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Effect of different orientations of screw fixation for radial head fractures: a biomechanical comparison

Effect of different orientations of screw fixation for radial head fractures: a biomechanical... Background: Screw fixation is a common method used for the treatment of Mason type II radial head fractures. The purpose of our study was to evaluate the mechanical properties of three different screw orientations used for fixation of Mason type II radial head fractures. Methods: We sawed 24 medium-frequency fourth-generation Synbone radial bones to simulate unstable radial head fractures, which we then fixed with three different screw orientations. Implants were tested under axial load by the tension-torsion composite test system. If the implant-radial constructs did not fail after the axial load test, an axial failure load was added to the remaining constructs. Results: The stiffness of the divergent group was the highest of the three orientations, and this group had statistically significant difference from the other two groups (p < 0.05). However, there was no statistically significant difference between the convergence group and the parallel group (p > 0.05). When the displacement reached 2 mm, the load of the divergent screw was still larger than the other two groups (p < 0.05). Conclusions: The divergent screw orientation was the most stable and had the greatest control of Mason type II fractures of these three groups. Therefore, it can be better applied in clinical settings. Keywords: Radial head fractures, Screw, Biomechanical comparison, Different orientation Background when the displacement is less than 2 mm [3]. Although Mason type was proposed for the first time in 1954 as a the management of displaced radial head fractures in definition of radial head fractures [1]. Mason type II adults remains unsatisfactory due to problems with loss fractures were 2-part fractures of the radial head with of reduction, and non-union [6–12], there has recently displacement and then were modified by Broberg and been a great interest in preserving the radial head using Morrey [2] as having more than 2 mm of displacement open reduction with internal fixation. Since the import- and involving at least 30% of the radial head. The opti- ant role of the radial head in elbow stability has been mal treatment for Mason type II fractures of the radial recognized [12], special implants for the maintenance of head is still controversial [3, 4]. Radial head fractures are radial head fractures have been developed to improve infrequently seen in adults, with a reported incidence of fixation stability. approximately 55.4 per 100,000 people [5]. The mechan- In clinical practice, two headless compression screws ism of injury in radial head fractures is usually caused by placed parallel to each other are used [13]. However, the arm reaching in a fall, and in a few cases it is caused there is no biomechanical data regarding this common by direct violence [1, 6]. Fortunately, type II radial head fixation method if the screws occur to be placed in a fractures can be managed with conservative treatment non-parallel orientation. The purpose of this study was to quantify and compare the stiffness of three different screw configurations used to stabilize a simulated Mason * Correspondence: 675331207@qq.com type II fracture. Department of Orthopaedics Surgery, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University, No.109, Xue Yuan West Road, Wenzhou, Zhejiang Province 325027, China © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 2 of 5 Methods was 2.28 cm. As in clinical use, the length of the screws Twenty-four Synbone radial bones (Malans Synbone did not exceed the contralateral cortex. Company, Switzerland) of the same size and density The axial load was applied to the radial head fragment were used. The radius was cut mid-shaft, leaving an ap- through a metal block (Fig. 3). Before the official test, a proximately 10-cm-long proximal segment. A Mason preload of 10 N was applied three times at the same vel- type II fracture was produced (Fig. 1). The fracture was ocity (2 mm/min) to the radial head fragment. This pos- created with an oscillating saw parallel to the longitu- ition was regarded as the baseline to record the dinal axis of the specimen. With this fragment size, the displacement of the fragment. The data was cleared from fracture ended at the radial neck without any bony sup- the strain analyzer. The construct was then loaded in port. The fragment included the safe zone that is the compression at the rate of 2 mm/min. The test stopped part of the radial head that does not articulate with the when the load was 1 mm from the baseline. proximal radioulnar joint. Reduction was performed and After the axial load test, if the fracture models did not maintained with a reposition clamp, and the screws were fail, they were performed to the failure load at the rate implanted. We used two screws (Wright, Beijing, China) of 2 mm/min. In our text, all 24 fracture models did not to fix the fracture model. The three different orienta- fail. Failure was defined as a new fracture seen on the ra- tions