1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

O-10
FEASIBILITY OF A NEW -JOINT CONSTRAINED- LOWER LIMB MODEL FOR
GAIT ANALYSIS APPLICATION
Pavan EE, PhD, Taboga P, Dr.Eng, and Frigo C, Ass Prof
Laboratory of Movement Biomechanics and Motor Control (TBM Lab)
Department of Bioengineering, Polytechnic of Milan, Milan, Italy
Summary/conclusions
A lower limb model has been developed in which kinematic constraints of hip, knee, and ankle
joints are defined on the basis of functional anatomy and data collected from MRI and
Fluoroscopy. In particular the femoral-tibial motion was supposed to be constrained by the
knee cruciate ligaments. The feasibility of the model was checked on a normal subject walking
on level at natural cadence and performing on site exercises. Thirty-one reflective markers
were positioned on pelvis and lower limbs: they were used to identify anatomical landmarks
and allowed us to connect a 3-D model of bones to the collected data. Our results show that
kinematics of femur in relation to pelvis and shank can be accurately obtained through
identification of hip joint centre, shank location, and knee joint kinematic constraints. The
markers located on the thigh (greater trochanter, medial and lateral femoral epicondyles),
which were the most affected by skin motion artefacts, can be profitably removed from our
protocol, and the advantage will be reduced encumbrance and improved accuracy.
Introduction
Protocols for clinical gait analysis can be subdivided into those who don’t impose any joint
constraint (each segment is an independent free body in space), and those who pre-define a
linkage between the anatomical segments. The advantage of the last ones is evident, in that the
congruency of the relative movement of adjacent segments is inherently guaranteed,
measurement errors of markers coordinates can be better distributed along the total limb, the
problem of magnification of orientation errors of the local reference axes, because the markers
are not positioned at the extremity of the anatomical segments, can be considerably reduced
[1]. On the other side the joint-constrained models adopt very simple spherical or cylindrical
hinges to describe the joint kinematics, which is inadequate particularly as far as the knee joint
is considered. Due to this inadequacy the rigid body hypothesis cannot be satisfied, and
considerable errors can be done in muscle-length estimation if muscle-tendon action lines are
just attached to the skeleton model. Our new model attempts at overcoming the previous
drawbacks by integrating imaging information into a model of the lower limb.
Statement of clinical significance
An improved identification of lower limb kinematics can be achieved trough proper modelling
and anthropometric data collection from biomedical imaging. According to our scheme the
markers on the thigh, which are the most affected by skin motion artefacts, can be avoided, and
this can be an advantage in terms of reduced encumbrance and preparation time, that could be
of interest for clinical application of gait analysis.
Methods
A motion analyser (SMART, eMotion, Italy) equipped with 6 TV-cameras located in a gait
analysis laboratory was used for our experimental sessions. The model proposed was
composed of four anatomical segments: pelvis, thigh, shank and foot. At variance with a
previous protocol [2] the number of markers (31 in total) was redundant, in order to check for
the relative inaccuracy. Five markers were located on the pelvis, and then, bilaterally, four on
the thigh, five on the shank, and three on the foot. The hip, knee and ankle joint centres were
tentatively identified as described in [3]. Then a 3-D model shank bones, obtained from
previous elaboration of MRI [4] was adapted to the present subject by making them to best
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