1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-09
THE SYMMETRICAL AXIS OF ROTATION APPROACH (SARA) FOR
DETERMINATION OF JOINT AXES IN CLINICAL GAIT ANALYSIS
Taylor, William, Ph.D.1, Ehrig, Rainald, Ph.D.2, Duda, Georg, Ph.D.1, Heller, Markus, Ph.D.1
1 Center for Musculoskeletal Research, Charité - Universitätsmedizin, Berlin, Germany
2 Zuse Institute Berlin, Berlin, Germany
Summary/conclusions
The goal of the study was to develop and evaluate a new technique, the Symmetrical Axis of
Rotation approach (SARA) for determining the axis of rotation in e.g. knee joints during gait.
This approach, capable of simultaneously considering two dynamic body segments, produced
the best axis, when compared against literature methods using generated data. Application of
this method in gait analysis should lead to improved clinical diagnosis and monitoring.
Introduction
Axes of rotation e.g. at the knee, are often generated from clinical gait analysis data to be used
in the assessment of the severity of kinematic abnormalities, the diagnosis of disease, or the
ongoing monitoring of a patient’s condition. Currently available methods to describe joint
motion from segment marker positions share the problem that when one segment is
transformed into the coordinate system another, measurement errors and artefacts associated
with motion of the markers relative to the bone are magnified [1]. We hypothesize that by
calculating the axis of rotation using a method that can consider the movement of two dynamic
body segments simultaneously, it should be possible to determine a unique axis of rotation
more accurately than currently available methods. The goal of this study was therefore to
develop a new robust approach that avoids the aforementioned problems and to compare its
performance with a number of previously proposed techniques.
Statement of clinical significance
Gait analysis can allow the assessment and diagnosis of kinematic irregularities or deformities
that may be unobservable even to a skilled clinician. Improvement in the accuracy of methods
to determine the axis of rotation will enhance the assessment and monitoring of kinematic
abnormalities.
Methods
A virtual hinge joint was created for which marker positions were generated computationally.
The two segments of the joint rotated around a common axis within a defined angular range of
motion (RoM), resulting in circular plane arcs. On each segment, 4 markers were attached
approximately 10 to 15 cm distant from the axis. Marker positions were then randomly
distributed around the arc and within different RoMs. In addition, the whole joint configuration
was able to randomly translate in space, simulating a non-stationary AoR. The following
approaches were employed to determine the AoR:
- Algebraic Axis Fit (Circle fitting) [2]
This technique presupposes that the AoR is fixed with respect to global coordinates.
- Mean Helical Axis [3]
This algorithm assumes that one segment remains stationary and describes the
movements as rotations around and translations parallel to the helical axis.
Transformation Methods: Transformation methods assume that the AoR is stationary only in
each segment’s local coordinates. Assuming at least 3 markers are present, then it is possible to
transform from the global into time dependent local coordinate systems.
- Schwartz Transformation Technique (STT) [4]
This approach determines the median of multiple pair-wise calculated axes.
- 54 -