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 

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. ...)



Mag. Andreas Kranzl
Waehringer Guertel 135/23
A-1180 Wien, Austria
Phone: +43 1 47 82 555
Mobil: 0676 5129787
Orthopaedisches Spital Speising
Labor fuer Gang- und Bewegungsanalyse
Speisinger Straße 109
1130 Wien
Tel: ++43-1-80182-276
Fax: ++43-1-80182-285

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:
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: 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:
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