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Treatment of acromioclavicular joint separation: Suture or suture anchors?
Treatment of acromioclavicular joint separation: Suture or suture anchors? Marc J. Breslow, MD, Laith M. Jazrawi, MD, Adam D. Bernstein, MD, Frederick J. Kummer, PhD, and Andrew S. Rokito, MD, New York, NY
This investigation compared the stability of 2 methods of fixation for acromioclavicular (AC) joint separations. A complete AC joint separation was simulated in 6 matched pairs of fresh-frozen human cadaveric shoulders. One specimen from each pair was repaired with two No. 5 nonabsorbable braided sutures passed around the base of the coracoid and the other with 2 suture anchors preloaded with the same suture material placed into the base of the coracoid process. The specimens were cyclically loaded for 104 cycles to simulate our early postoperative rehabilitation protocol for coracoclavicular repairs. Before cycling, the repairs had a mean superior laxity of 1.68 ⫾ 0.44 mm for the sutures alone and 1.23 ⫾ 0.31 mm for the suture anchors. After 104 cycles, the laxity was 1.32 ⫾ 0.59 mm and 1.33 ⫾ 0.94 mm, respectively. These differences were not statistically significant (P ⫽ .2). This study demonstrated that similar stability can be achieved for coracoclavicular fixation with suture anchors or with sutures placed around the base of the coracoid for the treatment of AC joint separations. The clinical relevance includes the following: (1) the potentially diminished risk of neurovascular injury with the use of suture anchors compared with the passage of sutures around the base of the coracoid and (2) the potentially reduced surgical time associated with the use of suture anchors. (J Shoulder Elbow Surg 2002; 11:225-9.)
INTRODUCTION Various operative procedures have been described for the treatment of acromioclavicular (AC) joint dislocations (types III-VI).3 These include dynamic muscle transfers,2,7,11,13 AC joint repair with From the Department of Orthopaedic Surgery, New York University-Hospital for Joint Diseases, New York, NY. Reprint requests: Laith M. Jazrawi, MD, New York UniversityHospital for Joint Diseases, Department of Orthopaedic Surgery, 301 E 17th St., New York, NY 10003. Copyright © 2002 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2002/$35.00 ⫹ 0 32/1/123904 doi:10.1067/mse.2002.123904
pins, plates, or screws,20,25,28 coracoacromial ligament transfer,31 and coracoclavicular (CC) reconstruction,9,23 with or without excision of the distal clavicle.24 Because of its high rate of clinical success and relatively low incidence of complications, CC reconstruction has become a common surgical procedure for the treatment of complete AC joint injuries. Fixation between the clavicle and coracoid can be successfully accomplished with the use of screws,9 suture, or surgical tape.6,21,29 The latter can be either looped around the base of the coracoid or passed through a transosseous tunnel in the coracoid.19 More recently, the use of suture anchors15,22 has been described for the treatment of AC joint injuries. These devices offer the potential advantages of technical ease of use and reduced risk of neurovascular injury, as they avoid passage of suture material around the base of the coracoid. The relative ease of use and improved pullout strength have led to their widespread use in the treatment of a variety of orthopaedic conditions.4,5,10 The purpose of this investigation was to compare the mechanical stability of 2 methods of CC fixation for AC joint dislocations. CC fixation with heavy nonabsorbable sutures passed around the base of the coracoid process was compared with that achieved with the same type of suture material placed directly into the base of the coracoid process by means of suture anchors. MATERIALS AND METHODS Six matched pairs of fresh-frozen human cadaveric shoulders were used for this study. All specimens were stored at ⫺20°C and allowed to thaw to room temperature for 24 hours before testing. The glenohumeral joint was disarticulated, and the proximal humerus was removed, leaving the scapula and clavicle and their ligamentous attachments undisturbed. Each specimen was dissected of all soft tissue, sparing the AC joint capsule and ligaments, the CC ligaments, and the coracoacromial ligament. The scapula was securely mounted on a wood block with 3 screws and washers. The testing apparatus was stabilized with a vice clamp and mounted onto a standard materials testing system machine (MTS Systems, Canton, Mass) so that the angle of the scapula with respect to the coronal plane was 30°, simulating its anatomic position.1 The clav-
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Figure 1 The AC joint custom testing rig is depicted. The clavicle and scapula are rigidly fixed to the testing apparatus with a series of metal clamps and screws. Inset on right illustrates the placement of one suture anchor into the coracoid process with its associated suture tied through the tunnel created in the midportion of the clavicle.
