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Metal 3DP Hybrid Suture Anchor for Osteoporosis
landmarks and tendonectomy was performed as close to The static pullout test results showed that the HSA
the insertion footprint as possible. failure strengths with and without the wing open were
A total of eight suture anchors for animal experiments, significantly higher (P < 0.05) than CSA regardless of
two HSAs with high-strength force fiber suture of No. 2 severely osteoporotic bone and osteoporotic bone. The
ultra-high molecular weight braided polyethylene average failure strength was 2.50 (105.43N/42.16N) and
(UHMWPE), and two CSAs with 5.5 mm fully threaded 1.95 (82.41N/42.16N) folds for HSA with and without
metallic suture anchors, were inserted into the left and the wing open than CSA in severely osteoporotic bone
right humeral head at an angle of 45°. A specific central (Figure 4), respectively. The corresponding folds were
hexagonal driver was applied to drive the internal screw 1.81 (464.55N/256.27N) and 1.54 (394.5/256.27)
to unfold the mechanism of anchor wing after the HSA for osteoporotic bone. A similar trend was observed
was driven into suitable bone depth using the outer sleeve in the pullout test after dynamic load was applied;
instrument. Reattachment of the tendon was performed average failure strength was 2.46 (128.01N/52.13N)
by single-row suturing with fiber wires threaded on both and 2.17 (113.12N/52.13N) folds for HSA with and
types of anchors. Finally, the wound was closed in layers without the wing open than CSA in severely osteoporotic
without a visible bleeding point. A topical antibiotic bone, respectively. The corresponding folds were
(penicillin 3000 IU/kg) was applied before wound closure 1.77 (532.74N/301.53) and 1.62 (489.39N/301.53N) for
to control surgical site infection. A prophylactic antibiotic osteoporotic bone. Table 3 shows that failure modes of
(enrofloxacin 5 mg/kg) was administered IM, QD for 5 pullout tests for suture anchors.
d. Once analgesia was no longer required, the animals Figure 5 shows the histomorphometrical images
were monitored once daily. Eight weeks after surgery, for CSA and HSA. Stained area (blue region) along the
under deep general anesthesia, the pigs were euthanized anchor contour indicates the amount of bone growth
with heart exsanguinations. Bilateral humerus was then with newly formed lamellar bone directly in contact
removed from the shoulder joint and tendon stumps of with the anchor. Table 4 lists percentage of stained area
rotator cuff muscles were kept with the sample. to total area along the anchor contour, 1 mm outward
Each anchor and its surrounding hard tissue were for histomorphometrical evaluation, with average
sectioned and dehydrated in a graded series of alcohol value ± standard deviation being 19.802% ± 2.08% for
(20 – 40 – 60 – 80 – 100%). The sample was then CSA and 18.21% ± 1.30% for HSA. No statistically
embedded, sliced, and ground for dyeing in blue for bone significant difference between wing-open hybrid anchors
tissue and anchor identification. Images of sliced sections and commercial anchors was observed.
were taken under ×12.5 magnification and analyzed
using an image processing software (ImageJ 1.53a for 4. Discussion
MacOS, National Institutes of Health, USA). Using hue Rotator cuff tear repairs are more challenging among the
adjustment in the color threshold function, the ratio of elderly population with osteoporotic or osteopenic bone
the stained (blue) to total area was calculated along the in the proximal humerus . Understanding the pullout
[6]
anchor contour 1 mm outward to quantify bone growth. strength of suture anchors in relation to their design
Statistical Mann–Whitney U test was performed to is important for surgeons to avoid early suture anchor
compare bone growth variation between CSAs and novel fixation failure and for designers to improve suture anchor
HSAs with the wing open. performance . Making higher demands on the structural
[6]
3. Results design of the anchor to increase contact area between
anchor and bone interface for enhancing the interfacial
Figure 2 shows the HSA after metal 3D printing retention strength is necessary. Therefore, we propose
manufacturing, the manufacturing accuracy, and the a novel suture anchor with micro-threads in the cortical
status of functional test. Figure 2C and 2E show anchor bone contact area and an open wing auxiliary structure
wings in unexpanded and opened states, respectively. that can enhance pullout performance in the osteoporotic
The manufacturing accuracy of 3D printing can be state. Figure 6 shows that internal matching siders were
controlled <6% for five random samples between the designed originally as cone and cylinder ball head.
design parameter and the actual measurement after However, adaption interface fitness between matching
printing (Table 2). Figure 2D shows the finished product slider and anchor was difficult to control accurately in
of the internal screw by machine milling, with front/top size, free crack, and tolerances when an anchor with
view scale and accuracy can be controlled at 0.04 mm. matching slider is printed together. Therefore, the
The X-ray image shows that the wings of the HSA can inserted internal screw, manufactured using traditional
be opened smoothly while inserted into the bone under machine milling, was later selected to drive the convex
the operation of the specific instrument after the anchor is surface of the wing mechanism because the slider was
inserted into the Sawbone (Figure 2F). prone to binding and unable to function due to the

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