View Full Version : Re: Marker-set independent gait analysis

07-08-2007, 06:00 PM
Dear all, sorry to jump in to this interesting discussion only now, but I'm
just back from the long trip to Taipei. It is hard for me today to address
the many interesting points raised, but I would like just to point out a few
references, as for my two-cents contribution to the topic.

In our recently proposed new model (Gait Posture 2007 Feb 7;
epub), I think we have tried to demonstrate the little better repeatability
over examiners of the measurements with respect to the 'conventional model',
likely accounted for the overall approach of looking to exact anatomical
landmarks, i.e. bony prominences, rather than aleged functional plane and
axes. Of course all landmarks necessarily worked out by functional
approaches are still affected more by the sources of error.

Another intriguing recent observation from our group
has been reported at the last JEGM, when we told how gait measurements look
like when taken from five different standard protocols for gait analysis
applied all together to exactly the same gait cycle, i.e. a marker-set union
of the five over the same subject. Beyond the interesting
observation that some of the measurements compare very well and other very
bad, we have also deduced that more than the marker-set is the biomechanical
model behind the protocol which makes the difference.

************************************************** ***********************
Alberto Leardini, DPhil
Movement Analysis Laboratory
Director Prof. Sandro Giannini
Centro di Ricerca Codivilla-Putti
Istituti Ortopedici Rizzoli
Via di Barbiano 1/10, 40136 Bologna ITALY
tel: +39 051 6366522
fax: +39 051 6366561
email: leardini@ior.it

"Where is the Life we have lost in living,
Where is the wisdom we have lost in knowledge,
Where is the knowledge we have lost in information."
Thomas Stearns Eliot, Choruses from ''The Rock'' (1934)
************************************************** ***********************

----- Original Message -----
From: "Arnel Aguinaldo"
Sent: Friday, July 06, 2007 10:28 PM
Subject: Re: [BIOMCH-L] Marker-set independent gait analysis

>I would like to thank Nancy and the respondents for initiating a fruitful
> and overdue discussion on a very clinically relevant topic.
> My two cents:
> Technically, a marker set is really just a reference system to which joint
> centers and bone segments are defined. Far too often, I hear marker sets
> being inappropriately referred to as biomechanical models when in fact
> they
> make up only a part of the "model." In its simplest form, a model used to
> measure kinematics from surface markers include:
> 1) Reference Systems: local "intermediate" coordinate systems to which
> joint
> centers and subsequent segments are defined. This is the so-called "marker
> set" and the major differences between sets involve how these reference
> systems are defined (ie, wands in Helen Hayes, triads in Cleveland Clinic)
> and their susceptibility to surface motion (Castagno et al. Gait &
> Posture,
> 3(2), 87, 1995).
> 2) Joint Centers and Bone Coordinate Systems: locations of joint
> centers/axes with reference to marker-based coordinate systems based on
> anthropometric ratios (standard in most gait analysis software) or
> functional determination (ie, sphere fit); bone segments are then defined
> between joint locations and tracked using the attached markers
> 3) Angle Conventions: calculations used to estimate joint angles based on
> movement of the marker-defined bone segments (ie, Euler, JCS, etc).
> Thus two labs that use the SAME marker set (ie, Helen Hayes, CCF) can in
> fact output different results if the joint/segment definitions and/or
> angle
> conventions used in their software are different. These definitions make
> up
> the heart of a kinematic model, regardless of the marker set used to
> define
> them.
> In most cases, the users have little control on how the "black box"
> software
> implement these estimations although I'm discovering that newer versions
> allow users to input more subject-specific parameters (ie, functional hip
> center in MAC's Orthotrak). As these functions become more readily
> available, it is only fitting (pardon the pun) that more clinicians use
> them
> as they are relatively straightforward to implement.
> For the hip center, we reported that it doesn't take a significant amount
> of
> ROM to functionally determine its location in patients with hip
> pathologies,
> where standard anthropometric ratios no longer apply (Aguinaldo et al,
> 2003). However, be careful when selecting a marker trajectory for fitting
> the sphere as it's been shown that certain optimization methods are more
> sensitive to random noise (Hicks and Richards, Gait & Posture, 22(2),
> 138-45, 2005).
> Bottomline, it really shouldn't matter what marker set is being used as
> long
> as the other elements of the kinematic model are known and ideally can be
> modified or controlled depending on the patient population. I understand
> this can be a nightmare for those of us pushing for standardization but I
> also believe we shouldn't blindly accept the current "standards" when the
> tools to improve the kinematic engine are there for us to use.
> Arnel Aguinaldo, MA, ATC
> Director, Center for Human Performance
> 3020 Childrens Way 5054
> San Diego, CA 92123
> 858.966.5424
> www.sdchp.com
> Assistant Professor, Biomechanics
> Department of Exercise and Nutritional Sciences
> San Diego State University
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