were as follows: (1) convergent group: two screws dial bone, an acute change in the load-displacement were inserted 30 ° convergent to each other in the trans- curve indicating a rapid change in displacement and loss verse plane; (2) parallel group: two screws were inserted of construct stability, or radial head displacement greater parallel to each other and perpendicular to the fracture than 2 mm (the fracture model had an intra-articular line; (3) divergent group: two screws were inserted 30 ° fracture, and the failure of intra-articular fracture fix- divergent to each other in the transverse plane. Figure 2 ation is defined as a displacement of more than 2 mm). shows X-rays of the reconstructed radial heads with the Axial stiffness and axial failure loads were recorded. three screw fixations described above. The screws were The stiffness was determined from the slope of the re- inserted 5 mm proximal to the top of the radial head. gression line fitted to the loading segment of the cyclic The screws were all spaced 5 mm apart at the medial load-displacement curves. Data from each group are pre- cortex regardless of orientation. sented as the mean ± standard deviation. SPSS 21.0 One fellowship-trained orthopedic surgeon performed (IBM Corporation, Armonk, NY, USA) was used for stat- the fixation on all 24 specimens to minimize the vari- istical analysis. Mechanical parameters were compared ability of fixation parameters. The Synbone surfaces using an LDS-test. p < 0.05 was considered statistically were smooth, and the initial reduction was only accepted significant. if it was anatomical. The clamps and drills used were the same in all three experimental groups. The transversely Results cut end of the radial shaft was potted in a metal tube We analyzed the stiffness of the three groups from five using polymethylmethacrylate. The average length of the levels. All the bending load data was collected and proc- proximal radius exposed outside of the potting material essed as the load-displacement curve seen in Fig. 4. The was 6.79 cm, and the average diameter of the radial head three curves in the figure represent three different load- displacement variations. It is easy to see that the load- displacement variations for the three groups were approximately linear in the range of 0–1 mm. The slope of the fold line represents the stiffness of the implant. As we can see from Table 1, the divergent group was the hardest with a stiffness of 213.9 ± 28.00 N/mm, and the stiffness of the convergent group was 123.5 ± 25.94 N/ mm (p < 0.05). The stiffness of the parallel group was 149.5 ± 23.32 N/mm (p < 0.05). Although the stiffness of the parallel group was higher than that of the conver- gent group, there was no statistically significant differ- ence between the two groups (p > 0.05). The three groups did not fail when loading to the dis- placement of 1 mm, so we selected the displacement of 2 mm as the failure load. All fracture models were not fail- ure after the axial load test and 24 specimens were sub- jected to failure load tests. The divergent screws were still Fig. 1 The production process of Mason II radial head fractures the hardest implant with a failure load of 357.6 ± 74.58 N, Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 3 of 5 Fig. 2 Radiographs of convergent group, parallel group, and divergent group and they had statistically significant differences from the other two groups. The load of the convergent screws was 256.5 ± 59.53 N, which was 39.44% smaller than that of the divergent screws, and the load of the parallel screws was 272.3 ± 65.46 N, which was 31.33% smaller than that of the divergent screws (Fig. 5). Discussion The results obtained via conservative treatment may be satisfactory if the fracture is not displaced or is minim- ally displaced but movement is not impeded [1]. In re- cent years, it has been generally acknowledged that these fractures are best treated by open reduction with in- ternal fixation if the fragment is displaced more than 2 mm or involves more than 30% of the radial head. In a study by Demiroglu et al. [13], 23 patients were treated operatively with screw fixations with a follow-up period Fig. 4 Comparison the axial stiffness of 24 specimens between Fig. 3 The radial head model was placed in the instrument for convergent group, parallel group, and divergent group. The slopes axial loading of the curves reflect the stiffness of three groups Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 4 of 5 Table 1 Average stiffness on axial load test of parallel group, fixation of transverse, non-comminuted radial neck convergent group, and divergent group fractures. Convergent Parallel Divergent In a recent article, Jeffrey et al. [23] evaluated high- group group group fidelity composite bone models used in the biomechan- Average stiffness(N/mm) 123.5 ± 25.94 149.5 ± 23.32 213.9 ± 28.00 ics study; Synbone brand models was well represented in the hand and upper extremity biomechanics research. In of more than 11 months. Their study showed that ana- our biomechanical experiments, the divergent screw tomical reduction of type II radial head fractures group showed the highest axial compression