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Headless Compression Screw Versus Kirschner Wire Fixation for Metacarpal Neck Fractures: A Biomechanical Study
SCIENTIFIC ARTICLE
Headless Compression Screw Versus Kirschner Wire Fixation for Metacarpal Neck Fractures: A Biomechanical Study Daniel M. Avery, III, MD,* Stephen Klinge, MD,* Felix Dyrna, MD,* Leo Pauzenberger, MD,* David Lam, BA,* Mark Cote, DPT, MS,* Jessica DiVenere, BS,* Elifho Obopilwe, ME,* Augustus Mazzocca, MS, MD,* Craig Rodner, MD*
Purpose This study aimed to determine the biomechanical stability of headless compression screws in the fixation of metacarpal neck fractures and to compare them with another common, less invasive form of fixation, K-wires. The hypothesis was that headless compression screws would show higher stiffness and peak load to failure than K-wire fixation. Methods Eight matched-paired hands (n ¼ 31), using the ring and little finger metacarpals, had metacarpal fractures simulated at the physeal scar. Each group was stabilized with either a 3.5-mm headless compression screw or 2 0.045-in (1.1-mm) K-wires. Nineteen metacarpals were tested in 3-point bending and 12 in axial loading. Peak load to failure and stiffness were calculated from the load displacement curve. Bone mineral density was recorded for each specimen. Results Bone mineral density was similar in the 2 groups tested for 3-point bending and axial loading. Stiffness was not significantly different in 3-point bending for headless compression screws and K-wires (means, 141.3 vs 194.5 N/mm) but it was significant in axial loading (means, 178.0 vs 111.6 N/mm). Peak load to failure was significantly higher in headless compression screws in 3-point bending (means, 401.2 vs 205.3 N) and axial loading (means, 467.5 vs 198.3 N). Conclusions Compared with K-wires, headless compression screws for metacarpal neck fractures are biomechanically superior in load to failure, 3-point bending, and axial loading. Clinical relevance Headless compression screws demonstrate excellent biomechanical stability in metacarpal neck fractures. In conjunction with promising clinical studies, these data suggest that headless compression screws may be an option for treating metacarpal neck fractures. (J Hand Surg Am. 2017;-(-):1.e1-e6. Copyright Ó 2017 by the American Society for Surgery of the Hand. All rights reserved.) Key words Metacarpal, neck, fracture, surgery, return to play.
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10% o 30% of all hand fractures. They can affect the athletic or working-age population and can have considerable socioeconomic impact with prolonged immobilization.2 Metacarpal neck fractures, ETACARPAL FRACTURES ACCOUNT FOR 1
From *UCONN Orthopaedic Sports Medicine, University of Connecticut Musculoskeletal Institute, Farmington, CT. Received for publication May 19, 2016; accepted in revised form February 9, 2017. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
particularly of the little finger, account for most of these injuries.1,3,4 Although nonsurgical treatment can be successful, operative treatment is indicated when there is unacceptable rotation, shortening, or volar angulation. Some controversy exists as to Corresponding author: Daniel M. Avery, III, MD, UCONN Orthopaedic Sports Medicine, University of Connecticut Musculoskeletal Institute, 263 Farmington Avenue, Farmington, CT 06030-4037; e-mail: [email protected]. 0363-5023/17/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2017.02.013
Ó 2017 ASSH
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Published by Elsevier, Inc. All rights reserved.
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the exact parameters that constitute acceptable alignment.5 There are numerous techniques reported in the literature for the fixation of metacarpal neck fractures. Closed reduction and K-wire fixation offer a relatively fast, minimally invasive option. Disadvantages of K-wire fixation, however, include the possibility of pin site infection, prominent hardware precluding early range of motion (ROM), and tethering of surrounding structures. On the other end of the spectrum, plate fixation provides strong fixation allowing early ROM and return to sports, but it comes at the expense of more extensive soft tissue disruption, risk of wound infection, possible hardware irritation, and tendon adherence.6e9 Headless compression screws have been accepted in the treatment of carpal fractures, most notably scaphoid fractures.10e14 With support for an intra-articular starting point,15 headless compression screw fixation for metacarpal neck and shaft fractures has been shown to be a reliable option for axially stable fractures.16 The advantages of headless compression screws are relatively fast insertion and the minimally invasive insertion technique, decreasing risks associated with more extensive soft tissue dissection, stability allowing early ROM, and that it is an intramedullary implant, which eliminates the risk of hardware irritation. Although there is supporting clinical evidence, there have been no biomechanical data to compare headless screws with other forms of fixation for the stabilization of metacarpal neck fractures. The purpose of this study was to perform a biomechanical comparison of 2 forms of metacarpal neck fixation, K-wire and headless compression screws. The hypothesis was that headless compression screws would show higher stiffness and peak load to failure than K-wire fixation.
