Page 170 - IJB-8-4

Metal 3DP Hybrid Suture Anchor for Osteoporosis
position, have been used for anchors that fail to provide the feasibility of the novel HSA for failure strength and
optimal fixation after insertion [1,2,4] . Improving anchor bone growth, respectively.
design to increase the retention between the anchor and
osteoporotic bone can be an alternative option . 2. Materials and methods
[6]
Numerous anchor constructs are available to 2.1. Design of the novel HSA and instruments
maximize retention on the anchor-bone interface and
avoid early suture anchor fixation failure. The failure We designed a screw-type anchor, which is 16 mm
strength of the suture anchor is known to be affected by in length, 5.5 mm in diameter, and dual-thread with
its design, including fixation type, anchor material, and micro-threads in the upper compressive taper head
suture type [7-9] . Anchors can be divided into screw- and (4-mm double-starts with 1.05-mm pitch) of the anchor
impaction-type devices . Screw-type anchors have for distributing stress because of supplementary contact
[2]
threads that are advanced into the bone and show higher between the micro-threads and cortical bone to improve
failure strength than smaller non-screw anchors designed mechanical retention (Figure 1). Macro single-threads
for glenoid repairs because screws impart increased with 2.10-mm pitch was designed in the remaining part
surface area for more holding strength and efficiency of the anchor. Two 0.8-mm diameter holes that allow the
compared with impaction-type devices [2,7,10,11] . No. 2 suture to pass through were placed symmetrically
Bioabsorbable and poly(ether-ether-ketone) (PEEK) on both sides of the head. The round and undercut thread
suture anchors are rapidly evolving and supplanting near the suture hole for suture protection and square hole
metallic anchors in rotator cuff surgery. However, at the anchor center for matching the instrument was also
although bioabsorbable anchors are absorbed with time considered at the compressive taper head. The anchor tip
after surgery, they do not provide suture stretching force . was designed to enable self-drilling and positioning when
[2]
Although the wing structure deployed with the PEEK inserted into the bone (Figure 1).
impaction-type anchor subcortically provides secure The HSA is designed with a symmetric wing
fixation to the bone , pushout strength is significantly mechanism on both sides that can be clamped to
[7]
greater for implants with porous titanium than PEEK, surrounding bone tissue to provide the anchor with a
with titanium being the only material showing adequate better holding power and failure strength between anchor
bone growth and proximity inside implant threads [9,12] . and bone when required. The wing mechanism needs to
The design concept of integrating the advantage of be designed as axially symmetrical to allow the internal
metal screw-type anchor and deploying wing structure fixation screw to push the wings with an average force
subcortically can improve retention between the metal after insertion. However, our anchor only designed to
anchor and the bone to increase anchor pullout strength. be symmetrical with two blades because the torsional
However, this novel design, with a complicated structure, strength of the anchor entity might be too weak when over
may encounter processing difficulties that traditional two blades were designed for the anchor. For unfolding
metal cutting processes cannot overcome. Recently, laser both wings, a screw is used to push the convex surface
powder bed fusion (LPBF), as an important laser-based at the anchor centric hole when inserting the 2-mm
additive manufacturing (AM) technique, also noted as diameter internal screw into the anchor (Figure 1). The
three-dimensional (3D) printing technique for metal barb function can be used when both wings are expanded
components, provides an opportunity to manufacture and the anchor is pulled out through the sutures. The
components with complex geometries in the aerospace, space created when the wings are open helped the bone
automotive, and medical applications [13-15] . The 3D printing to grow inward; three holes with 600-μm diameter were
technique is well established for building complicated 3D also created on both sides of the anchor for bone ingrowth
constructions from computer-aided design (CAD) models (Figure 1).
for controllable of precise dimension about 20 μm and The instruments with HSA must be used in
has great potential to solve the problems of creating a conjunction with arthroscopy and divided into the outer
porous (lattice) on a dense titanium and porous titanium sleeve instrument and central hexagonal driver. The main
body for enhancing bone growth . function of the outer sleeve is to implant the anchor into
[6]
In this study, we deployed a novel hybrid suture the bone and using a square connection to strengthen
anchor (HSA) with wing structure mechanism contained the locking force. The outer sleeve instrument was also
outer dual-threaded profile and inner hole threads with designed to be hollow to enable the central hexagonal
convex surface that complex geometry can be fabricated driver to pass through to lock the internal screw such
by titanium 3D printing technology. The wing mechanism that the anchor wings can be unfolded. The implantation
can be opened by an internal milling screw according to process involved inserting the suture anchor into the
the state of the osteoporotic bone. In vitro static/dynamic bone tissue by the outer sleeve to a suitable position and
testing and animal experiments were performed to verify then rotating the central hexagonal driver to drive the

162 International Journal of Bioprinting (2022)–Volume 8, Issue 4