Thanks for the new Case (super results, as usual, from Vienna!). I'm tempted to attempt a diagnosis before we get the video, and I must say it's not easy! This shows just how important video is to gait analysis - something I've been stressing lately to the motion analysis equipment manufacturers.
Well, what can we say? Long stance phase on the right and short step on the left. Right hemipelvis higher than left. A rather dorsiflexed left ankle with moderately reduced power generation, minimal flexion deformity of the knee (with as Andreas says, inappropriate rectus on the emg in swing, hamstrings overactivity in stance). Unusually, the largest kinematic abnormalities seem to be in the transverse plane, with increased trunk and pelvic rotation (compensation for reduced stride length), internal rotation of the hip (? femoral anteversion) and (perhaps most importantly) adducted feet (left > right).
So, at the risk of embarrassment when the videos arrive on the site (we'll all be on holiday here anyway, enjoying our last day in the British Empire!) I'm going to stick my neck out and say that this child's main problem is femoral anteversion & tibial torsion with reduced A2 power generation due to lever arm dysfunction. I wonder whether the rectus/hamstrings overactivity are compensations.
But I wouldn't bet on it until I see the video!
Anyone else care to stick their neck out before Monday?
Chris -- Dr. Chris Kirtley (Kwok Kei Chi) MD PhD Assistant Professor Department of Rehabilitation Sciences The Hong Kong Polytechnic University Hong Kong
I just reviewed the videos that Andreas has kindly added to the page at /archives/29-6-97
This is certainly quite a subtle case, and the videos add a lot more
information:
The foot position is, however, not as bad as I would have anticipated from the kinematics curves. I had forgotten that the foot position curve on Motion Analysis Corp. plots is relative to the Global Reference System, not the angle of progression.
I think I would stand by my initial verdict that femoral anteversion is the main problem. Do you agree?
If so, this would be an interesting discussion point, since, I think(?), it's impossible to measure femoral anteversion on the motion analysis. I hope someone more experienced will comment...
By the way, Andreas, I'd be interested to know whether there was anteversion on clinical examination. Also why there's no knee varus/valgus plot on the kinematics - did you judge the Euler angle artefact from rotation to be too large?
Chris
I have a student, working in our laboratory, Leonard D'Addesi finishing a masters degree in biomedical engineering at Drexel University who has developed a kinematic method for measuring femoral torsion (anteversion/retroversion) using kinematics. He is currently testing its validity. He presented at the last NAGCMA meeting in Chicago in April. If you are interested in more details, please let me know.
Lisa Selby-Silverstein, PhD.,PT.,NCS Director, Human Performance Laboratory Asst. Prof., Physical Therapy Thomas Jefferson University
Thanks to Henry for his comments on the case.
I looked at the video and gait curves, and I agree with Henry that there
does seem to be less range of motion at the ankle in the video than
in
the curves. There's also quite good push-off power generation
(that's
A2, by the way, to answer Henry's question), which is surprising, I
think. This patient has rather strange feet - very long with a very
hypermobile forefoot, and they certainly don't look very propulsive.
I
think what must have happened is that the toe marker on the hypermobile
forefoot is moving through a large angle, and this has resulted in
an
erroneous overestimation of ankle range of motion.
Full marks to Henry for spotting this one, and opening up two great
big
cans of worms to start us off into 1999:
1. Surely the time has come for the foot to be modelled by more than
the
single toe marker usually used in clinical gait analysis. Both
the
commonly-used marker-sets (Davis & Cleveland) have this limitation
(and
the former does not even attempt to measure varus/valgus). Are any
of
you out there routinely using more foot markers, I wonder?
2. It seems to me that even the most experienced gait analysers look
for
agreement between video and gait curves before accepting the curves
as
valid. Whilst this may be laudable, in that it follows standard medical
methodology in using a special test to confirm or reject a diagnostic
hypothesis, it seems to me that it is more often, in practice, because:
a. the clinician doesn't understand the gait results;
b. the clinician doesn't trust the gait results.
