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Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study
Journal Pre-proof Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study Miguel A. Diaz, MS, Eric A. Branch, MD, Luis A. Paredes, BS, Emily Oakley, PA-C, Christopher E. Baker, MD PII:
S0749-8063(19)31195-8
DOI:
https://doi.org/10.1016/j.arthro.2019.12.003
Reference:
YJARS 56711
To appear in:
Arthroscopy: The Journal of Arthroscopic and Related Surgery
Received Date: 14 July 2019 Revised Date:
4 December 2019
Accepted Date: 5 December 2019
Please cite this article as: Diaz MA, Branch EA, Paredes LA, Oakley E, Baker CE, Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study, Arthroscopy: The Journal of Arthroscopic and Related Surgery (2020), doi: https://doi.org/10.1016/ j.arthro.2019.12.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier on behalf of the Arthroscopy Association of North America
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Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study
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1
Miguel A. Diaz, MS; 2Eric A. Branch, MD;1Luis A. Paredes, BS; 3Emily Oakley, PAC;3Christopher E. Baker, MD†
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1
Foundation for Orthopaedic Research & Education, Tampa, FL, USA
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2
Department of Orthopaedic Surgery, University of South Florida, Tampa, FL, USA
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3
Florida Orthopaedic Institute, Tampa, FL, USA
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†Corresponding Author
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Christopher E. Baker, MD
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Florida Orthopaedic Institute
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13020 N. Telecom Parkway
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Tampa, FL 33637
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Tel. (813) 978-9700, Ext.6833
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Fax. (813) 558-6833
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[email protected]
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Running Title: CP-BSM raises threaded suture anchor fixation
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Acknowledgments
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This study was funded by Zimmer Biomet. MAD: Research Grant from Zimmer Biomet (Paid directly to institution1). EAB: has nothing to disclose. LAP: has nothing to disclose. EO: has nothing to disclose. CEB: receives speaking and consulting fees from Zimmer Biomet. All authors discussed results and have participated in writing the manuscript. All authors have read and approved the final submitted manuscript.
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Research Performed at the Phillip Spiegel Orthopaedic Research Laboratory at the Foundation for Orthopaedic Research and Education, Tampa, FL, 33607 U.S.A
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Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength:
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A Biomechanical Study
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Abstract
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Purpose: To compare the response to cyclical loading and ultimate pull-out strength of threaded
6
suture anchor with and without calcium phosphate bone void filler augmentation in a
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polyurethane foam block model and in vitro proximal humerus cadaveric model.
8 9
Methods: This controlled biomechanical study consisted of 2 parts: (1) preliminary polyurethane
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foam block model, and (2) in vitro cadaveric humeri model. The preliminary foam block model
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intended to mimic osteoporotic bone utilizing a 0.12 g/cc foam material. Half of the foam block
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models were first filled with injectable Calcium Phosphate Bone Substitute Material (CP-BSM)
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while the other half were not augmented with CP-BSM. Each specimen was then instrumented
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with a threaded suture anchor. The same technique and process was performed in a matched
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cadaveric humeri model. Testing then consisted of a step-wise, increasing axial load protocol for
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a total of 40 cycles. If the anchor remained intact after cyclic loading, the repair was loaded to
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failure. The number of completed cycles, failure load and failure modes were compared between
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groups.
19 20
Results: Average pull-out strength for suture anchor with CP-BSM in the osteoporotic foam
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block model was significantly higher at 332.68 N ± 47.61 compared to the average pull-out
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strength of suture anchor without CP-BSM at 144.38 N ± 14.58 (p=0.005). In the matched
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cadaveric humeri model, average pull-out strength for suture anchor with CP-BSM was
1
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significantly higher at 274.07 N ± 102.07 compared to the average pull-out strength of suture
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anchor without CP-BSM at 138.53 N ± 109.87 (p=0.029).
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Conclusions: In this time zero, biomechanical study, augmentation of osteoporotic foam block
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and cadaveric bone with calcium phosphate bone substitute material significantly increases pull-
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out strength of threaded suture anchors.
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Clinical Relevance: Considering concerns about suture anchor pull-out from osteoporotic bone,
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augmentation with calcium phosphate bone substitute material increases load to failure
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resistance.
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Introduction
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Arthroscopic rotator cuff repair is a commonly performed surgical intervention to treat patients
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with painful shoulders due to rotator cuff tears that have failed conservative management. Some
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patients with known deficiencies in the greater tuberosity (osteoporosis, cysts, prior fractures or
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prior failed rotator cuff repair) pose a more problematic clinical situation due to poor quality
39
bone not allowing adequate fixation of commonly used suture anchor devices.1,2 Soft tissue or
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bony fixation failure prior to healing is one of the most common failure mechanisms and
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represents a significant effect on outcomes.3-7 Generally, arthroscopic rotator cuff repair failure
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has been shown to commonly occur at the suture-tendon interface.8 However, in osteoporotic
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bone, bone-anchor interface becomes an increasingly relevant mode of failure.9-11 A recent study
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by Werner et al12 demonstrated osteoporosis as an independent risk factor affecting postoperative
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rotator cuff healing, with increased incidence of revision rotator cuff repairs in patients with
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osteoporosis.
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Prior biomechanical studies have investigated multiple methods to augment bone when poor
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bone quality or cysts are encountered during rotator cuff repair: the use of cement, open
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curettage with bone grafting, increasing the size of the implant, or even stacking multiple
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anchors to allow for appropriate fixation with variable success.13-15 Braunstein et al.16 described
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an augmentation technique where polymethylmethacrylate cement is injected into predrilled
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holes, before the anchor was potted into the injected cement. Moreover, Aziz et al17
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demonstrated increased pullout strength utilizing polymethylmethacrylate cement injected in situ
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into a fenestrated suture anchor, similar to techniques found with pedicle screw augmentation in
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spine surgery.
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AccuFill® Bone Substitute Material (Zimmer Biomet, Exton, PA) is an injectable calcium
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phosphate bone void filler commonly used in the knee to treat microtrabecular fractures
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(microdefects) in the subchondral bone. This commercially available injectable Calcium
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Phosphate Bone Substitute Material’s (CP-BSM) characteristics allow it to be placed
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percutaneously by a drillable delivery cannula to fill defects or voids in bone without the need to
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create a macrodefect. Once the material has cured the surgeon can drill into the bone void filler
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as they would for a standard repair. By implanting CP-BSM into the cancellous bone of the
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greater tuberosity in patients with deficient bone before rotator cuff repair, it stands to reason that
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improved fixation may be achieved. A case report has illustrated the viability of this procedure
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from a surgical technique stand point with negligible increase in operative time or complexity.18
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The purpose of this study was to compare the response to cyclical loading and ultimate pull-out
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strength of threaded suture anchor with and without calcium phosphate bone void filler
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augmentation in a polyurethane foam block model and in vitro proximal humerus cadaveric
71
model. We hypothesized that the addition of CP-BSM will significantly increase pull-out
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strength of threaded suture anchors in both foam block model and proximal humerus cadaveric
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model.
74 75
Methods
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This was a time-zero, controlled biomechanical study consisting of 2 parts: (1) a preliminary
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polyurethane foam block model and (2) an in vitro cadaveric humeral model. All tested
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constructs utilized a threaded, 5.5 mm Quattro® X PEEK (polyetheretherketone) Suture Anchor
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(Zimmer Biomet, Scottsdale, AZ) which requires the anchor to be screwed-in for fixation after
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drilling or taping a pilot hole. The suture anchors were double loaded with No.2 Force Fiber®, a
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high strength, ultra-high molecular weight polyethylene suture. In the preliminary foam block
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testing model, the American Society for Testing and Materials (ASTM) F-1839 was followed
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and a 0.12 g/cc [ 7.5 pound-force per cubic foot (PCF)] foam density material (Pacific Research
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Laboratories, Vashon, WA) was chosen to represent osteoporotic bone density.19-23
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Polyurethane Foam Block: Osteoporotic Model Testing
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A total of twelve 0.12 g/cc rigid polyurethane foam blocks were used for testing. Individual
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blocks were cut to 5 cm x 5 cm x 4 cm cubes. The control group (threaded suture anchor only, 6
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foam blocks) had the threaded suture anchor inserted into unaltered foam blocks. The
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experimental group (threaded suture anchor plus CP-BSM, 6 foam blocks) had the threaded
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suture anchor inserted into foam blocks after augmentation with calcium phosphate bone void
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filler.