stiffness of through open surgery and fixed with screws can have fa- the three groups; in contrast, the axial compression stiff- vorable results. Similarly, Pearce et al. [14] used Herbert ness of the convergent group was the lowest of the three screws to treat radial head fractures with satisfactory re- groups, which was consistent with our expected results. sults. Burkhart et al. [15] recommended surgery to avoid Amanatullah et al. [24] evaluated the mechanical proper- the development of post-traumatic arthritis. Van ties of three different screw orientations used for the fix- Glabbeek et al. [16] also reported satisfactory results ation of vertical shear fractures of the medial malleolus. with open reduction of Mason type II radial head frac- The use of a divergent screw pattern resulted in a stiffer tures. Consistent with these findings, the common inter- fixation construct when used to stabilize an osteotomy est in preservation of the radial head is steadily model of vertical shear medial malleolus fractures. In increasing. New techniques and implants have been de- their study, it was noted that when the screws were not veloped for the maintenance of radial head fractures. placed in parallel only the first screw caused compres- However, only a few biomechanical studies have exam- sion, and any non-parallel screws did not add additional ined Mason type II radial head fractures to date [17–22]. compression, but instead acted as a rotation, translation, Klaus et al. [17] evaluated the 3.0-mm headless compres- and tensile force neutralizer. However, in a non-rigid sion screw and the standard 2.0-mm cortical screw used system, each screw provides additional compression and for fixation of radial head fractures. No significant differ- acts as a rotation, translation, and tensile force ences concerning the stability achieved by the 3.0-mm neutralizer. Similar results can be drawn from our study headless compression screw, and the 2.0-mm cortical and their study: divergent screw placement allows the screw could be detected in the experimental setup pre- screws to be farther apart in the fracture plane. This sented. In a recent article, Christina et al. [22] compared wider screw orientation encompasses a larger surface of the mechanical properties of crossed screw and plate fix- bone in the fracture plane that is held in compression ation in the model of a radial neck fracture; the two and resists translation in the axial plane and rotation in strategies provided similar strength and stiffness for the the sagittal plane as a result of increased interfragmen- tary friction. According to our biomechanical results, the divergent screws showed the greatest axial stiffness in our standard Mason type II radial head fracture model. It is envisaged that in clinical applications, no matter what the direction of the two screws, the soft tissue detachment is similar and only a small range of stripping is needed. Therefore, if divergent screws are applied in the clinical setting, their effect may be better than the clinical use of parallel screws. Early postoperative exercise after radial head fractures is the basic factor of postoperative rehabilita- tion [13]. Stronger stiffness can be better for fixing the fracture block and preventing displacement of the frac- ture block after surgery, to achieve earlier and better postoperative rehabilitation exercise and prevent postop- erative complications. However, this is only our vision; the feasibility requires a large amount of clinical valid- ation. We can only form a purely biomechanical point of view, and pathogenesis and other internal fixation mech- Fig. 5 Comparison of axial failure load between convergent group anisms need to be taken into consideration for the treat- (8 specimens), parallel group (8 specimens), and divergent group (8 ment of radial head fractures. specimens). Standard deviation is represented with the range bars Our study also had some limitations. First, the stand- on top of each graph ard bone without muscle and other corresponding soft Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 5 of 5 tissue attachment cannot simulate the force transmission 3. Shulman BS, Lee JH, Liporace FA, Egol KA. Minimally displaced radial head/ neck fractures (Mason type-I, OTA types 21A2.2 and 21B2.1): are we “over and role of the real human elbow joint. Second, our treating” our patients? J Orthop Trauma. 2015;29(2):e31–5. sample size in the study was not big enough; axial load 4. Yoon A, Athwal GS, Faber KJ, King GJ. Radial head fractures. J Hand Surg direction cannot completely simulate the real daily activ- Am. 2012;37(12):2626–34. 5. Duckworth AD, Clement ND, Jenkins P, Aitken SA, Court-Brown CM, ities of the human body or the mechanical mechanism McQueen MM. The epidemiology of radial head and neck fractures. J Hand of the injury. What is more, the load application is not Surg Am. 2012;37(1):112–9. representative of how load is transferred through the 6. Johnston GW. A follow-up of one hundred cases of fracture of the head of the radius with a review of the literature. Ulster Med J. 1962;31:51–6. elbow. Finally, the biomechanics of this study only in- 7. Esser RD, Davis S, Taavao T. Fractures of the radial head treated by internal cluded axial and failure loads; the observed index was fixation: late results in 26 cases. J Orthop Trauma. 