Suture Anchors in Arthroscopic Rotator Cuff Repair Michael S. George, MD, and John E. Kuhn, MD The use of suture anchors in shoulder surgery has facilitated the rapid advancement of arthroscopic rotator cuff repair techniques. Innumerable anchor types have been developed which allow stronger, rapid, more effective arthroscopic rotator cuff repairs. Abundant research has been performed to maximize the efficacy of suture anchors in arthroscopic rotator cuff repair. This article reviews the literature regarding implant designs, technical considerations, clinical results, and complications of suture anchors in the arthroscopic treatment of rotator cuff tears. Oper Tech Sports Med 12:210-214 © 2004 Elsevier Inc. All rights reserved. KEYWORDS rotator cuff, suture anchors, complications, surgical techniques, shoulder
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ecent developments in arthroscopic surgery of the shoulder have permitted an arthroscopic approach to the patient with rotator cuff tears. Rotator cuff surgery has transitioned from arthroscopic evaluations combined with traditional repairs, to arthroscopic decompressions with deltoid splitting repairs, and recently to all-arthroscopic techniques. This transition has required the continual evolution of operative skills and surgical tools. The now common use of suture anchors in shoulder surgery has revolutionized arthroscopic rotator cuff repair. We review the literature regarding implant designs, technical considerations, clinical results, and complications of suture anchors in the arthroscopic treatment of rotator cuff tears.
Implants Considerations Arthroscopic Implants Innovative implants used in arthroscopic rotator cuff repair include suture anchors, tacks, and screws (Fig. 1). Suture anchors are unthreaded, rely on interference fit for fixation, and come in a variety of shapes which may employ barbs or widening of the anchor to secure it in the bone. While suture anchors require the passage of sutures through the rotator cuff, tacks do not require sutures and therefore may be easier to implant. Rotator cuff tacks are employed like nails with the head of the tack pressing on the bursal surface of the rotator cuff, which holds the tendon down to the bone. Arthroscopic screw type anchors are a third general classification of suture anchor device. These implants are characterized by having threads and are screwed into the bone.
Vanderbilt Sports Medicine, Vanderbilt University, Nashville, TN. Address reprint requests to John E. Kuhn, MD, Chief of Shoulder Surgery, Vanderbilt Sports Medicine, 2601 Jess Neely Drive, Nashville, TN 37212. E-mail:
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They vary by size, eyelet material and size, and the number of sutures in the eyelet. The variety of implant designs suggest that the ideal implant is not yet available. The ideal implant will be easy to implant, have excellent pullout strength, prevent suture abrasion, and will be bioabsorbable with no reaction from the patient as the material dissolves. A vast array of research has been conducted on the various rotator cuff fixation devices to see how well they hold to the ideal.
Research on the Failure of Arthroscopic Suture Anchors Much of the recent research on arthroscopic suture anchors has focused on potential sources of anchor failure. Goradia et al1 compared the rotator cuff repair strength of smooth and spiked bioabsorbable tacks to metal suture anchors and transosseous sutures after cyclic loading in a cadaver model. The number of cycles to 100% failure was significantly greater in the smooth tack group than in the transosseous suture group. There were no significant differences between the anchor and tack groups. In contrast, Cummins et al2 demonstrated inferior initial failure load properties in 2 of 3 types of bioabsorbable tacks when compared with the Mitek Rotator Cuff QuickAnchors (Norwood, MA) in the sheep rotator cuff model. Although easy to use, the tacks are not without complications. It should be noted that bioabsorbable tacks used in rotator cuff and labral repairs have been reported to break and back out from their insertion point,3 requiring some to have been removed from the market. In a similar effort to avoid arthroscopic knot tying, knotless suture anchors have recently been developed. These devices typically set the tension of the sutures of the repair by inserting the anchor deeper into the bone. Thal4 demonstrated increased suture strength in knotless suture anchors compared with standard suture anchors. In contrast, Zumstein et al5 compared the Mitek GII standard metal anchor and the
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Figure 1 Examples of arthroscopic implants. (A) Absorbable suture anchor device. This device involutes on itself making the anchor widen to produce an interference fit in the bone. (B) Rotator cuff tack device. Like a nail, the tack is placed through the rotator cuff and the head pushes the bursal surface of the cuff down to the bone. (C) Bioabsorbable screw device. This type of fixation requires the implant to be screwed into bone. Sutures on the head of the implant are passed through the rotator cuff and tied. (Color version of figure is available online.)
