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3DP Modularized Finger PIPJ Arthroplasty
Table 5. The dislocation force of 25°, 35° and 55° for PIP joint of 19N at a 25° angle under the action of playing the
implant. piano. The joint receives a force of 17N at a 35° angle
Angle S1 S2 S3 Mean±SD when holding the pen under writing action and the joint
25° 549.8N 513.0N 513.4N 525.3±21.2N receives a force of 45N at a 55° angle while opening a
35° 335.5N 309.5N 303.0N 316.0±17.2N can. The dislocation test result under three daily activity
55° 117.0N 114.1N 113.8N 115.0±1.8N load conditions showed that the dislocation force values
for the three stress degrees were much higher than those
normal joint force values with different actions. The
Table 6. Static strength and capable percentage of 25000 dynamic dislocation force decreased reasonably with larger joint
cyclic loads with different angles.
angle but produced maximum misalignment. The fatigue
Angle Static Strength Dynamic Fatigue Loading (%) force ratio of misalignment to the literature data was set
25° 525.3±21.2N 50 (26.25~262.5N) as the safety factor. The fatigue limit of the 25°, 35°, and
35° 316.0±17.2N 50 (15.8~158N) 55° groups was 262.5N, 158N, and 92N, respectively.
55° 115.0±1.8N 80 (9.2~92N) The corresponding three safety factors were about
14 (262.5N/19N), 9 (158N/17N), and 2 (92N/45N). This
was found at least more than twice the static acceptance
condition and addressed that the articular surface design
of our PIP joint can provide good anti-dislocation ability
under the force of daily activities.
The stem fixation methods are mechanical, cement,
and bone ingrowth. Due to the smaller PIP joint size,
the type of fixation depends mainly on the bone stock
condition, which was often interfered with by the severity
of arthritis. Therefore, cement or mechanical fixation
was often difficult and impractical. Our modularized
elliptical cone shape stem aimed to provide adequate
contact area and force between the metal and phalangeal
bone and decreases the stress-relaxing properties by
further bone resorption, which reduces implant loosening
and fracture.
Figure 6. Load-displacement diagram of dislocation tests. To optimize the osseointegration ability and
delaminate implant loosening, additive manufacturing
the modularized PIP joint implant showed in this study. with enhancement of cell-biomaterial interactions is an
Hence, we chose a commonly used combination of metal attractive option since it is able to meet biological and
on polymer. The main reason of using UHMWPE was its functional demands. To optimize the osseointegration
broad utility in current large joint arthroplasty, including ability and delaminate implant loosening, additive
hip, knee, ankle, and shoulder joint arthroplasty, as well manufacturing with enhancement of cell-biomaterial
as its good ability of decreasing the bearing surface wear interactions draw attention and is able to meet biological
[6]
and avoids debris or particles that induce third-body and functional demands . 3D structured material that
wear. Otherwise, the cross-linked polyethylene had not comprises a lattice design was adopted on the metaphysis
only shown superior results compared with previous surface to promote bone ingrowth. The constructs at
polymer-on-polymer, such as UHMWPE but also a wear distinctive well-defined range of length scales and
rate comparable to metal-on-polymer combinations [15,16] . parameter magnitudes are expected to differentially affect
Cross-linked polyethylene was also able to be fabricated on cellular and surface interaction of osseointegration.
by injection molding manufacturing to reduce production Hara et al. (2016) mentioned that metal-interfaced
costs. Cross-linked polyethylene was proposed as the implants with diamond-structured porous titanium-
articular surface of the middle phalanx and contact alloy (Porous Ti-alloy) can promote osseointegration
[17]
movement with 3D printing polished articular surface and enhance implant stability . The most important
of the proximal phalanx for our PIP joint resurfacing parameters that affect osseointegration are pore size and
prosthesis. porosity. The experimental group with a size of 640 μm
In many common finger joint movements in daily and a porosity of 70% had better bone tissue growth
life, such as playing the piano, writing with a pen and ability and the strongest mechanical performance. We
open a can, the magnitude and angle of the joint force already have the technology to design and fabricate this
are well known [11,12] . The joints are subjected to a force type of lattice on the elliptical-cone stem surface (0.8 mm

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