owing to previous deformity. Fractures were created by locating the physeal scar under fluoroscopy and creating an osteotomy using a sagittal saw 1 mm thick. For K-wire fixation, 2 0.045-in (1.1-mm) K-wires were introduced into the metacarpal head at the sulcus just radial and ulnar to the articular surface in a slightly dorsal position similar to that originally described by Lord.17 Each wire was advanced in a retrograde fashion in the medullary canal until a firm end point was reached signifying the metacarpal base. This end point was confirmed with fluoroscopic imaging. We took care to advance the wires perpendicular to the osteotomy site and not to cross or intersect them at the fracture site. The remainder of the K-wire was cut, leaving approximately 15 mm protruding from the bone (Fig. 1). For headless compression screw fixation, a 0.045-in guide wire with a trocar tip was inserted in a dorsal, central position in line with the metacarpal shaft. The distal segment (metacarpal head) was over-drilled using a 2.7-mm cannulated drill bit. A 3.5-mm, headless compression screw 32 mm long (Arthrex, Naples, FL) was then inserted over the guide wire to approximately 2 mm below the articular surface (Fig. 2). Testing protocol To test the most common deforming force of flexionextension, we subjected 19 metacarpals (10 with headless compression screws and 9 with K-wires) to 3-point bending, apex dorsal, on a Materials Testing System servohydraulic test frame (MTS Systems Corp, Eden Prairie, MN), generating a loaddisplacement curve. Metacarpals were placed on a custom-made base consisting of 2 posts with a 35-mm gap in between. We carefully ensured that the fracture was placed the same way for each specimen with the dorsal surface down. The loading plunger was placed over the distal shaft of the metacarpal and an axial force was applied at 100 mm/min. Sampling was recorded at 100 Hz. To test axial loading, which can be a common mode of failure, 12 metacarpals (6 with headless compression screws and 6 with K-wires) were potted in 1.5-in diameter polyvinyl chloride piping and plaster of Paris, leaving the equivalent of 15 mm of distal metacarpal exposed to be subjected to testing. Care was taken during potting to align the dorsal side of the metacarpal parallel to the polyvinyl chloride wall. Specimens were mounted onto the Materials Testing System frame using a custom-made clamp allowing alignment of the potted specimens to be
MATERIALS AND METHODS Specimen preparation and fixation Eight matched-paired hands, an average age at death of 59 6 years, and stored at e20 C, underwent dual-energy x-ray absorptiometry (DEXA) (Lunar DPI XQ Dexascan, Madison, WI). We measured a 1-cm2 region within the metacarpal neck of each specimen. Specimens were randomized as a pair of hands into 1 of 2 groups: one treated with a K-wire fixation technique (n ¼ 15) and the other with a headless compression screw technique (n ¼ 16). After complete thawing at room temperature, the ring and little finger metacarpals were dissected free of all soft tissue. One little finger metacarpal was excluded J Hand Surg Am.
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FIGURE 1: A Gross specimen with B anteroposterior and C lateral fluoroscopic images of fixation with K-wires.
Statistics Because of the exploratory nature of this study, an a priori power analysis was based on the following assumptions: A difference of 150 N between groups would correspond to a 75% difference assuming an estimated load to failure of 200 N with K-wire fixation and 350 N with headless compression screw fixation. A standard deviation of 100 N was assumed across both groups. Assuming these parameters, a sample size of 7/group would provide 80% power to detect a 125-N difference in load to failure at a ¼ 0.05.
corrected if needed, to ensure axial loading was perpendicular to the dorsal surface of the specimen. The loading plunger was centered over the articular surface in a dorsopalmar direction to simulate an axial loading force. Force was applied at 100 mm/min and recorded at 100 Hz. The load-displacement curve generated was used to calculate peak load to failure (N) and stiffness (N/mm). Stiffness corresponded to the linear slope whereas the peak load to failure was defined at the moment of abrupt change in the load-displacement curve. J Hand Surg Am.
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FIGURE 2: A Gross specimen with B anteroposterior and C lateral fluoroscopic images of headless compression screw fixation.
Descriptive statistics to characterize the study groups were calculated using means and SD. Differences between groups were analyzed with an independent t test. a for all analyses was set at 0.05.
migrating away from the osteotomy (Fig. 3A). The headless compression screw group failed when the palmar cortex of the shaft broke near the osteotomy site and the screw bent (Fig. 3B).
RESULTS Three-point bending We evaluated DEXA scanning for each ring and little finger metacarpal. Bone mineral density was similar between the K-wire group (n ¼ 9; 0.54 0.1 g/cm2) and the headless compression screw group (n ¼ 10; 0.54 0.2 g/cm2). There was no significant difference in the stiffness of the headless compression screws and the K-wires (P ¼ .20). Stiffness for headless compression screws was 141.3 80.2 N/mm, and for K-wires it was 194.5 86.3 N/mm. Peak load to failure showed a significant difference in favor of headless compression screws (P < .05). Peak load to failure for headless compression screws was 401.2 105.3 N, and for K-wires it was 205.3 65.9 N. All specimens failed in a group-specific uniform manner. The K-wire group failed with permanent deformation of the wires, with the distal fragment
Axial loading Bone mineral density was similar between the K-wire (n ¼ 6) and headless compression screw groups (n ¼ 6) with means and SDs of 0.46 0.1 and 0.40 0.2 g/cm2, respectively. Mean stiffness for K-wire fixation was 111.6 15.4 N/mm, and for headless compression screw fixation was 177.9 16.1 N/mm. The difference between groups was statistically significant (P < .05). Peak load to failure was significantly higher for headless compression screw fixation (P < .05). Mean peak load to failure was 467.4 205.7 and 198.3 9.6 N for headless compression screws and K-wires, respectively. The mode of failure for K-wires was bending of the hardware with gradual displacement until the K-wires cut through the metacarpal head. The headless compression screws absorbed the load until the proximal part of the screw dislodged from the metacarpal
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FIGURE 3: Gross specimens after load to failure showing modes for A K-wire and B headless compression screw constructs.
