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jkent87
03-30-2010, 02:29 AM
Dear Biomech-L subscribers,

I'm doing some work on the use of biomechanical models and marker sets
to study the kinematics of lower limb amputees. My efforts were
initially geared towards selecting an appropriate marker set for amputee
analysis that could also be applied broadly to all patient groups and
healthy subjects (as normative controls) to facilitate comparison, with
both clinical and research applications in mind. This would comprise a
standard configuration that could be built upon for specific
applications that require additional segments/parameters to be analysed,
but would ensure data collection uniformity as far as possible.

A lit search I conducted brought up many studies on individual amputees
or amputee cohorts using a variety of marker sets, although the majority
appeared to be some form of Helen Hayes derivative. On the prosthetic
side markers were commonly placed on mechanical centres of rotation
where obvious (e.g. on single axis joints) or "estimated from the sound
side".

I was concerned about the appropriateness of the use of several of the
common models and methods when analysing amputee function, particularly
when directly comparing the function/movement of prosthetic and sound
limbs. Examples of such applications would be comparing prosthetic gait
to normative data, evaluating limb symmetry (is this appropriate
anyway?! I'm doubtful in most cases, esp when it concerns unilateral
amputees), and comparing components that function differently
mechanically (e.g. 4-bar knee vs single axis knee, SACH foot vs foot
with articulated ankle joint).

I imagine it may be possible to achieve more reliable/valid results (and
a system that may be applied more universally) with joint centres
determined functionally, technical markers for tracking segmental
movement and perhaps the addition of extra markers to monitor relative
movement of the residual limb with respect to the socket (although I
won't even attempt to touch on the issues of placement and treatment of
soft tissue artefact here..). Regarding the selection/development of a
model that will enable prosthetic components that have not been designed
to reproduce natural segment movement to be adequately represented (e.g.
SACH foot, running blades) and that will allow different limb alignments
to be compared (where the neutral condition at joints may be altered by
nature of the study) I am a little lost. I anticipate when I begin to
consider the analysis of joint moments, torques and powers, which
undoubtedly will open yet another can of worms, I will be even more so.

I suspect that my idea of a universally applied base marker set and
model may be unrealistic, even given an allowance for additional
markers/segments for specific analyses, and that with amputee cohorts
kinematic models will have to be more specifically geared towards the
question that the analysis is required to answer.

I would be very grateful if anyone has any thoughts or advice to share
on the subject. I remember there was a very relevant presentation and
discussion at the CMAS UKI annual meeting and conference in Edinburgh
2009 - I am aware that there may be groups specifically looking into it
and I was wondering if there have been any recent developments that I
have not come across. I'll happily post a summary of replies - please
let me know if you'd prefer not to appear in it!

Many thanks

Jenny Kent
Higher Scientific Officer
Centre for Human Performance, Rehabilitation and Sports Medicine
DMRC Headley Court
Epsom, Surrey
UK
e: DMRC-HSO1@mod.uk