- Email: [email protected]
Stainless steel wire versus FiberWire suture cerclage fixation to stabilize the humerus in total shoulder arthroplasty
J Shoulder Elbow Surg (2014) -, 1-7
www.elsevier.com/locate/ymse
Stainless steel wire versus FiberWire suture cerclage fixation to stabilize the humerus in total shoulder arthroplasty Niklas Renner, MDa,*, Karl Wieser, MDa, Georg Lajtai, MDb, Mark E. Morrey, MDa, Dominik C. Meyer, MDa a b
Department of Orthopaedics, University of Z€ urich, Balgrist University Hospital, Z€urich, Switzerland Department of Ortrhopaedics, Private Hospital Maria Hilf, Klagenfurth, Austria Hypothesis: No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) and 1.25-mm stainless steel wire cerclage (SSWC) are biomechanically similar in resistance to prosthetic subsidence in shoulder arthroplasty. Methods: In this laboratory bench study, 3 different surgical knot configurations (4-throw knot, cow hitch, and simple hitch) using a No. 5 FWC were evaluated and compared with a 1.25-mm SSWC. First, distraction tests were performed using bovine femoral cortical half shells mounted on a testing jig. Cerclage tightening, load to a 3-mm gap opening, and load to total failure were measured. Second, uncemented humeral prosthetic stems were inserted into an experimentally split humeral medullary canal, secured by the cerclage. After 100 N of preloading, the prosthesis was advanced into the humerus at a speed of 0.2 mm/s, and resistance during subsidence up to a penetration depth of 10 mm, as well as gap opening, was measured. Results: Tightening force showed higher values for SSWC (618 N) than FWC (131-137 N) (P < .001). Load to total failure was comparable among the 3 different FWC knots (2,642-2,804 N), which were significantly stronger than SSWC (1,775 N, P < .001). At 3 mm of distraction, SSWC (1,820 N), cow hitch (1,803 N), and single-throw hitch (1,709 N) performed significantly better than a 4-throw knot (1,289 N) (P < .01). Subsidence testing showed no difference in force restraint or gap opening between the best FWC and SSWC. Conclusions: FWCs appear, in vitro, equally suitable to steel wires to stabilize nondisplaced periprosthetic humeral fractures. To actively reduce a displaced fracture, steel wires may still be the first choice. Level of evidence: Basic Science, Biomechanics. Ó 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Cerclage; periprosthetic humeral fracture; total shoulder arthroplasty
Institutional review board approval was not required because this was a biomechanical investigation. *Reprint requests: Niklas Renner, MD, Department of Orthopaedics, University of Z€ urich, Balgrist University Hospital, Forchstrasse 340, CH-8008 Z€ urich, Switzerland. E-mail address: [email protected] (N. Renner).
Wire cerclages have been well known for bone fixation for over half a century and have usually been performed with steel wires.1 With the advent of flexible high-strength polyblend-polyethylene suture fibers, the concept of using this material for cerclage purposes appears to be an attractive option. It may offer the advantages of not
1058-2746/$ - see front matter Ó 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2014.02.012
2 interfering with radiologic imaging, potentially easier handling, and no risk of metallosis in the case of metalmetal contact. Periprosthetic humeral fractures can occur during primary (1.2%)2,25 or revision shoulder arthroplasty (3.3%) and may require osseous stabilization.2-4,23,24 When fractures arise as a part of humeral insertion, the surgeon must know what fixation techniques will prevent propagation of the fracture6 during the average 17 weeks needed to heal,2 which is much longer than the typical immobilization period after surgery.19 Much of the work on intraoperative fracture fixation has relied on data from the hip and knee literature or from proximal humeral fractures without prostheses; however, no studies address fixation techniques specifically for shoulder arthroplasty and intraoperative fractures. There are a myriad of techniques that have been discussed, including the use of braided suture, wire, and cable cerclage techniques,2,9,13,18,20,21,25,27,28 to fix fractures or humeral osteotomies in revision surgery. However, the loading pattern occurring from a prosthesis in a fractured shaft is very difficult to predict, and small gapping of the fracture may result in considerable subsidence of the prosthetic shaft. Therefore, it was the purpose of this work to investigate the compression generated by each cerclage construct and to find the best method for creating a stable compressive fixation using high-strength sutures. As a second step, we tested the amount of subsidence of the prosthesis into an experimentally fractured shaft stabilized with a metallic versus a flexible cerclage.
Materials and methods Stainless steel wire cerclage (SSWC) of 1.25 mm in diameter (Synthes, Solothurn, Switzerland) and No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) were used in this study. FiberWire (FW) is made of ultrahigh–molecular weight polyethylene (UHMWPE) and polyester braided over a UHMWPE core.
Distraction test Cerclage testing followed a previously established protocol.16,29 Fresh-frozen bovine femur (–20 C) was used for the assessment. The bone was thawed and kept humid for the investigation. Before testing, all soft tissue surrounding the bone was removed and pieces of 65 mm in length were cut from the mid diaphysis. To fit the bone shells on the testing jig, the intramedullary canal was reamed up to 25 mm and the fragment was cut into 2 parts. The outer diameter of the 2 pieces was 40 mm. All cerclage systems were tested using the same specimen. After preparation of the bone shells, they were fit on the testing jig, which consisted of 2 metallic half cylinders with a radius of 25 mm, forming a full circle. The upper half cylinder was connected to a 20-kN load cell. Between the bone shells, a gap of 1 mm was maintained during the test to avoid load transfer via the testing machine. For all assessments, we used the same universal material testing machine (Zwick 1456; Zwick/Roell, Ulm, Germany), which recorded the
N. Renner et al. data using dedicated software (testExpert 10; Zwick/Roell). We evaluated the data regarding load (in newtons) and displacement (in millimeters), which were digitally recorded, and the deformation curve and the mode of failure were documented. We twisted 1.25-mm double-looped cerclage wires with dedicated pliers (M€ uller, St. Gallen, Switzerland) under permanent traction on the cerclage wires. Values of 940 26 N were determined in a series of 5 samples as the range of ultimate compressive force achieved by twisting. The cerclages were therefore twisted on the testing jig until approximately 90% of the maximally expected force was reached. After 6 turns, the free wire ends were cut outside the crimp, which was then bent forward (in the direction of the twisting) to minimize loss of pre-tension.29 Double-looped No. 5 FW slings were performed and secured with 3 different knots as described later. Each setup was tested 10 times. After preliminary testing, a standard surgical knot with 4 throws was deemed suitable as a control group. Furthermore, 2 sling hitches with 4 simple knots on top (cow hitch and singlethrow hitch) as depicted in Figures 1 and 2 were tested. At the cerclage setup, pre-tension was measured at the following time points: (1) after wire twisting, (2) after removal of pliers, (3) after cutting the wire ends, (4) after bending the crimp, and (5) 1 minute later. The FW pre-tension was measured after secure knot tying. After 1 minute, a constant tensile force with a speed of 0.2 mm/s was applied, and load leading to a 1-, 2-, and 3-mm gap opening, as well as load to total failure, was recorded. The end of the test was defined as 90% force shutdown or gap opening of 20 mm between the bone shells.
