title: Clinimetrics of postural instability in Parkinson’s disease Evidence-based medicine: what it is and what it is not. Influence of Perturbation Velocity on Balance Control in Parkinson’s Disease Effects of dopamine on postural control in parkinsonian subjects: scaling, set, and tone. Disease severity affects obstacle crossing in people with Parkinson's disease. Effects of Parkinson's disease and levodopa on functional limits of stability. Clinical and posturographic correlates of falling in Parkinson's disease.
abstract: Abstract Judgement of the ability to recover balance after a sudden shoulder pull is used as a clinical measure of postural instability in Parkinson ’s disease . To further evaluate its merits , we compared this ‘ retropulsion test ’ with dynamic posturography in 23 Parkinson patients .  Dynamic posturography involved 20 serial ‘ toe-up ’ support surface rotations , which induced backward body sway . We found a moderate correlation ( Spearman ’s ρ = 0.54 ; P < 0.05 ) between the retropulsion test and body sway after platform rotations during the ‘ off ’ phase , but no correlation during the ‘ on ’ phase ( Spearman ’s ρ = 0.43 ; P = 0.11 ) . These results cast doubt on the use of the retropulsion test as a measure of postural instability in Parkinson ’s disease The evidence -based medicine ( EBM ) related concepts of hierarchy of evidence , meta-analyses , confidence intervals , study design , etc . are nowadays so widespread , that clinicians willing to use today 's medical literature with underst and ing have no choice but to become familiar with EBM principles and method ologies . Although surgeons may perceive that evidence -based medicine m and ates a strict adherence to r and omised trials , it more accurately involves informed and effective use of all types of evidence ( from meta- analysis of r and omised trials to individual case series and case reports . With the ever-increasing amount of available information , surgeons must consider a shift in paradigm from traditional practice to one that involves question formulation , validity assessment of available studies and appropriate application of research evidence to individual patients Underlying somatosensory processing deficits of joint rotation velocities may cause patients with Parkinson ’s disease ( PD ) to be more unstable for fast rather than slow balance perturbations . Such deficits could lead to reduced proprioceptive amplitude feedback triggered by perturbations , and thereby to smaller or delayed stabilizing postural responses . For this reason , we investigated whether support surface perturbation velocity affects balance reactions in PD patients . We examined postural responses of seven PD patients ( OFF medication ) and eight age-matched controls following backward rotations of a support-surface platform . Rotations occurred at three different speeds : fast ( 60 deg/s ) , medium ( 30 deg/s ) or slow ( 3.8 deg/s ) , presented in r and om order . Each subject completed the protocol under eyes open and closed conditions . Full body kinematics , ankle torques and the number of near-falls were recorded . Patients were significantly more unstable than controls following fast perturbations ( 26 % larger displacements of the body ’s centre of mass ; P<0.01 ) , but not following slow perturbations . Also , more near-falls occurred in patients for fast rotations . Balance correcting ankle torques were weaker for patients than controls on the most affected side , but were stronger than controls for the least affected side . These differences were present both with eyes open and eyes closed ( P<0.01 ) . Fast support surface rotations caused greater instability and discriminated Parkinson patients better from controls than slow rotations . Although ankle torques on the most affected side were weaker , patients partially compensated for this by generating larger than normal stabilizing torques about the ankle joint on the least affected side . Without this compensation , instability may have been greater 1 . This study investigates the effects of parkinsonism and of dopamine replacement therapy ( levodopa ) on scaling the magnitude of automatic postural responses based on sensory feedback and on predictive central set . Surface reactive torques and electromyographic ( EMG ) activity in response to backward surface translations were compared in patients with parkinsonism ON and OFF levodopa and in elderly control subjects . Correlations between the earliest postural responses [ initial rate of change of torque and integrated EMG ( IEMG ) ] and translation velocity provided a measure of postural magnitude scaling using somatosensory feedback . Correlations of responses with expected translation amplitude provided a measure of scaling dependent on predictive central set because the responses preceded amplitude completion . 2 . Parkinsonian EMG responses in six leg and trunk muscles were not later than in elderly control subjects . In fact , quadriceps antagonist latencies were earlier than normal , result ing in coactivation at the knee not present in control subjects . EMG activation was fragmented , with short burst duration s and high tonic levels that often returned to baseline with multiple bursts . In addition , parkinsonian responses showed smaller-than-normal agonist extensor bursts and larger-than-normal activation in tibialis and rectus femorus antagonist flexors . 3 . Although parkinsonian subjects scaled postural responses to both displacement velocities and amplitudes , their torque response were smaller than those of elderly controls , especially in response to the largest displacement amplitudes . The gain ( slope ) of postural response magnitude scaling to displacement velocity was similar for parkinsonian and control subjects , although parkinsonian subjects had smaller torques . Parkinsonian subjects were also able to use prediction to scale responses to small expected displacement amplitudes , but many patients did not generate the larger plantarflexion torques required at larger displacement amplitudes . Reduced torque at large amplitudes was associated with less agonist gastrocnemius IEMG , increased tibialis antagonist burst responses , and increased tibialis tonic background activity . 4 . Levodopa further reduced the already low magnitude of initial torque and IEMG responses to displacement velocities and amplitudes in parkinsonian patients . The ability to scale postural responses to velocity feedback was not affected by levodopa , but the ability to scale responses to large displacement amplitudes based on central set was worsened by levodopa . Levodopa also significantly reduced the tonic , background levels of EMG , particularly the distal gastrocnemius and tibialis activity . 