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· DOS Abstracts
Biomechanical symmetry of a hip joint altered by
Perthes’ disease
Remel Salmingo, Tina Skytte, Marie Sand Traberg, Kaj-Åge Henneberg,
Klaus Hindsø, Christian Wong
Biomedical Engineering, Department of Electrical Engineering, Technical
University of Denmark; Department of Orthopaedics, Hvidovre Hosptial
Background:
Perthes is a disease characterized by a loss of blood supply of the
hip joint resulting to malformation of the femoral head. Until now, the underlying
biomechanical changes of Perthes’ disease need to be further elucidated.
Purpose / Aim of Study:
The objective of this study was to investigate the
changes specifically the biomechanical symmetry of a unilateral Perthes’ hip.
Materials and Methods:
Finite Element (FE) modeling was performed to in-
vestigate the biomechanics of a healthy and diseased hip of a unilateral Perthes’
case. The image MRI slices were obtained to segment the bones and cartilages,
and to build the 3D models. The elastic modulus for the pelvis, femur, cartilages
and necrotic bone (Perthes’ hip only) were, 5 GPa, 500 MPa, 50 MPa, 20 MPa,
respectively. The most distal part of the femur was fixed while the pelvis was
displaced to -1.5 mm to simulate load.
Findings / Results:
The result indicates that the symmetry of the hip joint of
the unilateral Perthes’ case was altered biomechanically. The highest displace-
ment of the healthy hip occurred at the supero-medial side of the femoral head.
On the other hand, in Perthes’ hip, the displacement occurred at the superior
part of the femoral head and gradually reduced towards the distal part of the
femur. Localized contact pressure and stresses were also found in the Perthes’
hip.
Conclusions:
As a mechanical analogy, the healthy hip is experiencing bend-
ing load similar to a curved-cantilever beam where the maximum displacement
is located at the end. The Perthes’ hip resembles a stacked column structure
where the load is transmitted through compression. This indicates an aggrava-
tion of Perthes’ disease because bone overloading by compression around the
proximal part might occur. The FE method developed in this study can be used
to estimate the prognosis of the Perthes’ disease.
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