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Penny Hewart
04-05-2001, 06:41 PM
Sorry, this is a slightly belated summary of replies to my request for
information about the use of planar x-rays to calculate the position on 3D
joint position.

Thanks to all who replied.

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Original request:

I am looking at methods to obtain a 3D position of the hip joint centre
relative to external markers placed on the ASIS and PSIS. This would seem to
be possible (in theory) by back projection from 2 planar X-rays if a
calibration object with 8 known points is included in both images.

What I have not been able to find out (I have searched the archives and the
web) are the realities of this method - specifically the level of errors.
Ideally I would like to know the marker positions to within 2mm - is this a
realistic aim?

An alternative method is to use MRI, again does anyone know the accuracy of
the 3D positions as calculated by MRI in the 3 planes (I assume this varies
with the machine model - but a rough idea would be very welcome).

I shall post a summary of replies, thank you in anticipation,

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And the responses, in no particular order:

>From Richard Baker, Belfast

We're working on this at the moment, at least the MRI side. I take it you
are familiar with the work of Leardini et al. (published in J. Biomechanics
a couple of years ago) comparing functional determination of HJC with
stereo-radiographs. He didn't do any calculations of theroetical accurcy but
did include a fairly sketchy account of repeatability of measurements.

You actually only need three points to reconstruct 3-d images from biplaar
x-rays and it is possible to use anatomical points on the x-ray images
rather than a calibration object. Be careful nt to use a sagittal plane view
as left and right sides will be superimposed and indentifying features from
one or other will be difficult.

We've got fairly good agreement (From A.Arnold, Stanford Uni

Here's a reference for the accuracy of dimensions obtained from MR images:

Smith DK, Berquist TH, An KN, Robb RA and Chao EYS
Validation of three-dimensional reconstructions of knee anatomy: CT vs MRI
Journal of Computer Assisted Tomography, 13(2):294-301, 1989

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>From Steve Paizza at Penn State:

We are also interested in evaluating methods of hip joint center (HJC)
location here at Penn State. Below I have listed three papers in which the
authors tested non-radiographic methods of HJC location by comparing their
results to those of a radiographic "gold standard". The results reported
in these papers suggest that you probably won't have a problem estimating
the HJC to within 2 mm using multiple planar x-rays: Leardini et al. (1999)
found that their radiographic technique (RSA) was accurate to within 0.2
mm. Perhaps some the papers below or the works cited in these papers will
be of help to you.

Bell, A. L., Pedersen, D. R. and Brand, R. A. (1990) A comparison of the
accuracy of several hip center location prediction methods. J Biomech 23,
617-21.

Kirkwood, R. N., Culham, E. G. and Costigan, P. (1999) Radiographic and
non-invasive determination of the hip joint center location: effect on hip
joint moments. Clin Biomech 14, 227-35.

Leardini, A., Cappozzo, A., Catani, F., Toksvig-Larsen, S., Petitto, A.,
Sforza, V., Cassanelli, G. and Giannini, S. (1999) Validation of a
functional method for the estimation of hip joint centre location. J
Biomech 32, 99-103.

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Again, thanks for all the replies,


Penny Hewart
Clinical Engineer
Gait Lab
Central Remedial Clinic
Clontarf
Dublin 3
Ireland

phone: +353 (0) 1805 7531
fax: +353 (0) 1833 5496
email: phewart@crc.ie
web: www.crc.ie

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