Defining spatial parameters for non-linear walking.

Current definitions of the spatial and temporal parameters of gait have been based on the premise that walking occurs in a straight line. When the direction of progression (DoP) is not consistent and walking is non-linear, these definitions do not provide meaningful information. An alternative method based on the changing direction of each stride is presented. This method is easy to understand and use, and requires no expensive technology. A comparison of the spatial parameters of the footstep pattern during linear trials and trials incorporating a 60 degrees turn was performed, using output derived from the old and the new definitions. The two methods produced very different results. Spatial output from the old definitions was merely dictated by the change of direction. Output calculated relative to the changing stride direction however, provided useful information about the footstep adjustments made for turning and how these would act to improve stability. This method of establishing spatial parameters during non-linear walking should form a useful tool for further investigation of functional locomotion.

Theoretical considerations in balance assessment.

Although balance control is an integral component of all daily activities, its complex and flexible nature makes it difficult to assess adequately. This paper discusses balance by examining it in relation to function and the physical environment. Balance is affected by both the task being undertaken and the surroundings in which it is performed. Different tasks and environments alter the biomechanical and information processing needs for balance control. These issues are discussed and a modification of Gentile s Taxonomy of Tasks is suggested for analysis of clinical balance tests, some of which are used as examples.

The biomechanics and motor control of gait in Parkinson disease.

Parkinson disease is a progressive neurological condition characterised by hypokinesia (reduced movement), akinesia (absent movement), tremor, rigidity and postural instability. These movement disorders are associated with a slow short-stepped, shuffling gait pattern. Analysis of the biomechanics of gait in response to medication, visual cues, attentional strategies and neurosurgery provides insight into the nature of the motor control deficit in Parkinson disease and the efficacy of current therapeutic interventions. In this article we supplement a critical evaluation of the Parkinson disease gait literature with two case examples. The first case describes the kinematic gait response of an individual with Parkinson disease to visual cues in the "off" phase of the levodopa medication cycle. The second case investigates the biomechanics and motor control of turning during walking in a patient with Parkinson disease compared with elderly and young control subjects. The results are interpreted in light of the need for gait analysis to investigate complex functional walking tasks rather than confining assessment to straight line walking, which has been the trend to date.

Physiological localisation in functional neurosurgery for movement disorders: a simple approach.

Controversy exists between anatomical methods and single cell recording as the preferred approach in target localisation in functional neurosurgery for movement disorders. The controversy centres on accuracy as compared to practicality. We describe a mapping technique of semi-microstimulation utilising threshold measurements which has been used in 66 procedures in 50 subjects. We compared the accuracy of anatomical localisation with the final chosen target using the above technique. We also compared the benefit, the side effects and the surgical complication rate with published data on single cell recording and anatomical localisation. The mean difference in 3-dimensional space between the anatomical target and the physiological target was 6.85 mm (P < 0.0001). A good response was obtained in 80% of procedures. Mortality was 1.5%. The surgical complication rate was 1.5%. Mild side effects, serious side effects, transient side effects and permanent side effects were evident in 4.5%, 10.6%, 6.1% and 9.1% of procedures. These figures compared better than anatomical studies and similar to single cell recording studies. It is concluded that this approach provides both accuracy and simplicity and is recommended as a compromise to the currently available methods.

Postural instability in Parkinson's disease: a comparison with and without a concurrent task.

The purpose of this investigation was to determine the effects of dual task performance on postural instability in subjects with idiopathic Parkinson's disease (PD) compared with healthy elderly people. In particular, we aimed to divert attention to a secondary task so the full extent of balance disturbance could be revealed without compensation by attentional mechanisms. Forty-five subjects were tested: 15 PD subjects with a past history of falls; 15 PD subjects with no history of falls; and 15 unimpaired individuals. Groups were matched for age and sex and subjects with PD were tested at peak dose in the levodopa medication cycle. Each subject was tested on their ability to maintain stability in three conditions: (1) steady standing (feet apart, feet together, step stance, tandem stance, single leg stance); (2) in response to perturbations generated by self-initiated movements (arm raise test, step test); and (3) in response to an unexpected external perturbation in upright stance, the shoulder tug test. The concurrent task was verbal-cognitive and required subjects to recite the days of the week backwards. The concurrent task produced a significant deterioration in performance for the arm raise test in all groups, the step test for the PD fallers and controls and for tandem stance in the PD fallers. Ceiling effects were evident for timed tests with feet apart and feet together resulting in poor discriminative validity for these tests. The external perturbation test showed differences between the three groups for both unitask and concurrent task conditions, yet similar rates of change from unitask to dual task conditions. Because PD fallers had a more severe initial deficit than controls, deterioration placed them in that part of the balance continuum at high risk of losing equilibrium.