head region with displacement at the osteotomy site, after which the apparatus loaded the screw directly.
Although no deleterious effect has been shown, access to the articular starting point requires incising of the sagittal band or splitting of the extensor tendon, which is a potential cause of complications. Peak load to failure for headless compression screws in 3-point bending was significantly higher than K-wire fixation and was approximately equivalent to that of plate fixation, as demonstrated in another study.18 In addition, we found that headless compression screws had significantly higher peak load to failure than K-wires in axial loading. Because the hardware remains in place, protection is conferred throughout healing. Clinically, Ruchelsman et al16 showed that fixation with headless screws allowed early rehabilitation and achieved excellent union rates, ROM, and grip strength with minimal complications. This suggests potential advantages of faster return to work or sports with axial loading data to support protection against repeated mode of injury. There were several limitations to this study. Because it was a cadaveric biomechanical study, stability from the adjacent soft tissue structures was not accounted for in the results. Furthermore, the osteotomies that were created simulated an axially stable fracture pattern, as described in previous biomechanical studies,25e29 which does not reflect all metacarpal neck fractures in vivo. The presence and variable amount of volar comminution of metacarpal neck fractures that may be present clinically were not evaluated and could have altered the results seen in this study. The primary deforming force in these fractures was the intrinsic and extrinsic flexors, which were modeled by an apex dorsal bending force, as was previously performed.25e29 We also tested axial loading, which is not only a common mode of injury but could be an at-risk force in early return to play in some sports. The study design did not account for rotational forces or cyclical loading, which are clinically relevant. This study was not intended to be a comprehensive comparison of constructs. We chose to compare headless compression screws with retrograde K-wire fixation because of their similar, minimally invasive nature. We also chose to
DISCUSSION This study sought to compare 2 different means of metacarpal neck fracture fixation: 2 retrograde K-wires versus a single headless compression screw. The results of the study showed that headless compression screws demonstrated stiffness similar to K-wires and significantly higher peak load to failure. A recent study by Malasitt et al18 comparing K-wires, plates, and metacarpal sleds (a device consisting of a plate with intramedullary prongs) demonstrated stiffness and peak loads for K-wire fixation similar to those of the current study. Our peak load for headless compression screws was higher than either the K-wires or the sled and plate fixation studied in that report. K-wire fixation in the current study demonstrated precise stability in 3-point bending and axial loading. With their ease of insertion and percutaneous nature, K-wires are a reasonable choice for maintaining alignment during healing for fractures that do not require early rehabilitation or rapid return to full function. K-wires preclude ROM while in place, usually 4 weeks, and the fracture may require continued protection after K-wire removal if healing is incomplete. Their disadvantages have been highlighted in previous studies, including pin site infection, delayed wound healing, soft tissue irritation, stiffness from continued immobilization and protruding hardware, and secondary procedures for removal.19e24 Headless compression screws offer a minimally invasive option to K-wire fixation without the hardware-associated complications. Articular violation is a common concern regarding the technique, however, Ten Berg et. al15 demonstrated that the articular violation is minimal and there is little effect on sagittal plane motion because the rim of the phalangeal base did not overlap the entrance point in 64% of cases in their 3-dimensional modeling. J Hand Surg Am.
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use cadaver specimens to more closely mimic in vivo effects, as opposed to using synthetic materials that are more uniform in shape and consistency. However, for this reason we performed DEXA scanning to compare the adequacy of the specimens, and found similar values between groups. Nonsurgical treatment is appropriate for the vast majority of metacarpal neck fractures. When surgery is indicated, K-wire fixation has been shown to be a reliable and biomechanically sound option. This study demonstrated that headless compression screws are a biomechanically superior form of fixation in load to failure compared with K-wires. Therefore, using headless compression screws to fix certain metacarpal neck fractures may allow for earlier initiation of postoperative rehabilitation than for those fixed with K-wires and thus promote earlier return to work or sports in the subset of patients who require this. Long-term clinical results are needed to substantiate their safety and efficacy in this application.