icle was rigidly fixed to the testing apparatus with a series of metal clamps. The AC and CC ligaments were then cut, simulating a complete AC joint injury (Figure 1). Two methods of AC reconstruction were compared. Six randomly selected specimens (1 from each matched pair) underwent CC fixation with sutures passed around the base of the coracoid (group 1), whereas the other one of each pair was fixed with a suture-anchor technique (group 2). In group 1, two No. 5 nonabsorbable braided sutures (Ethibond, Sommerville, NJ) were passed around the base of the coracoid process. These sutures were seated around the base of the coracoid by pulling the ends back and forth in a sawing motion. The sutures from the lateral side of the coracoid were then passed through a 1⁄8-in drill hole placed in the midportion of the clavicle in line with the base of the coracoid. With the clavicle held in a reduced position with respect to the medial acromion and coracoid, each of the braided sutures was tied. First, a surgeon’s knot was tied, followed by 5 square knots. In group 2, two 3.5-mm ROC XS suture fasteners (Innovasive Devices, Marlborough, Mass) were placed into the base of the coracoid process. Each anchor was preloaded with a No. 5 nonabsorbable braided suture (Ethibond). A 3.5-mm drill bit was used to create a pilot hole in the base of the coracoid. The anchor was preloaded on the delivery handle and deployed into the hole. The umbrella-like wings expand under the cortical surface, securing the implant into the bone (Figures 1 and 2). After each anchor was deployed, the sutures were pulled manually several times to ensure appropriate seating and secure fixation. One limb of each suture was passed through a 1⁄8-in drill hole created in the midportion of the distal clavicle in line with the base of the coracoid process. Once again, each of the sutures was tied in the same fashion as in group 1, whereas the clavicle was held in a reduced position. Loads were applied to the clavicle through a loop of wire placed 2 cm from its distal end, as has been previously
described.22 This wire was connected to the load cell of the materials testing system, allowing it to be loaded in a superior direction. The load was increased over 20 seconds to a maximum of 50 N, simulating the weight of the arm; it was then held for 10 seconds, allowing the system to equilibrate as was previously described.22 The intention was to test the shoulders physiologically, and 50 N was selected based on previous studies17,22 so that potential comparisons could be made, as well as to replicate our postoperative protocol of sling use for the first 2 weeks without any shoulder range of motion. Laxity was defined as superior displacement, measured at the end of a 10second loading cycle by an electronic caliper, which measured the distance from the inferior portion of the clavicle to the superior portion of the acromion. Load cycles were conducted 3 times for each of the fixation methods and the displacement measurements averaged. The specimens were then sinusoidally cycled at 1 Hz for 100, 1000, and 10,000 cycles to a maximum of 50 N. Statistical analysis was performed with the Student t-test for paired samples, which was used to compare the sutureanchor technique with the non-anchor technique for the initial loading and for each of the cyclic load intervals. Statistical significance was defined as P ⬍ .05.
RESULTS Mean superior laxity was 1.68 mm (SD, 0.31) for group 1 and 1.23 mm (SD, 0.44) for group 2. Mean laxity after 100 cycles of cyclical loading was 1.74 mm (SD, 0.38) for group 1 and 1.04 mm (SD, 0.54) for group 2 (P ⫽ .1). At 1000 cycles, displacement was 1.49 mm (SD, 0.40) and 0.91 mm (SD, 0.54), respectively, for groups 1 and 2 (P ⫽ .1). At 10,000 cycles, laxity was found to be 1.32 mm (SD, 0.59) for group 1 and 1.37 mm (SD, 0.94) for group 2 (P ⫽ .9)
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Table I The displacement at the AC joint seen in both the sutureonly and suture-anchor groups Displacement (mm) Cycles Baseline 100 1000 10,000
Suture 1.675 1.74 1.49 1.32
⫾ ⫾ ⫾ ⫾
0.31 0.41 0.38 0.59
Anchor 1.225 1.035 0.912 1.37
⫾ ⫾ ⫾ ⫾
0.44 0.54 0.51 0.94
and none of the sutures broke or cut out of the clavicle. DISCUSSION
Figure 2 The umbrella-like wings of the 3.5-mm ROC XS suture fastener (Innovasive Devices) achieve purchase under the cortical surface of bone.