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For both groups, the center point of each test sample, relative to designated top surface was
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identified and marked. Samples in the control group were only instrumented with a 5.5 mm
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suture anchor per manufacturer recommendations. To standardize trajectory of the suture anchor,
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a 2.0 mm pilot hole was created using a drill press, assuring the pilot hole was perpendicular to
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surface. Samples in the experimental group were injected with 5cc of CP-BSM before the suture
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anchor was instrumented. The CP-BSM injection site was 10 mm down along the mid-section of
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the lateral face of foam block (Figure 1). The depth of the cannula was approximately 24 mm to
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ensure placement of the CP-BSM into the area where the anchor would be placed. After
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implantation of CP-BSM, a therapeutic heating pad was used to bring the foam blocks above
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body temperature (98.6°F) for the curing process to begin. Foam blocks with CP-BSM were kept
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above 98.6°F for 10 minutes before the suture anchors were instrumented. A 2.0 mm pilot hole
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was created along the marked center point and into the area filled with CP-BSM, where the
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anchors were instrumented per manufacturer recommendations.
107 108
Biomechanical testing was performed on the same day of instrumentation to test the immediate
109
pull-out strength of the implanted suture anchor. A custom fixture was built and fixed to the base
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of a servo-hydraulic materials testing machine (MTS Bionix, MTS Inc., Eden Prairie, MN)
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equipped with a 5kN load cell (MTS Inc.) (Figure 2A). To ensure that the samples were properly
112
aligned in the plane of testing, the base of the fixture design allowed one to freely position (X-Y
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plane) a sample in such orientation to allow the direction of force to be in-line with the axis of
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suture anchor (uniaxial tensile testing). Sutures were hand tied around a 1.27 cm diameter
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cylinder with five alternating half-hitch knots, assuring equal lengths. The loop was then secured
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through a 6.35 mm (¼”) anchor shackle with a working load limit of 453.6 kg (1000 lbs.) and
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coupled to the load cell. Once the samples were properly aligned, a small preload (< 0.5 N) was
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applied to remove the slack from the system before testing, which was confirmed through tactile
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and visual inspection. Testing consisted of a step-wise and increasing load protocol.10,24,25 Each
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specimen was tested under axial loading rate of 1 mm/s consisting of 4 cyclic loading profiles of
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increasing tension: 10 – 50 N for 10 cycles, 10 – 100 N for 10 cycles, 10 – 150 N for 10 cycles
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and 10 – 200 N for 10 cycles, for a total of 40 cycles (Figure 3). If the anchor remained intact
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after cyclic loading, the repair was loaded to failure at 1 mm/s.
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Cadaveric Testing Model
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Ten cadavers (8 males and 2 females; average weight 83.9 ± 20kg) with bilateral shoulders were
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studied with the right shoulder being designated for anchor placement with CP-BSM and the
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matched left shoulder being designated for anchor placement without CP-BSM. Specimen ages
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ranged from 48 to 91years (mean, 71 years). Each humerus was stripped of soft tissues and
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shortened to a 20 cm length as measured from the apex of the humeral head. The distal diaphysis
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was potted in high strength resin (Bondo Body Filler, 3M Collision Repair Solutions, St. Paul,
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MN). For both groups, a 1 cm x 2 cm window was outlined along the superior facet of the
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greater tubercle with black marker to serve as decortication guideline for each sample.
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Decortication has been shown to significantly decrease pull-out strength of suture anchors in
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both humeri and femur.11,25,26 To create a worst-case scenario, 5 mm of decortication was
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performed on all samples by using a highspeed 3-mm burr within guidelines. To standardize
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trajectory of the suture anchor, the samples were clamped in a specialized vice at 45° (measured
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by digital goniometer) and the anchor was placed perpendicular to the surface. All anchors were
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placed centrally within decorticated footprint, 5 mm from anatomical neck line and 1cm from
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edge. Samples in the control group were only instrumented with a 5.5 mm suture anchor per
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manufacturer recommendations. Samples in the experimental group were injected with 5cc of
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CP-BSM before suture anchor was instrumented. The CP-BSM injection site was placed
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centrally within decorticated footprint, 5 mm from anatomical neck line and 1 cm from edge.
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The depth of the cannula was approximately 24 mm from the cortical surface (Figure 4). After
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implantation of CP- BSM, a therapeutic heating pad was used to bring the samples above body
146
temperature (98.6°F) for the curing process to begin. Samples with CP-BSM were kept above
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98.6°F for 10 minutes before the suture anchors were instrumented. Placement of suture anchor
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was directly into the cured CP-BSM.
149 150
As with the foam block model, biomechanical testing was performed on the same day of
151
instrumentation to test the immediate pull-out strength of suture anchor. A custom fixture was
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built and fixed to the base of the servo-hydraulic materials testing machine equipped with the
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same load cell and anchor shackle (Figure 2B). Similar to the foam block fixture, the design
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allows for consistent sample placement and the degree of freedom to align the suture anchor
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construct line of axis with direction of force. The additional degrees of freedom in the X-Z and
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Y-Z plane allowed the cadaveric samples to be positioned such that the suture and suture anchor
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were loaded perpendicularly, relative to the bone surface. Suture tying protocol and loading
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protocol were identical to those used for foam block testing. (Step-wise cyclic loading, followed
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by ramp to failure).
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For both foam block and cadaveric testing, the force data collected by MTS load cell and
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displacement data collected by the system linear variable differential transducer (LVDT) were
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used to create force-displacement curves (F-d curve). The F-d curve were used to identify failure
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load, failure displacement and stiffness. Failure was defined as the first significant decrease in
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the monotonically increasing force profile, where pull-out strength was defined as the peak load
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at failure. Peak load for each specimen was recorded whether failure occurred during or after
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cyclic loading. Failure displacement was measured as the difference between displacement at
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failure and displacement prior to monotonically increasing force. Stiffness was defined as the
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linear portion of the F-d curve. The primary focus of this study was to compare pull-out strength
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(peak load) between groups. Secondary data such as stiffness and failure displacement were also
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collected and analyzed.
172 173
Power Analysis
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Using mean and variance data from prior studies of similar scope19,27,28 a priori power of 0.80
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with a Type I error rate of 0.05 was used to calculate appropriate sample size using G*Power
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(V3.1.9.2, Franz Faul, Germany). For the foam block testing, with an effect size (Cohen’s d) of
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1.6, a sample size of 6 foam blocks per group was necessary to detect an increase in pullout force
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between groups. Similarly, with an effect size (Cohen’s d of 1.2), a sample size of 8 matched
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pairs of humeri was necessary to anticipate biomechanically and clinically relevant increase in
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pullout force in the CP-BSM augmented repairs.
181 182
Statistical Analysis
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The Shapiro-Wilk normality test was performed on all data confirming normal distribution. In
184
both foam block and cadaveric model, parametric statistics were used to evaluate data. A
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univariate ANOVA was performed on demographic data (Age, Sex, Weight) between two testing
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groups and no statistical difference was found. A paired sample T-test was performed to identify
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differences in pull-out strength between the control group and experimental group. Stiffness and
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displacement data were also analyzed with paired sample T-test. Data is presented as mean ±
189
standard deviation (SD). All statistical comparisons were performed with SPSS (v22, IBM, NY,
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USA) at a significance level of α=0.05.
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Results
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Osteoporotic Foam Block Model
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All samples in experimental group (with CP-BSM) completed the 40 cycles before ramp to
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failure. The average pull-out strength for suture anchor with CP-BSM (experimental group;
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332.68 ± 47.61 N) was found to be significantly higher (P=0.001) than the average pull-out
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strength of suture anchor without CP-BSM (control group; 144.39 ± 14.56 N) . In the control
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group (without CP-BSM), all samples failed within a loading level, where 67% of the samples
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failed at Load Level 3, completing only 20 cycles, and the remaining 33% failed at Load Level 4,
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completing 30 cycles. The construct stiffness at failure for the experimental group (50.58 ± 14.74
200
N/mm) was larger than the control group (26.78 ± 15.66 N/mm), however this difference was not
201
statistically significant. Similarly, the failure displacement between the experimental group and
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control group were not statistically significant, 4.25 ± 2.11 mm and 2.78 ± 1.99 mm, respectively
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(Table 1).
