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Editorial Commentary: Are All-Suture Anchors as Good as Conventional Anchors?
Editorial Commentary: Are All-Suture Anchors as Good as Conventional Anchors? F. Alan Barber, M.D., Associate Editor Emeritus
Abstract: Research in this issue, like other biomechanical testing, suggests that the all-suture anchors studied here seem strong enough for glenoid and acetabular applications. Testing suture anchors in nonbiologic material may be problematic unless that material is validated or there is a control. The cyclic loads used influence the data, and oscillating between 10 and 50 N does not allow for sufficient anchor performance differentiation. The next question is whether there will be any adverse events associated with the use of all-suture anchors clinically.
See related article on page 977
T
he research presented in the article “Cyclic and Load to Failure Properties of All-Suture Anchors in Synthetic Acetabular and Glenoid Cancellous Bone” by Douglass, Behn, and Safran1 establishes several points: All-suture anchor performance varies by anchor, and this performance is strongly influenced by the material into which the anchor is inserted. Although many of the all-suture anchors studied performed as well as the PEEK (polyether ether ketone) control anchor in lower-density foam, this performance for some anchors was worse in higher-density foam. Douglass et al.1 noted that the mechanism of anchor deployment may be an important consideration. The 1.8-mm Q-Fix (Smith & Nephew) has a mechanical deployment system and showed less displacement than the other all-suture anchors tested.1 The authors did not comment on the drill lengths associated with these types of anchors. It is important to note that instead of a biologic material such as cadaveric or animal bone, Douglass et al.1 used rigid polyurethane foam blocks of 2 different densities: 20 pounds per cubic foot (pcf) and 30 pcf. No biologic control such as a cadaveric acetabulum or glenoid was used with which to compare these data. The polyurethane foam block was not biphasic and had nothing that replicated the cortex of the glenoid or acetabulum.2
Ó 2017 by the Arthroscopy Association of North America 0749-8063/17122/$36.00 http://dx.doi.org/10.1016/j.arthro.2017.01.051
986
Every anchor regardless of insertion material survived cyclic loading from 10 to 50 N. Increasing the cyclic distraction to 10 to 100 N resulted in some anchor pullout that was more frequent in the 20-pcf foam blocks. Every control PEEK anchor pulled out during the higher cyclic loads in the 20-pcf polyurethane foam, whereas none pulled out from the 30-pcf polyurethane foam. The maximum anchor loads during destructive testing were significantly higher in the 30-pcf polyurethane foam as well. These findings call into question the suitability of 20-pcf polyurethane foam and the effectiveness of the 10- to 50-N cyclic loading tests. Consideration of the data from the 30-pcf polyurethane foam blocks and the 10- to 100-N cyclic loading shows that none of the control PEEK anchors or Q-Fix, Y-Knot (ConMed Linvatec), or JuggerKnot (Biomet Sports Medicine) anchors pulled out during cyclic loading, nor did most of the SutureFix (Smith & Nephew) anchors (90%) and Iconix (Stryker Endoscopy) anchors (84%). The displacement data also vary considerably depending on the material density. However, a 3- or 5-mm displacement level (the standard in many load-to-failure tests) should not be interpreted as suggesting a potential for clinical failure in this test. The good work of these authors should be validated by comparing the data from the 30-pcf polyurethane foam with an appropriate biologic model. This is a time-zero study, so the results cannot be applied directly to the clinical condition and the maximum load data should be considered cautiously. That being said, all these anchors showed good strength in the 30-pcf polyurethane foam.
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 5 (May), 2017: pp 986-987
987
EDITORIAL COMMENTARY
Every one of these all-suture anchors is made using ultrahighemolecular weight suture. It should be remembered that for all-suture anchors, the ultimate load at failure in biologic test models relates directly to the number of ultrahighemolecular weight polyethyleneecontaining sutures in the anchor.3 An anchor with 3 sutures is stronger than an anchor with 2 sutures, which is stronger than a single-suture anchor. Although not addressed in this report, a distinctive feature of these all-suture anchors is a longer drill, usually between 20 and 24 mm.2 This longer drill can over-penetrate the superior glenoid and reach the suprascapular nerve or, if in the inferior glenoid, the axillary nerve.4,5 During deployment, these all-suture anchors are tensioned by pulling the sutures into a ball that becomes the anchor. This suture ball is pulled until it is compressed against the cortex, becoming wider than the drilled insertion tunnel. Thus the drilled tunnel distal to the all-suture anchor is not filled with solid material, potentially creating a stress riser.6 An in vivo biomechanical and histologic canine glenoid study compared the JuggerKnot 1.4 mm with a conventional 2.4-mm anchor.6 By 8 weeks, the 1.4-mm JuggerKnot tunnels expanded to 6.3-mm-diameter cystlike cavities whereas the conventional 2.4-mm anchor sites showed only 2.7-mm diameters filled with intact anchors. Biomechanically, JuggerKnot displacement (13.7 6.6 mm) was significantly greater than conventional anchor displacement (3.2 0.5 mm).6 A clinical report of 20 patients who underwent glenoid labral repairs with all-suture anchors and were followed up for a mean of 19 months (range, 12-28 months) showed problems related to the anchors in 11 of 20 patients (55%). These adverse events included cyst formation in 2 patients, drill tunnel widening in 3 patients (mean, 3.3 mm; range, 3-4 mm), and bone edema at the anchor site in 6 patients.7
Take-Home Message The 20-pcf polyurethane foam block is not a good test material for these anchors. Cyclic loading between 10
and 50 N does not allow for differentiation of the anchor performance. A biphasic polyurethane foam block laminated on top with a fiber-filled epoxy coating similar in density, hardness, and strength to cortical bone would better replicate the glenoid and acetabular cortical bone environment for testing of all-suture anchors. The current biomechanical test findings show that these all-suture anchors are strong enough to do the job in the glenoid and acetabulum. The real question is whether or not there will be any clinical surprises over time with their use.