1995;9(4):318–23. only axial stiffness due to the lack of more biomechan- 8. Nalbantoglu U, Kocaoglu B, Gereli A, Aktas S, Guven O. Open reduction and internal fixation of Mason type III radial head fractures with and without an ical performance indicators. associated elbow dislocation. J Hand Surg Am. 2007;32(10):1560–8. 9. Cobb TK, Beckenbaugh RD. Nonunion of the radial neck following fracture of the radial head and neck: case reports and a review of the literature. Conclusion Orthopedics. 1998;21(3):364–8. Our findings demonstrated that the divergent screws 10. Faber FW, Verhaar JA. Nonunion of radial neck fracture. An unusual had more biomechanical advantages over the other two differential diagnosis of tennis elbow, a case report. Acta Orthop Scand. 1995;66(2):176. screw orientations. However, our conclusion needs to be 11. Faraj AA, Livesly P, Branfoot T. Nonunion of fracture of the neck of the supported by additional studies with large sample sizes radius: a report of three cases. J Orthop Trauma. 1999;13(7):513–5. looking at biomechanical and clinical applications. 12. Ring D, Quintero J, Jupiter JB. Open reduction and internal fixation of fractures of the radial head. J Bone Joint Surg Am. 2002;84-A(10):1811–5. Acknowledgments 13. Demiroglu M, Ozturk K, Baydar M, Kumbuloglu OF, Sencan A, Aykut S, Kilic The authors are grateful for the assistance from Yiwu high-level personnel B. Results of screw fixation in Mason type II radial head fractures. Spring. for scientific research projects and for technical support and equipment from 2016;5:545. the Tianjin Institute of Orthopedics. 14. Pearce MS, Gallannaugh SC. Mason type II radial head fractures fixed with Herbert bone screws. J R Soc Med. 1996;89(6):340P–4P. 15. Burkhart KJ, Wegmann K, Muller LP, Gohlke FE. Fractures of the radial head. Funding Hand Clin. 2015;31(4):533–46. This research was supported by the Yiwu high-level personnel for scientific 16. Van Glabbeek F, Van Riet R, Verstreken J. Current concepts in the treatment research projects (No.201603). The funders had no role in the study design, of radial head fractures in the adult. A clinical and biomechanical approach. data collection or analysis, decision to publish, or preparation of the Acta Orthop Belg. 2001;67(5):430–41. manuscript. 17. Burkhart KJ, Nowak TE, Appelmann P, Sternstein W, Rommens PM, Mueller LP. Screw fixation of radial head fractures: compression screw versus lag Availability of data and materials screw—a biomechanical comparison. Injury. 2010;41(10):1015–9. The data that support the findings of this study are available from the 18. Burkhart KJ, Mueller LP, Krezdorn D, Appelmann P, Prommersberger KJ, Wenzhou Medical University (Wenzhou, Zhejiang, China). Data are however Sternstein W, Rommens PM. Stability of radial head and neck fractures: a available from the authors upon reasonable request and with permission of biomechanical study of six fixation constructs with consideration of three Wenzhou Medical University (Wenzhou, Zhejiang, China). Please contact locking plates. J Hand Surg Am. 2007;32(10):1569–75. author for data requests. 19. Capo JT, Svach D, Ahsgar J, Orillaza NS, Sabatino CT. Biomechanical stability of different fixation constructs for ORIF of radial neck fractures. Orthopedics. Authors’ contributions 2008;31(10). XCS, JP, and RC designed the study. JP, DYW, and XCS obtained the funding. 20. Giffin JR, King GJ, Patterson SD, Johnson JA. Internal fixation of radial neck NYC, BL, and RZ collected the data. BL, NYC, and CWZ analyzed the data. JP, fractures: an in vitro biomechanical analysis. Clin Biomech (Bristol, Avon). XCS, and RC interpreted the data. TLP, DYW, and RZ composed the article. 2004;19(4):358–61. All authors read and approved the final manuscript. 21. Patterson JD, Jones CK, Glisson RR, Caputo AE, Goetz TJ, Goldner RD. Stiffness of simulated radial neck fractures fixed with 4 different devices. J Ethics approval and consent to participate Shoulder Elb Surg. 2001;10(1):57–61. Not applicable. 22. Gutowski CJ, Darvish K, Ilyas AM, Jones CM. Comparison of crossed screw versus plate fixation for radial neck fractures. Clin Biomech (Bristol, Avon). Consent for publication 2015;30(9):966–70. Not applicable. 23. Reed JD, Stanbury SJ, Menorca RM, Elfar JC. The emerging utility of composite bone models in biomechanical studies of the hand and upper Competing interests extremity. J Hand Surg Am. 2013;38(3):583–7. The authors declare that they have no competing interests. 24. Amanatullah DF, Khan SN, Curtiss S, Wolinsky PR. Effect of divergent screw fixation in vertical medial malleolus fractures. J Trauma Acute Care Surg. 2012;72(3):751–4. Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Received: 19 June 2017 Accepted: 20 September 2017 References 1. Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. Br J Surg. 1954;42(172):123–32. 2. Broberg MA, Morrey BF. Results of treatment of fracture-dislocations of the elbow. Clin Orthop Relat Res. 1987;216:109–19. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Orthopaedic Surgery and Research Springer Journals

