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Hunag, et al.
For the PIP joint implant stem design, the measured cross section were measured and noted as the minor
total length of the phalanx minus the resection thickness axis and major axis for the elliptical medullary cavity
of the cut ends was defined as the full length of phalangeal (Figure 1B). A total of 48 sets of measurements were
bone marrow because the planned resection thickness averaged to find the implant stem dimensions, including
was 4 mm for the proximal phalangeal articular surface the length, the major and minor axis of the metaphyseal
and 2 mm for the middle phalangeal articular surface to and diaphyseal sides of the proximal phalanx and middle
remove the worn cartilage. One-third of the full length phalanx stems (Figure 1B).
of bone marrow cavity, which was designed for part of PIP joint surface design and articular surface border
adequate metaphyseal contact surface for bone integration were defined according to the extensor tendon and
and part of press fit for diaphyseal portion, was defined as ligaments insertion sites. The joint was retained with 135˚
the length for the modularized stem (Figure 1A). Lengths articular curved surface. Clouds of points from 48 groups
in the medullary cavity sagittal plane and coronal plane of reconstructed phalanx articular surfaces were fitted

A

B

Figure 1. PIP joint implant design concept: medullary canal estimation and stem length.

International Journal of Bioprinting (2022)–Volume 8, Issue 3 153