Subsidence test Ten fresh-frozen (20 C) proximal humeri of human specimens were prepared for this investigation. Standard anteroposterior radiographs of each bone were obtained, and all bones were matched into 2 approximately equal groups regarding their cortical indexes.11 After thawing of all proximal cadaveric humeri, the heads were resected exactly at the level of the anatomic neck and a medial longitudinal split (‘‘humerotomy’’) of 10 cm in length was performed with the aid of an oscillating saw. The medullary canal was rasped manually using rasps from the Zimmer Anatomical Shoulder System (Zimmer, Winterthur, Switzerland) until solid resistance was felt from cortical contact in the canal. Each specimen was fixed in a vertical fixation device on the machine table, and an uncemented proximal humeral prosthesis stem (Anatomical Prosthesis; Zimmer), appropriate to the size of the bone canal (with reference to the radiograph to achieve a firm diaphyseal fit), was inserted into the medullary canal until a preload of 100 N was reached. The humerotomy was then secured 3 cm distal to the calcar using either a double-wire cerclage (n ¼ 5) or an FW double-loop cerclage (cow hitch) (n ¼ 5), which has previously been determined as best for the purpose (Fig. 3). For subsidence measurements, on the same test machine mentioned earlier, a compressive load was applied onto the prosthesis by lowering the cross-head at a constant speed of 0.2 mm/s and resistance during subsidence of the prosthesis was measured. Tests were completed when a penetration depth of 10 mm was reached. Load to subsidence was recorded with a force-strain curve. Videos were recorded using a Nikon D800 digital camera (Nikon, Tokyo, Japan) that was equipped with a specific macro-objective (Telecentric Visionmes Lenses 16/16/0.1;
Cerclage fixation in total shoulder arthroplasty
3
Figure 1 (A) For the FW cow hitch, a double-looped No. 5 FW was used. (B) The suture end was folded over to create a sling (cow hitch or ‘‘running eye’’). (C) Both single ends of the FW were passed through the sling, tightened, and secured with 4 throws.
Figure 2 Knot tying of FW single-throw hitch. (A) The double No. 5 FW was looped around the bone shells twice. (B) A single throw was created with the suture loop, and the loose suture ends were pulled through the FW loop and tightened. (C) To secure the knot, 4 throws were tied.
Carl Zeiss, Oberkochen, Germany) from every subsidence test, and gap opening was measured with Adobe Photoshop CS5 (Adobe Systems, Munich, Germany).
Statistical analysis To detect significant differences among the groups regarding loss of pre-tension, gap opening, total failure, and subsidence resistance force, 1-way analysis of variance was performed. The significance level was defined as a ¼ .05.
Results Distraction test Wire tightening of the 1.25-mm wire cerclage resulted in a primary pre-tension of 817 16 N and decreased to 806 20 N after removal of the pliers, to 780 27 N after cutting of the wire, and to 618 75 N after bending of the crimp; thereafter, it remained stable after 1 minute.
4
N. Renner et al.
Subsidence test Force required to press the prosthesis from 1 to 10 mm into the humerus (subsidence) after application of a cerclage is shown in Figure 5. There was no significant difference between the cerclage wires and FWCs. We recorded a slightly greater gap opening using SSWC compared with the FW group, without reaching a statistical difference (Fig. 6).
Discussion
Figure 3 Subsidence test setup. Ten proximal human humeri were resected at the level of the anatomic neck after thawing. The specimens were split longitudinally at a length of 10 cm. To fit the prosthesis stem, the medullary canal was rasped manually. The prosthesis stems were pushed into the medullary canal by a metallic pin in the testing machine. Load to subsidence at a speed of 0.2 mm/s was recorded, and the load-displacement curve was documented.
With 131 N for the 4-throw control knot, 137 N for the cow hitch, and 133 N for the single-throw hitch, the maximum pre-tension values of the FWC were not significantly different among the 3 knots (P > .05); however, maximum pre-tension was significantly lower than pretension of the wire cerclages. Distraction force and load at total failure of the different cerclage configurations are shown in Figure 4. All cerclages failed by either unraveling of the twist or wire breakage at the innermost turn of the twist. All FWCs ripped apart by rupture at the innermost thread of the knot. At 1 and 2 mm of displacement, all FWCs exhibited comparable results but showed significantly lower results than the SSWC. However, load at 3 mm of fragment separation showed similar results for the SSWC (1,820 N; range, 1539 – 2058 N; SD, 256 N), FW cow hitch (1,803 N; range, 1339 – 2040 N; SD, 246 N), and FW single-throw hitch (1,709 N; range, 1498 – 1867 N; SD, 113 N); these loads were significantly higher compared with that of the FW 4-throw knots (1,289 N; range, 741 – 1734 N; SD, 353 N). Load to total failure was, however, comparable among the 3 different FW cerclage knots, which were significantly stronger than SSWC.