(Table) (Figure 3). In summary, there was no statistically significant difference between the 2 groups for initial displacement or displacements at the various cycles. Although there was a trend for decreased laxity with the use of the suture-anchor technique, this was not statistically significant. None of the specimens fractured during testing, there was no evidence of fixation failure of the anchors and no suture fretting,
Stability of the AC joint is conferred by 2 sets of ligamentous structures. The AC ligaments provide horizontal joint stability, and the conoid and trapezoid ligaments (CC ligaments) provide vertical stability.8,14 A complete AC separation involves disruption of both the AC and CC ligaments. Numerous surgical methods have been described for reconstruction of the AC joint. AC fixation techniques that use screws, pins, and plates have been associated with a high incidence of complications including infection, AC arthritis, pin migration, hardware failure, and loss of fixation.6,18 Dynamic muscle transfers, in which the tip of the coracoid along with the conjoined tendon is fixed to the undersurface of the clavicle, has also been advocated for complete AC joint injuries. This procedure, however, does not provide static stability, and as such there is continued movement of the clavicle. In addition, complications including nonunion and musculocutaneous nerve injury have been reported.2,7,14 The difficulties described with the above techniques have led some surgeons to abandon these forms of treatment in favor of CC reconstruction (ie, screw or suture fixation).6,19,30 CC screw fixation, initially described by Bosworth9 and later popularized by Rockwood and Young,27 involves lag screw fixation of the clavicle to the base of the coracoid. However, placement of the screw is technically demanding, and there have been reported cases of screw breakage.27 A common surgical procedure for complete AC joint injuries involves excision of the distal clavicle and transfer of the coracoacromial ligament to the end of the resected distal clavicle, followed by augmentation with the use of suture or synthetic loops passed around the base of the coracoid and then through or around the distal clavicle.12,21,32 There is no agreement on the optimum augmentation technique. Several different fixation techniques have been attempted, each with its own strength, stiffness, and mode of failure.23 Braided nonabsorbable sutures
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Figure 3 The bar graph illustrates the relationship between the superior displacement at the AC joint and number of loading cycles performed on each specimen. Results for the suture-only fixation group and the suture-anchor fixation group are represented for each loading cycle.
were used in the reconstruction in this study. Motamedi et al23 found that a braided nonabsorbable suture has strength and stiffness similar to that of the intact CC ligament complex, thus protecting against physiologic loads, while allowing physiologic motion. Suture anchors have been used successfully for both rotator cuff10 and Bankart repairs.26 These devices offer the advantage of allowing quick fixation of soft tissue to bone, while minimizing extensive softtissue exposure. Goble et al15 performed biomechanical testing using in vitro and in vivo models and found suture anchors to be comparable to standard transosseous techniques and to 2-pronged staple techniques of fixation of soft tissues to bone. In a cadaveric model, cyclically loaded rotator cuff tears repaired with suture anchors were found to be significantly less prone to failure than transosseous fixation via bone tunnels.10 More recently, suture anchors have been used in reconstruction of AC joint disruptions. Moses et al22 performed a biomechanical study that evaluated fixation of suture anchors for reconstruction of AC joint injuries. They compared the normal cadaveric AC joint laxity with the laxity of a repair with a WeaverDunn technique and a repair incorporating a suture anchor into the base of the coracoid. Jerosch et al16 evaluated 8 different AC reconstruction techniques in 10 cadaver shoulders and found the suture-anchor repair to restore the anatomy best. In this study cyclical loading was performed to replicate upper extremity use during the early postop-
