Page 135 - DOS Kongressen 2012 - Abstracts

95.
Fully Automated Measurement of Radiological Angles in Hip
Dysplasia using CT Images
Sepp de Raedt, Marleen de Bruijne, Inger Mechlenburg, Maiken Stilling, Lone
Rømer, Kjeld Søballe
Orthopaedic Research Unit Aarhus University Hospital; Department of
Computer Science, University of Copenhagen; Orthopaedic Research Unit,
Aarhus University Hospital; Orthopaedic Research Unit, Holstebro Regional
Hospital; Department of Radiology, Aarhus University Hospital; Orthopaedic
Research Unit, Aarhus University Hospital
Background:
Developmental hip dysplasia is a debilitating condition that is
commonly diagnosed by manual measurements performed on x-rays or CT
slices. However, manual measurements are subjective and time consuming.
Purpose / Aim of Study:
To develop a fully automated method to measure the
angles used in the diagnosis of hip dysplasia using CT images.
Materials and Methods:
Using the automatically segmented hip, the center
point of the femoral head was determined by fitting a sphere to the surface of
the femoral head. The local axis was determined and corrected for the tilt of
the pelvis. Starting from the center point, the necessary reference points were
identified by automatically rotating a line until the edge of the acetabulum was
reached in the respective directions. Using the reference points, the CE-angle
(
CE), acetabular-anteversion (AcAV) angle, posterior sector (PS) angle and
anterior sector (AS) angle were calculated. The method was validated against
manual measurements as performed in daily practice on 52 hips. We report
mean, average difference with 95% limits of agreement, and concordance
correlation coefficient (CCC) between the two methods.
Findings / Results:
The mean CE angle was 21.2° (Avg. diff. 0.0 ± 5.4 , CCC:
0.93 ).
The mean AcAV angle was 19.8° (Avg. diff. -0.9 ± 3.6 , CCC: 0.95 ).
The mean PS angle was 86 .5° (Avg. diff. 1.8 ± 6.2 , CCC: 0.87 ). The mean
AS angle was 49.0° (Avg. diff. 0.8 ± 5.6 , CCC: 0.95 ). Three patients (6 hips)
were excluded from analysis due to outlying measurements (>2SD) due to
osteophytes.
Conclusions:
The new automated method achieves acceptable accuracy as
validated against manual measurements. In the future, the method will be
improved to correct for osteophytes and can be further developed to pre-
operatively determine the optimal rotation of the acetabulum before
periacetabular osteotomy.