Iatrogenic fractures or humeral osteotomies may occur in primary or revision shoulder arthroplasty. Factors such as osteopenia, female sex, and rheumatoid arthritis are associated with intraoperative fractures, have a prevalence of 0.6% to 3%, and account for nearly 20% of all complications.2,7,14,23,25,30,31 Various treatment options such as cerclage wiring, plating, and interfragmentary screw insertion12 have been proposed. Regarding the specific cerclage technique, various constructs addressing the violation of the bone have been reported,10,15,22 but to our knowledge, no systematic testing of the ideal biomechanical technique has been conducted in combination with a humeral prosthesis. We conducted our test setup because biomechanical testing of common suture materials showed that a single-loop No. 5 FW is the suture material that has the closest material properties regarding load to failure and stiffness compared with a 1.25-mm stainless steel wire.20 Cerclage fixation of bone may follow 2 purposes: first, to reduce a displaced fracture, and second, to secure bone against further fracture crack propagation. Regarding the first task, we could show that cerclage wires are far more suitable to actively compress bone, with an approximately 5-fold higher compressive load created as compared with the suture construct, which might be an advantage to reduce a fracture. Beyond that, SSWC provided more resistance to fragment separation at small distances (1-2 mm) in combination with strong cortical bovine femur shells in our laboratory bench test because of the higher elasticity of the FWC. However, resistance against gap formation of more than 3 mm and ultimate load to failure were significantly higher using an FW suture cerclage. The cow hitch presented in this study with simple throws performed best regarding ultimate failure load and stiffness. As described by Lenz et al,16 failure of all cerclages occurred by either unraveling of the twist or wire breakage at the innermost turn of the twist. However, all FWCs ripped apart by rupture at the innermost thread of the knot, and knot slippage was never observed, despite the small number of only 4 throws.17 These very different resistance and strain behaviors among the tested suture and wire cerclage models, however, did not significantly influence resistance and opening of the gap during prosthetic stem subsidence. Although
Cerclage fixation in total shoulder arthroplasty
5
Figure 4 Distraction to 1, 2, and 3 mm ( standard deviation), as well as load leading to total failure ( standard deviation), for tested cerclage types (n ¼ 10; )) P < .01; ))) P < .001).
Figure 5 Force needed ( standard deviation) to press the shaft of the proximal humeral prosthesis 1 to 10 mm into the medullary canal. Testing showed no difference between the cerclage systems.
Figure 6
Gap opening ( standard deviation) (in millimeters) at proximal humerus split at 1 to 10 mm of subsidence of prosthesis stem.
there was a slightly greater gap opening during the test for the SSWC compared with the FW group, no statistical difference was found and gap opening was only 1 to 1.5 mm in the case of 1 cm of prosthetic stem subsidence. It is questionable whether the potential pre-tensioning of the SSWC up to 966 N is of practical importance, especially on osteopenic or osteoporotic bone, because the wires may cut through the bone. Vice versa, the use of a
nonmetallic cerclage construct has potential advantages such as better adaptation to the bone surface, decrease of soft tissue irritation by the crimp, and no risk of metal-onmetal debris. The equivalent results in subsidence testing of the FW and the stainless steel wire despite the higher stiffness of the metallic SSWC may be explained by 2 aspects. First, the suture construct may compensate for its elasticity with
6
N. Renner et al.
the greater surface area to distribute the load on the bone and may thus cut less into the soft periosteum and bone. Second, the weakest area appears to be the soft cancellous canal even though radiologically measured well-tapered prostheses were implanted. Therefore, the elasticity of the wire construct is not the weakest link and thus not the limiting factor for subsidence. There are some limitations of this investigation. First, we used very strong cortical bovine femur shells for our laboratory bench test, which did not allow any plastic deformation as occurs in vivo but which was necessary to isolate the behavior of the wire and suture. Second, subsidence testing was performed with different stem sizes and cadaveric humeri having, despite matching, variable biomechanical characteristics. Furthermore, to limit the variables of the test setup, we decided against performing cyclic testing.5,18 However, despite the aforementioned limitations, our results appear to be in line with comparable data on the use of nonmetallic cerclage material in orthopaedic surgery8,10,22,26 and even with a report assessing a specifically designed commercial braided UHMWPE fiber cable to fix a periprosthetic fracture in revision shoulder arthroplasty.10 In summary, because we could not find relevant downsides to the suture cerclage fixation on the humerus in combination with prostheses assessed in this study, the associated advantages, such as ease of handling, low cost, good tissue compatibility, and no interference with radiologic imaging, may make this method an attractive option in patients in whom no relevant bone gap needs to be closed.
Conclusion Suture (FW) cerclages in shoulder arthroplasty provide a safe, affordable, simple, and readily available technique to stabilize periprosthetic fractures or humeral osteotomies as long as no gap needs to be actively closed by the cerclage. Particularly in patients with osteopenic or osteoporotic bone, the use of an FWC provides sufficient stability comparable with established wire cerclages, with the benefit of no radiologic interference. The shortcoming of this study is the lack of cyclic testing, which may be further assessed to confirm our results in a repeated load assessment.