erative period for our patients (full-time sling use for 2 weeks) when the repair is most at risk for failure. Under simulated loads, there was no failure of either construct. The suture loop group, on the whole, demonstrated increased, but not significant, laxity when compared with the suture-anchor group at 100, 1000, and 10,000 cycles. The overall trend for decreased laxity observed with the suture-anchor reconstruction might be explained by the fact that with this technique, sutures are fixed directly to the coracoid. Although the suture loop technique attempted to seat the sutures directly on bone at the base of the coracoid and to minimize soft-tissue interposition, further settling of the sutures around the coracoid base with loading can be responsible for the increased laxity observed with this technique. Clinically, this may also contribute to apparent stretching of the repair, which has been observed after AC reconstruction. There were several limitations to this study. The model used only approximates the true physiology of the AC joint in vivo, as no simulated muscle forces were placed on the repair, simply the estimated force provided by the weight of the arm. However, the 50-N force most likely approximates the forces seen in a compliant patient during our postoperative rehabilitation protocol, which includes no active or passive shoulder motion during the first 2 weeks. In addition, as the amount of AC displacement necessary to cause clinical symptoms is unknown, it may be proved that the minimal difference in displacement between the 2 repair techniques used in this study
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may be clinically significant despite the lack of statistical significance. In conclusion, this study demonstrated that a similar degree of stability can be achieved after CC fixation with the use of suture anchors or sutures placed around the base of the coracoid for the treatment of complete AC joint injuries. This may have important clinical significance, as the use of suture anchors can potentially diminish the risk of neurovascular injury that is associated with the passage of sutures around the base of the coracoid and can potentially reduce surgical time. REFERENCES
1. Allman FL Jr. Fractures and ligamentous injuries of the clavicle and its articulation. J Bone Joint Surg Am 1967;49:774-84. 2. Bailey RW, O’Connor GA, Titus PD, et al. A dynamic repair for acute and chronic injuries of the acromioclavicular area [abstract]. J Bone Joint Surg Am 1972;54:1802. 3. Bannister GC, Wallace WA, Stableforth PG, et al. The management of acute acromioclavicular dislocation: a randomized, prospective, controlled trial. J Bone Joint Surg Br 1989;71:848-50. 4. Barber FA, Cawley P, Prudich JF. Suture anchor failure strength—an in vivo study. Arthroscopy 1993;9:647-52. 5. Barber FA, Herbert MA, Click PA. The ultimate strength of suture anchors. Arthroscopy 1995;11:21-8. 6. Bargren JH, Erlanger S, Dick HM. Biomechanics and comparison of two operative methods of treatment of complete acromioclavicular separation. Clin Orthop 1978;130:267-72. 7. Berson BL, Gilbert MS, Green S. Acromioclavicular dislocations: treatment by transfer of the conjoined tendon and distal end of the coracoid process to the clavicle. Clin Orthop 1978;135:15764. 8. Bjerneld JM, Hovelius L, Thorling J. Acromioclavicular separations treated conservatively. Acta Orthop Scand 1983;54:743-5. 9. Bosworth BM. Acromioclavicular separation: new method of repair. Surg Gynecol Obstet 1941;73:866-71. 10. Burkhart SS, Diaz Pagan JL, Wirth MA, et al. Cyclic loading of anchor-based rotator cuff repairs: confirmation of the tension overload phenomenon and comparison of suture anchor fixation with transosseous fixation. Arthroscopy 1997;13:720-4. 11. Dewar FP, Barrington TW. The treatment of chronic acromioclavicular dislocation. J Bone Joint Surg Br 1965;47:32-5. 12. Dumontier C, Sautet A, Man M, et al. Acromioclavicular dislocations: treatment by coracoacromial ligamentoplasty. J Shoulder Elbow Surg 1995;4:130-4. 13. Ferris BD, Bhamra M, Paton DF. Coracoid process transfer for acromioclavicular dislocations: a report of 20 cases. Clin Orthop 1989;242:184-94. 14. Fukuda K, Craig EV, An KN, et al. Biomechanical study of the ligamentous system of the acromioclavicular joint. J Bone Joint Surg Am 1986;68:434-9.