5 . High baseline muscle tone was apparent in parkinsonian subjects from their high background EMG activity in quiet stance , especially in tibialis and quadriceps , and the slow initial velocity of center of mass falling in response to displacements . By reducing tone , levodopa reduced passive stiffness to perturbations without increasing EMG burst magnitudes , result ing in less resistance to external displacements and thus faster center of body mass ( COM ) displacements . 6 . The biggest postural deficit in parkinsonian subjects was not in response latency , pattern , or reactive or predictive scaling of response magnitude , but in quickly generating an adequate level of postural force . Dopamine improved tonic background postural tone but further weakened automatic postural responses to external displacements . Thus the basal ganglia may participate in postural control by regulating appropriate levels of background postural tone and by enabling adequate force generation for resisting external displacements The current study evaluated the effects of disease severity on the control of obstacle crossing in people with idiopathic Parkinson 's disease ( PD ) . Forty-five subjects participated in the study , including 15 patients with mild PD ( classified as stage 1 to 1.5 of the Hoehn and Yahr Rating Scale ) , 15 patients with moderate PD ( classified as stage 2 to 3 of the Hoehn and Yahr Rating Scale ) , and 15 neurologically healthy individuals . Groups were matched by sex , age , body mass , and body height . The obstacle crossing task required participants to walk along a pathway and step over an obstacle ( half of the knee height , positioned in the middle of the pathway ) .  Patients were tested in a typically medicated state .  Kinematic data were recorded using an optoelectronic tridimensional system . The outcome measures included spatiotemporal measures of obstacle avoidance . There were no significant differences between patients with mild PD and healthy individuals . Patients with moderate PD exhibited shorter distances for leading toe clearance and leading foot placement after the obstacle than did healthy individuals . Patients with moderate PD tended to exhibit a lower leading horizontal mean velocity during obstacle crossing than did healthy individuals . We found significant negative relationships between obstacle crossing measures and disease severity ( score on the motor section of the Unified Parkinson 's Disease Rating Scale ) . These findings suggest that disease severity affects locomotor behavior during obstacle crossing in PD . Specifically , obstacle avoidance was not affected in the early stages of PD ; however , bradykinesia and hypometria influenced obstacle crossing in patients with moderate PD BACKGROUND The voluntary , maximum inclined posture reflects the self-perceived limits of stability . Parkinson 's disease is associated with small , bradykinetic postural weight shifts while st and ing but it is unclear whether this is due to reduced limits of stability and /or to the selection of abnormal strategies for leaning . The aim of this study was to investigate the effects of Parkinson 's disease and levodopa medication on voluntary limits of stability and strategies used to reach these limits . METHODS Fourteen subjects with Parkinson 's disease ( OFF and ON levodopa ) and 10 age-matched controls participated in the study . Functional limits of stability were quantified as the maximum center of pressure excursion during voluntary forward and backward leaning . Postural strategies to achieve functional limits of stability were assessed by ( i ) body segments alignment , ( ii ) the difference between center of pressure and center of mass in preparation for a lean , ( iii ) the timing and the velocity of the preparation phase . FINDINGS Functional limits of stability were significantly smaller in subjects with Parkinson 's disease compared to control subjects . Subjects with Parkinson 's disease maintained their stooped posture while leaning , initiated leaning with a smaller difference between center of pressure and center of mass and had a slower leaning velocity compared to control subjects . Levodopa enlarged the limits of stability in subjects with Parkinson 's disease because of an increase in maximum forward , but not backward leans , but did not significantly improve postural alignment , preparation for a leaning movement , or velocity of leaning . INTERPRETATION Parkinson 's disease reduces functional limits of stability as well as the magnitude and velocity of postural preparation during voluntary , forward and backward leaning while st and ing . Levodopa improves the limits of stability but not the postural strategies used to achieve the leaning Various clinical tests and balance scales have been used to assess postural stability and the risk of falling in patients with idiopathic Parkinson 's disease ( IPD ) .  Quantitative posturography allows a more objective assessment but the findings in previous studies have been inconsistent and few studies have investigated which posturographic measures correlate best with a history of falling . The purpose of this study was to determine the efficacy of clinical tests , balance scales , and  stable-platform posturography  in detecting postural instability and discriminating between fallers and non-fallers in a home-dwelling PD cohort . Forty-eight PD subjects ( Hoehn & Yahr stage 1 - 3 ) and 17 age-matched controls had the following assessment s : Activities-specific Balance Confidence scale , Berg Balance Scale , Unified Parkinson 's Disease Rating Scale ( UPDRS ) ( motor ) , pull-test , timed up- and -go , static posturography , and dynamic posturography to assess multidirectional leaning balance . Of the clinical assessment s , all but the pull-test were closely correlated with a history of falling .  Static posturography  discriminated between PD fallers and controls but not between PD fallers and non-fallers , whereas  dynamic posturography ( reaction time , velocity , and target hit-time ) also discriminated between fallers and non-fallers . Our findings suggest that this combination of clinical and posturographic measures would be useful in the prospect i ve assessment of falls risk in PD patients . A further prospect i ve study is now required to assess their predictive value . © 2013 Movement Disorder Society
target: Overall , there are many scales and tests used to assess the balance disorders and disabilities of people with PD .
background: Postural instability is common in Parkinson ’s disease ( PD ) , often contributing to falls , injuries , and reduced mobility .
  In the clinical setting , balance disorder is commonly diagnosed using clinical tests and balance scales , but it is suggested that the most sensitive measurement is the force platform .
  The aim of this systematic review was to summarize the methods and various posturographic procedures used to assess the body balance and gait in PD .