204 205
The modes of failure in the low-density foam block model were predominately anchor pull-out
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(Figure 3). Those augmented with CP-BSM also experienced anchor pull-out (83%), though
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there was one instance where failure occurred at the suture anchor eyelet (suture pulled cleanly
208
through the anchor leaving the anchor intact within the specimen)..
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Cadaveric Humeri
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In the control group (without CP-BSM), two humeri had to be removed from analysis due to
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severe osteoporosis which was observed during instrumentation of suture anchor where loss of
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fixation occurred prior to loading the first cycle (<10N). The matched pairs of these humeri, in
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the experimental group, first implanted with CP-BSM, although not included in statistical
215
analysis, were still tested and showed pullout strengths similar to other specimens tested, 329 N
216
and 200 N. Therefore, only 8 matched pairs (n=16) were used for statistical analysis, maintaining
217
statistical power.
218 219
The average pull-out strength for suture anchor with CP-BSM (experimental group; 274.07 ±
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102.07 N) was significantly higher (P=0.029) compared to the average pull-out strength of suture
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anchor without CP-BSM (control group; 138.53 ± 109.87 N) . The construct stiffness at failure
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in the experimental group was significantly larger than that of the control group, 109.37 ± 15.65
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N/mm and 64.83 ± 51.88 N/mm, respectively (P=0.043). The difference in failure displacement
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between experimental and control group was not statistically significant, 4.26 ± 1.22 mm and 3.1
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± 1.66 mm, respectively (Table 1). In the experimental group, 75% (6/8) survived all four testing
226
conditions where the remaining 12.5% (1/8) failed in the third load step and 12.5% (1/8) failed in
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the fourth load step. Only 25% (2/8) of the control group survived all four testing conditions. The
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remaining 37.5% (3/8) failed in the first load step, 12.5% (1/8) failed in second load step, and
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25% (2/8) in the fourth load step.
230 231
The modes of failure were predominately anchor pull-out for both testing groups (Figure 5).
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Those augmented with CP-BSM also experienced suture rupture and one instance where failure
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occurred at anchor eyelet. Cross sections of the experimental group were taken to demonstrate
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penetration of calcium phosphate and thread interaction (Figure 6).
235 236
Discussion
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This study supports our hypothesis, demonstrating that augmenting an osteoporotic foam block
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model (0.12 g/cc) with 5cc of CP-BSM can provide threaded suture anchors significantly higher
239
load to failure (332.68 N ± 47.61; P=0.005) than threaded suture anchors without the use of CP-
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BSM (144.38 N ± 14.58). This study also supports our hypothesis regarding cadaveric testing.
241
Though not the primary focus of this study, no significant differences in stiffness and failure
242
displacement between study groups in foam block testing were noted. In the cadaveric testing,
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stiffness was found to be significantly larger in anchors augmented with CP-BSM compared to
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anchors without CP-BSM. However, no significant difference was detected between failure
245
displacement.
246 247
Based on previous biomechanical studies, 0.12 g/cc foam block was chosen to represent poor
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bone quality.19-23 Bone quality is one of the many factors shown to influence suture anchor
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resistance to pull-out and may lead to a compromised rotator cuff repair.17,29 Horoz et al30
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evaluated various anchor techniques to evaluate which was suitable for osteoporotic bone, while
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Barber et al27,28 concluded that failure load was dependent on anchor type and not anchor
252
location (cancellous or cortical bone). Despite the conflicting data in literature, there is still a
253
need to improve suture anchor fixation in patients with compromised bone quality.
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For cadaveric testing, we followed a matched-pair design, with the assumption that bone density
255
is equal within specimen pair allowing for comparable testing between the two testing groups.
256
Decortication has been shown to adversely affect suture anchor pull-out strength.24,26 Ruder et
257
al26 performed greater tuberosity decortication to a mean depth of 1.7 mm and reported a
258
significant difference in ultimate load to failure for the decorticated and non-decorticated cohorts
259
to be 314 N and 386 N, respectively. Similarly, Hyatt et al24 studied the effects of decortication
260
(mean depth of 5.6 mm) and reported a significant decrease in ultimate load to failure from 244
261
N to 63 N in decorticated specimens.
262 263
To create a worst-case, osteoporotic model, we decorticate all cadaveric specimens, mean depth
264
was 5 mm, to reduce ultimate load to failure. Interestingly, the ultimate failure loads of both
265
testing groups in cadaveric specimens closely resemble those of the osteoporotic foam block
266
model, adding validation to the choice of using 0.12 g/cc foam block to represent osteoporotic
267
bone. Joo Han Oh et al22 studied the effect of the insertion and traction angle on suture anchor
268
pull-out strength and performed preliminary tests on two synthetic bone models (Osteoporotic
269
[0.16 g/cc; 10 PCF] and Non-osteoporotic [0.32 g/cc; 20 PCF]). They found a significant
270
difference (P<0.001) in ultimate load to failure between the osteoporotic model (181.9 N ± 13.7)
271
and the non-osteoporotic model (403.7 N ± 22.3). While these two studies are not directly
272
comparable, it can be concluded that decorticating effectively reduced the ultimate load to failure
273
of suture anchor to a level comparable to an osteoporotic surrogate model.
274 275
Barber et al27 evaluated the biomechanical and design characteristics of several suture anchors in
276
a porcine model, of which the 5.5 mm Quattro X suture anchor was tested. They reported the
277
mean failure force of the Quattro X suture anchor (5.5 mm) in porcine cortical bone was 370.6 N
278
± 26.8 and 384.0 N ± 21.3 in cancellous bone. While direct comparison between our data and
279
Barber et al is difficult to do because of varying test medium, the pull-out strength achieved by
280
anchor with calcium phosphate in 0.12 g/cc foam block and cadaveric model are in the lower
281
testing range.
282
283
Tingart et al10 studied different anchor designs in poor bone quality and the effect on pull-out
284
strength. They found the mean pull-out strength of metal screw-type anchors was 273 ± 99 N in
285
proximal region of greater tuberosity and 184 ± 54 N in distal region of greater tuberosity,
286
whereas the biodegradable hook-type anchors had 162 ± 25 N and 112 ± 30 N, respectively.
287
Interestingly, the pull-out strength of threaded anchors with CP- BSM in the current study fall
288
within range of non-decorticated groups and those of metal screw-type anchors in poor bone
289
density presented by Tingart et al10.Anecdotally, tactile feedback is often used by Surgeons to
290
test the quality of a repair. This form of measurement is difficult to quantify due to high
291
subjectivity, but samples in both testing models (osteoporotic foam block and cadaveric) with
292
CP-BSM were observed to have a better ‘bite’; similar to the resistance expected in patients with
293
denser bone quality. The purpose of this biomechanical study was to evaluate the pull-out
294
strength of standard threaded anchors placed with and without the implantation of calcium
295
phosphate bone void filler in a rigid polyurethane foam block model and in a cadaveric humeri in
296
vitro model. Along with the successful use of CP-BSM for arthroscopic cuff repair in
297
osteoporotic patients18, the data presented in this study may improve clinical outcomes, though
298
the effect on repair healing is still unknown.
299 300
Limitations
301
This study is not without its limitations. One limitation was the inability to quantitatively
302
measure the bone density of each matched-pair donor. By decorticating all the samples, we
303
sought to reduce the ultimate load to failure to a level comparable to poor bone density.
304
Moreover, the study did not attempt comparisons of various anchor type or material. Another
305
limitation was the depth of decortication. Our model has a mean depth of 5 mm, which is quite
306
aggressive compared to the mean depth of 1.7 mm seen in Ruder et al26, but comparable to the
307
mean depth of 5.6 mm seen in Hyatt et al24. Both Ruder et al26 and Hyatt et al24 showed a
308
significant difference between suture anchor pull-out strengths in non-decorticated and
309
decorticated humeri. Furthermore, analysis of the secondary data of stiffness and failure
310
displacement were found to be under powered, however the difference in pull-out strength was
311
not. Lastly, this study represents time-zero biomechanical load study and does not address
312
change in pull-out strength over time (repair healing).
313 314
Conclusion
315
In this time zero, biomechanical study, augmentation of osteoporotic foam block and
316
decorticated cadaveric bone with calcium phosphate bone substitute material significantly
317
increases pull-out strength of threaded suture anchors.
