Deficits underlying impaired visually triggered step adjustments in mildly affected stroke patients.
BACKGROUND
The ability to make step adjustments while walking is often impaired following a stroke, but the basic sensorimotor control deficits responsible have not been established.


OBJECTIVE
To identify these deficits in Patients who have recovered from stroke leaving only mild lower limb impairment.


METHODS
Ten stroke and 10 age-matched control patients stepped onto an illuminated rectangle. In 40% of trials it jumped 140 mm either medially or laterally when the stepping foot left the ground, thus provoking a mid-step adjustment. In a separate block, patients performed the same task but with the body supported by a frame to eliminate balance responses.


RESULTS
Irrespective of support condition stroke patients produced short-latency foot trajectory adjustments compatible with a fast-acting, possibly subcortical, visuomotor process. However, the latency was slightly but significantly longer for the contralesional leg (148 ms) than the ipsilesional leg (141 ms) and longer than for controls (129 ms). Stroke patients' foot adjustments were executed slower and undershot the target more than controls. These deficits were most pronounced in the medial direction when the body was unsupported. The pattern of undershooting was the same for ipsilesional and contralesional legs.


CONCLUSIONS
Mildly impaired stroke patients have deficits in initiating and executing visually triggered step adjustments but more profound difficulties with balance control during the adjustment, which caused them to suppress mid-step adjustments of foot placement in the medial direction where balance demands were greatest. Paradoxically, such suppression outside the laboratory may also threaten balance if it leads to unsafe foot placement or obstacle collision.
Nonnekes
Jorik H
JH
UCL Institute of Neurology, London, United Kingdom, Radboud University, Nijmegen, The Netherlands.
Talelli
Penny
P
de Niet
Mark
M
Reynolds
Raymond F
RF
Weerdesteyn
Vivian
V
Day
Brian L
BL
D000328:Adult; D001696:Biomechanical Phenomena; D005260:Female; D005528:Foot / Q000503:physiopathology; D007839:Functional Laterality; D006801:Humans; D008297:Male; D008875:Middle Aged; D004856:Postural Balance; D011597:Psychomotor Performance / Q000502:physiology; D012720:Severity of Illness Index; D020521:Stroke / Q000503:physiopathology; D013997:Time Factors; D014796:Visual Perception; D016138:Walking / Q000502:physiology