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15. Goble EM, Somers WK, Clark R, et al. The development of suture anchors for use in soft tissue fixation to bone. Am J Sports Med 1994;22:236-9. 16. Jerosch J, Filler T, Peuker E, et al. Which stabilization technique corrects anatomy best in patients with A—separation? An experimental study. Knee Surg Sports Traumatol Arthrosc 1999;7:36572. 17. Klimkiewicz JJ, Williams GR, Sher JS, Karduna A, Des Jardins JD, Iannotti JP. The acromioclavicular capsule as a restraint to posterior translation of the clavicle: a biomechanical analysis. J Shoulder Elbow Surg 1999;8:119-24. 18. Lancaster S, Horowitz M, Alonso J. Complete acromioclavicular separations: a comparison of operative methods. Clin Orthop 1987;216:80-8. 19. Larsen E, Bjerg-Nielsen A, Cristensen P. Conservative or surgical treatment of acromioclavicular dislocation: a prospective, controlled, randomized study. J Bone Joint Surg Am 1986;68: 552-5. 20. Lizaur A, Marco L, Cebrian R. Acute dislocation of the acromioclavicular joint. Traumatic anatomy and the importance of deltoid and trapezius. J Bone Joint Surg Br 1994;76:602-6. 21. Morrison DS, Lemos MJ. Acromioclavicular separation: reconstruction using synthetic loop augmentation. Am J Sports Med 1995;23:105-10. 22. Moses JM, Wilson DR, Zilberfarb JL, Hayes WC. A biomechanical comparison of acromioclavicular joint reconstruction techniques. Presented at the 44th Annual Meeting of Orthopaedic Research Society; New Orleans, La; March 16-19, 1998. 23. Motamedi AR, Blevins FT, Willis MC, et al. Biomechanics of the coracoclavicular ligament complex and augmentations used in its repair and reconstruction. Am J Sports Med 2000;28:380-4. 24. Mumford EB. Acromioclavicular dislocation. J Bone Joint Surg 1941;23:799-802. 25. Paavolainen P, Bjorkenheim JM, Paukku P, et al. Surgical treatment of acromioclavicular dislocation: a review of 39 patients. Injury 1983;14:415-20. 26. Richmond JC, Donaldson WR, Fu F, Harner CD. Modification of the Bankart reconstruction with a suture anchor: report of a new technique. Am J Sports Med 1991;19:343-6. 27. Rockwood CA Jr, Young DC. Disorders of the acromioclavicular joint. In: Rockwood CA, Matsen FA III, editors. The shoulder. Volume 1. Philadelphia: Saunders; 1990, p. 413-76. 28. Sage FP, Salvatore JE. Injuries of the acromioclavicular joint: study of results in 96 patients. South Med J 1963;56:486-95. 29. Stam L, Dawson I. Complete acromioclavicular dislocations: treatment with a Dacron ligament. Injury 1991;22:173-6. 30. Taft TN, Wilson FC, Oglesby JW. Dislocation of the acromioclavicular joint: an end result study. J Bone Joint Surg Am 1987;69: 1045-51. 31. Weaver JK, Dunn HK. Treatment of acromioclavicular injuries, especially complete acromioclavicular separation. J Bone Joint Surg Am 1972;54:1187-94. 32. Weinstein DM, McCann PD, McIlveen SJ, et al. Surgical treatment of complete acromioclavicular dislocation. Am J Sports Med 1995;23:324-31.
This investigation compared the stability of 2 methods of fixation for acromioclavicular (AC) joint separations. A complete AC joint separation was simulated in 6 matched pairs of fresh-frozen human cadaveric shoulders. One specimen from each pair was repaired with two No. 5 nonabsorbable braided sutures passed around the base of the coracoid and the other with 2 suture anchors preloaded with the same suture material placed into the base of the coracoid process. The specimens were cyclically loaded for 104 cycles to simulate our early postoperative rehabilitation protocol for coracoclavicular repairs. Before cycling, the repairs had a mean superior laxity of 1.68 ⫾ 0.44 mm for the sutures alone and 1.23 ⫾ 0.31 mm for the suture anchors. After 104 cycles, the laxity was 1.32 ⫾ 0.59 mm and 1.33 ⫾ 0.94 mm, respectively. These differences were not statistically significant (P ⫽ .2). This study demonstrated that similar stability can be achieved for coracoclavicular fixation with suture anchors or with sutures placed around the base of the coracoid for the treatment of AC joint separations. The clinical relevance includes the following: (1) the potentially diminished risk of neurovascular injury with the use of suture anchors compared with the passage of sutures around the base of the coracoid and (2) the potentially reduced surgical time associated with the use of suture anchors. (J Shoulder Elbow Surg 2002; 11:225-9.)
