Pelvis Model for Reconstruction with Autografted Long Bones following Hindquarter Amputation - Computational Biomechanics of the Musculoskeletal System - page 134

(a) (b)

FIgure 11.8 Finite element models: (a) using the femoral condyle to substitute the tuberosity of the ischium
after left ilium amputation; (b) using the tibial plateau to substitute the tuberosity of the ischium after left ilium
amputation.

table 11.5
maximum von mises Stress of various Parts in three models (mPa)

Intact or
reconstructed left
hemipelvis

model Sacrum right hemipelvis bridging bone

Intact 5.40 6.21 5.84 N/A

FCR 21.3 23.7 13.9 2.43

TPR 68.1 32.1 6.41 3.49

Note: FCR indicates the model using the femoral condyle to substitute the tuberosity of the ischium after left ilium amputation;
TPR indicates the model using the tibial plateau to substitute the tuberosity of the ischium after left ilium amputation.

Both models were assigned the same boundary and loading conditions as described previously for
the intact pelvic model. The peak von Mises stresses of the two reconstructed models and intact model
are listed in Table 11.5. There was an obvious difference in results between the intact and FCR models.
Stress concentrations in the FCR model occurred mainly around the connection between the femur
and the left auricular surface (AS) of the sacrum, the right SIJ, and the left side of the screws. The peak
von Mises stress of each region was larger in the FC-reconstructed model than in the intact model.
There was a general agreement of stress distributions between the two reconstructed models.
The stress at the right ilium, sacrum, bridging bone, and screws in the TPR model was larger than
that in the FCR model. As shown in Figure 11.9, the peak von Mises stress of the tibia in the TPR
model was lower than that of the femur in the FCR model. However, the regions and extents of stress
concentration differed greatly between the two models.
The surgical reconstruction was unable to completely recover the biomechanical function of the
normal pelvis. The peak stresses in the sacrum in the two reconstructed models were both much
larger than those in the intact model. The two long screws worked like shoulder poles, which ran
through both sides of the sacrum and carried the load. The screws shielded stress from the SIJ.
Therefore, the sacrum bore most of the load and was subjected to the greatest stress and strain. The
peak stresses of the two screws were both distributed at the reconstructed side (Figure 11.10). The
right iliac bone offered a wider contact area than the reconstructed femur or tibia, leading to a larger
surface for loading and greater stress in the reconstructed side.