Biomechanical Effects of Partial Decortication on All-Suture and Conventional Suture Anchors in Different Bone Densities

Summary

Here, we describe a protocol to evaluate biomechanical effects of partial decortication on all-suture anchors (ASAs) and conventional suture anchors (CAs) in Sawbones of varying densities.

Abstract

While biomechanical testing has shown a correlation between decortication and anchor failure load, the effects of partial decortication on the biomechanical properties of all-suture anchors remain unclear. We aimed to evaluate the biomechanical effects of partial decortication on all-suture anchors and conventional suture anchors in Sawbones of varying densities. Suture anchors were tested in nondecorticated, partially decorticated, and completely decorticated Sawbones. Two types of all-suture anchors and one type of conventional anchor were evaluated. Two types of biphasic polyurethane foam were used to mimic normal bone: 0.32 g/cm³ density (20 pounds per cubic foot, pcf 20) and osteoporotic bone: 0.16 g/cm³ density (10 pounds per cubic foot, pcf 10). Cyclic loadings were applied, and peak displacement was recorded. After cyclic loading tests, surviving anchors were subjected to pull-to-failure tests. The number of cycles, peak displacement, ultimate failure loads, and failure modes were determined.

First, peak displacement was significantly influenced by bone density and anchor type: normal bone models exhibited lower peak displacement than osteoporotic models, and conventional screw-type anchors consistently demonstrated reduced peak displacement compared to all-suture anchors. In contrast, the extent of bone decortication-whether non-decorticated, partially decorticated, or completely decorticated-showed no significant effect on peak displacement. Second, in osteoporotic bone models (10 pounds per cubic foot), no significant difference in failure load was observed between the partially and non-decorticated groups, but both exhibited significantly higher values than the completely decorticated group.

Introduction

Rotator cuff tears are the most common cause of shoulder pain, and arthroscopic rotator cuff repair is the primary treatment option owing to its satisfactory clinical outcomes. Suture anchors play a crucial role in this procedure. Advancements in suture anchors have contributed to improved anchoring stability and enhanced healing rates^1,2,3. All-suture anchors (ASAs) are a newer type of anchors that primarily consist of two components: the suture material and sheath^4,5. Upon insertion into the bone, anchors are deployed by tensioning the suture material of the ASAs to cinch the sheath into various shapes, with the sleeve compressed against the cortical bone^3,6. Compared to conventional suture anchors (CAs), ASAs allow for smaller bone tunnels, enabling increased points of fixation and less bone disruption^7,8. Consequently, these anchors are increasingly being favored in surgical practice.

Decortication of the rotator cuff footprint, a widely adopted technique in rotator cuff repair, facilitates tendon-bone healing by liberating endogenous bone marrow material⁹. Decortication is commonly performed to enhance the healing response at the tendon-bone suture anchor repair site. Introduced by McLaughlin et al.¹⁰ in 1944, this technique involves creating a trough of bleeding bone to promote healing during rotator cuff repair by inducing the infiltration of mesenchymal stem cells, which contribute to bone microvascularization at the tendon interface⁹. Partial decortication involves preserving the cortical bone surrounding the suture anchor, with the width of the region of preservation matching the diameter of the anchor. The remaining cortical bone is removed to complete the decortication procedure. This method aims to maintain sufficient cortical bone for anchor stability while facilitating the benefits of decortication.

Notably, unlike CAs, ASAs rely significantly on cortical bone for fixation^3,6. This reliance poses a challenge, as decortication can diminish the pullout strength of ASAs^11,12. This requires the effects of decortication to be balanced during rotator cuff repair, which is potentially addressed by partial decortication. ASAs are designed with force-fit anchoring mechanisms that require secure placement beneath an intact cortical surface, and there has always been a concern regarding the effects of decortication on the biomechanical properties of ASAs^11,12,13,14. Ruder et al.¹¹ evaluated the effects on displacement after cyclic loading and on failure load of ASAs and found that decortication significantly decreased the failure load without significantly affecting the mean displacement. Similarly, a recent biomechanical study by Natlos et al.¹² quantitatively measured cortical thickness using Micro-computed tomography in a human cadaveric shoulder model. Their results demonstrated a strong correlation between the pullout strength of ASAs and adjacent cortical thickness (P < 0.05).

Biomechanical testing has shown a correlation between decortication and anchor failure load, but the implications of partial decortication on the biomechanical properties of ASAs remain unclear owing to the limited literature^11,12. Therefore, this study aimed to assess the effects of partial decortication on the biomechanical properties of both ASAs and CAs and compare the mechanical properties of ASAs and CAs.