318 319 320
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Frank JB, El Attrache NS, Dines JS, Blackburn A, Crues J, Tibone JE. Repair site
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integrity after arthroscopic transosseous-equivalent suture-bridge rotator cuff repair. Am
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J Sports Med 2008;36:1496-1503.
341
8.
342 343
identified at revision surgery. J Shoulder Elbow Surg. 2003 Mar-Apr;12(2):128-33. 9.
344 345
Cummins CA, Murrell GA. Mode of failure for rotator cuff repair with suture anchors
Chung SW, Oh JH, Gong HS, Kim JY, Kim SH. Factors affecting rotator cuff healing after arthroscopic repair. Am J Sports Med 2011;39:2099-2107.
10.
Tingart MJ, Apreleva M, Lehtinen J, Zurakowski D, Warner JJ. Anchor design and bone
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mineral density affect the pull-out strength of suture anchors in rotator cuff repair: which
347
anchors are best to use in patients with low bone quality? Am J Sports Med.
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2004;32:1466-1473.
349
11.
Yakacki CM, Poukalova M, Guldberg RE, Lin A, Saing M, Gillogly S, Gall K. J. The
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effect of the trabecular microstructure on the pullout strength of suture anchors. Biomech.
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2010 Jul 20;43(10):1953-9. doi: 10.1016/j.jbiomech.2010.03.013. Epub 2010 Apr 18.
352
12.
Werner, Cancienne, Brockmeier, Kew, Deasey, and Werner. The Association of
353
Osteoporosis and Bisphosphonate Use with Revision Shoulder Surgery after Rotator Cuff
354
Repair.
355
13.
356 357
anchor fixation. Clin Orthop Relat Res. 2006;451:236-241. 14.
358 359
Giori NJ, Sohn DH, Mirza FM, Lindsey DP, Lee AT. Bone cement improves suture
Brady PC, Arrigoni P, Burkhart SS. What do you do when you have a loose screw? Arthroscopy. 2006;22:925-930.
15.
Burkhart SS, Klein JR. Arthroscopic repair of rotator cuff tears associated with large
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bone cysts of the proximal humerus: compaction bone grafting technique. Arthroscopy.
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2005;21:1149.
362
16.
Braunstein, B. Ockert, M. Windolf, et al.Increasing pullout strength of suture anchors in
363
osteoporotic bone using augmentation—a cadaver study Clin. Biomech., 30 (3) (2015),
364
pp. 243-247
365
17.
Aziz KT1, Shi BY2, Okafor LC3, Smalley J4, Belkoff SM5, Srikumaran U6. Pullout
366
strength of standard vs. cement-augmented rotator cuff repair anchors in cadaveric bone.
367
Clin Biomech (Bristol, Avon). 2018 May;54:132-136. doi:
368
10.1016/j.clinbiomech.2018.03.016. Epub 2018 Mar 20.
369
18.
Branch EA, Ali AH, Baker CE. Novel Use of Calcium Phosphate Bone Void Filler in
370
Rotator Cuff and Labral Repair. Techniques in Shoulder & Elbow Surgery. 2019;20:19-
371
25.
372
19.
Er MS, Altinel L, Eroglu M, Verim O, Demir T, Atmaca H. Suture anchor fixation
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strength with or without augmentation in osteopenic and severely osteoporotic bones in
374
rotator cuff repair: a biomechanical study on polyurethane foam model. J Orthop Surg
375
Res. 2014;9:48.
376
20.
Thompson MS, McCarthy ID, Lidgren L, Ryd L. Compressive and Shear Properties of
377
Commercially Available Polyurethane Foams. Journal of Biomechanical Engineering.
378
2003;125:732.
379
21.
Standard Specification for Rigid Polyurethane Foam for Use as a Standard Material for
380
Testing Orthopaedic Devices and Instruments, ASTM F1839-08(2016). West
381
Conshohocksen, PA: ASTM International; 2016.
382
22.
383 384
Oh JH, Jeong HJ, Yang SH, et al. Pullout Strength of All-Suture Anchors: Effect of the Insertion and Traction Angle-A Biomechanical Study. Arthroscopy. 2018;34:2784-2795.
23.
Patel PS, Shepherd DE, Hukins DW. Compressive properties of commercially available
385
polyurethane foams as mechanical models for osteoporotic human cancellous bone. BMC
386
Musculoskelet Disord. 2008;9:137.
387
24.
388 389
Hyatt AE, Lavery K, Mino C, Dhawan A. Suture Anchor Biomechanics After Rotator Cuff Footprint Decortication. Arthroscopy. 2016;32:544-550.
25.
Putnam JG, Chhabra A, Castaneda P, et al. Does Greate Trochanter Decortication Affect
390
Suture Anchor Pullout Strength in Abductor Tendon Repairs? Am J Sports Med.
391
2018;46(7):1668-1673.
392
26.
Ruder JA, Dickinson EY, Peindl RD, Habet NA, Fleischli JE. Greater tuberosity
393
decortication decreases load to failure of all-suture anchor constructs in rotator cuff
394
repair. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2018;34:2777-
395
2781.
396
27.
397 398 399
Barber FA, Herbert MA. Cyclic loading biomechanical analysis of the pullout strengths of rotator cuff and glenoid anchors: 2013 update. Arthroscopy. 2013;29:832-844.
28.
Barber FA, Herbert MA. All-Suture Anchors: Biomechanical Analysis of Pullout Strength, Displacement, and Failure Mode. Arthroscopy. 2017;33:1113-1121.
400
29.
Postl LK, Ahrens P, Beirer M, et al. Pull-out stability of anchors for rotator cuff repair is
401
also increased by bio-absorbable augmentation: a cadaver study. Arch Orthop Trauma
402
Surg. 2016;136:1153-1158.
403
30.
Horoz L, Hapa O, Barber FA, Husemoglu B, Ozkan M, Havitcioglu H. Suture Anchor
404
Fixation in Osteoporotic Bone: A Biomechanical Study in an Ovine Model. Arthroscopy.
405
2017;33:68-74.
406 407 408 409
Figure Legends
410
Figure 1. Illustrations of anchor placement and CP-BSM injection site on foam block sample
411
where (A) is a 3D representation of Anchor placement and insertion of CP-BSM; (B) Sample
412
with cannula inserted to a depth of 24 mm; (C) Sample with cured CP-BSM being prepped; and
413
(D) Example of anchor instrumented into foam block augmented with CP-BSM.
414 415
Figure 2. Testing fixture allowing for X-Y adjustment (blue and orange arrows) and rotation
416
(green arrow) for specimen alignment. Direction of pull is colinear to anchor placement. (A)
417
Illustrates the mechanical test set-up for foam blocks model while (B) illustrates test set-up for
418
cadaveric model.
419 420
Figure 3. Example of Displacement-Time graph for a test sample where (A) is the first loading
421
step (10-50 N), (B) is the second loading step (10-100 N), (C) is the third loading step (10-150
422
N) and (D) is the fourth loading (10-200 N).
423
424
Figure 4. Illustration of anchor placement and CP-BSM injection site on cadaveric samples
425
where (A) depicts the decortication window; (B) shows the position and location for anchor
426
placement, and (C) shows the orientation and process for injection CP-BSM.
427 428
Figure 5. Anchor pull-out was predominately the mode of failure in foam block testing model
429
(A) without CP-BSM and (B) with CP-BSM. Similarly, anchor pull-out was the predominate
430
mode of failure in cadaveric testing with (C) CP-BSM and (D) without CP-BSM.
431 432
Figure 6. Cross section to show distribution and anchor interaction. (A) Osteoporotic foam block
433
model, where the red dashed square highlights the imprint of suture anchor threads; and (B) Post-
434
test cross section display the distribution and anchor interaction in cadaveric humeral head.