Disclaimer Zimmer provided the proximal humeral prosthesis stem from the Anatomical Shoulder System for our test setup. The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Arnesen AJ. Encircling suture (cerclage) in oblique fractures. Acta Chir Scand 1951;102:267-74. 2. Athwal GS, Sperling JW, Rispoli DM, Cofield RH. Periprosthetic humeral fractures during shoulder arthroplasty. J Bone Joint Surg Am 2009;91:594-603. http://dx.doi.org/10.2106/JBJS.H.00439 3. Boileau P, Melis B, Duperron D, Moineau G, Rumian AP, Han Y. Revision surgery of reverse shoulder arthroplasty. J Shoulder Elbow Surg 2013;22:1359-70. http://dx.doi.org/10.1016/j.jse.2013.02.004 4. Bonutti PM, Hawkins RJ. Fracture of the humeral shaft associated with total replacement arthroplasty of the shoulder. A case report. J Bone Joint Surg Am 1992;74:617-8. 5. Bostrom MP, Asnis SE, Ernberg JJ, Wright TM, Giddings VL, Berberian WS, et al. Fatigue testing of cerclage stainless steel wire fixation. J Orthop Trauma 1994;8:422-8. 6. Boyd AD Jr, Thornhill TS, Barnes CL. Fractures adjacent to humeral prostheses. J Bone Joint Surg Am 1992;74:1498-504. 7. Campbell JT, Moore RS, Iannotti JP, Norris TR, Williams GR. Periprosthetic humeral fractures: mechanisms of fracture and treatment options. J Shoulder Elbow Surg 1998;7:406-13. 8. Carofino BC, Santangelo SA, Kabadi M, Mazzocca AD, Browner BD. Olecranon fractures repaired with FiberWire or metal wire tension banding: a biomechanical comparison. Arthroscopy 2007;23:964-70. http://dx.doi.org/10.1016/j.arthro.2007.03.008 9. Dietz SO, Broos P, Nijs S. Suture fixation versus cable cerclage of the tuberosities in shoulder arthroplastydclinical and radiologic results. Arch Orthop Trauma Surg 2012;132:793-800. http://dx.doi.org/10. 1007/s00402-012-1470-2 10. Edwards TB, Stuart KD, Trappey GJ, O’Connor DP, Sarin VK. Utility of polymer cerclage cables in revision shoulder arthroplasty. Orthopedics 2011;34(4):264. http://dx.doi.org/10.3928/0147744720110228-13 11. Giannotti S, Bottai V, Dell’osso G, Donati D, Bugelli G, De Paola G, et al. Indices of risk assessment of fracture of the proximal humerus. Clin Cases Miner Bone Metab 2012;9:37-9. 12. Groh GI, Heckman MM, Wirth MA, Curtis RJ, Rockwood CA Jr. Treatment of fractures adjacent to humeral prostheses. J Shoulder Elbow Surg 2008;17:85-9. http://dx.doi.org/10.1016/j.jse.2007.05.007 13. Han SM. Comparison of wiring techniques for bone fracture fixation in total hip arthroplasty. Tohoku J Exp Med 2000;192:41-8. 14. Kumar S, Sperling JW, Haidukewych GH, Cofield RH. Periprosthetic humeral fractures after shoulder arthroplasty. J Bone Joint Surg Am 2004;86:680-9. 15. Lenz M, Perren SM, Gueorguiev B, Richards RG, Krause F, Fernandez Dell’Oca A, et al. Underneath the cerclage: an ex vivo study on the cerclage-bone interface mechanics. Arch Orthop Trauma Surg 2012; 132:1467-72. http://dx.doi.org/10.1007/s00402-012-1572-x 16. Lenz M, Perren SM, Richards RG, Muckley T, Hofmann GO, Gueorguiev B, et al. Biomechanical performance of different cable and wire cerclage configurations. Int Orthop 2013;37:125-30. http:// dx.doi.org/10.1007/s00264-012-1702-7 17. Lo IKY, Burkhart SS, Chan KC, Athanasiou K. Arthroscopic knots: determining the optimal balance of loop security and knot security. Arthroscopy 2004;20:489-502. http://dx.doi.org/10.1016/j.arthro. 2004.03.005 18. Meyer DC, Ramseier LE, Lajtai G, Notzli H. A new method for cerclage wire fixation to maximal pre-tension with minimal elongation to failure. Clin Biomech (Bristol, Avon) 2003;18:975-80. 19. Mulieri PJ, Holcomb JO, Dunning P, Pliner M, Bogle RK, Pupello D, et al. Is a formal physical therapy program necessary after total shoulder arthroplasty for osteoarthritis? J Shoulder Elbow Surg 2010; 19:570-9. http://dx.doi.org/10.1016/j.jse.2009.07.012 20. Najibi S, Banglmeier R, Matta J, Tannast M. Material properties of common suture materials in orthopaedic surgery. Iowa Orthop J 2010; 30:84-8.
Cerclage fixation in total shoulder arthroplasty 21. Roe SC. Mechanical characteristics and comparisons of cerclage wires: introduction of the double-wrap and loop/twist tying methods. Vet Surg 1997;26:310-6. 22. Sarin VK, Mattchen TM, Pratt WR, Hack B. Novel iso-elastic cerclage cable for fracture treatment. J Bone Joint Surg Br 2008;90:189. 23. Singh JA, Sperling J, Schleck C, Harmsen W, Cofield R. Periprosthetic fractures associated with primary total shoulder arthroplasty and primary humeral head replacement: a thirty-three-year study. J Bone Joint Surg Am 2012;94:1777-85. http://dx.doi.org/10.2106/JBJS.J. 01945 24. Sperling JW, Cofield RH. Humeral windows in revision shoulder arthroplasty. J Shoulder Elbow Surg 2005;14:258-63. http://dx.doi.org/ 10.1016/j.jse.2004.09.004 25. Steinmann SP, Cheung EV. Treatment of periprosthetic humerus fractures associated with shoulder arthroplasty. J Am Acad Orthop Surg 2008;16:199-207. 26. Ting NT, Wera GD, Levine BR, Della Valle CJ. Early experience with a novel nonmetallic cable in reconstructive hip surgery. Clin Orthop
7
27.
28.
29.
30. 31.
Relat Res 2010;468:2382-6. http://dx.doi.org/10.1007/s11999-0101284-x Van Thiel GS, Halloran JP, Twigg S, Romeo AA, Nicholson GP. The vertical humeral osteotomy for stem removal in revision shoulder arthroplasty: results and technique. J Shoulder Elbow Surg 2011;20: 1248-54. http://dx.doi.org/10.1016/j.jse.2010.12.013 Voigt C, Hurschler C, Rechi L, Vosshenrich R, Lill H. Additive fibercerclages in proximal humeral fractures stabilized by locking plates: no effect on fracture stabilization and rotator cuff function in human shoulder specimens. Acta Orthop 2009;80:465-71. http://dx.doi.org/ 10.3109/17453670903110659 Wahnert D, Lenz M, Schlegel U, Perren S, Windolf M. Cerclage handling for improved fracture treatment. A biomechanical study on the twisting procedure. Acta Chir Orthop Traumatol Cech 2011;78:208-14. Worland RL, Kim DY, Arredondo J. Periprosthetic humeral fractures: management and classification. J Shoulder Elbow Surg 1999;8:590-4. Wright TW, Cofield RH. Humeral fractures after shoulder arthroplasty. J Bone Joint Surg Am 1995;77:1340-6.