Effect of different orientations of screw fixation for radial head fractures: a biomechanical comparison

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Abstract

Background: Screw fixation is a common method used for the treatment of Mason type II radial head fractures. The purpose of our study was to evaluate the mechanical properties of three different screw orientations used for fixation of Mason type II radial head fractures. Methods: We sawed 24 medium-frequency fourth-generation Synbone radial bones to simulate unstable radial head fractures, which we then fixed with three different screw orientations. Implants were tested under axial load by the tension-torsion composite test system. If the implant-radial constructs did not fail after the axial load test, an axial failure load was added to the remaining constructs. Results: The stiffness of the divergent group was the highest of the three orientations, and this group had statistically significant difference from the other two groups (p < 0.05). However, there was no statistically significant difference between the convergence group and the parallel group (p > 0.05). When the displacement reached 2 mm, the load of the divergent screw was still larger than the other two groups (p < 0.05). Conclusions: The divergent screw orientation was the most stable and had the greatest control of Mason type II fractures of these three groups. Therefore, it can be better applied in clinical settings. Keywords: Radial head fractures, Screw, Biomechanical comparison, Different orientation Background when the displacement is less than 2 mm [3]. Although Mason type was proposed for the first time in 1954 as a the management of displaced radial head fractures in definition of radial head fractures [1]. Mason type II adults remains unsatisfactory due to problems with loss fractures were 2-part fractures of the radial head with of reduction, and non-union [6–12], there has recently displacement and then were modified by Broberg and been a great interest in preserving the radial head using Morrey [2] as having more than 2 mm of displacement open reduction with internal fixation. Since the import- and involving at least 30% of the radial head. The opti- ant role of the radial head in elbow stability has been mal treatment for Mason type II fractures of the radial recognized [12], special implants for the maintenance of head is still controversial [3, 4]. Radial head fractures are radial head fractures have been developed to improve infrequently seen in adults, with a reported incidence of fixation stability. approximately 55.4 per 100,000 people [5]. The mechan- In clinical practice, two headless compression screws ism of injury in radial head fractures is usually caused by placed parallel to each other are used [13]. However, the arm reaching in a fall, and in a few cases it is caused there is no biomechanical data regarding this common by direct violence [1, 6]. Fortunately, type II radial head fixation method if the screws occur to be placed in a fractures can be managed with conservative treatment non-parallel orientation. The purpose of this study was to quantify and compare the stiffness of three different screw configurations used to stabilize a simulated Mason * Correspondence: 675331207@qq.com type II fracture. Department of Orthopaedics Surgery, The Second Affiliated Hospital and Yuying Children’s Hospital of Wenzhou Medical University, No.109, Xue Yuan West Road, Wenzhou, Zhejiang Province 325027, China © The Author(s). 2017 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 2 of 5 Methods was 2.28 cm. As in clinical use, the length of the screws Twenty-four Synbone radial bones (Malans Synbone did not exceed the contralateral cortex. Company, Switzerland) of the same size and density The axial load was applied to the radial head fragment were used. The radius was cut mid-shaft, leaving an ap- through a metal block (Fig. 3). Before the official test, a proximately 10-cm-long proximal segment. A Mason preload of 10 N was applied three times at the same vel- type II fracture was produced (Fig. 1). The fracture was ocity (2 mm/min) to the radial head fragment. This pos- created with an oscillating saw parallel to the longitu- ition was regarded as the baseline to record the dinal axis of the specimen. With this fragment size, the displacement of the fragment. The data was cleared from fracture ended at the radial neck without any bony sup- the strain analyzer. The construct was then loaded in port. The fragment included the safe zone that is the compression at the rate of 2 mm/min. The test stopped part of the radial head that does not articulate with the when the load was 1 mm from the baseline. proximal radioulnar joint. Reduction was performed and After the axial load test, if the fracture models did not maintained with a reposition clamp, and the screws were fail, they were performed to the failure load at the rate implanted. We used two screws (Wright, Beijing, China) of 2 mm/min. In our text, all 24 fracture models did not to fix the fracture model. The three different orienta- fail. Failure was defined as a new fracture seen on the