435
Tables
436
Table 1. Data Summary of Load to Failure, Stiffness and Displacement for Osteoporotic Foam
437
block and Cadaveric Humeri Testing Models Study Group Test
n
Mean Load to Failure, N
Mean Stiffness, N/mm
Suture Anchor (5.5 mm): With CP-BSM
6
332.68 ± 47.61 (282.71-382.65)
50.58 ± 14.74 (35.11-66.05)
Mean Displacement, mm 4.25 ± 2.11 (0.68-4.88)
Suture Anchor (5.5 mm): Without CPBSM
6
144.39 ± 14.56 (129.10-159.70)
26.78 ± 15.66 (10.34-43.21)
2.78 ± 1.99 (2.18-4.85)
Suture Anchor (5.5 mm): With CP-BSM
8
0.001 274.07 ± 102.07 (188.73-359.40)
0.094 109.37 ± 15.65 (96.28-122.45)
0.321 4.26 ± 1.22 (3.24-5.28)
Suture Anchor (5.5 mm): Without CPBSM
8
138.53 ± 109.87 (46.67-230.40)
64.83 ± 51.88 (21.46-108.21)
3.1 ± 1.61 (1.734.43)
0.029
0.043
0.059
Configuration
Osteoporotic Foam Block Model Data
P value
Cadaveric Humeri Model Data
P value
438
NOTE. Data are presented as mean ± s tandard deviation (95% Confidence Interval s ).
S0749-8063(19)31195-8
DOI:
https://doi.org/10.1016/j.arthro.2019.12.003
Reference:
YJARS 56711
To appear in:
Arthroscopy: The Journal of Arthroscopic and Related Surgery
Received Date: 14 July 2019 Revised Date:
4 December 2019
Accepted Date: 5 December 2019
Please cite this article as: Diaz MA, Branch EA, Paredes LA, Oakley E, Baker CE, Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study, Arthroscopy: The Journal of Arthroscopic and Related Surgery (2020), doi: https://doi.org/10.1016/ j.arthro.2019.12.003. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier on behalf of the Arthroscopy Association of North America
1 2
Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength: A Biomechanical Study
3 4
1
Miguel A. Diaz, MS; 2Eric A. Branch, MD;1Luis A. Paredes, BS; 3Emily Oakley, PAC;3Christopher E. Baker, MD†
5 6
1
Foundation for Orthopaedic Research & Education, Tampa, FL, USA
7
2
Department of Orthopaedic Surgery, University of South Florida, Tampa, FL, USA
8
3
Florida Orthopaedic Institute, Tampa, FL, USA
9 10
†Corresponding Author
11
Christopher E. Baker, MD
12
Florida Orthopaedic Institute
13
13020 N. Telecom Parkway
14
Tampa, FL 33637
15
Tel. (813) 978-9700, Ext.6833
16
Fax. (813) 558-6833
17
[email protected]
18 19
Running Title: CP-BSM raises threaded suture anchor fixation
20 21 22
Acknowledgments
23 24 25 26 27
This study was funded by Zimmer Biomet. MAD: Research Grant from Zimmer Biomet (Paid directly to institution1). EAB: has nothing to disclose. LAP: has nothing to disclose. EO: has nothing to disclose. CEB: receives speaking and consulting fees from Zimmer Biomet. All authors discussed results and have participated in writing the manuscript. All authors have read and approved the final submitted manuscript.
28 29 30 31
Research Performed at the Phillip Spiegel Orthopaedic Research Laboratory at the Foundation for Orthopaedic Research and Education, Tampa, FL, 33607 U.S.A
1
Calcium Phosphate Bone Void Filler Increases Threaded Suture Anchor Pullout Strength:
2
A Biomechanical Study
3 4
Abstract
5
Purpose: To compare the response to cyclical loading and ultimate pull-out strength of threaded
6
suture anchor with and without calcium phosphate bone void filler augmentation in a
7
polyurethane foam block model and in vitro proximal humerus cadaveric model.
8 9
Methods: This controlled biomechanical study consisted of 2 parts: (1) preliminary polyurethane
10
foam block model, and (2) in vitro cadaveric humeri model. The preliminary foam block model
11
intended to mimic osteoporotic bone utilizing a 0.12 g/cc foam material. Half of the foam block
12
models were first filled with injectable Calcium Phosphate Bone Substitute Material (CP-BSM)
13
while the other half were not augmented with CP-BSM. Each specimen was then instrumented
14
with a threaded suture anchor. The same technique and process was performed in a matched
15
cadaveric humeri model. Testing then consisted of a step-wise, increasing axial load protocol for
16
a total of 40 cycles. If the anchor remained intact after cyclic loading, the repair was loaded to
17
failure. The number of completed cycles, failure load and failure modes were compared between
18
groups.
19 20
Results: Average pull-out strength for suture anchor with CP-BSM in the osteoporotic foam
21
block model was significantly higher at 332.68 N ± 47.61 compared to the average pull-out
22
strength of suture anchor without CP-BSM at 144.38 N ± 14.58 (p=0.005). In the matched
23
cadaveric humeri model, average pull-out strength for suture anchor with CP-BSM was
1
24
significantly higher at 274.07 N ± 102.07 compared to the average pull-out strength of suture
25
anchor without CP-BSM at 138.53 N ± 109.87 (p=0.029).
26 27
Conclusions: In this time zero, biomechanical study, augmentation of osteoporotic foam block
28
and cadaveric bone with calcium phosphate bone substitute material significantly increases pull-
29
out strength of threaded suture anchors.
30 31
Clinical Relevance: Considering concerns about suture anchor pull-out from osteoporotic bone,
32
augmentation with calcium phosphate bone substitute material increases load to failure
33
resistance.
34
Introduction
35
Arthroscopic rotator cuff repair is a commonly performed surgical intervention to treat patients
36
with painful shoulders due to rotator cuff tears that have failed conservative management. Some
37
patients with known deficiencies in the greater tuberosity (osteoporosis, cysts, prior fractures or
38
prior failed rotator cuff repair) pose a more problematic clinical situation due to poor quality
39
bone not allowing adequate fixation of commonly used suture anchor devices.1,2 Soft tissue or
40
bony fixation failure prior to healing is one of the most common failure mechanisms and
41
represents a significant effect on outcomes.3-7 Generally, arthroscopic rotator cuff repair failure
42
has been shown to commonly occur at the suture-tendon interface.8 However, in osteoporotic
43
bone, bone-anchor interface becomes an increasingly relevant mode of failure.9-11 A recent study
44
by Werner et al12 demonstrated osteoporosis as an independent risk factor affecting postoperative
45
rotator cuff healing, with increased incidence of revision rotator cuff repairs in patients with
46
osteoporosis.
47
Prior biomechanical studies have investigated multiple methods to augment bone when poor
48
bone quality or cysts are encountered during rotator cuff repair: the use of cement, open
49
curettage with bone grafting, increasing the size of the implant, or even stacking multiple
50
anchors to allow for appropriate fixation with variable success.13-15 Braunstein et al.16 described
51
an augmentation technique where polymethylmethacrylate cement is injected into predrilled
52
holes, before the anchor was potted into the injected cement. Moreover, Aziz et al17
53
demonstrated increased pullout strength utilizing polymethylmethacrylate cement injected in situ
54
into a fenestrated suture anchor, similar to techniques found with pedicle screw augmentation in
55
spine surgery.
56 57
AccuFill® Bone Substitute Material (Zimmer Biomet, Exton, PA) is an injectable calcium
58
phosphate bone void filler commonly used in the knee to treat microtrabecular fractures
59
(microdefects) in the subchondral bone. This commercially available injectable Calcium
60
Phosphate Bone Substitute Material’s (CP-BSM) characteristics allow it to be placed
61
percutaneously by a drillable delivery cannula to fill defects or voids in bone without the need to
62
create a macrodefect. Once the material has cured the surgeon can drill into the bone void filler
63
as they would for a standard repair. By implanting CP-BSM into the cancellous bone of the
64
greater tuberosity in patients with deficient bone before rotator cuff repair, it stands to reason that
65
improved fixation may be achieved. A case report has illustrated the viability of this procedure
66
from a surgical technique stand point with negligible increase in operative time or complexity.18
67 68
The purpose of this study was to compare the response to cyclical loading and ultimate pull-out
69
strength of threaded suture anchor with and without calcium phosphate bone void filler
70
augmentation in a polyurethane foam block model and in vitro proximal humerus cadaveric
71
model. We hypothesized that the addition of CP-BSM will significantly increase pull-out
72
strength of threaded suture anchors in both foam block model and proximal humerus cadaveric
73
model.
