1st Joint ESMAC-GCMAS Meeting - Análise de Marcha

similarity measure while a volume penalty term discourages improbable or impossible
deformations. In a final step, the positions of the patient’s muscle origins in the respective
image volume are retrieved after applying the resulting 3D deformation field to the original
atlas coordinates.
Results
The muscle attachments of 8 major hip muscles were manually identified in T1 weighted MR
images from a 23 year old, non-pathologic male subject. These were compared to the locations
identified using the atlas-based non-rigid registration. Absolute distances between the
automatically detected muscle origins and their manually defined positions were calculated
[table 1]. In addition, the muscle paths were further delineated to quantify the difference
between both approaches for the calculation of moment arm lengths at the hip in adduction,
flexion, and rotation [table 1]. The centre of the hip joint was automatically detected by fitting
a sphere to the segmented femoral head using the ICP algorithm [7].
Table 1: Comparison between manual and automatic detection of muscle origins.
Absolute distance between Difference in moment arm length with
automatically and manually respect to the hip joint (mm)
defined muscle origin (mm) Adduction Rotation Flexion
Adductor longus 31.1 24.7 0.2 0.2
Adductor brevis 15.9 11.1 0.7 3.4
Rectus femoris 5.9 4.5 1.21 1.0
Gracilis 4.4 3.9 0.9 1.2
Semimembranosu
s
1.9 0.4 0.5 2.2
Semitendinosus 4.3 3.0 1.5 5.1
Biceps femoris 10.9 0.8 0.3 0.6
Sartorius 1.8 1.4 0.1 0.7
Discussion
Except for the adductor longus muscle, all origins were automatically defined with satisfying
accuracy compared to previously proposed work [8]. Only limited changes in moment arms
would be introduced when applying this automated method. Therefore this method would yield
a good initial guess for user evaluation of the muscle attachment points when constructing
subject specific musculoskeletal models.
The present work focussed primarily on the muscular anatomy around the hip joint, an area of
specific interest in children with CP who often present significant musculoskeletal
deformations around the hip joint. Previously proposed methods for subject-specific definition
of muscle attachments adapt generic muscle attachments by rescaling and deforming the bone
structures [6,8]. this procedure would maximize the use of all available tissue types (fat,
muscle and bone tissue) in the MRI data for personalization of generic muscle models.
However, future research is needed to estimate the applicability and accuracy of atlas-based
non rigid registration for identification of muscle insertion points in subjects with bony
deformations at the proximal femur.
References
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[4] Loeckx D, Maes F, Vandermeulen D, Suetens P. (2004), MICCAI , I, 639-646
[5] Maes F, Collignon A, Vandermeulen D, Marchal G, Suetens P. (1997), Trans. Med. Imag., 16(2), 187-198
[6] Arnold A, Blemker S, Delp S, (2001), Annals of Biomedical Engineering, 29, 263–274
[7] Besl P, McKay N, (1992), Trans. Pattern Anal. Machine Intell., 14, 239-256
[8] Kaptein BL, van der Helm FCT, (2003), J. of Biomechanics, 37, 263-273
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