9. Etier BE, Scillia AJ, Tessier DD, et al. Return to play following metacarpal fractures in football players. Hand (N Y). 2015;10(4): 762e766. 10. Gereli A, Nalbantoglu U, Sener IU, Kocaoglu B, Turkmen M. Comparison of headless compression screws used in the treatment of proximal nonunion of scaphoid bone. Int Orthop. 2011;35(7):1031e1035. 11. Rutgers M, Mudgal CS, Shin R. Combined fractures of the distal radius and scaphoid. J Hand Surg Eur Vol. 2008;33(4):478e483. 12. Singisetti K, Aldyami E, Middleton A. Early results of a new 3.0mm headless compression screw for scaphoid fracture fixation. J Hand Surg Eur Vol. 2012;37(7):690e693. 13. Henry M. Variable pitch headless compression screw treatment of distal phalangeal nonunions. Tech Hand Up Extrem Surg. 2010;14(4):230e233. 14. Ruchelsman DE, Tejwani NC, Kwon YW, Egol KA. Open reduction and internal fixation of capitellar fractures with headless screws. J Bone Joint Surg Am. 2008;90(6):1321e1329. 15. Ten Berg P, Mudgal CS, Leibman MI, Belsky MR, Ruchelsman DE. Quantitative 3D-CT analysis of intramedullary headless screw fixation for metacarpal neck fractures. J Hand Surg Am. 2013;38(2):322e330. 16. Ruchelsman DE, Puri S, Feinberg-Zadek N, Leibman MI, Belsky MR. Clinical outcomes of limited-open retrograde intramedullary headless screw fixation of metacarpal fractures. J Hand Surg Am. 2014;39(12):2390e2395. 17. Lord RE. Intramedullary fixation of metacarpal fractures. J Am Med Assoc. 1957;164(16):1746e1749. 18. Malasitt P, Owen JR, Tremblay M, Wayne JS, Isaacs JE. Fixation for metacarpal neck fracture: a biomechanical study. Hand (N Y). 2015;10(3):438e443. 19. Hsu LP, Schwart EG, Kalainov DM, et al. Complications of k-wire fixation in procedures involving the hand and wrist. J Hand Surg Am. 2011;36(4):610e616. 20. Hargreaves DG, Drew SJ, Eckersley R. Kirschner wire pin tract infection rates: a randomized controlled trial between percutaneous and buried wires. J Hand Surg Br. 2004;29(4):374e376. 21. Xu J, Zhang C. Mini plate versus Kirschner wire internal fixation for treatment of metacarpal and phalangeal fractures in Chinese Han population: a meta-analysis. J Orthop Surg Res. 2014;9:24. 22. Kim JK, Kim DJ. Antegrade intramedullary pinning versus retrograde intramedullary pinning for displaced fifth metacarpal neck fractures. Clin Orthop Relat Res. 2015;473:1747e1754. 23. Yammine K, Harvey A. Antegrade intramedullary nailing for fifth metacarpal neck fractures: a systematic review and meta-analysis. Eur J Orthop Surg Traumatol. 2014;24(3):273e278. 24. Foucher G. “Bouquet” osteosynthesis in metacarpal neck fractures: a series of 66 patients. J Hand Surg Am. 1995;20(suppl):S86eS90. 25. Dona E, Gillies RM, Gianoutsos MP, et al. Plating of metacarpal fractures: unicortical or bicortical screws? J Hand Surg Br. 2004;29(3):218e221. 26. Prevel CD, Eppley BL, Jackson JR, et al. Mini and micro plating of phalangeal and metacarpal fractures: a biomechanical study. J Hand Surg Am. 1995;20(1):44e49. 27. Doht S, Jansen H, Meffert RH, et al. Higher stability with locking plates in hand surgery? Biomechanical investigation of the TriLock system in a fracture model. Int Orthop. 2012;36(8):1641e1646. 28. Mudrick CA, Owen JR, Wayne JS, et al. Unicortical PEEK inset locking fixation for metacarpal fractures: a biomechanical study. Eur J Orthop Surg Traumatol. 2013;24(8):1415e1420. 29. Ochman S, Doht S, Paletta J, et al. Comparison between locking and non-locking plates for fixation of metacarpal fractures in an animal model. J Hand Surg Am. 2010;35(4):597e603.
ACKNOWLEDGMENTS Special thanks to Arthrex for donating cadaver specimens and hardware for fixation used in this study. REFERENCES 1. Anakwe RE, Aiken SA, Cowie JG, et al. The epidemiology of fractures of the hand and the influence of social deprivation. J Hand Surg Eur Vol. 2011;36(1):62e65. 2. Poolman RW, Goslings JC, Lee JB, Statius Muller M, Steller EP, Struijs PA. Conservative treatment for closed fifth (small finger) metacarpal neck fractures. Cochrane Database Syst Rev. 2005;3:CD003210. 3. Fujitani R, Omokawa S, Shigematsu K, et al. Comparison of the intramedullary nail and low profile plate for unstable metacarpal neck fractures. J Orthop Sci. 2012;17(4):450e456. 4. Schadel-Hopfner M, Wild M, Windolf J, et al. Antegrade intramedullary splinting or percutaneous retrograde crossed pinning for displaced neck fractures of the fifth metacarpal? Arch Orthop Trauma Surg. 2007;127(6):435e440. 5. Strub B, Schindele S, Sondregger J, Sproedt J, von Campe A, Gruenert JG. Intramedullary splinting or conservative treatment for displaced fractures of the little finger metacarpal neck? A prospective study. J Hand Surg Eur Vol. 2010;35(9):725e729. 6. Botte MJ, Davis JL, Rose BA, et al. Complications of smooth pin fixation of fractures and dislocations in the hand and wrist. Clin Orthop Relat Res. 1992;276:194e201. 7. Facca S, Ramdhian R, Pelissier A, et al. Fifth metacarpal neck fracture fixation: locking plate versus K-wires? Orthop Traumatol Surg Res. 2010;96(5):506e512. 8. Weinstein LP, Hanel DP. Metacarpal fractures. J Am Soc Surg Hand. 2002;2:168e180.