74 75
Methods
76
This was a time-zero, controlled biomechanical study consisting of 2 parts: (1) a preliminary
77
polyurethane foam block model and (2) an in vitro cadaveric humeral model. All tested
78
constructs utilized a threaded, 5.5 mm Quattro® X PEEK (polyetheretherketone) Suture Anchor
79
(Zimmer Biomet, Scottsdale, AZ) which requires the anchor to be screwed-in for fixation after
80
drilling or taping a pilot hole. The suture anchors were double loaded with No.2 Force Fiber®, a
81
high strength, ultra-high molecular weight polyethylene suture. In the preliminary foam block
82
testing model, the American Society for Testing and Materials (ASTM) F-1839 was followed
83
and a 0.12 g/cc [ 7.5 pound-force per cubic foot (PCF)] foam density material (Pacific Research
84
Laboratories, Vashon, WA) was chosen to represent osteoporotic bone density.19-23
85 86
Polyurethane Foam Block: Osteoporotic Model Testing
87
A total of twelve 0.12 g/cc rigid polyurethane foam blocks were used for testing. Individual
88
blocks were cut to 5 cm x 5 cm x 4 cm cubes. The control group (threaded suture anchor only, 6
89
foam blocks) had the threaded suture anchor inserted into unaltered foam blocks. The
90
experimental group (threaded suture anchor plus CP-BSM, 6 foam blocks) had the threaded
91
suture anchor inserted into foam blocks after augmentation with calcium phosphate bone void
92
filler.
93
94
For both groups, the center point of each test sample, relative to designated top surface was
95
identified and marked. Samples in the control group were only instrumented with a 5.5 mm
96
suture anchor per manufacturer recommendations. To standardize trajectory of the suture anchor,
97
a 2.0 mm pilot hole was created using a drill press, assuring the pilot hole was perpendicular to
98
surface. Samples in the experimental group were injected with 5cc of CP-BSM before the suture
99
anchor was instrumented. The CP-BSM injection site was 10 mm down along the mid-section of
100
the lateral face of foam block (Figure 1). The depth of the cannula was approximately 24 mm to
101
ensure placement of the CP-BSM into the area where the anchor would be placed. After
102
implantation of CP-BSM, a therapeutic heating pad was used to bring the foam blocks above
103
body temperature (98.6°F) for the curing process to begin. Foam blocks with CP-BSM were kept
104
above 98.6°F for 10 minutes before the suture anchors were instrumented. A 2.0 mm pilot hole
105
was created along the marked center point and into the area filled with CP-BSM, where the
106
anchors were instrumented per manufacturer recommendations.
107 108
Biomechanical testing was performed on the same day of instrumentation to test the immediate
109
pull-out strength of the implanted suture anchor. A custom fixture was built and fixed to the base
110
of a servo-hydraulic materials testing machine (MTS Bionix, MTS Inc., Eden Prairie, MN)
111
equipped with a 5kN load cell (MTS Inc.) (Figure 2A). To ensure that the samples were properly
112
aligned in the plane of testing, the base of the fixture design allowed one to freely position (X-Y
113
plane) a sample in such orientation to allow the direction of force to be in-line with the axis of
114
suture anchor (uniaxial tensile testing). Sutures were hand tied around a 1.27 cm diameter
115
cylinder with five alternating half-hitch knots, assuring equal lengths. The loop was then secured
116
through a 6.35 mm (¼”) anchor shackle with a working load limit of 453.6 kg (1000 lbs.) and
117
coupled to the load cell. Once the samples were properly aligned, a small preload (< 0.5 N) was
118
applied to remove the slack from the system before testing, which was confirmed through tactile
119
and visual inspection. Testing consisted of a step-wise and increasing load protocol.10,24,25 Each
120
specimen was tested under axial loading rate of 1 mm/s consisting of 4 cyclic loading profiles of
121
increasing tension: 10 – 50 N for 10 cycles, 10 – 100 N for 10 cycles, 10 – 150 N for 10 cycles
122
and 10 – 200 N for 10 cycles, for a total of 40 cycles (Figure 3). If the anchor remained intact
123
after cyclic loading, the repair was loaded to failure at 1 mm/s.
124 125
Cadaveric Testing Model
126
Ten cadavers (8 males and 2 females; average weight 83.9 ± 20kg) with bilateral shoulders were
127
studied with the right shoulder being designated for anchor placement with CP-BSM and the
128
matched left shoulder being designated for anchor placement without CP-BSM. Specimen ages
129
ranged from 48 to 91years (mean, 71 years). Each humerus was stripped of soft tissues and
130
shortened to a 20 cm length as measured from the apex of the humeral head. The distal diaphysis
131
was potted in high strength resin (Bondo Body Filler, 3M Collision Repair Solutions, St. Paul,
132
MN). For both groups, a 1 cm x 2 cm window was outlined along the superior facet of the
133
greater tubercle with black marker to serve as decortication guideline for each sample.
134
Decortication has been shown to significantly decrease pull-out strength of suture anchors in
135
both humeri and femur.11,25,26 To create a worst-case scenario, 5 mm of decortication was
136
performed on all samples by using a highspeed 3-mm burr within guidelines. To standardize
137
trajectory of the suture anchor, the samples were clamped in a specialized vice at 45° (measured
138
by digital goniometer) and the anchor was placed perpendicular to the surface. All anchors were
139
placed centrally within decorticated footprint, 5 mm from anatomical neck line and 1cm from
140
edge. Samples in the control group were only instrumented with a 5.5 mm suture anchor per
141
manufacturer recommendations. Samples in the experimental group were injected with 5cc of
142
CP-BSM before suture anchor was instrumented. The CP-BSM injection site was placed
143
centrally within decorticated footprint, 5 mm from anatomical neck line and 1 cm from edge.
144
The depth of the cannula was approximately 24 mm from the cortical surface (Figure 4). After
145
implantation of CP- BSM, a therapeutic heating pad was used to bring the samples above body
146
temperature (98.6°F) for the curing process to begin. Samples with CP-BSM were kept above
147
98.6°F for 10 minutes before the suture anchors were instrumented. Placement of suture anchor
148
was directly into the cured CP-BSM.
149 150
As with the foam block model, biomechanical testing was performed on the same day of
151
instrumentation to test the immediate pull-out strength of suture anchor. A custom fixture was
152
built and fixed to the base of the servo-hydraulic materials testing machine equipped with the
153
same load cell and anchor shackle (Figure 2B). Similar to the foam block fixture, the design
154
allows for consistent sample placement and the degree of freedom to align the suture anchor
155
construct line of axis with direction of force. The additional degrees of freedom in the X-Z and
156
Y-Z plane allowed the cadaveric samples to be positioned such that the suture and suture anchor
157
were loaded perpendicularly, relative to the bone surface. Suture tying protocol and loading
158
protocol were identical to those used for foam block testing. (Step-wise cyclic loading, followed
159
by ramp to failure).
160 161
For both foam block and cadaveric testing, the force data collected by MTS load cell and
162
displacement data collected by the system linear variable differential transducer (LVDT) were
163
used to create force-displacement curves (F-d curve). The F-d curve were used to identify failure
164
load, failure displacement and stiffness. Failure was defined as the first significant decrease in
165
the monotonically increasing force profile, where pull-out strength was defined as the peak load
166
at failure. Peak load for each specimen was recorded whether failure occurred during or after
167
cyclic loading. Failure displacement was measured as the difference between displacement at
168
failure and displacement prior to monotonically increasing force. Stiffness was defined as the
169
linear portion of the F-d curve. The primary focus of this study was to compare pull-out strength
170
(peak load) between groups. Secondary data such as stiffness and failure displacement were also
171
collected and analyzed.
172 173
Power Analysis
174
Using mean and variance data from prior studies of similar scope19,27,28 a priori power of 0.80
175
with a Type I error rate of 0.05 was used to calculate appropriate sample size using G*Power
176
(V3.1.9.2, Franz Faul, Germany). For the foam block testing, with an effect size (Cohen’s d) of
177
1.6, a sample size of 6 foam blocks per group was necessary to detect an increase in pullout force
178
between groups. Similarly, with an effect size (Cohen’s d of 1.2), a sample size of 8 matched
179
pairs of humeri was necessary to anticipate biomechanically and clinically relevant increase in
180
pullout force in the CP-BSM augmented repairs.