INTRODUCTION Various operative procedures have been described for the treatment of acromioclavicular (AC) joint dislocations (types III-VI).3 These include dynamic muscle transfers,2,7,11,13 AC joint repair with From the Department of Orthopaedic Surgery, New York University-Hospital for Joint Diseases, New York, NY. Reprint requests: Laith M. Jazrawi, MD, New York UniversityHospital for Joint Diseases, Department of Orthopaedic Surgery, 301 E 17th St., New York, NY 10003. Copyright © 2002 by Journal of Shoulder and Elbow Surgery Board of Trustees. 1058-2746/2002/$35.00 ⫹ 0 32/1/123904 doi:10.1067/mse.2002.123904
pins, plates, or screws,20,25,28 coracoacromial ligament transfer,31 and coracoclavicular (CC) reconstruction,9,23 with or without excision of the distal clavicle.24 Because of its high rate of clinical success and relatively low incidence of complications, CC reconstruction has become a common surgical procedure for the treatment of complete AC joint injuries. Fixation between the clavicle and coracoid can be successfully accomplished with the use of screws,9 suture, or surgical tape.6,21,29 The latter can be either looped around the base of the coracoid or passed through a transosseous tunnel in the coracoid.19 More recently, the use of suture anchors15,22 has been described for the treatment of AC joint injuries. These devices offer the potential advantages of technical ease of use and reduced risk of neurovascular injury, as they avoid passage of suture material around the base of the coracoid. The relative ease of use and improved pullout strength have led to their widespread use in the treatment of a variety of orthopaedic conditions.4,5,10 The purpose of this investigation was to compare the mechanical stability of 2 methods of CC fixation for AC joint dislocations. CC fixation with heavy nonabsorbable sutures passed around the base of the coracoid process was compared with that achieved with the same type of suture material placed directly into the base of the coracoid process by means of suture anchors. MATERIALS AND METHODS Six matched pairs of fresh-frozen human cadaveric shoulders were used for this study. All specimens were stored at ⫺20°C and allowed to thaw to room temperature for 24 hours before testing. The glenohumeral joint was disarticulated, and the proximal humerus was removed, leaving the scapula and clavicle and their ligamentous attachments undisturbed. Each specimen was dissected of all soft tissue, sparing the AC joint capsule and ligaments, the CC ligaments, and the coracoacromial ligament. The scapula was securely mounted on a wood block with 3 screws and washers. The testing apparatus was stabilized with a vice clamp and mounted onto a standard materials testing system machine (MTS Systems, Canton, Mass) so that the angle of the scapula with respect to the coronal plane was 30°, simulating its anatomic position.1 The clav-
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Figure 1 The AC joint custom testing rig is depicted. The clavicle and scapula are rigidly fixed to the testing apparatus with a series of metal clamps and screws. Inset on right illustrates the placement of one suture anchor into the coracoid process with its associated suture tied through the tunnel created in the midportion of the clavicle.
