional balance correction. These results indicate important step type differences in center of mass control in recovering balance with a single lateral sidestep as opposed to a two-step sequence among older adults.

Perturbation-evoked lateral steps in older adults: Why take two steps when one will do?

BACKGROUND: Hip fractures in older adults often result from a fall in the lateral direction. While younger adults tend to recover balance from a lateral perturbation with a single lateral sidestep, older adults are prone to multistep responses which are associated with an increased fall risk. This study compared the stepping characteristics and stability of single and multistep responses to lateral perturbation in healthy older adults. METHODS: Eighty-four older adults received lateral waist-pull perturbations to either side. Spatio-temporal stepping characteristics and balance stability were quantified. FINDINGS: Fewer steps were taken to recover balance when the first step was a lateral sidestep. The stability margin of single lateral sidesteps was greater than medial sidesteps and cross-over steps to the back but not significantly different from single cross-over steps to the front at step termination. Single step responses were more stable than multistep responses at step termination and at step initiation for lateral sidesteps and cross-over steps to the front. The decreased stability of multistep responses was attributed to an increased center of mass velocity and a smaller distance between the center of mass and base-of-support at step termination. INTERPRETATION: Although lateral sidesteps result in fewer steps than cross-over steps to the front, the stability margin was not significantly different at step termination. These results suggest difficulty terminating center of mass motion and/or inefficient center of mass control differentiates single and multistep responses. Future studies should investigate perturbation training and/or hip abductor muscle conditioning as a means of improving compensatory stepping reactions.

The high morbidity of blunt cerebrovascular injury in an unscreened population: more evidence of the need for mandatory screening protocols.

BACKGROUND: Blunt cerebrovascular injuries are rare injuries causing substantial morbidity and mortality. The appropriate screening methods and treatment options for these injuries are controversial. We examined our experience with these injuries at a community Level I Trauma center over a 51 month period. STUDY DESIGN: A retrospective review and analysis was done of all patients with the diagnosis of a blunt cerebrovascular injury during this period. RESULTS: Fourteen patients had blunt carotid injury (0.40%) and three had blunt vertebral injury (0.09%) out of 3,480 total blunt admissions. The overall incidence of blunt cerebrovascular injury was 0.49%. The most common associated injuries were to the head (59%) and chest (47%) regions. The overall mortality rate was 59% (10 of 17), with death occurring in 8 of 14 (57%) blunt carotid injury patients and 2 of 3 (67%) blunt vertebral injury patients. Eight of ten (80%) deaths were directly attributable to the blunt cerebrovascular injury. Median time until diagnosis was 12.5 h (range 1-336 h) for the entire group and 19.5 h for nonsurvivors. Diagnosis was delayed > 24h in 7 patients and > 48h in 5 patients. All five patients whose diagnoses were delayed > 48 h developed complications, and four (80%) of these patients died. CONCLUSIONS: Blunt cerebrovascular injury is uncommon, but lethal; particularly when the diagnosis is delayed. Aggressive screening protocols based on mechanism of injury, associated injuries, and physical findings are justified to minimize morbidity and mortality. Head and chest injuries may serve as markers for blunt cerebrovascular injury. Most deaths are directly attributable to the blunt cerebrovascular injury and not to associated injuries.