1. 5/9/2016 Instituto Superior Técnico
Novel Morphologies of Hip
Joint Prosthesis based on the
Oval Shape

2. Problem Statement
5/9/2016 Instituto Superior Técnico
Need for
better
models of
the hip
joint
Orthopedic
community: articular
surfaces of the hip
joint are widely
considered to be
best modeled by
spheres.
Medical evidence
and computational
studies suggest that
these surfaces are
only symmetric in a
limited number of
axes.

3. Motivation
• Design of a next generation of hip
prosthetic devices:
– More natural
– Improved mechanical behavior
– Lower wear rate
– Better contact forces distribuition in the
joint
5/9/2016 Instituto Superior Técnico

4. Proposed Solution
• Phase 1
– Approximation of different surfaces to point clouds retrieved
from CT images of 11 subjects.
– Statistical analysis of surface fitting errors.
– Considered surfaces: sphere, conchoid, ellipsoids and
ovoids in their implicit representation.
• Phase 2
– Contact modeling of the hip joint in OpenSim, using the
Elastic Foundation model.
– Study of the multibody dynamic behavior of hip joint
prostheses, using previous described surfaces.
5/9/2016 Instituto Superior Técnico

5. O
Preliminary Results
5/9/2016 Instituto Superior Técnico
Acetabular
cavity
Femoral head
O SO O SO
Fitting
error (11
subjects)
μ 0.9873 0.9439 0.4837 0.4928
σ 0.6430 0.6264 0.4652 0.4657
min -3.4634-3.4637 -2.6042 -2.5444
max 3.4641 3.2307 3.4634 3.4639
O