www.elsevier.com/locate/ymse
Stainless steel wire versus FiberWire suture cerclage fixation to stabilize the humerus in total shoulder arthroplasty Niklas Renner, MDa,*, Karl Wieser, MDa, Georg Lajtai, MDb, Mark E. Morrey, MDa, Dominik C. Meyer, MDa a b
Department of Orthopaedics, University of Z€ urich, Balgrist University Hospital, Z€urich, Switzerland Department of Ortrhopaedics, Private Hospital Maria Hilf, Klagenfurth, Austria Hypothesis: No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) and 1.25-mm stainless steel wire cerclage (SSWC) are biomechanically similar in resistance to prosthetic subsidence in shoulder arthroplasty. Methods: In this laboratory bench study, 3 different surgical knot configurations (4-throw knot, cow hitch, and simple hitch) using a No. 5 FWC were evaluated and compared with a 1.25-mm SSWC. First, distraction tests were performed using bovine femoral cortical half shells mounted on a testing jig. Cerclage tightening, load to a 3-mm gap opening, and load to total failure were measured. Second, uncemented humeral prosthetic stems were inserted into an experimentally split humeral medullary canal, secured by the cerclage. After 100 N of preloading, the prosthesis was advanced into the humerus at a speed of 0.2 mm/s, and resistance during subsidence up to a penetration depth of 10 mm, as well as gap opening, was measured. Results: Tightening force showed higher values for SSWC (618 N) than FWC (131-137 N) (P < .001). Load to total failure was comparable among the 3 different FWC knots (2,642-2,804 N), which were significantly stronger than SSWC (1,775 N, P < .001). At 3 mm of distraction, SSWC (1,820 N), cow hitch (1,803 N), and single-throw hitch (1,709 N) performed significantly better than a 4-throw knot (1,289 N) (P < .01). Subsidence testing showed no difference in force restraint or gap opening between the best FWC and SSWC. Conclusions: FWCs appear, in vitro, equally suitable to steel wires to stabilize nondisplaced periprosthetic humeral fractures. To actively reduce a displaced fracture, steel wires may still be the first choice. Level of evidence: Basic Science, Biomechanics. Ó 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. Keywords: Cerclage; periprosthetic humeral fracture; total shoulder arthroplasty
Institutional review board approval was not required because this was a biomechanical investigation. *Reprint requests: Niklas Renner, MD, Department of Orthopaedics, University of Z€ urich, Balgrist University Hospital, Forchstrasse 340, CH-8008 Z€ urich, Switzerland. E-mail address: [email protected] (N. Renner).
Wire cerclages have been well known for bone fixation for over half a century and have usually been performed with steel wires.1 With the advent of flexible high-strength polyblend-polyethylene suture fibers, the concept of using this material for cerclage purposes appears to be an attractive option. It may offer the advantages of not
1058-2746/$ - see front matter Ó 2014 Journal of Shoulder and Elbow Surgery Board of Trustees. http://dx.doi.org/10.1016/j.jse.2014.02.012
2 interfering with radiologic imaging, potentially easier handling, and no risk of metallosis in the case of metalmetal contact. Periprosthetic humeral fractures can occur during primary (1.2%)2,25 or revision shoulder arthroplasty (3.3%) and may require osseous stabilization.2-4,23,24 When fractures arise as a part of humeral insertion, the surgeon must know what fixation techniques will prevent propagation of the fracture6 during the average 17 weeks needed to heal,2 which is much longer than the typical immobilization period after surgery.19 Much of the work on intraoperative fracture fixation has relied on data from the hip and knee literature or from proximal humeral fractures without prostheses; however, no studies address fixation techniques specifically for shoulder arthroplasty and intraoperative fractures. There are a myriad of techniques that have been discussed, including the use of braided suture, wire, and cable cerclage techniques,2,9,13,18,20,21,25,27,28 to fix fractures or humeral osteotomies in revision surgery. However, the loading pattern occurring from a prosthesis in a fractured shaft is very difficult to predict, and small gapping of the fracture may result in considerable subsidence of the prosthetic shaft. Therefore, it was the purpose of this work to investigate the compression generated by each cerclage construct and to find the best method for creating a stable compressive fixation using high-strength sutures. As a second step, we tested the amount of subsidence of the prosthesis into an experimentally fractured shaft stabilized with a metallic versus a flexible cerclage.
Materials and methods Stainless steel wire cerclage (SSWC) of 1.25 mm in diameter (Synthes, Solothurn, Switzerland) and No. 5 FiberWire (Arthrex, Naples, FL, USA) cerclage (FWC) were used in this study. FiberWire (FW) is made of ultrahigh–molecular weight polyethylene (UHMWPE) and polyester braided over a UHMWPE core.
Distraction test Cerclage testing followed a previously established protocol.16,29 Fresh-frozen bovine femur (–20 C) was used for the assessment. The bone was thawed and kept humid for the investigation. Before testing, all soft tissue surrounding the bone was removed and pieces of 65 mm in length were cut from the mid diaphysis. To fit the bone shells on the testing jig, the intramedullary canal was reamed up to 25 mm and the fragment was cut into 2 parts. The outer diameter of the 2 pieces was 40 mm. All cerclage systems were tested using the same specimen. After preparation of the bone shells, they were fit on the testing jig, which consisted of 2 metallic half cylinders with a radius of 25 mm, forming a full circle. The upper half cylinder was connected to a 20-kN load cell. Between the bone shells, a gap of 1 mm was maintained during the test to avoid load transfer via the testing machine. For all assessments, we used the same universal material testing machine (Zwick 1456; Zwick/Roell, Ulm, Germany), which recorded the
N. Renner et al. data using dedicated software (testExpert 10; Zwick/Roell). We evaluated the data regarding load (in newtons) and displacement (in millimeters), which were digitally recorded, and the deformation curve and the mode of failure were documented. We twisted 1.25-mm double-looped cerclage wires with dedicated pliers (M€ uller, St. Gallen, Switzerland) under permanent traction on the cerclage wires. Values of 940 26 N were determined in a series of 5 samples as the range of ultimate compressive force achieved by twisting. The cerclages were therefore twisted on the testing jig until approximately 90% of the maximally expected force was reached. After 6 turns, the free wire ends were cut outside the crimp, which was then bent forward (in the direction of the twisting) to minimize loss of pre-tension.29 Double-looped No. 5 FW slings were performed and secured with 3 different knots as described later. Each setup was tested 10 times. After preliminary testing, a standard surgical knot with 4 throws was deemed suitable as a control group. Furthermore, 2 sling hitches with 4 simple knots on top (cow hitch and singlethrow hitch) as depicted in Figures 1 and 2 were tested. At the cerclage setup, pre-tension was measured at the following time points: (1) after wire twisting, (2) after removal of pliers, (3) after cutting the wire ends, (4) after bending the crimp, and (5) 1 minute later. The FW pre-tension was measured after secure knot tying. After 1 minute, a constant tensile force with a speed of 0.2 mm/s was applied, and load leading to a 1-, 2-, and 3-mm gap opening, as well as load to total failure, was recorded. The end of the test was defined as 90% force shutdown or gap opening of 20 mm between the bone shells.