icle was rigidly fixed to the testing apparatus with a series of metal clamps. The AC and CC ligaments were then cut, simulating a complete AC joint injury (Figure 1). Two methods of AC reconstruction were compared. Six randomly selected specimens (1 from each matched pair) underwent CC fixation with sutures passed around the base of the coracoid (group 1), whereas the other one of each pair was fixed with a suture-anchor technique (group 2). In group 1, two No. 5 nonabsorbable braided sutures (Ethibond, Sommerville, NJ) were passed around the base of the coracoid process. These sutures were seated around the base of the coracoid by pulling the ends back and forth in a sawing motion. The sutures from the lateral side of the coracoid were then passed through a 1⁄8-in drill hole placed in the midportion of the clavicle in line with the base of the coracoid. With the clavicle held in a reduced position with respect to the medial acromion and coracoid, each of the braided sutures was tied. First, a surgeon’s knot was tied, followed by 5 square knots. In group 2, two 3.5-mm ROC XS suture fasteners (Innovasive Devices, Marlborough, Mass) were placed into the base of the coracoid process. Each anchor was preloaded with a No. 5 nonabsorbable braided suture (Ethibond). A 3.5-mm drill bit was used to create a pilot hole in the base of the coracoid. The anchor was preloaded on the delivery handle and deployed into the hole. The umbrella-like wings expand under the cortical surface, securing the implant into the bone (Figures 1 and 2). After each anchor was deployed, the sutures were pulled manually several times to ensure appropriate seating and secure fixation. One limb of each suture was passed through a 1⁄8-in drill hole created in the midportion of the distal clavicle in line with the base of the coracoid process. Once again, each of the sutures was tied in the same fashion as in group 1, whereas the clavicle was held in a reduced position. Loads were applied to the clavicle through a loop of wire placed 2 cm from its distal end, as has been previously
described.22 This wire was connected to the load cell of the materials testing system, allowing it to be loaded in a superior direction. The load was increased over 20 seconds to a maximum of 50 N, simulating the weight of the arm; it was then held for 10 seconds, allowing the system to equilibrate as was previously described.22 The intention was to test the shoulders physiologically, and 50 N was selected based on previous studies17,22 so that potential comparisons could be made, as well as to replicate our postoperative protocol of sling use for the first 2 weeks without any shoulder range of motion. Laxity was defined as superior displacement, measured at the end of a 10second loading cycle by an electronic caliper, which measured the distance from the inferior portion of the clavicle to the superior portion of the acromion. Load cycles were conducted 3 times for each of the fixation methods and the displacement measurements averaged. The specimens were then sinusoidally cycled at 1 Hz for 100, 1000, and 10,000 cycles to a maximum of 50 N. Statistical analysis was performed with the Student t-test for paired samples, which was used to compare the sutureanchor technique with the non-anchor technique for the initial loading and for each of the cyclic load intervals. Statistical significance was defined as P ⬍ .05.
RESULTS Mean superior laxity was 1.68 mm (SD, 0.31) for group 1 and 1.23 mm (SD, 0.44) for group 2. Mean laxity after 100 cycles of cyclical loading was 1.74 mm (SD, 0.38) for group 1 and 1.04 mm (SD, 0.54) for group 2 (P ⫽ .1). At 1000 cycles, displacement was 1.49 mm (SD, 0.40) and 0.91 mm (SD, 0.54), respectively, for groups 1 and 2 (P ⫽ .1). At 10,000 cycles, laxity was found to be 1.32 mm (SD, 0.59) for group 1 and 1.37 mm (SD, 0.94) for group 2 (P ⫽ .9)
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Table I The displacement at the AC joint seen in both the sutureonly and suture-anchor groups Displacement (mm) Cycles Baseline 100 1000 10,000
Suture 1.675 1.74 1.49 1.32
⫾ ⫾ ⫾ ⫾
0.31 0.41 0.38 0.59
Anchor 1.225 1.035 0.912 1.37
⫾ ⫾ ⫾ ⫾
0.44 0.54 0.51 0.94
and none of the sutures broke or cut out of the clavicle. DISCUSSION
Figure 2 The umbrella-like wings of the 3.5-mm ROC XS suture fastener (Innovasive Devices) achieve purchase under the cortical surface of bone.
