zi 
x 
x 
  
  
19 
Fig. 2: Anatomy based coordinate system of right thigh. 
For evaluation of the dynamics of the right lower 
extremity during walking, one typical gait cycle of each 
person was chosen for manual digitization of 3D marker 
positions from paired synchronous images with real time in 
milliseconds marked on each 16mm filmframe. Translational 
and angular velocities and accelerations of the right thigh and 
shank-foot segments in space were calculated. The reactive 
forces and moments occuring at the hip and knee were 
obtained from the prevalently gravitational loading of the 
force measuring platforms and the effects of segmental mass 
accelerations produced by muscle activity during swing and 
stance phase of the steps. For these calculations the inverse 
dynamic approach was used. (Schär et al. 1989). 
RESULTS 
The usefulness of data from gait analysis for medical 
purposes depends on the reliability of measurements, their 
linking to accustomed anatomical knowledge and 
presentations permitting rapid appraisal. Graphic reports are 
therefore obligatory. The ability shown here to extract 
measurements from images of the whole person in motion 
and to link other data from electronic transducers to them, 
allows data to be shown within the context of these total 
body images. This permits the observer to link measured 
phenomena with large sets of information gathered rapidly 
from body proportions and the actual position of hundreds of 
large and small joints during the particular phase of the 
movement. The evaluation of the relative value of results 
from limited measurements in the context of a highly 
complex situation is thus greatly facilitated. This may be 
decisive to the widespread acceptance of motion analysis as a 
diagnostic medical tool. 
The biostereometrics approach has proven to be ideal as a 
technique for producing inertial body segment information 
for handicapped subjects for two reasons. The subject time 
involved is greatly reduced for that necessary to collect an- 
thropometric data used in prediction equations of segmental 
parameters. Secondly, the photogrammetric technique is in a 
sense a customized estimation process not hampered by 
    
contralateral body asymmetry often seen in CP patients. This 
research project has clearly demonstrated the ability to 
combine two different and independent analyses, through the 
use of common reference points which could be used for axis 
systems definition necessary for both the gait analysis and the 
body segment parameter computation. 
The addition of the segmental mass distribution, parameters 
provided information for the kinetic evaluation of the two 
groups of subjects. These data were used in calculating 
external forces and moments at the knee and hip in the 
anatomical axis systems. Several examples of the analyis 
follow: 
a. Hip Forces: A rapid and strong force acting to push the 
femoral head forward and thus favouring the increase of its 
anteversion was observed in the antero-posterior hip force 
during weight acceptance of the CP patients. In the extreme 
case, this force was more than twice the average normal 
value and in several patients this net anterior hip force 
continued throughout the entire stance phase. 
b. Knee Moments: In comparison to the normal subjects, a 
much stronger and more prolonged reactive abduction 
moment was seen following the initial ground contact of the 
spastic diplegic subjects. Perhaps this phenomenon was 
explained by abductor muscle spasticity. Even more 
important to the gait analysis was the finding that the 
flexion-extension knee moment coinciding with the early and 
late swing phases was twice the value of the normal subjects. 
c. Hip Moments: Typically seen were increased adduction 
and abduction moments (due to the increased moment of the 
shank-foot) during the swing phase of the stiff appearing 
spastic gait. A strong flexion moment of twice the normal 
intensity was observed in the late swing phase of the CP 
patients. 
The spastic diplegic patients demonstrated a more powerful 
and longer lasting flexion moment after initial ground contact 
which lasted throughout the stance phase. In summary, all of 
these increased moments and forces quite simply contribute 
to a decrease in the efficiency of the energy utilization of the 
child with spastic diplegia. The results of our study are 
consistent with the clinical observations of both the normal 
and pathological gait patterns observed. However, the quanti- 
fication of the contributions of the inertial properties allows 
comparison of groups of subjects throughout the various 
portions of the gait cycle. By normalizing the gait cycles, the 
moments and forces can be compared for subjects of dif- 
fering sizes and weights.