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3DP Modularized Finger PIPJ Arthroplasty
inflammatory medication and local injection. For those specifications and sizes may not be suitable for various
patients with late stage arthritis that has failed to respond patients due to racial and individual diversity. Further, the
to conservative treatments, joint spacer arthroplasty is design of PIP joint implant needs to be adjusted to establish
one of the surgical strategies to preserve joint motion. a modularized PIP joint implant with suitable implant stem
At present, two PIP joint spacer arthroplasty and articular surface size combinations that can meet the
choices that include silicone spacer and joint resurfacing clinical use of various patients . Therefore, developing
[8]
are used in surgical treatment. One-piece silicone a modularized implant that consistently preserves PIP
implants have been used for decades and have been the joint stability with appropriate stem fitness for the bone
gold standard for PIP joint arthroplasty. However, the marrow cavity with relative natural articular surface shape
limitations of PIP joint arthroplasty could be the lack for long-term durability is needed. A new manufacturing
of material rigidity, lateral instability, and the inability process is required for such an implant device.
to provide force transmission. Furthermore, the fingers This study developed a modularized PIP joint
cannot bear a forceful pinch . When the joint moves implant system that closely resembles the anatomical
[1]
repeatedly and bends under force, the implant is prone articular resurfacing and stem based on reconstructed
to fatigue and fracture. The overall complication rates computed tomography (CT) images using the iterative
are as high as 32% [2-4] . The range of motion after silicone closest points approach. Each component of the newly
implantation is only about 60° compared with 110° in designed PIP joint with complex geometric shapes was
the native joint. This limitation makes it impossible to fabricated through metal 3D printing. Biomechanical
effectively restore the joint normal range of motion after tests including anti-loosening pull-out strength for the
the operation . On the contrary, metal three-dimensional proximal phalanx, elliptical-cone stem, and articular
[5]
(3D) printing techniques are well established for building surface connection strength for the middle phalanx, and
complicated 3D constructions from computer-aided static/dynamic dislocation tests under three daily activity
design (CAD) models and have great potential to solve load conditions for the PIP joint implant were performed
the problems of creating a porous (lattice) surface coating to verify joint stability and dislocation reduction.
on a dense titanium and porous titanium body . Many
[6]
studies indicate that titanium implant manufactured by 2. Materials and methods
3D printing with porous design of 60 – 70% porosity and 2.1. PIP joint implant design concept
pore size under 800 μm can enhance biologically active
and mechanically stable surface for implant fixation to The PIP joint is a hinge joint with a bicondylar-
bone . shaped proximal phalangeal head articulating with
[6]
Joint resurfacing (surface replacement) implants the bi-concave-shaped middle phalangeal base. It is
were introduced and commonly used in the last two stabilized with collateral ligaments and the volar plate,
decades. Various designs with different materials are providing a motion arc of about 110° in flexion-extension.
available on the market. Surface replacement arthroplasty Therefore, our joint design concept is to resemble the
has better structural strength and biomechanical anatomical contours and structure as closely as possible.
performance compared with silicon arthroplasty, providing Modularized models of the metaphyseal stem and joint
a larger range of joint activities. However, the shape and surface replacement provide diverse combinations for
size of the stem mismatch with the bone marrow cavity proper fit of a wider variety of human fingers.
size and the lack of osseointegration makes the implant In terms of the PIP joint implant design, a total of
prone to loosening under repetitive force. This leads to 48 CT image sets (Aquilion Prime SP, Canon Medical
implant failure and the need for a second operation in Systems USA, Inc., CA, US) including the index finger,
symptomatic patients . Commercially available products middle finger, ring finger and little finger were obtained
[2]
have articular surfaces that do not resemble the natural from 12 patients (including seven males and five females)
articular surface shape. This results in unstable joint arc aged between 20 and 65 years old. We obtained the CT
motion and easy joint dislocation [5,7] . These factors present files from the Picture Archiving and Communication
a large challenge and time consuming because it involves System by the location of exam at wrist and fingertips of
traditional machine manufacturing processes to fabricate all digits. Any suspicions or findings of injury or arthritic
the small PIP joint implant. The implant stem elliptical change were excluded from the study. Ethic approval was
cross-section must completely fit into the medullary not applied in this study since all patients’ demographic
cavity, matching the complex anatomical bimodal shape data were not revealed. CT images were reconstructed to
of the articular surface to prevent dislocation. measure the size, shape of the metaphyseal, diaphyseal,
In current clinical practice, most finger joint and medullary cavity at both proximal and middle
implants were designed in accordance with simplified phalanxes in medical image processing software (Mimics
size specifications. However, PIP joint implant restricted 22.0, Materialize NV, Leuven, Belgium).

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