J Hand Surg Am.
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Headless Compression Screw Versus Kirschner Wire Fixation for Metacarpal Neck Fractures: A Biomechanical Study Daniel M. Avery, III, MD,* Stephen Klinge, MD,* Felix Dyrna, MD,* Leo Pauzenberger, MD,* David Lam, BA,* Mark Cote, DPT, MS,* Jessica DiVenere, BS,* Elifho Obopilwe, ME,* Augustus Mazzocca, MS, MD,* Craig Rodner, MD*
Purpose This study aimed to determine the biomechanical stability of headless compression screws in the fixation of metacarpal neck fractures and to compare them with another common, less invasive form of fixation, K-wires. The hypothesis was that headless compression screws would show higher stiffness and peak load to failure than K-wire fixation. Methods Eight matched-paired hands (n ¼ 31), using the ring and little finger metacarpals, had metacarpal fractures simulated at the physeal scar. Each group was stabilized with either a 3.5-mm headless compression screw or 2 0.045-in (1.1-mm) K-wires. Nineteen metacarpals were tested in 3-point bending and 12 in axial loading. Peak load to failure and stiffness were calculated from the load displacement curve. Bone mineral density was recorded for each specimen. Results Bone mineral density was similar in the 2 groups tested for 3-point bending and axial loading. Stiffness was not significantly different in 3-point bending for headless compression screws and K-wires (means, 141.3 vs 194.5 N/mm) but it was significant in axial loading (means, 178.0 vs 111.6 N/mm). Peak load to failure was significantly higher in headless compression screws in 3-point bending (means, 401.2 vs 205.3 N) and axial loading (means, 467.5 vs 198.3 N). Conclusions Compared with K-wires, headless compression screws for metacarpal neck fractures are biomechanically superior in load to failure, 3-point bending, and axial loading. Clinical relevance Headless compression screws demonstrate excellent biomechanical stability in metacarpal neck fractures. In conjunction with promising clinical studies, these data suggest that headless compression screws may be an option for treating metacarpal neck fractures. (J Hand Surg Am. 2017;-(-):1.e1-e6. Copyright Ó 2017 by the American Society for Surgery of the Hand. All rights reserved.) Key words Metacarpal, neck, fracture, surgery, return to play.
M
10% o 30% of all hand fractures. They can affect the athletic or working-age population and can have considerable socioeconomic impact with prolonged immobilization.2 Metacarpal neck fractures, ETACARPAL FRACTURES ACCOUNT FOR 1
From *UCONN Orthopaedic Sports Medicine, University of Connecticut Musculoskeletal Institute, Farmington, CT. Received for publication May 19, 2016; accepted in revised form February 9, 2017. No benefits in any form have been received or will be received related directly or indirectly to the subject of this article.
particularly of the little finger, account for most of these injuries.1,3,4 Although nonsurgical treatment can be successful, operative treatment is indicated when there is unacceptable rotation, shortening, or volar angulation. Some controversy exists as to Corresponding author: Daniel M. Avery, III, MD, UCONN Orthopaedic Sports Medicine, University of Connecticut Musculoskeletal Institute, 263 Farmington Avenue, Farmington, CT 06030-4037; e-mail: [email protected]. 0363-5023/17/---0001$36.00/0 http://dx.doi.org/10.1016/j.jhsa.2017.02.013
Ó 2017 ASSH
r
Published by Elsevier, Inc. All rights reserved.