Mitek knotless suture anchors in cadaveric glenoids and found that the standard anchor allowed significantly less suture displacement than the knotless anchor, although the ultimate tensile strength and mode of failure were similar. Suture anchors may fail at the suture-tendon interface, in the suture substance, at the suture-anchor interface, in the anchor itself, or at the anchor-bone interface. The strength of the suture material may play a large role in the efficacy of suture anchors in arthroscopic rotator cuff repair. Barber et al6 biomechanically evaluated several suture and anchor types in the porcine femur model. Using an Instron machine, No.2 Ethibond (Ethicon, Somerville, NJ) failed at 92 N of load, No.5 Ethibond at 193 N, No.2 Panacryl (Ethicon) at 99 N, and No. 2, No. 5, and 2-0 Fiberwire (Arthrex, Naples, FL) at 188 N, 483 N, and 82 N, respectively. The suture anchors all failed at higher loads than their associated sutures (Fig. 2). The interface between the suture anchor and the suture strands may also play a role in the rate of suture abrasion and subsequent suture failure. Bardana et al7 showed that under cyclic loading, sutures oriented at 45° to the anchor are significantly more prone to abrasion and breakage. The rotation of the suture with respect to the anchor, however, did not significantly affect the abrasion rate of the suture. Meyer et al8
confirmed the increased suture abrasion at 45° and added that abrasion in this setting may decrease suture failure load by 73%. They added that anchor eyelet design may also influence suture abrasion. Anchor mechanical strength varies widely with anchor design and material. With the increased use of biodegradable polymers in orthopaedic surgery, bioabsorbable suture anchors are rapidly developing in arthroscopic rotator cuff repair. Most bioabsorbable suture anchors are copolymers consisting of varying ratios of polylactic acid (PLA) and polyglycolic acid (PGA) that biodegrade by hydrolytic scission of their ester bonds. The time period for significant mass loss depends on the molecular weight of the polymer, its crystallinity, and its porosity.9 Bioabsorbable suture anchors have the benefit of little artifact generation on MRI and may also avoid problems with permanent implants such as during revision surgery. However, bioabsorbable anchors are significantly more expensive than metallic anchors and may have increased wear characteristics particularly at the anchor eyelet.7,10 Studies comparing the biomechanical strength of absorbable and nonabsorbable anchors have yielded mixed results. Demirhan et al11 demonstrated a 75% loss of initial pullout
Figure 2 Pullout strength of a variety of anchors in subcortical metaphyseal bone. For most anchors the pullout strength is higher than the tensile strength of sutures, however with bioabsorbable implants the properties may decline with time as the implant dissolves. (Reprinted with permission from Barber et al.6)
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strength of PGA wedge-type suture anchors within the first 3 weeks in the sheep tibia model compared with no change in the pullout strength of similar nonabsorbable anchors within the same time frame. Bardana et al7 found that eyelet failure contributed to failure in bioabsorbable anchors but not in nonabsorbable anchors. In contrast, Dejong et al12 found no significant differences in strength or function between absorbable and nonabsorbable anchors. With all the conflicting data, it may be important to understand that studies regarding absorbable anchor strength may be influenced by multiple factors including test temperature and loading speed. It has been shown that bioabsorbable anchors may fail at a lower load when experimentally tested at higher temperatures and lower loading speeds.13 In general, suture anchors have faired favorably in comparison studies with transosseous rotator cuff sutures. Reed et al14 found that in the cadaver model the suture anchor construct was significantly stronger than the standard transosseous tunnel technique. Failures occurred in the bone in the suture tunnel technique, but occurred in the suture in the anchor technique. Burkhart et al15 also demonstrated in the cadaver model that rotator cuff repair using Mitek RC suture anchors with No. 2 Ethibond were less likely to fail under cyclic loading than transosseous suture tunnels. Lewis et al16 used an in vivo sheep model to compare healing time for rotator cuff repairs using bioabsorbable suture anchor fixation to transosseous sutures. No differences were detected between the two techniques except that at time zero the transosseous technique failed at a greater tensile force than the suture anchor technique. Regardless of the type of suture anchor used, certain implant characteristics have been shown to increase anchor pullout strength. Barber et al17 compared the pullout strength of screw and nonscrew suture anchors in the porcine femur model. For screw anchors, larger minor screw diameters exhibited significantly greater pullout strength. For nonscrew anchors, larger drill holes were associated with lower failure strength. In summary, there are many factors that affect the strength of suture anchors. Different suture anchors may be beneficial in different circumstances. The surgeon must consider the suture type, implant design, and implant material to determine the most appropriate implant.
