OTA 2006 Posters
Scientific Poster #89 Basic Science
Patient-Specific Modeling of Increased Contact Stress Exposure following
Intra-Articular Fracture of the Ankle
Jane Goldsworthy, BSE (*); Donald D. Anderson, PhD (*);
Thad Thomas, BSE (*); Valerie L. Muehling, MS (*);
J. Lawrence Marsh, MD (*); Thomas Brown, PhD (*);
University of IowaUniversity of Iowa Hospitals and Clinics, Iowa City, Iowa,
USA
Purpose: Articular surface incongruities resulting from intra-articular
fractures of the ankle lead to abnormal tibiotalar contact stress distribution
and are a critical determinant of posttraumatic osteoarthritis (OA). Unfortunately,
it has not been possible to measure increased contact stress produced by
fracture incongruity in patients. This study reports the first use of a
finite element (FE) modeling approach to measure the contact stress distribution
in ankles with tibial plafond fractures as compared to the contralateral
normal ankle.
Methods: Computed tomography (CT) datasets obtained of the noninjured
and injured ankles after reduction and fracture fixation are segmented to
yield bone surfaces. Data Manager, a medical data visualization program,
is used to bring the surfaces into weight-bearing apposition (Figure 1).
A commercial meshing program is used to construct a FE mesh. The FE model
is then subjected to a gait simulation, in which the axially loaded tibia
is rotated about the flexion/extension axis, while the talus is free to
rotate as dictated by the articulation with the tibia. Chronic contact stress
exposures are calculated for each patient.
Results: Computed contact stress exposures for intact ankles were
continuous and relatively uniform, and located on a consistent region of
the tibial articular surface. Fractured ankles exhibited higher magnitude,
less consistently located, and more focal contact stress exposures (Figure
2). The average peak computed contact stress exposure was 11.1±1.2
MPa for the intact ankles and 13.9±1.8 MPa for the fractured ankles.
Fractured ankles had a larger percentage of contact area with higher magnitudes
of contact stress exposure and a smaller percentage exposed to lower stresses.
Figure 1. Apposition of segmented ankle CT. a) Voxellated segmentation
of relaxed ankle. b) Smoothed surfaces of relaxed
Figure 2. Anterior-inferior views of the cumulative contact stress
exposure distributions in a) intact and b) fractured ankles.
Conclusion/Significance: Patient-specific FE models developed from
CT datasets demonstrated different patterns and magnitudes of contact loading
in ankles with fractures of the tibial articular surface compared to the
contralateral normal ankles. This is the first time the mechanical effect
of intra-articular fracture displacements has been measured. Further work
will assess the effect of the measured contact loading abnormalities on
the articular cartilage and on clinical outcome. This technique has the
potential to increase our understanding of the mechanical effects of articular
surface step-off's and may have clinical utility in the future.
If noted, the author indicates something of value received.
The codes are identified as a-research or institutional support; b-miscellaneous
funding; c-royalties; d-stock options; e-consultant or employee; n-no conflicts
disclosed, and *disclosure not available at time of printing.
·
The FDA has not cleared this drug and/or medical device for the use
described in this presentation (i.e., the drug or medical device is being
discussed for an "off label" use). · · FDA
information not available at time of printing.
