CGA FAQ: Hip Joint Center definition

Dear Colleagues,

We had a discussion about the accuracy of the hip joint definition in 
patients with deformities. 

I know that different systems uses different ways to calculate the 
position of the hip joint. But mostly of them uses two or more 
landmark distances to calculate the location. This calculations were 
based on different studies but this values represent the mean of 
"normal".  

In CP patients we often have bone deformities. So what I want to 
know is:
Do you adapt this values?
If yes. How do you adapt  this values for the individual patient. (x-
rays. ...)

Regards,

Andreas

Privat:
Mag. Andreas Kranzl
Waehringer Guertel 135/23
A-1180 Wien, Austria
Phone: +43 1 47 82 555
Mobil: 0676 5129787
e-mail a8720580@unet.univie.ac.at
WWW: http://members.xoom.com/Paddler
--------------------------------------
Arbeit:
Orthopaedisches Spital Speising
Labor fuer Gang- und Bewegungsanalyse
Speisinger Straße 109
1130 Wien
Tel: ++43-1-80182-276
Fax: ++43-1-80182-285
e-mail: krana@orthospeising.at
CGA: 

Dear Andres and colleagues,

You adressed a serious problem, 

please read the article of Alberto Leardini et al. (1999) "Validation of a
functional method for the estimation of hip joint centre location' in:
J.Biomechanics 32, pp99-103

in this study he compared a RSA method with two prediction estimate-rules as
well as a functional calculation of the hip joint centre of roration. 
It was done in male adults, prediction estimates rms error is 25-30 mm. in
this group, in children this will be less (because their size is less) but
in case of bony deformities this can be more.
The functional method (estimation of the joint centre of rotation ) gives
less error, however it assumes the use of clusters of markers, which is not
common in most clinical commercial systems of movement analysis.
I think time (i.e. technology) should be ready by now to adopt this
technique (see work of Capozzo et al) in clinical movement analysis.

Kind regards,  Jaap Harlaar

Jaap Harlaar, PhD, MSEE
department of rehabilitation medicine
University Hospital "Vrije Universiteit" 
pob. 7057, 
1007 MB  Amsterdam
the Netherlands
tel. +31 20 44 40 773 /  40 763
Fax/voicemail +31 20 883 04 75 (xiop messaging)
E-mail: j.harlaar@azvu.nl         http://www.azvu.nl

Dear Jaap and colleagues,
yes, the issue is critical in gait analysis. Following our study on
J.Biomechanics we are now preparing a final manuscript with the measure of
the effect of these mislocations on the traditional used gait data (joint
angles and moments). It should show up soon on the same journal.

Yes, I expect even larger estimation errors in children, not only becase of
the likely bony deformities in CP, but also because of the different
population used to obtain the parameters of the regression equations
proposed in the literature (male adults). 

The functional method estimates the joint centre of rotation by means of an
extra exercise, a 3D rotation of the hip joint. Marker(s) on the distal
segment (thigh) segment can be used to locate a ball-and-socket like joint
centre in a proximal (pelvis) segment. The use of specific clusters of
markers is therefore not necessary, as long as you have at least 3 markers
on the pelvis and one on the thigh. Most of the currently used protocols
proposed with commercial systems of movement analysis include this minimum
marker set. Of course, a fourth marker on the pelvis, and more markers on
the thigh would improve the estimation by exploiting the marker redundancy.

Concerns can instead be arisen for the application of the method in
specific populations (children, elderly, etc.) for which we are interested
to share experience on the associated practical problems.

Kind regards,
Alberto Leardini

Alberto Leardini M.Eng.
Movement Analysis Laboratory
Istituti Ortopedici Rizzoli
Via di Barbiano 1/10, 40136 Bologna ITALY
tel: +39 051 6366522
fax: +39 051 6366561
email: leardini@ior.it
http://www.ior.it/movlab/

Address in Oxford
Oxford Orthopaedic Engineering Centre
Nuffield Orthopaedic Centre
Windmill Road, Headington, Oxford OX3 7LD ENGLAND
tel: ++ (0)1865 227684
fax: ++ (0)1865 742348
email: alberto.leardini@ooec.ox.ac.uk

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