181 182
Statistical Analysis
183
The Shapiro-Wilk normality test was performed on all data confirming normal distribution. In
184
both foam block and cadaveric model, parametric statistics were used to evaluate data. A
185
univariate ANOVA was performed on demographic data (Age, Sex, Weight) between two testing
186
groups and no statistical difference was found. A paired sample T-test was performed to identify
187
differences in pull-out strength between the control group and experimental group. Stiffness and
188
displacement data were also analyzed with paired sample T-test. Data is presented as mean ±
189
standard deviation (SD). All statistical comparisons were performed with SPSS (v22, IBM, NY,
190
USA) at a significance level of α=0.05.
191
Results
192
Osteoporotic Foam Block Model
193
All samples in experimental group (with CP-BSM) completed the 40 cycles before ramp to
194
failure. The average pull-out strength for suture anchor with CP-BSM (experimental group;
195
332.68 ± 47.61 N) was found to be significantly higher (P=0.001) than the average pull-out
196
strength of suture anchor without CP-BSM (control group; 144.39 ± 14.56 N) . In the control
197
group (without CP-BSM), all samples failed within a loading level, where 67% of the samples
198
failed at Load Level 3, completing only 20 cycles, and the remaining 33% failed at Load Level 4,
199
completing 30 cycles. The construct stiffness at failure for the experimental group (50.58 ± 14.74
200
N/mm) was larger than the control group (26.78 ± 15.66 N/mm), however this difference was not
201
statistically significant. Similarly, the failure displacement between the experimental group and
202
control group were not statistically significant, 4.25 ± 2.11 mm and 2.78 ± 1.99 mm, respectively
203
(Table 1).
204 205
The modes of failure in the low-density foam block model were predominately anchor pull-out
206
(Figure 3). Those augmented with CP-BSM also experienced anchor pull-out (83%), though
207
there was one instance where failure occurred at the suture anchor eyelet (suture pulled cleanly
208
through the anchor leaving the anchor intact within the specimen)..
209 210
Cadaveric Humeri
211
In the control group (without CP-BSM), two humeri had to be removed from analysis due to
212
severe osteoporosis which was observed during instrumentation of suture anchor where loss of
213
fixation occurred prior to loading the first cycle (<10N). The matched pairs of these humeri, in
214
the experimental group, first implanted with CP-BSM, although not included in statistical
215
analysis, were still tested and showed pullout strengths similar to other specimens tested, 329 N
216
and 200 N. Therefore, only 8 matched pairs (n=16) were used for statistical analysis, maintaining
217
statistical power.
218 219
The average pull-out strength for suture anchor with CP-BSM (experimental group; 274.07 ±
220
102.07 N) was significantly higher (P=0.029) compared to the average pull-out strength of suture
221
anchor without CP-BSM (control group; 138.53 ± 109.87 N) . The construct stiffness at failure
222
in the experimental group was significantly larger than that of the control group, 109.37 ± 15.65
223
N/mm and 64.83 ± 51.88 N/mm, respectively (P=0.043). The difference in failure displacement
224
between experimental and control group was not statistically significant, 4.26 ± 1.22 mm and 3.1
225
± 1.66 mm, respectively (Table 1). In the experimental group, 75% (6/8) survived all four testing
226
conditions where the remaining 12.5% (1/8) failed in the third load step and 12.5% (1/8) failed in
227
the fourth load step. Only 25% (2/8) of the control group survived all four testing conditions. The
228
remaining 37.5% (3/8) failed in the first load step, 12.5% (1/8) failed in second load step, and
229
25% (2/8) in the fourth load step.
230 231
The modes of failure were predominately anchor pull-out for both testing groups (Figure 5).
232
Those augmented with CP-BSM also experienced suture rupture and one instance where failure
233
occurred at anchor eyelet. Cross sections of the experimental group were taken to demonstrate
234
penetration of calcium phosphate and thread interaction (Figure 6).
235 236
Discussion
237
This study supports our hypothesis, demonstrating that augmenting an osteoporotic foam block
238
model (0.12 g/cc) with 5cc of CP-BSM can provide threaded suture anchors significantly higher
239
load to failure (332.68 N ± 47.61; P=0.005) than threaded suture anchors without the use of CP-
240
BSM (144.38 N ± 14.58). This study also supports our hypothesis regarding cadaveric testing.
241
Though not the primary focus of this study, no significant differences in stiffness and failure
242
displacement between study groups in foam block testing were noted. In the cadaveric testing,
243
stiffness was found to be significantly larger in anchors augmented with CP-BSM compared to
244
anchors without CP-BSM. However, no significant difference was detected between failure
245
displacement.
246 247
Based on previous biomechanical studies, 0.12 g/cc foam block was chosen to represent poor
248
bone quality.19-23 Bone quality is one of the many factors shown to influence suture anchor
249
resistance to pull-out and may lead to a compromised rotator cuff repair.17,29 Horoz et al30
250
evaluated various anchor techniques to evaluate which was suitable for osteoporotic bone, while
251
Barber et al27,28 concluded that failure load was dependent on anchor type and not anchor
252
location (cancellous or cortical bone). Despite the conflicting data in literature, there is still a
253
need to improve suture anchor fixation in patients with compromised bone quality.
254
For cadaveric testing, we followed a matched-pair design, with the assumption that bone density
255
is equal within specimen pair allowing for comparable testing between the two testing groups.
256
Decortication has been shown to adversely affect suture anchor pull-out strength.24,26 Ruder et
257
al26 performed greater tuberosity decortication to a mean depth of 1.7 mm and reported a
258
significant difference in ultimate load to failure for the decorticated and non-decorticated cohorts
259
to be 314 N and 386 N, respectively. Similarly, Hyatt et al24 studied the effects of decortication
260
(mean depth of 5.6 mm) and reported a significant decrease in ultimate load to failure from 244
261
N to 63 N in decorticated specimens.
262 263
To create a worst-case, osteoporotic model, we decorticate all cadaveric specimens, mean depth
264
was 5 mm, to reduce ultimate load to failure. Interestingly, the ultimate failure loads of both
265
testing groups in cadaveric specimens closely resemble those of the osteoporotic foam block
266
model, adding validation to the choice of using 0.12 g/cc foam block to represent osteoporotic
267
bone. Joo Han Oh et al22 studied the effect of the insertion and traction angle on suture anchor
268
pull-out strength and performed preliminary tests on two synthetic bone models (Osteoporotic
269
[0.16 g/cc; 10 PCF] and Non-osteoporotic [0.32 g/cc; 20 PCF]). They found a significant
270
difference (P<0.001) in ultimate load to failure between the osteoporotic model (181.9 N ± 13.7)
271
and the non-osteoporotic model (403.7 N ± 22.3). While these two studies are not directly
272
comparable, it can be concluded that decorticating effectively reduced the ultimate load to failure
273
of suture anchor to a level comparable to an osteoporotic surrogate model.
274 275
Barber et al27 evaluated the biomechanical and design characteristics of several suture anchors in
276
a porcine model, of which the 5.5 mm Quattro X suture anchor was tested. They reported the
277
mean failure force of the Quattro X suture anchor (5.5 mm) in porcine cortical bone was 370.6 N
278
± 26.8 and 384.0 N ± 21.3 in cancellous bone. While direct comparison between our data and
279
Barber et al is difficult to do because of varying test medium, the pull-out strength achieved by
280
anchor with calcium phosphate in 0.12 g/cc foam block and cadaveric model are in the lower
281
testing range.
282
283
Tingart et al10 studied different anchor designs in poor bone quality and the effect on pull-out
284
strength. They found the mean pull-out strength of metal screw-type anchors was 273 ± 99 N in
285
proximal region of greater tuberosity and 184 ± 54 N in distal region of greater tuberosity,
286
whereas the biodegradable hook-type anchors had 162 ± 25 N and 112 ± 30 N, respectively.
287
Interestingly, the pull-out strength of threaded anchors with CP- BSM in the current study fall
288
within range of non-decorticated groups and those of metal screw-type anchors in poor bone
289
density presented by Tingart et al10.Anecdotally, tactile feedback is often used by Surgeons to
290
test the quality of a repair. This form of measurement is difficult to quantify due to high
291
subjectivity, but samples in both testing models (osteoporotic foam block and cadaveric) with
292
CP-BSM were observed to have a better ‘bite’; similar to the resistance expected in patients with
293
denser bone quality. The purpose of this biomechanical study was to evaluate the pull-out
294
strength of standard threaded anchors placed with and without the implantation of calcium
295
phosphate bone void filler in a rigid polyurethane foam block model and in a cadaveric humeri in
296
vitro model. Along with the successful use of CP-BSM for arthroscopic cuff repair in
297
osteoporotic patients18, the data presented in this study may improve clinical outcomes, though
298
the effect on repair healing is still unknown.