Technical Considerations As the use of suture anchors in arthroscopic rotator cuff repair becomes more common, surgical techniques continue to evolve. Studies regarding anchor orientation, implantation patterns, and implant locations have contributed to the growing body of knowledge regarding arthroscopic suture anchors. Burkhart18 likened the ideal orientation of suture anchors in rotator cuff repair to that of the “deadman” used to support a corner fence (Fig. 3). He postulated that placing the anchor at the lateral edge of the rotator cuff, rather than directly under the cuff, would minimize tension in the suture and increase anchor pullout strength. Furthermore, the ideal angle between the anchor and the pull of the rotator cuff should be ⱕ45°. However, Liporace et al19 conducted an in vitro
Figure 3 Inserting the implant at an angle improves the mechanical advantage of the construct, much like the “deadman” stone used in cattle fences. (A) Free body diagram of the “deadman” concept. (B) An anchor placed vertically does not have the support that the “deadman” provides. (C) Placing the screw in at an angle restores the “deadman” effect. (Reprinted with permission from Burkhart.18)
study in which the pullout strength was similar for all anchor orientations between 30° and 90°. In addition, suture anchors may be placed in single or double rows in the greater tuberosity. Double rows may reestablish the rotator cuff footprint, which may allow for better healing and may restore the biomechanical properties of the healed cuff.20 Waltrip et al21 and Demirhan et al22 independently showed that dual site fixation with a combination
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of suture anchors and transosseous sutures had greater initial fixation strength than single-row fixation with either suture anchors or transosseous sutures alone. Moreover, the repair strength of two suture anchors could be doubled by the addition of one transosseous suture. The location of anchor placement in the bone may also play an important role in anchor pullout strength. According to Meyer et al,23 bone mineral density below the articular surface and in the greater tuberosity was significantly lower in cadaver specimens with full-thickness rotator cuff tears when compared with specimens with intact rotator cuffs. Barber et al24 studied the effects of bone mineral density on pullout strength of threaded anchors in the greater tuberosity of cadavers with an average age of 80 years. They found greater pullout strength in the posterior area of the greater tuberosity than in the anterior area, but no significant differences between the pullout strength in the greater tuberosity, lesser tuberosity, and humeral neck. They found no correlation between bone mineral density and suture anchor pullout strength. Conflicting data are presented by Tingart et al,25 who used computed tomography to measure total, trabecular, and cortical bone mineral density in different regions of the greater and lesser tuberosities. Suture anchors were placed in each region and cyclically loaded. Like Barber, they found that the posterior portion of the greater tuberosity had higher trabecular bone mineral densities; however, they also demonstrated a clear association between bone mineral density and load to failure.
Clinical Results Using Arthroscopic Suture Anchors Reports of rotator cuff repair using arthroscopic suture anchors have been encouraging. Tauro26 reported on 53 patients who underwent arthroscopic rotator cuff repair using suture anchors and 0-PDS or 1-PDS sutures. At a minimum 2-year follow-up, patients had improved overall with no postoperative suture anchor pullout, although rotator cuff integrity was not documented. Galatz et al27 evaluated 18 patients at 12 and 24 months after arthroscopic rotator cuff repair using bioabsorbable corkscrew suture anchors. Although they found no anchor failures, recurrent tears were found on ultrasound in 17 of 18 patients. Despite these recurrent tears, the 12-month evaluation showed excellent pain relief and functional improvement that deteriorated by the 24-month evaluation.
Complications of Anchor Use Despite technological advances, complications may occur with arthroscopic suture anchors. Complications are most likely to occur with failure of the tissue, suture, or anchor before healing has occurred. Kaar et al28 reported on eight patients who had complications from metallic anchors, including extraosseous anchor placement, anchor migration, and intraarticular anchor dislodgement with consequent articular damage. Evaluation of such anchor complications can be facilitated by the use of MRI (Fig. 4), which can be used to locate migrated anchors and to evaluate rotator cuff integrity.29 Both bioabsorbable and nonabsorbable anchors may cause
Figure 4 MRI and arthroscopic detection of rotator cuff anchor failure. (A) Anchor that has remained in the bone on follow-up MRI. (B) Anchor that has pulled out on follow-up MRI. Note the indistinct edges of the anchor and the bottom of the anchor which no longer is in the bottom of the hole. (C) Arthroscopic view of bursal surface of the greater tuberosity. The solid white structure is the absorbable suture screw-type anchor that has pulled out approximately 4 mm. (Color version of figure is available online.)
