Page 167 - IJB-8-3

Hunag, et al.
joint resurfacing arthroplasty produces better motion arc, for experimentation. The combination of stem
structural strength, and biomechanical performance, modularized components with an additional 10% in
symmetrical condyles over a range of sizes for all the size and the articular surface with an additional 20%
fingers compromise the natural finger joint alignment. in size were chosen. Larger articular surfaces lead to
Faced with clinically diverse patients with individual a larger stress area in the joints and the overall joint
differences, joint implants with a single specification and phalanx stress is also large. If the most dangerous
cannot adapt to various anatomical types. Articular modularized meets the acceptable standard through
surface and fixating stem mismatch to the bone marrow the experimental results, the remaining eight groups
cavity and the inadequate osseointegration to higher of modularized can meet the acceptable functional
incidence of implant loosening. mechanical test standard.
This study designed modularized 3-part components, About functional biomechanical testing, the phalanx
including bicondylar surface, bi-concave articular models were duplicated in ABS using a 3D printer
surface, and elliptical-cone stem according to the CT to mimic the bone material for resurfacing prosthesis
image data base. The modularized condylar components implantation. To uniformly simplify the material and
were fabricated using metal 3D printing technique which anatomical phalangeal bone, although ABS material is
can achieve a tolerance of <5% under complex PIP joint quite different from the real bone material, the functional
shapes. The modularized implant design can provide biomechanical tests were able to show a reference trend
better compliance in current clinical practice with according to similar bone contours. Similar methods were
consistent joint stability with worthy stem fitness in bone also applied in many literatures [10,14] .
marrow cavity and long-term durability. Butz simulated a hand-held 4.5 kgw weight ,
[11]
Considering the time and cost-effectiveness of the proximal joint received a force of 84N at a 60°
functional mechanical testing, it is necessary to select angle and the vertical component force at the articular
a group of the clinically most dangerous modularized surface was 42N (noted as the standard force). The
from the nine groups of standard modularized proximal phalanx PIP joint anti-loosening pull-out test
showed that the average maximum pull-out force was
727.8N, and it was as high as 17 times compared to the
A B
standard force. The corresponding value of the medial
articular UHMWPE surface with hook mechanism was
49.9 ± 2.0N, which was also higher than the standard
force. In addition, the middle 3D printing phalanx was
not extracted, indicating that the retention strength
between middle phalanx and ABS bone was enough.
These results demonstrate that the elliptical-cone stem
of our PIP joint can provide good anti-loosening ability
under the force of daily activities.
Figure 5. (A) 3D printing modularized PIP joint prosthesis; (B) 3D Concurrent joint prostheses commonly used a
printing lattice with 0.8mm thickness, length of 6 mm for proximal combination of metal on polymer or pyro carbon and
phalanx stem and 4 mm for middle phalanx stem in our PIP joint demonstrated low friction and wear. Due to our good
prosthesis to promote bone growth. performance of anti-loosening and anti-pull-out test of

Table 3. The product dimension, design dimension and error percentages of major axis and minor axis of the metaphyseal and diaphyseal
ellipses and the total length of the stem for proximal phalanxes.
Proximal stem Top major axis Top minor axis Bottom major axis Bottom minor axis Stem length
Measurement 6.89±0.05 4.90±0.05 4.80±0.01 2.60±0.04 13.44±0.02
Design 6.93 4.73 4.95 2.64 13.20
Error (%) −0.52 3.66 −3.12 −1.65 1.84

Table 4. The product dimension, design dimension and error percentages of major axis and minor axis of the metaphyseal and diaphyseal
ellipses and the total length of the stem for middle phalanxes.
Middle stem Top major axis Top minor axis Bottom major axis Bottom minor axis Stem length
Measurement 9.68±0.03 6.83±0.06 5.37±0.05 2.91±0.03 8.56±0.02
Design 9.79 6.82 5.61 2.97 8.25
Error (%) −1.09 0.18 −4.24 −2.00 3.86

International Journal of Bioprinting (2022)–Volume 8, Issue 3 159