r
1.e1
1.e2
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the exact parameters that constitute acceptable alignment.5 There are numerous techniques reported in the literature for the fixation of metacarpal neck fractures. Closed reduction and K-wire fixation offer a relatively fast, minimally invasive option. Disadvantages of K-wire fixation, however, include the possibility of pin site infection, prominent hardware precluding early range of motion (ROM), and tethering of surrounding structures. On the other end of the spectrum, plate fixation provides strong fixation allowing early ROM and return to sports, but it comes at the expense of more extensive soft tissue disruption, risk of wound infection, possible hardware irritation, and tendon adherence.6e9 Headless compression screws have been accepted in the treatment of carpal fractures, most notably scaphoid fractures.10e14 With support for an intra-articular starting point,15 headless compression screw fixation for metacarpal neck and shaft fractures has been shown to be a reliable option for axially stable fractures.16 The advantages of headless compression screws are relatively fast insertion and the minimally invasive insertion technique, decreasing risks associated with more extensive soft tissue dissection, stability allowing early ROM, and that it is an intramedullary implant, which eliminates the risk of hardware irritation. Although there is supporting clinical evidence, there have been no biomechanical data to compare headless screws with other forms of fixation for the stabilization of metacarpal neck fractures. The purpose of this study was to perform a biomechanical comparison of 2 forms of metacarpal neck fixation, K-wire and headless compression screws. The hypothesis was that headless compression screws would show higher stiffness and peak load to failure than K-wire fixation.
owing to previous deformity. Fractures were created by locating the physeal scar under fluoroscopy and creating an osteotomy using a sagittal saw 1 mm thick. For K-wire fixation, 2 0.045-in (1.1-mm) K-wires were introduced into the metacarpal head at the sulcus just radial and ulnar to the articular surface in a slightly dorsal position similar to that originally described by Lord.17 Each wire was advanced in a retrograde fashion in the medullary canal until a firm end point was reached signifying the metacarpal base. This end point was confirmed with fluoroscopic imaging. We took care to advance the wires perpendicular to the osteotomy site and not to cross or intersect them at the fracture site. The remainder of the K-wire was cut, leaving approximately 15 mm protruding from the bone (Fig. 1). For headless compression screw fixation, a 0.045-in guide wire with a trocar tip was inserted in a dorsal, central position in line with the metacarpal shaft. The distal segment (metacarpal head) was over-drilled using a 2.7-mm cannulated drill bit. A 3.5-mm, headless compression screw 32 mm long (Arthrex, Naples, FL) was then inserted over the guide wire to approximately 2 mm below the articular surface (Fig. 2). Testing protocol To test the most common deforming force of flexionextension, we subjected 19 metacarpals (10 with headless compression screws and 9 with K-wires) to 3-point bending, apex dorsal, on a Materials Testing System servohydraulic test frame (MTS Systems Corp, Eden Prairie, MN), generating a loaddisplacement curve. Metacarpals were placed on a custom-made base consisting of 2 posts with a 35-mm gap in between. We carefully ensured that the fracture was placed the same way for each specimen with the dorsal surface down. The loading plunger was placed over the distal shaft of the metacarpal and an axial force was applied at 100 mm/min. Sampling was recorded at 100 Hz. To test axial loading, which can be a common mode of failure, 12 metacarpals (6 with headless compression screws and 6 with K-wires) were potted in 1.5-in diameter polyvinyl chloride piping and plaster of Paris, leaving the equivalent of 15 mm of distal metacarpal exposed to be subjected to testing. Care was taken during potting to align the dorsal side of the metacarpal parallel to the polyvinyl chloride wall. Specimens were mounted onto the Materials Testing System frame using a custom-made clamp allowing alignment of the potted specimens to be
MATERIALS AND METHODS Specimen preparation and fixation Eight matched-paired hands, an average age at death of 59 6 years, and stored at e20 C, underwent dual-energy x-ray absorptiometry (DEXA) (Lunar DPI XQ Dexascan, Madison, WI). We measured a 1-cm2 region within the metacarpal neck of each specimen. Specimens were randomized as a pair of hands into 1 of 2 groups: one treated with a K-wire fixation technique (n ¼ 15) and the other with a headless compression screw technique (n ¼ 16). After complete thawing at room temperature, the ring and little finger metacarpals were dissected free of all soft tissue. One little finger metacarpal was excluded J Hand Surg Am.
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FIGURE 1: A Gross specimen with B anteroposterior and C lateral fluoroscopic images of fixation with K-wires.
Statistics Because of the exploratory nature of this study, an a priori power analysis was based on the following assumptions: A difference of 150 N between groups would correspond to a 75% difference assuming an estimated load to failure of 200 N with K-wire fixation and 350 N with headless compression screw fixation. A standard deviation of 100 N was assumed across both groups. Assuming these parameters, a sample size of 7/group would provide 80% power to detect a 125-N difference in load to failure at a ¼ 0.05.
corrected if needed, to ensure axial loading was perpendicular to the dorsal surface of the specimen. The loading plunger was centered over the articular surface in a dorsopalmar direction to simulate an axial loading force. Force was applied at 100 mm/min and recorded at 100 Hz. The load-displacement curve generated was used to calculate peak load to failure (N) and stiffness (N/mm). Stiffness corresponded to the linear slope whereas the peak load to failure was defined at the moment of abrupt change in the load-displacement curve. J Hand Surg Am.
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FIGURE 2: A Gross specimen with B anteroposterior and C lateral fluoroscopic images of headless compression screw fixation.
Descriptive statistics to characterize the study groups were calculated using means and SD. Differences between groups were analyzed with an independent t test. a for all analyses was set at 0.05.
migrating away from the osteotomy (Fig. 3A). The headless compression screw group failed when the palmar cortex of the shaft broke near the osteotomy site and the screw bent (Fig. 3B).
