John G. Buckley

Postural sway and active balance performance in highly active lower-limb amputees.

Buckley JG, O’Driscoll D, Bennett SJ: Postural sway and active balance performance in highly active lower-limb amputees. Am J Phys Med Rehabil 2002;81:13–20. ObjectiveTo determine the balance performance of active lower-limb amputees during quiet standing and under dynamic conditions. DesignCenter-of-pressure excursions during quiet standing and the standing balance performance on a single axis stabilimeter was assessed in six unilateral lower-limb amputees and six able-bodied controls. Stabilimeter trials were repeated with subjects standing so that pivoting occurred either in the anteroposterior or mediolateral direction or in the mediolateral direction but with vision occluded. ResultsCenter-of-pressure excursions were significantly greater (P < 0.05) for amputees in both the mediolateral and anteroposterior directions. During all stabilimeter tests, amputees spent significantly less time in balance than able-bodied controls (P < 0.05), and this was attributed to a nonsignificant increase in the average time the stabilimeter spent in contact with the ground. Group differences in the average time of contact in the anteroposterior test condition were meaningful (effect size, 1.19). ConclusionsAmputees had poorer static and dynamic balance than able-bodied controls. Amputees had a greater problem controlling dynamic balance in the anteroposterior direction than the mediolateral direction. Findings highlight the importance of the ankle in maintaining balance in situations that involve body movements in the sagittal plane.

The effect of refractive blur on postural stability

The effect of refractive blur upon postural stability was investigated under three conditions: normal standing, standing with input from the somatosensory system disrupted and standing with input from the somatosensory and vestibular systems disrupted. Standing stability was assessed using the centre of pressure (COP) signal from force plate data in four young subjects (mean 23.9 ± 3.1 years) and five repeated sets of measurements were taken. The subjects looked straight ahead at a horizontal and vertical square wave pattern of 2.5 cycles (degree)−1. Under each of the three test conditions, standing stability was measured with the optimal refractive correction and under binocular blur levels of 0, + 1, + 2, + 4, and + 8 D and with eyes closed. In the normal standing condition, dioptric blur had only a mild effect on postural stability. However refractive blur produced large increases in postural instability when input from one or both of the other two sensory systems were disrupted. We hypothesized that dioptric blur would have an even great effect on postural stability if the visual target used was of higher spatial frequency. This was confirmed by repeated measurements on one subject using a target of 8 cycles (degree)−1. The study highlights the possible importance of an optimal correction to postural stability, particular in situations (or people) where input from the somatosensory and/or vestibular systems are disrupted, and where the visual surrounds are of high spatial frequency.

Peripheral visual cues affect minimum-foot-clearance during overground locomotion

The importance of peripheral visual cues in the control of minimum-foot-clearance during overground locomotion on a clear path was investigated. Eleven subjects walked at their natural speed whilst wearing goggles providing four different visual conditions: upper occlusion, lower occlusion, circumferential-peripheral occlusion and full vision. Results showed that under circumferential-peripheral occlusion, subjects were more cautious and increased minimum-foot-clearance and decreased walking speed and step length. The minimum-foot-clearance increase can be interpreted as a motor control strategy aiming to safely clear the ground when online visual exproprioceptive cues from the body are not available. The lack of minimum-foot-clearance increase in lower occlusion suggests that the view of a clear pathway from beyond two steps combined with visual exproprioception and optic flow in the upper field were adequate to guide gait. A suggested accompanying safety strategy of reducing the amount of variability of minimum-foot-clearance under circumferential-peripheral occlusion conditions was not found, likely due to the lack of online visual exproprioceptive cues provided by the peripheral visual field for fine-tuning foot trajectory.

Utility of peripheral visual cues in planning and controlling adaptive gait.