Protocol

This study utilized synthetic bone models. No human or animal subjects were involved, and ethical approval was not required.

1. Suture anchor preparation

NOTE: Store anchors in dry, room-temperature conditions until use. Commercial identifiers are provided in the Table of Materials.

1. Prepare three anchor types.
   1. Select the All-Suture Anchor 1 (ASA1 = UHT). To follow this protocol, ensure that ASA1 consists of a flat braided ultra-high molecular weight polyethylene (UHMWPE) tube threaded with the UHMWPE suture, with a predilatation drill diameter of 2.8 mm that expands to 4.5 mm.
      NOTE: Its structural feature is a collapsible cylindrical construct forming subcortical sphere upon tensioning.
2. Select the All-Suture Anchor 2 (ASA2 = Y-Knot). To follow this protocol, ensure that ASA2 concists of a flat braided ultra-high molecular weight polyethylene (UHMWPE) tube threaded with the UHMWPE suture, with a predilatation drill diameter of 2.8 mm that expands to 5.0 mm.
   NOTE: Its structural feature is a collapsible cylindrical construct forming subcortical sphere upon tensioning.
3. Select the Conventional screw-type anchor (CA = Biocorkscrew). To follow this protocol, ensure that CA is made of polyetheretherketone (PEEK) with a screw of 4.5 mm outer diameter.
   NOTE: Its structural feature is the fully threaded design.

2. Bone model preparation

1. Bone model selection
   1. Use synthetic bone owing to its biomechanical properties being comparable to those of cadaveric bone.
2. Material composition
   1. Use two types of biphasic polyurethane foam: normal bone: 0.32 g/cm³ density (20 pounds per cubic foot, pcf 20) and osteoporotic bone: 0.16 g/cm³ density (10 pounds per cubic foot, pcf 10)^15,16.
      NOTE: The manufacturing process preapplies the 3 mm-thick, short-fiber-filled epoxy coating to only one surface of the polyurethane foam blocks as an integral component of the commercially manufactured material. The coated side simulates cortical bone, while the uncoated porous polyurethane foam simulates cancellous bone^8,16,17.
3. Random group assignment
   NOTE: See step 2.4 for the decortication procedure.
   1. Randomize bone blocks into three decortication groups using a computer-generated sequence:
      1. For the ND (No Decortication) group, do not perform any decortication.
      2. For the PD group (Partial Decortication) group, perform decortication at 2.5 mm from the suture anchor insertion point.
      3. For the CD group (Complete Decortication) group, carry out full decortication of the bone model.
         NOTE: The 2.5 mm offset corresponds to the all-suture anchor radius, ensuring decortication outside its expansion zone without deployment interference.
4. Decortication procedure (Figure 1):
   1. Mount a 5.5 mm round burr on a computer-assisted grinding tool (See the Table of Materials).
   2. Open the three-axis grinding tool control software (See the Table of Materials)
   3. Press the emergency reset button until the indicator light stops flashing.
   4. Click Load G-code and select the preconfigured machining file.
   5. Press the TAB key to activate the manual control mode.
   6. Use the arrow keys to move the toolhead to the starting position.
   7. Press TAB again to exit manual mode.
   8. Click the Zero button to reset all axes (X, Y, Z, A) to 0.000 mm.
   9. Click Cycle Start to initiate bone surface polishing.
      NOTE: The use of the computer-assisted grinding tool requires careful handling to avoid injury. Proper protective equipment, including safety goggles and gloves, should be worn at all times. Ensure the emergency stop button remains accessible during operation.

3. Implant placement

1. Insert all anchors following the manufacturers' specifications: insert the ASAs perpendicular to the bone block surface and the CAs at a 45° angle.
2. Create pilot holes using a drill guide.
3. Position ASA anchors perpendicular to the bone surface (see the Table of Materials for details about suture anchors used in the protocol).
4. Insert CA anchors at a 45° angle relative to the bone surface (see the Table of Materials for details about suture anchors used in the protocol).
   NOTE: Deploy ASA anchors until a sudden drop in resistance is felt (indicating anchor expansion completion), confirmed by visual alignment of the laser marker on the inserter with the cortical surface. Discard models with visible insertion anomalies.