Subsidence test Ten fresh-frozen (20 C) proximal humeri of human specimens were prepared for this investigation. Standard anteroposterior radiographs of each bone were obtained, and all bones were matched into 2 approximately equal groups regarding their cortical indexes.11 After thawing of all proximal cadaveric humeri, the heads were resected exactly at the level of the anatomic neck and a medial longitudinal split (‘‘humerotomy’’) of 10 cm in length was performed with the aid of an oscillating saw. The medullary canal was rasped manually using rasps from the Zimmer Anatomical Shoulder System (Zimmer, Winterthur, Switzerland) until solid resistance was felt from cortical contact in the canal. Each specimen was fixed in a vertical fixation device on the machine table, and an uncemented proximal humeral prosthesis stem (Anatomical Prosthesis; Zimmer), appropriate to the size of the bone canal (with reference to the radiograph to achieve a firm diaphyseal fit), was inserted into the medullary canal until a preload of 100 N was reached. The humerotomy was then secured 3 cm distal to the calcar using either a double-wire cerclage (n ¼ 5) or an FW double-loop cerclage (cow hitch) (n ¼ 5), which has previously been determined as best for the purpose (Fig. 3). For subsidence measurements, on the same test machine mentioned earlier, a compressive load was applied onto the prosthesis by lowering the cross-head at a constant speed of 0.2 mm/s and resistance during subsidence of the prosthesis was measured. Tests were completed when a penetration depth of 10 mm was reached. Load to subsidence was recorded with a force-strain curve. Videos were recorded using a Nikon D800 digital camera (Nikon, Tokyo, Japan) that was equipped with a specific macro-objective (Telecentric Visionmes Lenses 16/16/0.1;
Cerclage fixation in total shoulder arthroplasty
3
Figure 1 (A) For the FW cow hitch, a double-looped No. 5 FW was used. (B) The suture end was folded over to create a sling (cow hitch or ‘‘running eye’’). (C) Both single ends of the FW were passed through the sling, tightened, and secured with 4 throws.
Figure 2 Knot tying of FW single-throw hitch. (A) The double No. 5 FW was looped around the bone shells twice. (B) A single throw was created with the suture loop, and the loose suture ends were pulled through the FW loop and tightened. (C) To secure the knot, 4 throws were tied.
Carl Zeiss, Oberkochen, Germany) from every subsidence test, and gap opening was measured with Adobe Photoshop CS5 (Adobe Systems, Munich, Germany).
Statistical analysis To detect significant differences among the groups regarding loss of pre-tension, gap opening, total failure, and subsidence resistance force, 1-way analysis of variance was performed. The significance level was defined as a ¼ .05.
Results Distraction test Wire tightening of the 1.25-mm wire cerclage resulted in a primary pre-tension of 817 16 N and decreased to 806 20 N after removal of the pliers, to 780 27 N after cutting of the wire, and to 618 75 N after bending of the crimp; thereafter, it remained stable after 1 minute.
4
N. Renner et al.
Subsidence test Force required to press the prosthesis from 1 to 10 mm into the humerus (subsidence) after application of a cerclage is shown in Figure 5. There was no significant difference between the cerclage wires and FWCs. We recorded a slightly greater gap opening using SSWC compared with the FW group, without reaching a statistical difference (Fig. 6).
Discussion
Figure 3 Subsidence test setup. Ten proximal human humeri were resected at the level of the anatomic neck after thawing. The specimens were split longitudinally at a length of 10 cm. To fit the prosthesis stem, the medullary canal was rasped manually. The prosthesis stems were pushed into the medullary canal by a metallic pin in the testing machine. Load to subsidence at a speed of 0.2 mm/s was recorded, and the load-displacement curve was documented.
With 131 N for the 4-throw control knot, 137 N for the cow hitch, and 133 N for the single-throw hitch, the maximum pre-tension values of the FWC were not significantly different among the 3 knots (P > .05); however, maximum pre-tension was significantly lower than pretension of the wire cerclages. Distraction force and load at total failure of the different cerclage configurations are shown in Figure 4. All cerclages failed by either unraveling of the twist or wire breakage at the innermost turn of the twist. All FWCs ripped apart by rupture at the innermost thread of the knot. At 1 and 2 mm of displacement, all FWCs exhibited comparable results but showed significantly lower results than the SSWC. However, load at 3 mm of fragment separation showed similar results for the SSWC (1,820 N; range, 1539 – 2058 N; SD, 256 N), FW cow hitch (1,803 N; range, 1339 – 2040 N; SD, 246 N), and FW single-throw hitch (1,709 N; range, 1498 – 1867 N; SD, 113 N); these loads were significantly higher compared with that of the FW 4-throw knots (1,289 N; range, 741 – 1734 N; SD, 353 N). Load to total failure was, however, comparable among the 3 different FW cerclage knots, which were significantly stronger than SSWC.