References 1. Douglass NP, Behn AW, Safran MR. Cyclic and load to failure properties of all-suture anchors in synthetic acetabular and glenoid cancellous bone. Arthroscopy 2017;33:977-985. 2. Barber FA, Herbert MA. All-suture anchors: Biomechanical analysis of pullout strength, displacement, and failure mode [published online December 22, 2016]. Arthroscopy. doi:10.1016/j.arthro.2016.09.031. 3. 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. 4. Morgan RT, Henn RF III, Paryavi E, Dreese J. Injury to the suprascapular nerve during superior labrum anterior and posterior repair: Is a rotator interval portal safer than an anterosuperior portal? Arthroscopy 2014;30: 1418-1423. 5. Koh KH, Park WH, Lim TK, Yoo JC. Medial perforation of the glenoid neck following SLAP repair places the suprascapular nerve at risk: A cadaveric study. J Shoulder Elbow Surg 2011;20:245-250. 6. Pfeiffer FM, Smith MJ, Cook JL, Kuroki K. The histologic and biomechanical response of two commercially available small glenoid anchors for use in labral repairs. J Shoulder Elbow Surg 2014;23:1156-1161. 7. Willemot L, Elfadalli R, Jaspars KC, et al. Radiological and clinical outcome of arthroscopic labral repair with allsuture anchors. Acta Orthop Belg 2016;82:174-178.
Abstract: Research in this issue, like other biomechanical testing, suggests that the all-suture anchors studied here seem strong enough for glenoid and acetabular applications. Testing suture anchors in nonbiologic material may be problematic unless that material is validated or there is a control. The cyclic loads used influence the data, and oscillating between 10 and 50 N does not allow for sufficient anchor performance differentiation. The next question is whether there will be any adverse events associated with the use of all-suture anchors clinically.
See related article on page 977
T
he research presented in the article “Cyclic and Load to Failure Properties of All-Suture Anchors in Synthetic Acetabular and Glenoid Cancellous Bone” by Douglass, Behn, and Safran1 establishes several points: All-suture anchor performance varies by anchor, and this performance is strongly influenced by the material into which the anchor is inserted. Although many of the all-suture anchors studied performed as well as the PEEK (polyether ether ketone) control anchor in lower-density foam, this performance for some anchors was worse in higher-density foam. Douglass et al.1 noted that the mechanism of anchor deployment may be an important consideration. The 1.8-mm Q-Fix (Smith & Nephew) has a mechanical deployment system and showed less displacement than the other all-suture anchors tested.1 The authors did not comment on the drill lengths associated with these types of anchors. It is important to note that instead of a biologic material such as cadaveric or animal bone, Douglass et al.1 used rigid polyurethane foam blocks of 2 different densities: 20 pounds per cubic foot (pcf) and 30 pcf. No biologic control such as a cadaveric acetabulum or glenoid was used with which to compare these data. The polyurethane foam block was not biphasic and had nothing that replicated the cortex of the glenoid or acetabulum.2
Ó 2017 by the Arthroscopy Association of North America 0749-8063/17122/$36.00 http://dx.doi.org/10.1016/j.arthro.2017.01.051
986
Every anchor regardless of insertion material survived cyclic loading from 10 to 50 N. Increasing the cyclic distraction to 10 to 100 N resulted in some anchor pullout that was more frequent in the 20-pcf foam blocks. Every control PEEK anchor pulled out during the higher cyclic loads in the 20-pcf polyurethane foam, whereas none pulled out from the 30-pcf polyurethane foam. The maximum anchor loads during destructive testing were significantly higher in the 30-pcf polyurethane foam as well. These findings call into question the suitability of 20-pcf polyurethane foam and the effectiveness of the 10- to 50-N cyclic loading tests. Consideration of the data from the 30-pcf polyurethane foam blocks and the 10- to 100-N cyclic loading shows that none of the control PEEK anchors or Q-Fix, Y-Knot (ConMed Linvatec), or JuggerKnot (Biomet Sports Medicine) anchors pulled out during cyclic loading, nor did most of the SutureFix (Smith & Nephew) anchors (90%) and Iconix (Stryker Endoscopy) anchors (84%). The displacement data also vary considerably depending on the material density. However, a 3- or 5-mm displacement level (the standard in many load-to-failure tests) should not be interpreted as suggesting a potential for clinical failure in this test. The good work of these authors should be validated by comparing the data from the 30-pcf polyurethane foam with an appropriate biologic model. This is a time-zero study, so the results cannot be applied directly to the clinical condition and the maximum load data should be considered cautiously. That being said, all these anchors showed good strength in the 30-pcf polyurethane foam.