RESULTS Three-point bending We evaluated DEXA scanning for each ring and little finger metacarpal. Bone mineral density was similar between the K-wire group (n ¼ 9; 0.54 0.1 g/cm2) and the headless compression screw group (n ¼ 10; 0.54 0.2 g/cm2). There was no significant difference in the stiffness of the headless compression screws and the K-wires (P ¼ .20). Stiffness for headless compression screws was 141.3 80.2 N/mm, and for K-wires it was 194.5 86.3 N/mm. Peak load to failure showed a significant difference in favor of headless compression screws (P < .05). Peak load to failure for headless compression screws was 401.2 105.3 N, and for K-wires it was 205.3 65.9 N. All specimens failed in a group-specific uniform manner. The K-wire group failed with permanent deformation of the wires, with the distal fragment
Axial loading Bone mineral density was similar between the K-wire (n ¼ 6) and headless compression screw groups (n ¼ 6) with means and SDs of 0.46 0.1 and 0.40 0.2 g/cm2, respectively. Mean stiffness for K-wire fixation was 111.6 15.4 N/mm, and for headless compression screw fixation was 177.9 16.1 N/mm. The difference between groups was statistically significant (P < .05). Peak load to failure was significantly higher for headless compression screw fixation (P < .05). Mean peak load to failure was 467.4 205.7 and 198.3 9.6 N for headless compression screws and K-wires, respectively. The mode of failure for K-wires was bending of the hardware with gradual displacement until the K-wires cut through the metacarpal head. The headless compression screws absorbed the load until the proximal part of the screw dislodged from the metacarpal
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FIGURE 3: Gross specimens after load to failure showing modes for A K-wire and B headless compression screw constructs.
head region with displacement at the osteotomy site, after which the apparatus loaded the screw directly.
Although no deleterious effect has been shown, access to the articular starting point requires incising of the sagittal band or splitting of the extensor tendon, which is a potential cause of complications. Peak load to failure for headless compression screws in 3-point bending was significantly higher than K-wire fixation and was approximately equivalent to that of plate fixation, as demonstrated in another study.18 In addition, we found that headless compression screws had significantly higher peak load to failure than K-wires in axial loading. Because the hardware remains in place, protection is conferred throughout healing. Clinically, Ruchelsman et al16 showed that fixation with headless screws allowed early rehabilitation and achieved excellent union rates, ROM, and grip strength with minimal complications. This suggests potential advantages of faster return to work or sports with axial loading data to support protection against repeated mode of injury. There were several limitations to this study. Because it was a cadaveric biomechanical study, stability from the adjacent soft tissue structures was not accounted for in the results. Furthermore, the osteotomies that were created simulated an axially stable fracture pattern, as described in previous biomechanical studies,25e29 which does not reflect all metacarpal neck fractures in vivo. The presence and variable amount of volar comminution of metacarpal neck fractures that may be present clinically were not evaluated and could have altered the results seen in this study. The primary deforming force in these fractures was the intrinsic and extrinsic flexors, which were modeled by an apex dorsal bending force, as was previously performed.25e29 We also tested axial loading, which is not only a common mode of injury but could be an at-risk force in early return to play in some sports. The study design did not account for rotational forces or cyclical loading, which are clinically relevant. This study was not intended to be a comprehensive comparison of constructs. We chose to compare headless compression screws with retrograde K-wire fixation because of their similar, minimally invasive nature. We also chose to
DISCUSSION This study sought to compare 2 different means of metacarpal neck fracture fixation: 2 retrograde K-wires versus a single headless compression screw. The results of the study showed that headless compression screws demonstrated stiffness similar to K-wires and significantly higher peak load to failure. A recent study by Malasitt et al18 comparing K-wires, plates, and metacarpal sleds (a device consisting of a plate with intramedullary prongs) demonstrated stiffness and peak loads for K-wire fixation similar to those of the current study. Our peak load for headless compression screws was higher than either the K-wires or the sled and plate fixation studied in that report. K-wire fixation in the current study demonstrated precise stability in 3-point bending and axial loading. With their ease of insertion and percutaneous nature, K-wires are a reasonable choice for maintaining alignment during healing for fractures that do not require early rehabilitation or rapid return to full function. K-wires preclude ROM while in place, usually 4 weeks, and the fracture may require continued protection after K-wire removal if healing is incomplete. Their disadvantages have been highlighted in previous studies, including pin site infection, delayed wound healing, soft tissue irritation, stiffness from continued immobilization and protruding hardware, and secondary procedures for removal.19e24 Headless compression screws offer a minimally invasive option to K-wire fixation without the hardware-associated complications. Articular violation is a common concern regarding the technique, however, Ten Berg et. al15 demonstrated that the articular violation is minimal and there is little effect on sagittal plane motion because the rim of the phalangeal base did not overlap the entrance point in 64% of cases in their 3-dimensional modeling. J Hand Surg Am.
