title: Lateral stepping for postural correction in Parkinson's disease.
abstract: OBJECTIVE
  To characterize the lateral stepping strategies for postural correction in patients with Parkinson's disease (PD) and the effect of their anti-parkinson medication.
  
  
  METHODS
  Observational study.
  
  
  METHODS
  Outpatient neuroscience laboratory.
  
  
  METHODS
  Thirteen participants with idiopathic PD in their on (PD on) and off (PD off) levodopa state and 14 healthy elderly controls.
  
  
  METHODS
  Movable platform with lateral translations of 12 cm at 14.6 cm/s ramp velocity.
  
  
  METHODS
  The incidence and characteristics of 3 postural strategies were observed: lateral side-step, crossover step, or no step. Corrective stepping was characterized by latency to step after perturbation onset, step velocity, and step length and presence of an anticipatory postural adjustment (APA). Additionally, percentages of trials resulting in falls were identified for each group.
  
  
  RESULTS
  Whereas elderly control participants never fell, PD participants fell in 24% and 35% of trials in the on and off medication states, respectively. Both PD and control participants most often used a lateral side-step strategy; 70% (control), 67% (PD off), and 73% (PD on) of all trials, respectively. PD participants fell most often when using a crossover strategy (75% of all crossover trials) or no-step strategy (100% of all no-step trials). In the off medication state, PD participants' lateral stepping strategies were initiated later than controls (370+/-37 ms vs 280+/-10 ms, P<.01), and steps were smaller (254+/-20 mm vs 357+/-17 mm, P<.01) and slower (0.99+/-0.08 m/s vs 1.20+/-0.07 m/s, P<.05). No differences were found between the PD off versus PD on state in the corrective stepping characteristics. Unlike control participants, PD participants often (56% of side-step strategy trials) failed to activate an APA before stepping, although their APAs, when present, were of similar latency and magnitude as for control participants. Levodopa on or off state did not significantly affect falls, APAs, or lateral step latency, velocity, or amplitude (P>.05).
  
  
  CONCLUSIONS
  PD participants showed significantly more postural instability and falls than age-matched controls when stepping was required for postural correction in response to lateral disequilibrium. Although PD participants usually used a similar lateral stepping strategy as controls in response to lateral translations, lack of an anticipatory lateral weight shift, and bradykinetic characteristics of the stepping responses help explain the greater rate of falls in participants with PD. Differences were not found between the levodopa on and off states. The results suggest that rehabilitation aimed at improving lateral stability in PD should include facilitating APAs before a lateral side-stepping strategy with faster and larger steps to recover equilibrium.
authors.affiliation: Neurological Sciences Institute, Oregon Health and Sciences University, Beaverton, OR 97006, USA.
authors.forename: Laurie A
authors.initials: LA
authors.lastname: King
authors.forename: Fay B
authors.initials: FB
authors.lastname: Horak
mesh_terms: D000058:Accidental Falls / Q000517:prevention & control* / Q000706:statistics & numerical data; D000328:Adult; D000368:Aged; D000553:Ambulatory Care; D016022:Case-Control Studies; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D005684:Gait / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D015994:Incidence; D007980:Levodopa / Q000627:therapeutic use*; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000175:diagnosis / Q000188:drug therapy* / Q000534:rehabilitation*; D004856:Postural Balance / Q000502:physiology; D011187:Posture / Q000502:physiology; D011930:Reaction Time; D012016:Reference Values; D012720:Severity of Illness Index; D018709:Statistics, Nonparametric
chemical_list: D007980:Levodopa