Both these possibilities have big implications for the future of
clinical gait analysis, of course, and I'd like to see some discussion
of the topic. As well as the limitations of the marker set nicely
illustrated by this example, there are also problems arising from the
Euler angle sequence chosen, for example. In a paper at the
recent ESMAC
meeting in Belfast, the Edinburgh group found that the sequence
resulting in optimal agreement between video and curves was different
for sagittal (flex-ext, ab-ad, rotn) and frontal (ab-ad, flex-ext,
rotn)
planes. I know that the purists are going to say that this is mere
mathematical semantics, but I think it's one more example of a
fundamental issue that we need to address - getting results that
match
the clinical picture. Gait labs will never be taken seriously
while
there are discrepancies. I think it's salient to ponder that, while
we
can rely on the clinical eye to spot gross distortions in the curves,
I
wonder how many more subtle ones get through?
I wondered whether one possible way of checking the fit might be to
use
VRML - and Isam Hilal in France has kindly supplied me with a very
nice
H-VRML-animation of the curves, which you can download as a
QuickTime
movie. It's large at 9.5Mb, but well worth the wait. I'm wondering
whether you think this adds anything, as I'm hoping to incorporate
H-VRML in the new CGA site. Work on this has finally begun, I'm glad
to
say. If all goes well, the new site will be fully automated, plotting
curves direct from the data files and logging your comments. This will
save Andreas and me a lot of work, and more importantly make the site
into a useful research resource for studying and improving the
interpretation of gait analysis reports. I'll let you know how it
develops.
Best wishes,
Chris
--
Dr. Chris Kirtley MD PhD
Dept. of Rehabilitation Sciences
The Hong Kong Polytechnic University
In my MS thesis I used two toe markers to measure the movements of
the toe. One marker to measure the FOOT is a bit ridiculous. There
are more bones in the feet than the rest of the body put together,
barring the hands.
Having said that I do not believe it is currently practical or
worthwhile to use many markers on the feet. The difficulties with
normal anatomical alignment and skin elasticity will introduce more
problems than they solve. The experiments I did on cadavers produced
severe marker alignment problems, and the bones were clamped and
bolted to the lab floor!
That extra toe marker makes a huge difference when it comes to
interpreting the results.
These results are now being put to good use in analysing the
foot bones each within its own inertial reference frame. The result
is analysable in 4D, using a general relativistic model (I hope ;)
.
The Newtonian model in present use has served its purpose.
In my PhD thesis, I will be measuring all the bones in the foot in
terms of the 4D model. I have successfully validated the philosophical
solution; the logic is sound. The new theory is predictive rather
than descriptive. The antithesis, the Newtonian solution taken from
the perspective of the abslolute frame of reference of the laboratory
camera, is demonstrably invalidated by de facto data and
explicit statements in the literature.
So far so good!
It may be too optimistic to suggest that the solution is at hand.
...It is more correct to say the solution is at foot...
:-)
2. It seems to me that even the most experienced gait analysers
look for
agreement between video and gait curves before accepting the curves
as
valid. Whilst this may be laudable, in that it follows standard
medical
methodology in using a special test to confirm or reject a
diagnostic
hypothesis, it seems to me that it is more often, in practice, because:
a. the clinician doesn't understand the gait results;
b. the clinician doesn't trust the gait results.
There are also problems arising from the Euler angle sequence
The Euler angle sequence is based on the six degrees of freedom in a
3D coordinate system. There is no unique solution. In a 4D analysis
there are no degrees of freedom and the problem is solved
immediately. (The problem being the Newtonian model).
Gait labs will never be taken seriously while there are
discrepancies.
A discrepancy between data and the Newtonian ideal motion?
There is no such thing as a failed experiment, merely a failed
explanation of the result. The lack of being taken seriousness is
perhaps deserved. Gait analysis is based on a theory invalidated (in
principle) nearly 100 years ago.
The result of any gait analysis should be able to be intepreted
independantly of the video. THAT is predictive science. Only then
will gait analysis be taken seriously.
I am not sure what others are doing with their foot marker sets.
Happy New Year!
Craig Nevin
University of Cape Town