(Table) (Figure 3). In summary, there was no statistically significant difference between the 2 groups for initial displacement or displacements at the various cycles. Although there was a trend for decreased laxity with the use of the suture-anchor technique, this was not statistically significant. None of the specimens fractured during testing, there was no evidence of fixation failure of the anchors and no suture fretting,
Stability of the AC joint is conferred by 2 sets of ligamentous structures. The AC ligaments provide horizontal joint stability, and the conoid and trapezoid ligaments (CC ligaments) provide vertical stability.8,14 A complete AC separation involves disruption of both the AC and CC ligaments. Numerous surgical methods have been described for reconstruction of the AC joint. AC fixation techniques that use screws, pins, and plates have been associated with a high incidence of complications including infection, AC arthritis, pin migration, hardware failure, and loss of fixation.6,18 Dynamic muscle transfers, in which the tip of the coracoid along with the conjoined tendon is fixed to the undersurface of the clavicle, has also been advocated for complete AC joint injuries. This procedure, however, does not provide static stability, and as such there is continued movement of the clavicle. In addition, complications including nonunion and musculocutaneous nerve injury have been reported.2,7,14 The difficulties described with the above techniques have led some surgeons to abandon these forms of treatment in favor of CC reconstruction (ie, screw or suture fixation).6,19,30 CC screw fixation, initially described by Bosworth9 and later popularized by Rockwood and Young,27 involves lag screw fixation of the clavicle to the base of the coracoid. However, placement of the screw is technically demanding, and there have been reported cases of screw breakage.27 A common surgical procedure for complete AC joint injuries involves excision of the distal clavicle and transfer of the coracoacromial ligament to the end of the resected distal clavicle, followed by augmentation with the use of suture or synthetic loops passed around the base of the coracoid and then through or around the distal clavicle.12,21,32 There is no agreement on the optimum augmentation technique. Several different fixation techniques have been attempted, each with its own strength, stiffness, and mode of failure.23 Braided nonabsorbable sutures
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Figure 3 The bar graph illustrates the relationship between the superior displacement at the AC joint and number of loading cycles performed on each specimen. Results for the suture-only fixation group and the suture-anchor fixation group are represented for each loading cycle.
were used in the reconstruction in this study. Motamedi et al23 found that a braided nonabsorbable suture has strength and stiffness similar to that of the intact CC ligament complex, thus protecting against physiologic loads, while allowing physiologic motion. Suture anchors have been used successfully for both rotator cuff10 and Bankart repairs.26 These devices offer the advantage of allowing quick fixation of soft tissue to bone, while minimizing extensive softtissue exposure. Goble et al15 performed biomechanical testing using in vitro and in vivo models and found suture anchors to be comparable to standard transosseous techniques and to 2-pronged staple techniques of fixation of soft tissues to bone. In a cadaveric model, cyclically loaded rotator cuff tears repaired with suture anchors were found to be significantly less prone to failure than transosseous fixation via bone tunnels.10 More recently, suture anchors have been used in reconstruction of AC joint disruptions. Moses et al22 performed a biomechanical study that evaluated fixation of suture anchors for reconstruction of AC joint injuries. They compared the normal cadaveric AC joint laxity with the laxity of a repair with a WeaverDunn technique and a repair incorporating a suture anchor into the base of the coracoid. Jerosch et al16 evaluated 8 different AC reconstruction techniques in 10 cadaver shoulders and found the suture-anchor repair to restore the anatomy best. In this study cyclical loading was performed to replicate upper extremity use during the early postop-
erative period for our patients (full-time sling use for 2 weeks) when the repair is most at risk for failure. Under simulated loads, there was no failure of either construct. The suture loop group, on the whole, demonstrated increased, but not significant, laxity when compared with the suture-anchor group at 100, 1000, and 10,000 cycles. The overall trend for decreased laxity observed with the suture-anchor reconstruction might be explained by the fact that with this technique, sutures are fixed directly to the coracoid. Although the suture loop technique attempted to seat the sutures directly on bone at the base of the coracoid and to minimize soft-tissue interposition, further settling of the sutures around the coracoid base with loading can be responsible for the increased laxity observed with this technique. Clinically, this may also contribute to apparent stretching of the repair, which has been observed after AC reconstruction. There were several limitations to this study. The model used only approximates the true physiology of the AC joint in vivo, as no simulated muscle forces were placed on the repair, simply the estimated force provided by the weight of the arm. However, the 50-N force most likely approximates the forces seen in a compliant patient during our postoperative rehabilitation protocol, which includes no active or passive shoulder motion during the first 2 weeks. In addition, as the amount of AC displacement necessary to cause clinical symptoms is unknown, it may be proved that the minimal difference in displacement between the 2 repair techniques used in this study
J Shoulder Elbow Surg Volume 11, Number 3
may be clinically significant despite the lack of statistical significance. In conclusion, this study demonstrated that a similar degree of stability can be achieved after CC fixation with the use of suture anchors or sutures placed around the base of the coracoid for the treatment of complete AC joint injuries. This may have important clinical significance, as the use of suture anchors can potentially diminish the risk of neurovascular injury that is associated with the passage of sutures around the base of the coracoid and can potentially reduce surgical time. REFERENCES
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