ra- tions were as follows: (1) convergent group: two screws dial bone, an acute change in the load-displacement were inserted 30 ° convergent to each other in the trans- curve indicating a rapid change in displacement and loss verse plane; (2) parallel group: two screws were inserted of construct stability, or radial head displacement greater parallel to each other and perpendicular to the fracture than 2 mm (the fracture model had an intra-articular line; (3) divergent group: two screws were inserted 30 ° fracture, and the failure of intra-articular fracture fix- divergent to each other in the transverse plane. Figure 2 ation is defined as a displacement of more than 2 mm). shows X-rays of the reconstructed radial heads with the Axial stiffness and axial failure loads were recorded. three screw fixations described above. The screws were The stiffness was determined from the slope of the re- inserted 5 mm proximal to the top of the radial head. gression line fitted to the loading segment of the cyclic The screws were all spaced 5 mm apart at the medial load-displacement curves. Data from each group are pre- cortex regardless of orientation. sented as the mean ± standard deviation. SPSS 21.0 One fellowship-trained orthopedic surgeon performed (IBM Corporation, Armonk, NY, USA) was used for stat- the fixation on all 24 specimens to minimize the vari- istical analysis. Mechanical parameters were compared ability of fixation parameters. The Synbone surfaces using an LDS-test. p < 0.05 was considered statistically were smooth, and the initial reduction was only accepted significant. if it was anatomical. The clamps and drills used were the same in all three experimental groups. The transversely Results cut end of the radial shaft was potted in a metal tube We analyzed the stiffness of the three groups from five using polymethylmethacrylate. The average length of the levels. All the bending load data was collected and proc- proximal radius exposed outside of the potting material essed as the load-displacement curve seen in Fig. 4. The was 6.79 cm, and the average diameter of the radial head three curves in the figure represent three different load- displacement variations. It is easy to see that the load- displacement variations for the three groups were approximately linear in the range of 0–1 mm. The slope of the fold line represents the stiffness of the implant. As we can see from Table 1, the divergent group was the hardest with a stiffness of 213.9 ± 28.00 N/mm, and the stiffness of the convergent group was 123.5 ± 25.94 N/ mm (p < 0.05). The stiffness of the parallel group was 149.5 ± 23.32 N/mm (p < 0.05). Although the stiffness of the parallel group was higher than that of the conver- gent group, there was no statistically significant differ- ence between the two groups (p > 0.05). The three groups did not fail when loading to the dis- placement of 1 mm, so we selected the displacement of 2 mm as the failure load. All fracture models were not fail- ure after the axial load test and 24 specimens were sub- jected to failure load tests. The divergent screws were still Fig. 1 The production process of Mason II radial head fractures the hardest implant with a failure load of 357.6 ± 74.58 N, Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 3 of 5 Fig. 2 Radiographs of convergent group, parallel group, and divergent group and they had statistically significant differences from the other two groups. The load of the convergent screws was 256.5 ± 59.53 N, which was 39.44% smaller than that of the divergent screws, and the load of the parallel screws was 272.3 ± 65.46 N, which was 31.33% smaller than that of the divergent screws (Fig. 5). Discussion The results obtained via conservative treatment may be satisfactory if the fracture is not displaced or is minim- ally displaced but movement is not impeded [1]. In re- cent years, it has been generally acknowledged that these fractures are best treated by open reduction with in- ternal fixation if the fragment is displaced more than 2 mm or involves more than 30% of the radial head. In a study by Demiroglu et al. [13], 23 patients were treated operatively with screw fixations with a follow-up period Fig. 4 Comparison the axial stiffness of 24 specimens between Fig. 3 The radial head model was placed in the instrument for convergent group, parallel group, and divergent group. The slopes axial loading of the curves reflect the stiffness of three groups Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 4 of 5 Table 1 Average stiffness on axial load test of parallel group, fixation of transverse, non-comminuted radial neck convergent group, and divergent group fractures. Convergent Parallel Divergent In a recent article, Jeffrey et al. [23] evaluated high- group group group fidelity composite bone models used in the biomechan- Average stiffness(N/mm) 123.5 ± 25.94 149.5 ± 23.32 213.9 ± 28.00 ics study; Synbone brand models was well represented in the hand and upper extremity biomechanics research. In of more than 11 months. Their study showed that ana- our biomechanical experiments, the divergent screw tomical reduction of type II radial head fractures group showed the highest axial compression