Iatrogenic fractures or humeral osteotomies may occur in primary or revision shoulder arthroplasty. Factors such as osteopenia, female sex, and rheumatoid arthritis are associated with intraoperative fractures, have a prevalence of 0.6% to 3%, and account for nearly 20% of all complications.2,7,14,23,25,30,31 Various treatment options such as cerclage wiring, plating, and interfragmentary screw insertion12 have been proposed. Regarding the specific cerclage technique, various constructs addressing the violation of the bone have been reported,10,15,22 but to our knowledge, no systematic testing of the ideal biomechanical technique has been conducted in combination with a humeral prosthesis. We conducted our test setup because biomechanical testing of common suture materials showed that a single-loop No. 5 FW is the suture material that has the closest material properties regarding load to failure and stiffness compared with a 1.25-mm stainless steel wire.20 Cerclage fixation of bone may follow 2 purposes: first, to reduce a displaced fracture, and second, to secure bone against further fracture crack propagation. Regarding the first task, we could show that cerclage wires are far more suitable to actively compress bone, with an approximately 5-fold higher compressive load created as compared with the suture construct, which might be an advantage to reduce a fracture. Beyond that, SSWC provided more resistance to fragment separation at small distances (1-2 mm) in combination with strong cortical bovine femur shells in our laboratory bench test because of the higher elasticity of the FWC. However, resistance against gap formation of more than 3 mm and ultimate load to failure were significantly higher using an FW suture cerclage. The cow hitch presented in this study with simple throws performed best regarding ultimate failure load and stiffness. As described by Lenz et al,16 failure of all cerclages occurred by either unraveling of the twist or wire breakage at the innermost turn of the twist. However, all FWCs ripped apart by rupture at the innermost thread of the knot, and knot slippage was never observed, despite the small number of only 4 throws.17 These very different resistance and strain behaviors among the tested suture and wire cerclage models, however, did not significantly influence resistance and opening of the gap during prosthetic stem subsidence. Although
Cerclage fixation in total shoulder arthroplasty
5
Figure 4 Distraction to 1, 2, and 3 mm ( standard deviation), as well as load leading to total failure ( standard deviation), for tested cerclage types (n ¼ 10; )) P < .01; ))) P < .001).
Figure 5 Force needed ( standard deviation) to press the shaft of the proximal humeral prosthesis 1 to 10 mm into the medullary canal. Testing showed no difference between the cerclage systems.
Figure 6
Gap opening ( standard deviation) (in millimeters) at proximal humerus split at 1 to 10 mm of subsidence of prosthesis stem.
there was a slightly greater gap opening during the test for the SSWC compared with the FW group, no statistical difference was found and gap opening was only 1 to 1.5 mm in the case of 1 cm of prosthetic stem subsidence. It is questionable whether the potential pre-tensioning of the SSWC up to 966 N is of practical importance, especially on osteopenic or osteoporotic bone, because the wires may cut through the bone. Vice versa, the use of a
nonmetallic cerclage construct has potential advantages such as better adaptation to the bone surface, decrease of soft tissue irritation by the crimp, and no risk of metal-onmetal debris. The equivalent results in subsidence testing of the FW and the stainless steel wire despite the higher stiffness of the metallic SSWC may be explained by 2 aspects. First, the suture construct may compensate for its elasticity with
6
N. Renner et al.
the greater surface area to distribute the load on the bone and may thus cut less into the soft periosteum and bone. Second, the weakest area appears to be the soft cancellous canal even though radiologically measured well-tapered prostheses were implanted. Therefore, the elasticity of the wire construct is not the weakest link and thus not the limiting factor for subsidence. There are some limitations of this investigation. First, we used very strong cortical bovine femur shells for our laboratory bench test, which did not allow any plastic deformation as occurs in vivo but which was necessary to isolate the behavior of the wire and suture. Second, subsidence testing was performed with different stem sizes and cadaveric humeri having, despite matching, variable biomechanical characteristics. Furthermore, to limit the variables of the test setup, we decided against performing cyclic testing.5,18 However, despite the aforementioned limitations, our results appear to be in line with comparable data on the use of nonmetallic cerclage material in orthopaedic surgery8,10,22,26 and even with a report assessing a specifically designed commercial braided UHMWPE fiber cable to fix a periprosthetic fracture in revision shoulder arthroplasty.10 In summary, because we could not find relevant downsides to the suture cerclage fixation on the humerus in combination with prostheses assessed in this study, the associated advantages, such as ease of handling, low cost, good tissue compatibility, and no interference with radiologic imaging, may make this method an attractive option in patients in whom no relevant bone gap needs to be closed.
Conclusion Suture (FW) cerclages in shoulder arthroplasty provide a safe, affordable, simple, and readily available technique to stabilize periprosthetic fractures or humeral osteotomies as long as no gap needs to be actively closed by the cerclage. Particularly in patients with osteopenic or osteoporotic bone, the use of an FWC provides sufficient stability comparable with established wire cerclages, with the benefit of no radiologic interference. The shortcoming of this study is the lack of cyclic testing, which may be further assessed to confirm our results in a repeated load assessment.
Disclaimer Zimmer provided the proximal humeral prosthesis stem from the Anatomical Shoulder System for our test setup. The authors, their immediate families, and any research foundations with which they are affiliated have not received any financial payments or other benefits from any commercial entity related to the subject of this article.