214 a local foreign-body reaction. Burkart et al30 reported four cases of foreign-body reaction to bioabsorbable tacks used for labral repair in which synovial biopsy revealed massive infiltration of phagocytic cells and birefringent polymeric particles. Chow and Gu31 reported a case in which foreign-body reaction to a metallic anchor resulted in bony erosion, local tissue necrosis, and protrusion of the anchor into the joint.
Conclusions Arthroscopic rotator cuff repair using suture anchors has gained wide popularity. Many design features, including suture type, anchor size and geometry, and anchor material, play a role in the overall strength of the anchor. In addition, technical considerations such as implant orientation, pattern, and location may affect the ultimate success of the repair. Continued research and development is needed to further maximize the efficacy of suture anchors in arthroscopic rotator cuff repair.
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M.S. George and J.E. Kuhn 12. Dejong ES, DeBerardino TM, Brooks DE, et al: In vivo comparison of a metal versus biodegradable suture anchor. Arthroscopy 20:511-516, 2004 13. Meyer DC, Felix E, Ruffieux K, et al: Influence of test temperature and test speed on the mechanical strength of absorbable suture anchors. Arthroscopy 20:185-190, 2004 14. Reed SC, Glossop N, Ogilvie-Harris DJ: Full thickness rotator cuff tears. A biomechanical comparison of suture versus bone anchor techniques. Am J Sports Med 24:46-48, 1996 15. Burkhart SS, Diaz Pagan JL, Wirth MA, et al: Cyclic loading of anchorbased rotator cuff repairs: Confirmation of the tension overload phenomenon and comparison of suture anchor fixation with transosseous fixation. Arthroscopy 13:720-724, 1997 16. Lewis CW, Schlegel TF, Hawkins RJ, et al: Comparison of tunnel suture and suture anchor methods as a function of time in a sheep model. Biomed Sci Instrum 35:403-408, 1999 17. Barber FA, Herbert MA, Click JN: Suture anchor strength revisited. Arthroscopy 12:32-38, 1996 18. Burkhart SS: The deadman theory of suture anchors: Observations along a south Texas fence line. Arthroscopy 11:119-123, 1995 19. Liporace FA, Bono CM, Caruso SA, et al: The mechanical effects of suture anchor insertion angle for rotator cuff repair. Orthopedics 25: 399-402, 2002 20. Lo IK, Burkhart SS: Double-row arthroscopic rotator cuff repair: reestablishing the footprint of the rotator cuff. Arthroscopy 19:10351042, 2003 21. Waltrip RL, Zheng N, Dugas JR, et al: Rotator cuff repair. A biomechanical comparison of three techniques. Am J Sports Med 31:493497, 2003 22. Demirhan M, Atalar AC, Kilicoglu O: Primary fixation strength of rotator cuff repair techniques: A comparative study. Arthroscopy 19:572576, 2003 23. Meyer DC, Fucentese SF, Koller B, et al: Association of osteopenia of the humeral head with full-thickness rotator cuff tears. J Shoulder Elbow Surg 13:333-337, 2004 24. Barber FA, Feder SM, Burkhart SS, et al: The relationship of suture anchor failure and bone density to proximal humerus location: A cadaveric study. Arthroscopy 13:340-345, 1997 25. Tingart MJ, Apreleva M, Zurakowski D, et al: Pullout strength of suture anchors used in rotator cuff repair. J Bone Joint Surg Am 85A:21902198, 2003 26. Tauro JC: Arthroscopic rotator cuff repair: Analysis of technique and results at 2- and 3-year follow-up. Arthroscopy 14:45-51, 1998 27. Galatz LM, Ball CM, Teefey SA, et al: The outcome and repair integrity of completely arthroscopically repaired large and massive rotator cuff tears. J Bone Joint Surg Am 86A:219-224, 2004 28. Kaar TK, Schenck RC Jr, Wirth MA, et al: Complications of metallic suture anchors in shoulder surgery: A report of 8 cases. Arthroscopy 17:31-37, 2001 29. Magee T, Shapiro M, Hewell G, et al: Complications of rotator cuff surgery in which bioabsorbable anchors are used. Am J Roentgenol 181:1277-1231, 2003 30. Burkart A, Imhoff AB, Roscher E: Foreign-body reaction to the bioabsorbable Suretac device. Arthroscopy 16:91-95, 2000 31. Chow JC, Gu Y: Material reaction to suture anchor. Arthroscopy 20: 314-316, 2004