stiffness of through open surgery and fixed with screws can have fa- the three groups; in contrast, the axial compression stiff- vorable results. Similarly, Pearce et al. [14] used Herbert ness of the convergent group was the lowest of the three screws to treat radial head fractures with satisfactory re- groups, which was consistent with our expected results. sults. Burkhart et al. [15] recommended surgery to avoid Amanatullah et al. [24] evaluated the mechanical proper- the development of post-traumatic arthritis. Van ties of three different screw orientations used for the fix- Glabbeek et al. [16] also reported satisfactory results ation of vertical shear fractures of the medial malleolus. with open reduction of Mason type II radial head frac- The use of a divergent screw pattern resulted in a stiffer tures. Consistent with these findings, the common inter- fixation construct when used to stabilize an osteotomy est in preservation of the radial head is steadily model of vertical shear medial malleolus fractures. In increasing. New techniques and implants have been de- their study, it was noted that when the screws were not veloped for the maintenance of radial head fractures. placed in parallel only the first screw caused compres- However, only a few biomechanical studies have exam- sion, and any non-parallel screws did not add additional ined Mason type II radial head fractures to date [17–22]. compression, but instead acted as a rotation, translation, Klaus et al. [17] evaluated the 3.0-mm headless compres- and tensile force neutralizer. However, in a non-rigid sion screw and the standard 2.0-mm cortical screw used system, each screw provides additional compression and for fixation of radial head fractures. No significant differ- acts as a rotation, translation, and tensile force ences concerning the stability achieved by the 3.0-mm neutralizer. Similar results can be drawn from our study headless compression screw, and the 2.0-mm cortical and their study: divergent screw placement allows the screw could be detected in the experimental setup pre- screws to be farther apart in the fracture plane. This sented. In a recent article, Christina et al. [22] compared wider screw orientation encompasses a larger surface of the mechanical properties of crossed screw and plate fix- bone in the fracture plane that is held in compression ation in the model of a radial neck fracture; the two and resists translation in the axial plane and rotation in strategies provided similar strength and stiffness for the the sagittal plane as a result of increased interfragmen- tary friction. According to our biomechanical results, the divergent screws showed the greatest axial stiffness in our standard Mason type II radial head fracture model. It is envisaged that in clinical applications, no matter what the direction of the two screws, the soft tissue detachment is similar and only a small range of stripping is needed. Therefore, if divergent screws are applied in the clinical setting, their effect may be better than the clinical use of parallel screws. Early postoperative exercise after radial head fractures is the basic factor of postoperative rehabilita- tion [13]. Stronger stiffness can be better for fixing the fracture block and preventing displacement of the frac- ture block after surgery, to achieve earlier and better postoperative rehabilitation exercise and prevent postop- erative complications. However, this is only our vision; the feasibility requires a large amount of clinical valid- ation. We can only form a purely biomechanical point of view, and pathogenesis and other internal fixation mech- Fig. 5 Comparison of axial failure load between convergent group anisms need to be taken into consideration for the treat- (8 specimens), parallel group (8 specimens), and divergent group (8 ment of radial head fractures. specimens). Standard deviation is represented with the range bars Our study also had some limitations. First, the stand- on top of each graph ard bone without muscle and other corresponding soft Shi et al. Journal of Orthopaedic Surgery and Research (2017) 12:143 Page 5 of 5 tissue attachment cannot simulate the force transmission 3. Shulman BS, Lee JH, Liporace FA, Egol KA. Minimally displaced radial head/ neck fractures (Mason type-I, OTA types 21A2.2 and 21B2.1): are we “over and role of the real human elbow joint. Second, our treating” our patients? J Orthop Trauma. 2015;29(2):e31–5. sample size in the study was not big enough; axial load 4. Yoon A, Athwal GS, Faber KJ, King GJ. Radial head fractures. J Hand Surg direction cannot completely simulate the real daily activ- Am. 2012;37(12):2626–34. 5. Duckworth AD, Clement ND, Jenkins P, Aitken SA, Court-Brown CM, ities of the human body or the mechanical mechanism McQueen MM. The epidemiology of radial head and neck fractures. J Hand of the injury. What is more, the load application is not Surg Am. 2012;37(1):112–9. representative of how load is transferred through the 6. Johnston GW. A follow-up of one hundred cases of fracture of the head of the radius with a review of the literature. Ulster Med J. 1962;31:51–6. elbow. Finally, the biomechanics of this study only in- 7. Esser RD, Davis S, Taavao T. Fractures of the radial head treated by internal cluded axial and failure loads; the observed index was fixation: late results in 26 cases. J Orthop Trauma. 