Purpose. To determine the relative importance to adaptive locomotion of peripheral visual cues provided by different parts of the visual field. Methods. Twelve subjects completed obstacle crossing trials while wearing goggles that provided four visual conditions: upper visual field occlusion, lower visual field occlusion (LO), circumferential peripheral visual field occlusion (CPO), and full vision. The obstacle was either positioned as a lone structure or within a doorframe. Results. Given that subjects completed the task safely without cues from the lower or peripheral visual field, this suggests that subjects used exteroceptive information provided in a feed-forward manner under these conditions. LO and CPO led to increased foot placement distance from the obstacle and to increased toe clearance over the obstacle with a reduced crossing-walking velocity. The increased variability of dependent measures under LO and CPO suggests that exproprioceptive information from the peripheral visual field is generally used to provide online control of lower limbs. The presence of the doorframe facilitated lead-foot placement under LO by providing exproprioceptive cues in the upper visual field. However, under CPO conditions, the doorframe led to a further reduction in crossing velocity and increase in trail-foot horizontal distance and lead-toe clearance, which may have been because of concerns about hitting the doorframe with the head and/or upper body. Conclusions. Our findings suggest that exteroceptive cues are provided by the central visual field and are used in a feed-forward manner to plan the gait adaptations required to safely negotiate an obstacle, whereas exproprioceptive information is provided by the peripheral visual field and used online to “fine tune” adaptive gait. The loss of the upper and lower peripheral visual fields together had a greater effect on adaptive gait compared with the loss of the lower visual field alone, likely because of the absence of lamellar flow visual cues used to control egomotion.

Changes to Control of Adaptive Gait in Individuals with Long-standing Reduced Stereoacuity

PURPOSE Gait during obstacle negotiation is adapted in visually normal subjects whose vision is temporarily and unilaterally blurred or occluded. This study was conducted to examine whether gait parameters in individuals with long-standing deficient stereopsis are similarly adapted. METHODS Twelve visually normal subjects and 16 individuals with deficient stereopsis due to amblyopia and/or its associated conditions negotiated floor-based obstacles of different heights (7-22 cm). Trials were conducted during binocular viewing and monocular occlusion. Analyses focused on foot placement before the obstacle and toe clearance over it. RESULTS Across all viewing conditions, there were significant group-by-obstacle height interactions for toe clearance (P < 0.001), walking velocity (P = 0.003), and penultimate step length (P = 0.022). Toe clearance decreased (approximately 0.7 cm) with increasing obstacle height in visually normal subjects, but it increased (approximately 1.5 cm) with increasing obstacle height in the stereo-deficient group. Walking velocity and penultimate step length decreased with increasing obstacle height in both groups, but the reduction was more pronounced in stereo-deficient individuals. Post hoc analyses indicated group differences in toe clearance and penultimate step length when negotiating the highest obstacle (P < 0.05). CONCLUSIONS Occlusion of either eye caused significant and similar gait changes in both groups, suggesting that in stereo-deficient individuals, as in visually normal subjects, both eyes contribute usefully to the execution of adaptive gait. Under monocular and binocular viewing, obstacle-crossing performance in stereo-deficient individuals was more cautious when compared with that of visually normal subjects, but this difference became evident only when the subjects were negotiating higher obstacles; suggesting that such individuals may be at greater risk of tripping or falling during everyday locomotion.

Use of single-vision eyeglasses improves stepping precision and safety when elderly habitual multifocal wearers negotiate a raised surface.

justed for age, activities of daily living, mental status, skin condition, and 20 medical diagnoses, including organic psychotic disorders, Parkinson’s disease, and diabetes mellitus. After adjustments, the residents catheterized for 76% or more of days were three times as likely to die, be hospitalized, or require antibiotics. Excess deaths attributed to Foley catheters are apparently related to infection and kidney damage. Additional concerns include to the ‘‘one-point immobilization’’ mentioned in the Holroyd-Leduc article, as well as a potential need for restraints and sedation to avoid catheterrelated trauma or removal with an inflated bulb. Urinary catheters provide a biofilm-laden conduit for skin and bowel flora to enter the bladder. The catheter may become a sharp-edged instrument coated with encrusted bacterial biofilm and struvite crystals that can abrade and even lacerate the mucosa if differing forces are applied to the torso and drainage system. Self-manipulation with trauma, especially removal with the bulb inflated or catheter obstruction, are dangerous and may be associated with fatal bacteremia. In one case series, 13 consecutive admissions with urosepsis had catheter obstruction, traumatic manipulation, or removal with an inflated balloon within the previous 72 hours. There is also some evidence that men have more problems with urethral catheters, because the catheter may interfere with drainage of seminal secretions. Urethral catheterization in men is associated with epididymitis, orchitis, scrotal abscess, prostatitis, and prostatic abscess, conditions not present in women. I would appreciate if the authors could check their database to determine whether excess deaths were more prominent in men.

