Page 424 - IJB-9-3

International Journal of Bioprinting 3DP PILF cage for osteoporotic

Corp., Kyoto, Japan) (Figure 5B and C). The yielding load, Table 2. The average subsidence for L2 – L5 superior and
stiffness, and fracture pattern were recorded. The torsion inferior endplates at 25%, 50%, and 75% of the length at the
was tested at a rate of 60°/min with a downward preload coronal and sagittal planes, respectively
of 500 N until the cage was destroyed or the maximum Endplate Coronal plane (mm) Sagittal plane (mm)
torque value was reduced by 20% (Figure 5D). The yielding
torque, stiffness, and damage were also recorded. 25% 50% 75% 25% 50% 75%
L2 superior 1.30 1.85 1.30 2.12 1.85 1.79
3. Results L2 inferior 1.71 1.83 1.71 1.58 1.83 1.94
Table 2 shows the average subsidence for L2 – L5 superior L3 superior 1.17 1.45 1.17 1.43 1.45 1.59
and inferior endplates at 25%, 50%, and 75% of the length L3 inferior 2.21 2.33 2.21 1.84 2.33 2.09
at the coronal and sagittal planes, respectively, for a total of L4 superior 1.60 1.70 1.60 1.61 1.70 1.76
20 osteoporosis patients with HU values between 70 and L4 inferior 3.18 3.20 3.18 1.55 3.20 1.97
120. The constructed FE model was designed to simplify L5 superior 1.54 1.47 1.54 1.08 1.47 1.77
the sagittal plane into a symmetrical plane. Subsidence L5 inferior 2.97 2.99 2.97 1.59 2.99 2.30
of 25% and 75% of the length at the coronal plane were
presented with the same value. Relevant data were input to
reconstruct the FE model endplate. At the L3/L4 disk where A
the cage was placed, subsidence of 50% in the coronal and
sagittal planes was 2.33 mm for L3 inferior endplate and
1.70 mm for L4 superior endplate (Figures 1 and 2, Table 2).
The middle part of Figure 3 shows the analysis results
from the L3/L4 intervertebral disc topology optimization
under a single load. The gray triangular grid position is the
place where the structure must be reserved. The bottom
right part of Figure 3 shows that the shape of a single
posterior cage can be projected from the contours of half
of the transverse cross-section plane and the sagittal plane.
Figure 4 shows the size and implantation positions for the
CS- and P-type cages designed in this study. The bottom B
right part of this figure also shows the FE mesh models for
these two cages.
The biomechanical FE analysis result showed that the
maximum stress values at the L3 inferior and L4 superior
endplates under flexion, extension, lateral bending, and
torsion for the P-type cage implantation model were
all higher than those for the CS-type cage (Figure 6).
Fracture or cracking might occur for the P-type cage
implantation because the maximum stresses found Figure 6. The maximum stress values of CS-type and P-type cages at the
in the endplates exceeded the ultimate strength value L3 inferior (A) and L4 superior (B) endplates under flexion, extension,
when the inferior part of L3 was subjected to flexion and lateral bending, and torsion.
torsion loads, and the superior part of L4 was subjected
to flexion and bending loads. Figure 7 showed the stress 4. Discussion
distribution for the L3 inferior and L4 superior endplates
under all load conditions for the CS-type and P-type cage The FE analysis result found that the maximum stresses
implantations. in the superior and inferior endplates using the P-type
cage were relatively high regardless of the type of load
Table 3 lists the yielding load and stiffness of our conditions, and the stress concentration was also relatively
designed CS-type cage and the optional ISO 23089 standard serious. Figure 9 shows the contact status of the two cages
acceptance criteria under compression, compression- and endplates, which can explains why the P-type cage
shear, and torsion. Figure 8 shows the corresponding and endplate can easily cause point contact that obviously
fracture types under three load conditions. generates stress concentration. The CS-type cage and

Volume 9 Issue 3 (2023) 416 https://doi.org/10.18063/ijb.697