4. Testing conditions

1. Biomechanical testing setup
   1. Conduct biomechanical testing using a mechanical testing machine (Table of Materials).
      1. Secure synthetic bone blocks in a purpose-built jig to align anchor sutures with the actuator arm (Figure 2).
      2. Orient the bone block's long axis at 135° relative to the load actuator.
         NOTE: The 135° orientation simulates physiological tension conditions of the supraspinatus tendon in postrepair scenarios, as established in prior biomechanical studies^7,13.
2. Suture attachment
   1. Secure suture strands manually around a circular hook attached to the testing machine.
   2. Tie a surgeon's knot and reinforce with four alternating half-hitches.
   3. Maintain a 100 mm distance between the suture anchor and the hook.
      NOTE: Refer to Figure 2 for a schematic of the testing setup.
3. Preload application
   1. Ramp to 10 N at 1 N/s¹¹.
   2. Hold for 5 s to establish zero displacement baseline.
4. Cyclic loading
   1. Launch the mechanical test console software (see the Table of Materials).
   2. Navigate to the Test Setup tab on the main interface.
   3. Click New Project in the upper toolbar to initialize a test sequence.
   4. Within the Test Method Library, locate and select the preconfigured Cyclic Testing method.
   5. Define zero displacement position during preload application.
   6. Program the mechanical tester to apply 10-60 N load at 1 Hz frequency.
   7. Click the Start button (green icon) in the upper-right corner to initiate the cyclic loading protocol.
   8. Run 200 consecutive cycles.
   9. Monitor real-time cyclic load-displacement curves in the left-side graphical output panel.
   10. Export displacement-time data to the connected acquisition software (.xls format).
5. Pull-to-failure testing
   1. Launch mechanical test console software (see the Table of Materials).
   2. Navigate to the Test Setup tab on the main interface.
   3. Click New Project in the upper toolbar to initialize a test sequence.
   4. Within the Test Method Library, locate and select the preconfigured Anchorage Failure Test method.
   5. Set the displacement rate to 33 mm/s.
   6. Click the Start button (green icon, upper-right corner) to initiate the failure protocol.
   7. The failure load data is automatically recorded in the spreadsheet and can be viewed directly. Export failure load-time data to the connected acquisition software (.xls format).
   8. Classify failure modes as:
      1. Type I: Anchor pullout: displacement of the anchor from the bone due to insufficient fixation force or compromised bone density, typically seen in osteoporotic conditions.
      2. Type II: Suture cutout: structural failure where the suture cuts through the anchor's eyelet or the eyelet fractures, leading to suture displacement or tissue penetration.
      3. Type III: Suture strand breakage: rupture of the suture material caused by excessive tension^8,18.

Results

Cyclic testing
In the CD group, one UHT anchor and three Y-Knot anchors failed on being pulled out from the pcf 10 testing blocks. In the PD group, one Y-Knot anchor failed when pulled out from the pcf 20 testing blocks. In the ND group, all the anchors survived the cyclic testing.

The peak displacements during the cyclic testing are listed in Table 1. Notably, no significant differences in peak displacement were observed among the ND, PD, and CD groups, r...

Discussion

This study analyzed the effects of decortication on the biomechanical performance of suture anchors by examining two types of ASAs and one type of CA in bone blocks of varying densities. Peak displacement was influenced by bone density (lower in normal bone models) and anchor type (lower in conventional screw-type anchors), while decortication extent showed no significant influence. In osteoporotic models, failure loads between partially decorticated and non-decorticated groups showed no significant difference, yet both ...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Biocorkscrew	Arthrex, Naples, USA	AR-1927bcf-45	Conventional screw-type suture anchor (CA)
Bluehill Universal	Norwood, MA, USA	E10KNBL5086	Mechanical test console software
Computer Numerical Control 2030 Engraving Machine	JPX Technology Co., Shenzhen, China	JD2030F400W	Computer-assisted grinding tool
Instron, E10k,	Norwood, MA, USA	E10KNBL5086	Mechanical testing machine
Mach3Mill	ArtSoft Corporation, Sarasota, FL,USA	Mach3 R3.043.066	3-axis CNC control software
Pcf 10 Sawbone	Pacific Research Laboratories, Vashon, WA, USA	1522-319	Osteoporotic bone model
Pcf 20 Sawbone	Pacific Research Laboratories, Vashon, WA, USA	1522-315	Normal bone model
UHT	Star, Beijing, China	F19000001	All-suture anchors 2 (ASA 1)
Y-Knot RC	ConMed, New York, USA	YPRC02	All-suture anchors 1 (ASA 2)