Attenuation of centre-of-pressure trajectory fluctuations under the prosthetic foot when using an articulating hydraulic ankle attachment compared to fixed attachment

BACKGROUND Disruptions to the progress of the centre-of-pressure trajectory beneath prosthetic feet have been reported previously. These disruptions reflect how body weight is transferred over the prosthetic limb and are governed by the compliance of the prosthetic foot device and its ability to simulate ankle function. This study investigated whether using an articulating hydraulic ankle attachment attenuates centre-of-pressure trajectory fluctuations under the prosthetic foot compared to a fixed attachment. METHODS Twenty active unilateral trans-tibial amputees completed walking trials at their freely-selected, comfortable walking speed using both their habitual foot with either a rigid or elastic articulating attachment and a foot with a hydraulic ankle attachment. Centre-of-pressure displacement and velocity fluctuations beneath the prosthetic foot, prosthetic shank angular velocity during stance, and walking speed were compared between foot conditions. FINDINGS Use of the hydraulic device eliminated or reduced the magnitude of posteriorly directed centre-of-pressure displacements, reduced centre-of-pressure velocity variability across single-support, increased mean forward angular velocity of the shank during early stance, and increased freely chosen comfortable walking speed (P ≤ 0.002). INTERPRETATION The attenuation of centre-of-pressure trajectory fluctuations when using the hydraulic device indicated bodyweight was transferred onto the prosthetic limb in a smoother, less faltering manner which allowed the centre of mass to translate more quickly over the foot.

Does my step look big in this? A visual illusion leads to safer stepping behaviour

Background Tripping is a common factor in falls and a typical safety strategy to avoid tripping on steps or stairs is to increase foot clearance over the step edge. In the present study we asked whether the perceived height of a step could be increased using a visual illusion and whether this would lead to the adoption of a safer stepping strategy, in terms of greater foot clearance over the step edge. The study also addressed the controversial question of whether motor actions are dissociated from visual perception. Methodology/Principal Findings 21 young, healthy subjects perceived the step to be higher in a configuration of the horizontal-vertical illusion compared to a reverse configuration (p = 0.01). During a simple stepping task, maximum toe elevation changed by an amount corresponding to the size of the visual illusion (p<0.001). Linear regression analyses showed highly significant associations between perceived step height and maximum toe elevation for all conditions. Conclusions/Significance The perceived height of a step can be manipulated using a simple visual illusion, leading to the adoption of a safer stepping strategy in terms of greater foot clearance over a step edge. In addition, the strong link found between perception of a visual illusion and visuomotor action provides additional support to the view that the original, controversial proposal by Goodale and Milner (1992) of two separate and distinct visual streams for perception and visuomotor action should be re-evaluated.

Obstacle crossing during locomotion: Visual exproprioceptive information is used in an online mode to update foot placement before the obstacle but not swing trajectory over it

Although gaze during adaptive gait involving obstacle crossing is typically directed two or more steps ahead, visual information of the swinging lower-limb and its relative position in the environment (termed visual exproprioception) is available in the lower visual field (lvf). This study determined exactly when lvf exproprioceptive information is utilised to control/update lead-limb swing trajectory during obstacle negotiation. 12 young participants negotiated an obstacle wearing smart-glass goggles which unpredictably occluded the lvf for certain periods during obstacle approach and crossing. Trials were also completed with lvf occluded for the entirety of the trial. When lvf was occluded throughout, foot-placement distance and toe-clearance became significantly increased; which is consistent with previous work that likewise used continuous lvf occlusion. Both variables were similarly affected by lvf occlusion from instant of penultimate-step contact, but both were unaffected when lvf was occluded from instant of final-step contact. These findings suggest that lvf (exproprioceptive) input is typically used in an online manner to control/update final foot-placement, and that without such control, uncertainty regarding foot placement causes toe-clearance to be increased. Also that lvf input is not normally exploited in an online manner to update toe-clearance during crossing: which is contrary to what previous research has suggested.

Adaptive gait changes in long-term wearers of contact lens monovision correction

Introduction:  The aim of the present study was to determine adaptive gait changes in long‐term wearers of monovision correction contact lenses by comparing gait parameters when wearing monovision correction to those observed when wearing binocular distance correction contact lenses.