Arthroscopy: The Journal of Arthroscopic and Related Surgery, Vol 33, No 5 (May), 2017: pp 986-987
987
EDITORIAL COMMENTARY
Every one of these all-suture anchors is made using ultrahighemolecular weight suture. It should be remembered that for all-suture anchors, the ultimate load at failure in biologic test models relates directly to the number of ultrahighemolecular weight polyethyleneecontaining sutures in the anchor.3 An anchor with 3 sutures is stronger than an anchor with 2 sutures, which is stronger than a single-suture anchor. Although not addressed in this report, a distinctive feature of these all-suture anchors is a longer drill, usually between 20 and 24 mm.2 This longer drill can over-penetrate the superior glenoid and reach the suprascapular nerve or, if in the inferior glenoid, the axillary nerve.4,5 During deployment, these all-suture anchors are tensioned by pulling the sutures into a ball that becomes the anchor. This suture ball is pulled until it is compressed against the cortex, becoming wider than the drilled insertion tunnel. Thus the drilled tunnel distal to the all-suture anchor is not filled with solid material, potentially creating a stress riser.6 An in vivo biomechanical and histologic canine glenoid study compared the JuggerKnot 1.4 mm with a conventional 2.4-mm anchor.6 By 8 weeks, the 1.4-mm JuggerKnot tunnels expanded to 6.3-mm-diameter cystlike cavities whereas the conventional 2.4-mm anchor sites showed only 2.7-mm diameters filled with intact anchors. Biomechanically, JuggerKnot displacement (13.7 6.6 mm) was significantly greater than conventional anchor displacement (3.2 0.5 mm).6 A clinical report of 20 patients who underwent glenoid labral repairs with all-suture anchors and were followed up for a mean of 19 months (range, 12-28 months) showed problems related to the anchors in 11 of 20 patients (55%). These adverse events included cyst formation in 2 patients, drill tunnel widening in 3 patients (mean, 3.3 mm; range, 3-4 mm), and bone edema at the anchor site in 6 patients.7
Take-Home Message The 20-pcf polyurethane foam block is not a good test material for these anchors. Cyclic loading between 10
and 50 N does not allow for differentiation of the anchor performance. A biphasic polyurethane foam block laminated on top with a fiber-filled epoxy coating similar in density, hardness, and strength to cortical bone would better replicate the glenoid and acetabular cortical bone environment for testing of all-suture anchors. The current biomechanical test findings show that these all-suture anchors are strong enough to do the job in the glenoid and acetabulum. The real question is whether or not there will be any clinical surprises over time with their use.
References 1. Douglass NP, Behn AW, Safran MR. Cyclic and load to failure properties of all-suture anchors in synthetic acetabular and glenoid cancellous bone. Arthroscopy 2017;33:977-985. 2. Barber FA, Herbert MA. All-suture anchors: Biomechanical analysis of pullout strength, displacement, and failure mode [published online December 22, 2016]. Arthroscopy. doi:10.1016/j.arthro.2016.09.031. 3. 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. 4. Morgan RT, Henn RF III, Paryavi E, Dreese J. Injury to the suprascapular nerve during superior labrum anterior and posterior repair: Is a rotator interval portal safer than an anterosuperior portal? Arthroscopy 2014;30: 1418-1423. 5. Koh KH, Park WH, Lim TK, Yoo JC. Medial perforation of the glenoid neck following SLAP repair places the suprascapular nerve at risk: A cadaveric study. J Shoulder Elbow Surg 2011;20:245-250. 6. Pfeiffer FM, Smith MJ, Cook JL, Kuroki K. The histologic and biomechanical response of two commercially available small glenoid anchors for use in labral repairs. J Shoulder Elbow Surg 2014;23:1156-1161. 7. Willemot L, Elfadalli R, Jaspars KC, et al. Radiological and clinical outcome of arthroscopic labral repair with allsuture anchors. Acta Orthop Belg 2016;82:174-178.