Biomedical Engineering Reference
In-Depth Information
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(a) Patellar tendon
(b) Popliteal depression
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(d) Anteromedial tibia
(c) Anterolateral tibia
FIgure 13.6
Peak pressures on residual during the whole gait cycle (the finite element model considered
the pre-stresses after donning the prosthetic socket).
13.3.2 i
interface.
S
treSS
tHrouGHout
a
G
ait
c
ycle
Figures 13.6 and 13.7 display the peak pressures and resultant stresses over the patella tendon, pop-
liteal depression, anterolateral tibia, and anteromedial tibia regions during a gait cycle. Generally
speaking, all the stress curves had a double-peaked shape, which was similar to the resultant ground
reaction force (GRF). Around the first peak, the GRF produced a moment to extend the limb and
increased the pressure over the anterior-proximal and posterior-distal sides, and decreased pres-
sures over the anterior-distal and posterior-proximal sides.
At the initiation of the swing phase, even though the GRFs disappeared, angular acceleration
was positive. The inertial forces explained the non-zero normal and shear stresses at the prosthetic
socket-residual limb interface during the swing phase.
13.4 aPPlICatIonS
This study used an automated contact method to simulate the contact between the prosthetic
socket and the residual limb, while considering pre-stresses. Due to the difference in limb and
socket shape, there were some regions of the limb that penetrated into the socket at the initial
configuration. The penetrated limb surface was automatically deformed such that it just con-
tacted the inner surface of the socket, thus producing a pre-stress condition. At subsequent stages
when loading was applied, the limb surface was automatically constrained not to penetrate the
inner surface of the socket. The limb was allowed to slide if the shear stress exceeded the fric-
tional limit.
The difference in shape between the residual limb and socket imposes challenges in contact sim-
ulation at the limb-socket interface. Simplifications are usually made at this stage, such as assuming
that the limb and socket have the same shape. However, ignoring this pre-stress could lead to inac-
curacies in the model. In this investigation, it was shown that peak normal and shear stresses over
the patellar tendon, anterolateral and anteromedial tibia, and popliteal depression would be notice-
ably decreased if such simplifying assumptions were incorporated into the model.
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