299 300
Limitations
301
This study is not without its limitations. One limitation was the inability to quantitatively
302
measure the bone density of each matched-pair donor. By decorticating all the samples, we
303
sought to reduce the ultimate load to failure to a level comparable to poor bone density.
304
Moreover, the study did not attempt comparisons of various anchor type or material. Another
305
limitation was the depth of decortication. Our model has a mean depth of 5 mm, which is quite
306
aggressive compared to the mean depth of 1.7 mm seen in Ruder et al26, but comparable to the
307
mean depth of 5.6 mm seen in Hyatt et al24. Both Ruder et al26 and Hyatt et al24 showed a
308
significant difference between suture anchor pull-out strengths in non-decorticated and
309
decorticated humeri. Furthermore, analysis of the secondary data of stiffness and failure
310
displacement were found to be under powered, however the difference in pull-out strength was
311
not. Lastly, this study represents time-zero biomechanical load study and does not address
312
change in pull-out strength over time (repair healing).
313 314
Conclusion
315
In this time zero, biomechanical study, augmentation of osteoporotic foam block and
316
decorticated cadaveric bone with calcium phosphate bone substitute material significantly
317
increases pull-out strength of threaded suture anchors.
318 319 320
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321
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Frank JB, El Attrache NS, Dines JS, Blackburn A, Crues J, Tibone JE. Repair site
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Tingart MJ, Apreleva M, Lehtinen J, Zurakowski D, Warner JJ. Anchor design and bone
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Yakacki CM, Poukalova M, Guldberg RE, Lin A, Saing M, Gillogly S, Gall K. J. The
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Werner, Cancienne, Brockmeier, Kew, Deasey, and Werner. The Association of
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anchor fixation. Clin Orthop Relat Res. 2006;451:236-241. 14.
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Giori NJ, Sohn DH, Mirza FM, Lindsey DP, Lee AT. Bone cement improves suture
Brady PC, Arrigoni P, Burkhart SS. What do you do when you have a loose screw? Arthroscopy. 2006;22:925-930.
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Burkhart SS, Klein JR. Arthroscopic repair of rotator cuff tears associated with large
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Braunstein, B. Ockert, M. Windolf, et al.Increasing pullout strength of suture anchors in
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Aziz KT1, Shi BY2, Okafor LC3, Smalley J4, Belkoff SM5, Srikumaran U6. Pullout
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strength of standard vs. cement-augmented rotator cuff repair anchors in cadaveric bone.
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Er MS, Altinel L, Eroglu M, Verim O, Demir T, Atmaca H. Suture anchor fixation
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strength with or without augmentation in osteopenic and severely osteoporotic bones in
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rotator cuff repair: a biomechanical study on polyurethane foam model. J Orthop Surg
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Thompson MS, McCarthy ID, Lidgren L, Ryd L. Compressive and Shear Properties of
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Standard Specification for Rigid Polyurethane Foam for Use as a Standard Material for
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Testing Orthopaedic Devices and Instruments, ASTM F1839-08(2016). West
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Conshohocksen, PA: ASTM International; 2016.
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Oh JH, Jeong HJ, Yang SH, et al. Pullout Strength of All-Suture Anchors: Effect of the Insertion and Traction Angle-A Biomechanical Study. Arthroscopy. 2018;34:2784-2795.
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Patel PS, Shepherd DE, Hukins DW. Compressive properties of commercially available
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Hyatt AE, Lavery K, Mino C, Dhawan A. Suture Anchor Biomechanics After Rotator Cuff Footprint Decortication. Arthroscopy. 2016;32:544-550.
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Putnam JG, Chhabra A, Castaneda P, et al. Does Greate Trochanter Decortication Affect
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Suture Anchor Pullout Strength in Abductor Tendon Repairs? Am J Sports Med.
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2018;46(7):1668-1673.
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Ruder JA, Dickinson EY, Peindl RD, Habet NA, Fleischli JE. Greater tuberosity
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decortication decreases load to failure of all-suture anchor constructs in rotator cuff
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repair. Arthroscopy: The Journal of Arthroscopic & Related Surgery. 2018;34:2777-
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Barber FA, Herbert MA. Cyclic loading biomechanical analysis of the pullout strengths of rotator cuff and glenoid anchors: 2013 update. Arthroscopy. 2013;29:832-844.
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Barber FA, Herbert MA. All-Suture Anchors: Biomechanical Analysis of Pullout Strength, Displacement, and Failure Mode. Arthroscopy. 2017;33:1113-1121.
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Postl LK, Ahrens P, Beirer M, et al. Pull-out stability of anchors for rotator cuff repair is
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also increased by bio-absorbable augmentation: a cadaver study. Arch Orthop Trauma
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Surg. 2016;136:1153-1158.
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Horoz L, Hapa O, Barber FA, Husemoglu B, Ozkan M, Havitcioglu H. Suture Anchor
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Fixation in Osteoporotic Bone: A Biomechanical Study in an Ovine Model. Arthroscopy.
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2017;33:68-74.
406 407 408 409
Figure Legends
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Figure 1. Illustrations of anchor placement and CP-BSM injection site on foam block sample
411
where (A) is a 3D representation of Anchor placement and insertion of CP-BSM; (B) Sample
412
with cannula inserted to a depth of 24 mm; (C) Sample with cured CP-BSM being prepped; and
413
(D) Example of anchor instrumented into foam block augmented with CP-BSM.
414 415
Figure 2. Testing fixture allowing for X-Y adjustment (blue and orange arrows) and rotation
416
(green arrow) for specimen alignment. Direction of pull is colinear to anchor placement. (A)
417
Illustrates the mechanical test set-up for foam blocks model while (B) illustrates test set-up for
418
cadaveric model.
419 420
Figure 3. Example of Displacement-Time graph for a test sample where (A) is the first loading
421
step (10-50 N), (B) is the second loading step (10-100 N), (C) is the third loading step (10-150
422
N) and (D) is the fourth loading (10-200 N).
423
424
Figure 4. Illustration of anchor placement and CP-BSM injection site on cadaveric samples
425
where (A) depicts the decortication window; (B) shows the position and location for anchor
426
placement, and (C) shows the orientation and process for injection CP-BSM.
427 428
Figure 5. Anchor pull-out was predominately the mode of failure in foam block testing model
429
(A) without CP-BSM and (B) with CP-BSM. Similarly, anchor pull-out was the predominate
430
mode of failure in cadaveric testing with (C) CP-BSM and (D) without CP-BSM.
431 432
Figure 6. Cross section to show distribution and anchor interaction. (A) Osteoporotic foam block
433
model, where the red dashed square highlights the imprint of suture anchor threads; and (B) Post-
434
test cross section display the distribution and anchor interaction in cadaveric humeral head.
435
Tables
436
Table 1. Data Summary of Load to Failure, Stiffness and Displacement for Osteoporotic Foam
437
block and Cadaveric Humeri Testing Models Study Group Test
n
Mean Load to Failure, N
Mean Stiffness, N/mm
Suture Anchor (5.5 mm): With CP-BSM
6
332.68 ± 47.61 (282.71-382.65)
50.58 ± 14.74 (35.11-66.05)
Mean Displacement, mm 4.25 ± 2.11 (0.68-4.88)
Suture Anchor (5.5 mm): Without CPBSM
6
144.39 ± 14.56 (129.10-159.70)
26.78 ± 15.66 (10.34-43.21)
2.78 ± 1.99 (2.18-4.85)
Suture Anchor (5.5 mm): With CP-BSM
8
0.001 274.07 ± 102.07 (188.73-359.40)
0.094 109.37 ± 15.65 (96.28-122.45)
0.321 4.26 ± 1.22 (3.24-5.28)
Suture Anchor (5.5 mm): Without CPBSM
8
138.53 ± 109.87 (46.67-230.40)
64.83 ± 51.88 (21.46-108.21)
3.1 ± 1.61 (1.734.43)
0.029
0.043
0.059
Configuration
Osteoporotic Foam Block Model Data
P value
Cadaveric Humeri Model Data
P value
438
NOTE. Data are presented as mean ± s tandard deviation (95% Confidence Interval s ).