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Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA-CUP:
A METHODS FOR MIGRATION MEASUREMENT OF ACETABULAR COMPONENTS OF THRs IN DIGITAL STANDARD RADIOGRAPHS
PETER MAYRHOFER, revisited April 2012
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA INSTALLATIONSOUTSIDE EUROPE• San Francisco, US
• Los Angeles, US
• New Orleans, US
• Memphis Arlington, US
• New York, US
• Cleveland Ohio, US
• Ottawa, Canada
• Montreal, Canada
• Tokyo (2), Japan
• Osaka, Japan
• Adelaide, Australia
• Melbourne, Australia
• Shanghai, China
EUROPE• Belgium (1)
• Austria (8)
• Belgium (1)
• Denmark (5)
• France (5)
• Germany (23)
• Greece (3)
• Italy (2)
• Netherlands (1)
• Norway (1)
• Sweden (2)
• Switzerland (5)
• United Kingdom (13)
April 2012:
84 Installations
EBRA has become an International Standard.
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EARLY MIGRATION > 1mm IS PREDICTIVE FOR PROSTHETIC LOOSENING!
J Bone Joint Surg Br. 1996 May;78(3):422-26. Early migration predicts late aseptic failure of hip sockets.Krismer M, Stockl B, Fischer M, Bauer R, Mayrhofer P, Ogon M.
J Bone Joint Surg Br. 1999 Mar;81(2):273-80. The prediction of failure of the stem in THR by measurement of early migration using EBRA-FCA. Einzel-Bild-Roentgen-Analyse-femoral component analysis.Krismer M, Biedermann R, Stockl B, Fischer M, Bauer R, Haid C.
EBRA ENABLES QUALITY CONTROL FOR
IMPLANT DESIGN & SURGICAL TECHNIQUE
Migration is only measurable in serial radiographs of the same patient whose position (exterior orientation) is never exactly the same.
time
mm
EBRA requires at least 4 x-rays per series!
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA-CUP REQUIRES FULL SIZED AP PELVIS RADIOGRAPHS OF SIZE 430 x 350 mm
Resolution min. 75dpi
digitized with film scanner
or
retrieved from PACS system including a scale for calibration!
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA-FCA ALSO ACCEPTS HIP RADIOGRAPHS NOT SHOWING THE WHOLE PELVIS.
Resolution min. 75dpi
As the image is calibrated by the true head size, no scale is needed.
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
Tip of stem must be visible!
EBRA RSA
• 1 standard x-ray per observation• no ball markers• retrospective studies
• 2 special x-rays per observation• markers required• prospective studies
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA-CUP PARAMETERS
x
zy
cup inclination& anteversion
head & cup
x-migrationy-migration
z-migration not possible
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EXACT INTRINSICORIENTATIONIS UNKNOWN INSTANDARD X-RAY
X-ray focus
principal point
film planeFocus-film-distance and position of central beam have to be assessed approximatively.
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA - LANDMARKS
film center
approximative principal point
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
cup
principal point film
focus
spatial parameter of migration
3D-METHOD EBRA-CUP
reference plane
reference line
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
ERRORS CAUSED BY CHANGES OF INTRINSIC ORIENTATION
Focus variation within cuboid 60 x 110 x 400 mm affects parameters of migration in a magnitude of only 0.01 mm (experimental study based on 78 radiographs)
900mm
1300mm
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
COMPENSATION OF ERRORS
• by use of an approximative intrinsic orientation bound to pelvic contours(based on study of 78 random x-rays)
• by use of variable reference planes passing through the x-ray focus
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EXTRINSIC ORIENTATION VARIES REMARKABLY
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
ERRORS CAUSED BY CHANGES OF EXTERIOR ORIENTATIONRotations of the pelvic bone cause remarkable errors up to 7 mm of simulated migration!
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
COMPENSATION OF ERRORS
• by use of a comparability strategy which compares radiographs with respect to similar conditions at exposure
• migration is measured only in pairs of comparable radiographs
• overlapping trends are weighted and averaged
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA COMPARABILITY ALGORITHM
time
mig
ratio
n
non comparable x-ray
raw data
smoothed data
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
ACCURACY TESTS
• zero migration experiment (27 x-rays)• 33 pairs of x-rays taken within 1 month
• comparison with RSA (T. Ilchman et al.)
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
J Arthroplasty. 1992 Jun;7(2):121-27. Measurement accuracy in acetabular cup migration. A comparison of fourradiologic methods versus roentgen stereophotogrammetric analysis.Ilchmann T, Franzen H, Mjoberg B, Wingstrand H.
EBRA - ACCURACY
MIGRATION MEASUREMENT
• medio-lateral mig: 0.8 mm (95% CI)• cranial migration: 1.0 mm (95% CI)
ANGULAR MEASUREMENT
• cup anteversion: 3.3°• cup inclination: 2.5°
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria
EBRA GRAPHICS PROGRAM
PRINTER
EXCEL
Department of Engineering Mathematics, Geometry and Computer Science, University of Innsbruck, Austria