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use cadaver specimens to more closely mimic in vivo effects, as opposed to using synthetic materials that are more uniform in shape and consistency. However, for this reason we performed DEXA scanning to compare the adequacy of the specimens, and found similar values between groups. Nonsurgical treatment is appropriate for the vast majority of metacarpal neck fractures. When surgery is indicated, K-wire fixation has been shown to be a reliable and biomechanically sound option. This study demonstrated that headless compression screws are a biomechanically superior form of fixation in load to failure compared with K-wires. Therefore, using headless compression screws to fix certain metacarpal neck fractures may allow for earlier initiation of postoperative rehabilitation than for those fixed with K-wires and thus promote earlier return to work or sports in the subset of patients who require this. Long-term clinical results are needed to substantiate their safety and efficacy in this application.
9. Etier BE, Scillia AJ, Tessier DD, et al. Return to play following metacarpal fractures in football players. Hand (N Y). 2015;10(4): 762e766. 10. Gereli A, Nalbantoglu U, Sener IU, Kocaoglu B, Turkmen M. Comparison of headless compression screws used in the treatment of proximal nonunion of scaphoid bone. Int Orthop. 2011;35(7):1031e1035. 11. Rutgers M, Mudgal CS, Shin R. Combined fractures of the distal radius and scaphoid. J Hand Surg Eur Vol. 2008;33(4):478e483. 12. Singisetti K, Aldyami E, Middleton A. Early results of a new 3.0mm headless compression screw for scaphoid fracture fixation. J Hand Surg Eur Vol. 2012;37(7):690e693. 13. Henry M. Variable pitch headless compression screw treatment of distal phalangeal nonunions. Tech Hand Up Extrem Surg. 2010;14(4):230e233. 14. Ruchelsman DE, Tejwani NC, Kwon YW, Egol KA. Open reduction and internal fixation of capitellar fractures with headless screws. J Bone Joint Surg Am. 2008;90(6):1321e1329. 15. Ten Berg P, Mudgal CS, Leibman MI, Belsky MR, Ruchelsman DE. Quantitative 3D-CT analysis of intramedullary headless screw fixation for metacarpal neck fractures. J Hand Surg Am. 2013;38(2):322e330. 16. Ruchelsman DE, Puri S, Feinberg-Zadek N, Leibman MI, Belsky MR. Clinical outcomes of limited-open retrograde intramedullary headless screw fixation of metacarpal fractures. J Hand Surg Am. 2014;39(12):2390e2395. 17. Lord RE. Intramedullary fixation of metacarpal fractures. J Am Med Assoc. 1957;164(16):1746e1749. 18. Malasitt P, Owen JR, Tremblay M, Wayne JS, Isaacs JE. Fixation for metacarpal neck fracture: a biomechanical study. Hand (N Y). 2015;10(3):438e443. 19. Hsu LP, Schwart EG, Kalainov DM, et al. Complications of k-wire fixation in procedures involving the hand and wrist. J Hand Surg Am. 2011;36(4):610e616. 20. Hargreaves DG, Drew SJ, Eckersley R. Kirschner wire pin tract infection rates: a randomized controlled trial between percutaneous and buried wires. J Hand Surg Br. 2004;29(4):374e376. 21. Xu J, Zhang C. Mini plate versus Kirschner wire internal fixation for treatment of metacarpal and phalangeal fractures in Chinese Han population: a meta-analysis. J Orthop Surg Res. 2014;9:24. 22. Kim JK, Kim DJ. Antegrade intramedullary pinning versus retrograde intramedullary pinning for displaced fifth metacarpal neck fractures. Clin Orthop Relat Res. 2015;473:1747e1754. 23. Yammine K, Harvey A. Antegrade intramedullary nailing for fifth metacarpal neck fractures: a systematic review and meta-analysis. Eur J Orthop Surg Traumatol. 2014;24(3):273e278. 24. Foucher G. “Bouquet” osteosynthesis in metacarpal neck fractures: a series of 66 patients. J Hand Surg Am. 1995;20(suppl):S86eS90. 25. Dona E, Gillies RM, Gianoutsos MP, et al. Plating of metacarpal fractures: unicortical or bicortical screws? J Hand Surg Br. 2004;29(3):218e221. 26. Prevel CD, Eppley BL, Jackson JR, et al. Mini and micro plating of phalangeal and metacarpal fractures: a biomechanical study. J Hand Surg Am. 1995;20(1):44e49. 27. Doht S, Jansen H, Meffert RH, et al. Higher stability with locking plates in hand surgery? Biomechanical investigation of the TriLock system in a fracture model. Int Orthop. 2012;36(8):1641e1646. 28. Mudrick CA, Owen JR, Wayne JS, et al. Unicortical PEEK inset locking fixation for metacarpal fractures: a biomechanical study. Eur J Orthop Surg Traumatol. 2013;24(8):1415e1420. 29. Ochman S, Doht S, Paletta J, et al. Comparison between locking and non-locking plates for fixation of metacarpal fractures in an animal model. J Hand Surg Am. 2010;35(4):597e603.
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