References 1. Arnesen AJ. Encircling suture (cerclage) in oblique fractures. Acta Chir Scand 1951;102:267-74. 2. Athwal GS, Sperling JW, Rispoli DM, Cofield RH. Periprosthetic humeral fractures during shoulder arthroplasty. J Bone Joint Surg Am 2009;91:594-603. http://dx.doi.org/10.2106/JBJS.H.00439 3. Boileau P, Melis B, Duperron D, Moineau G, Rumian AP, Han Y. Revision surgery of reverse shoulder arthroplasty. J Shoulder Elbow Surg 2013;22:1359-70. http://dx.doi.org/10.1016/j.jse.2013.02.004 4. Bonutti PM, Hawkins RJ. Fracture of the humeral shaft associated with total replacement arthroplasty of the shoulder. A case report. J Bone Joint Surg Am 1992;74:617-8. 5. Bostrom MP, Asnis SE, Ernberg JJ, Wright TM, Giddings VL, Berberian WS, et al. Fatigue testing of cerclage stainless steel wire fixation. J Orthop Trauma 1994;8:422-8. 6. Boyd AD Jr, Thornhill TS, Barnes CL. Fractures adjacent to humeral prostheses. J Bone Joint Surg Am 1992;74:1498-504. 7. Campbell JT, Moore RS, Iannotti JP, Norris TR, Williams GR. Periprosthetic humeral fractures: mechanisms of fracture and treatment options. J Shoulder Elbow Surg 1998;7:406-13. 8. Carofino BC, Santangelo SA, Kabadi M, Mazzocca AD, Browner BD. Olecranon fractures repaired with FiberWire or metal wire tension banding: a biomechanical comparison. Arthroscopy 2007;23:964-70. http://dx.doi.org/10.1016/j.arthro.2007.03.008 9. Dietz SO, Broos P, Nijs S. Suture fixation versus cable cerclage of the tuberosities in shoulder arthroplastydclinical and radiologic results. Arch Orthop Trauma Surg 2012;132:793-800. http://dx.doi.org/10. 1007/s00402-012-1470-2 10. Edwards TB, Stuart KD, Trappey GJ, O’Connor DP, Sarin VK. Utility of polymer cerclage cables in revision shoulder arthroplasty. Orthopedics 2011;34(4):264. http://dx.doi.org/10.3928/0147744720110228-13 11. Giannotti S, Bottai V, Dell’osso G, Donati D, Bugelli G, De Paola G, et al. Indices of risk assessment of fracture of the proximal humerus. Clin Cases Miner Bone Metab 2012;9:37-9. 12. Groh GI, Heckman MM, Wirth MA, Curtis RJ, Rockwood CA Jr. Treatment of fractures adjacent to humeral prostheses. J Shoulder Elbow Surg 2008;17:85-9. http://dx.doi.org/10.1016/j.jse.2007.05.007 13. Han SM. Comparison of wiring techniques for bone fracture fixation in total hip arthroplasty. Tohoku J Exp Med 2000;192:41-8. 14. Kumar S, Sperling JW, Haidukewych GH, Cofield RH. Periprosthetic humeral fractures after shoulder arthroplasty. J Bone Joint Surg Am 2004;86:680-9. 15. Lenz M, Perren SM, Gueorguiev B, Richards RG, Krause F, Fernandez Dell’Oca A, et al. Underneath the cerclage: an ex vivo study on the cerclage-bone interface mechanics. Arch Orthop Trauma Surg 2012; 132:1467-72. http://dx.doi.org/10.1007/s00402-012-1572-x 16. Lenz M, Perren SM, Richards RG, Muckley T, Hofmann GO, Gueorguiev B, et al. Biomechanical performance of different cable and wire cerclage configurations. Int Orthop 2013;37:125-30. http:// dx.doi.org/10.1007/s00264-012-1702-7 17. Lo IKY, Burkhart SS, Chan KC, Athanasiou K. Arthroscopic knots: determining the optimal balance of loop security and knot security. Arthroscopy 2004;20:489-502. http://dx.doi.org/10.1016/j.arthro. 2004.03.005 18. Meyer DC, Ramseier LE, Lajtai G, Notzli H. A new method for cerclage wire fixation to maximal pre-tension with minimal elongation to failure. Clin Biomech (Bristol, Avon) 2003;18:975-80. 19. Mulieri PJ, Holcomb JO, Dunning P, Pliner M, Bogle RK, Pupello D, et al. Is a formal physical therapy program necessary after total shoulder arthroplasty for osteoarthritis? J Shoulder Elbow Surg 2010; 19:570-9. http://dx.doi.org/10.1016/j.jse.2009.07.012 20. Najibi S, Banglmeier R, Matta J, Tannast M. Material properties of common suture materials in orthopaedic surgery. Iowa Orthop J 2010; 30:84-8.
Cerclage fixation in total shoulder arthroplasty 21. Roe SC. Mechanical characteristics and comparisons of cerclage wires: introduction of the double-wrap and loop/twist tying methods. Vet Surg 1997;26:310-6. 22. Sarin VK, Mattchen TM, Pratt WR, Hack B. Novel iso-elastic cerclage cable for fracture treatment. J Bone Joint Surg Br 2008;90:189. 23. Singh JA, Sperling J, Schleck C, Harmsen W, Cofield R. Periprosthetic fractures associated with primary total shoulder arthroplasty and primary humeral head replacement: a thirty-three-year study. J Bone Joint Surg Am 2012;94:1777-85. http://dx.doi.org/10.2106/JBJS.J. 01945 24. Sperling JW, Cofield RH. Humeral windows in revision shoulder arthroplasty. J Shoulder Elbow Surg 2005;14:258-63. http://dx.doi.org/ 10.1016/j.jse.2004.09.004 25. Steinmann SP, Cheung EV. Treatment of periprosthetic humerus fractures associated with shoulder arthroplasty. J Am Acad Orthop Surg 2008;16:199-207. 26. Ting NT, Wera GD, Levine BR, Della Valle CJ. Early experience with a novel nonmetallic cable in reconstructive hip surgery. Clin Orthop
7
27.
28.
29.
30. 31.
Relat Res 2010;468:2382-6. http://dx.doi.org/10.1007/s11999-0101284-x Van Thiel GS, Halloran JP, Twigg S, Romeo AA, Nicholson GP. The vertical humeral osteotomy for stem removal in revision shoulder arthroplasty: results and technique. J Shoulder Elbow Surg 2011;20: 1248-54. http://dx.doi.org/10.1016/j.jse.2010.12.013 Voigt C, Hurschler C, Rechi L, Vosshenrich R, Lill H. Additive fibercerclages in proximal humeral fractures stabilized by locking plates: no effect on fracture stabilization and rotator cuff function in human shoulder specimens. Acta Orthop 2009;80:465-71. http://dx.doi.org/ 10.3109/17453670903110659 Wahnert D, Lenz M, Schlegel U, Perren S, Windolf M. Cerclage handling for improved fracture treatment. A biomechanical study on the twisting procedure. Acta Chir Orthop Traumatol Cech 2011;78:208-14. Worland RL, Kim DY, Arredondo J. Periprosthetic humeral fractures: management and classification. J Shoulder Elbow Surg 1999;8:590-4. Wright TW, Cofield RH. Humeral fractures after shoulder arthroplasty. J Bone Joint Surg Am 1995;77:1340-6.