1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-33
EXTRINSIC AND INTRINSIC VARIATION IN KINEMATIC DATA FROM THE
GAIT OF HEALTHY ADULT SUBJECTS
Eve Linda, McNee Anne, Shortland Adam
One Small Step Gait Laboratory, Guy’s Hospital, London, UK
Summary/Conclusions
3D kinematic data from 10 healthy adult subjects were collected from 3 sessions within a
week. In one session, marker placement was guided by indelible pen marks made on the
subjects in a data collection 2 days previously. Using this experimental design, we were able to
distinguish variation due to marker placement and that due to the intrinsic variation of human
walking. We found that, under near ideal circumstances, marker placement accounted for only
a small amount of inter-sessional variation, with the greater proportion due to intrinsic
differences in the gait patterns of the study subjects.
Introduction
3D gait analysis is used clinically to assist treatment planning and assess outcome following
intervention. The ability to report changes in gait with confidence is reliant on repeatable data
collection. The validity of gait analysis has been questioned (1,2) with variation in the data
collected, in the interpretation of the results and in the subsequent recommendations. Previous
studies have reported better repeatability in kinematic data recorded on the same day than from
sessions recorded on different days, with the greater variability attributed to marker placement
(3,4,5,6). In this study, we wished to quantify the variation in kinematic data due to marker
placement and the intrinsic inter-sessional variability of normal walking.
Statement of clinical significance
Our results suggest when a single therapist applies retroreflective markers on subjects of
moderate body-mass index, the portion of the inter-sessional standard error due to marker
misplacement is less than 0.3 degrees for a set of commonly used kinematic variables. Most of
the inter-sessional variation observed in pathological groups is likely to be due to intrinsic
variation in human walking.
Methods
3D gait data was collected from 10 adult volunteers (mean age 31.4 years, mean BMI 22.65),
with no history of musculo-skeletal abnormality, using Vicon 612 motion analysis system. A
lower limb marker set was applied (modified Helen Hayes), by the same experienced therapist
to each subject, on 3 separate occasions within a week. On one of the occasions, indelible ink
was used to mark the skin over the anatomical locations prior to application of the marker set.
These pen marks were then used to guide the marker placement for the subsequent data
collection session 2 days later. One other data collection session was conducted two days
before or after the marked sessions (randomised). The ink marks made on the skin were not
visible during this session. In each session, data were collected during five walking trials with
the subjects walking at their own self selected speed. Data were processed using the plug-ingait
model (Vicon Workstation) at which time thigh rotation was adjusted to correct the knee
varus curve in swing (7). The intra- and inter- sessional standard errors (SEs) were calculated
(6) for each of 9 commonly-used kinematic variables and for a combination of all these
variables (Table 1). The average SE over the gait cycle was calculated for those trials
belonging to a single session (intra-sessional), for those trials in marked and unmarked sessions
(inter-sessional, including marker error), and for those belonging to the two marked sessions
(inter-sessional, excluding marker error). Data were analysed using a two factor ANOVA
(subjects, source of error). Post-hoc paired t-tests were conducted to establish if there were
significant differences in the size of the error sources.
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