1995;9(4):318–23. only axial stiffness due to the lack of more biomechan- 8. Nalbantoglu U, Kocaoglu B, Gereli A, Aktas S, Guven O. Open reduction and internal fixation of Mason type III radial head fractures with and without an ical performance indicators. associated elbow dislocation. J Hand Surg Am. 2007;32(10):1560–8. 9. Cobb TK, Beckenbaugh RD. Nonunion of the radial neck following fracture of the radial head and neck: case reports and a review of the literature. Conclusion Orthopedics. 1998;21(3):364–8. Our findings demonstrated that the divergent screws 10. Faber FW, Verhaar JA. Nonunion of radial neck fracture. An unusual had more biomechanical advantages over the other two differential diagnosis of tennis elbow, a case report. Acta Orthop Scand. 1995;66(2):176. screw orientations. However, our conclusion needs to be 11. Faraj AA, Livesly P, Branfoot T. Nonunion of fracture of the neck of the supported by additional studies with large sample sizes radius: a report of three cases. J Orthop Trauma. 1999;13(7):513–5. looking at biomechanical and clinical applications. 12. Ring D, Quintero J, Jupiter JB. Open reduction and internal fixation of fractures of the radial head. J Bone Joint Surg Am. 2002;84-A(10):1811–5. Acknowledgments 13. Demiroglu M, Ozturk K, Baydar M, Kumbuloglu OF, Sencan A, Aykut S, Kilic The authors are grateful for the assistance from Yiwu high-level personnel B. Results of screw fixation in Mason type II radial head fractures. Spring. for scientific research projects and for technical support and equipment from 2016;5:545. the Tianjin Institute of Orthopedics. 14. Pearce MS, Gallannaugh SC. Mason type II radial head fractures fixed with Herbert bone screws. J R Soc Med. 1996;89(6):340P–4P. 15. Burkhart KJ, Wegmann K, Muller LP, Gohlke FE. Fractures of the radial head. Funding Hand Clin. 2015;31(4):533–46. This research was supported by the Yiwu high-level personnel for scientific 16. Van Glabbeek F, Van Riet R, Verstreken J. Current concepts in the treatment research projects (No.201603). The funders had no role in the study design, of radial head fractures in the adult. A clinical and biomechanical approach. data collection or analysis, decision to publish, or preparation of the Acta Orthop Belg. 2001;67(5):430–41. manuscript. 17. Burkhart KJ, Nowak TE, Appelmann P, Sternstein W, Rommens PM, Mueller LP. Screw fixation of radial head fractures: compression screw versus lag Availability of data and materials screw—a biomechanical comparison. Injury. 2010;41(10):1015–9. The data that support the findings of this study are available from the 18. Burkhart KJ, Mueller LP, Krezdorn D, Appelmann P, Prommersberger KJ, Wenzhou Medical University (Wenzhou, Zhejiang, China). Data are however Sternstein W, Rommens PM. Stability of radial head and neck fractures: a available from the authors upon reasonable request and with permission of biomechanical study of six fixation constructs with consideration of three Wenzhou Medical University (Wenzhou, Zhejiang, China). Please contact locking plates. J Hand Surg Am. 2007;32(10):1569–75. author for data requests. 19. Capo JT, Svach D, Ahsgar J, Orillaza NS, Sabatino CT. Biomechanical stability of different fixation constructs for ORIF of radial neck fractures. Orthopedics. Authors’ contributions 2008;31(10). XCS, JP, and RC designed the study. JP, DYW, and XCS obtained the funding. 20. Giffin JR, King GJ, Patterson SD, Johnson JA. Internal fixation of radial neck NYC, BL, and RZ collected the data. BL, NYC, and CWZ analyzed the data. JP, fractures: an in vitro biomechanical analysis. Clin Biomech (Bristol, Avon). XCS, and RC interpreted the data. TLP, DYW, and RZ composed the article. 2004;19(4):358–61. All authors read and approved the final manuscript. 21. Patterson JD, Jones CK, Glisson RR, Caputo AE, Goetz TJ, Goldner RD. Stiffness of simulated radial neck fractures fixed with 4 different devices. J Ethics approval and consent to participate Shoulder Elb Surg. 2001;10(1):57–61. Not applicable. 22. Gutowski CJ, Darvish K, Ilyas AM, Jones CM. Comparison of crossed screw versus plate fixation for radial neck fractures. Clin Biomech (Bristol, Avon). Consent for publication 2015;30(9):966–70. Not applicable. 23. Reed JD, Stanbury SJ, Menorca RM, Elfar JC. The emerging utility of composite bone models in biomechanical studies of the hand and upper Competing interests extremity. J Hand Surg Am. 2013;38(3):583–7. The authors declare that they have no competing interests. 24. Amanatullah DF, Khan SN, Curtiss S, Wolinsky PR. Effect of divergent screw fixation in vertical medial malleolus fractures. J Trauma Acute Care Surg. 2012;72(3):751–4. Publisher’sNote Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. Received: 19 June 2017 Accepted: 20 September 2017 References 1. Mason ML. Some observations on fractures of the head of the radius with a review of one hundred cases. Br J Surg. 1954;42(172):123–32. 2. Broberg MA, Morrey BF. Results of treatment of fracture-dislocations of the elbow. Clin Orthop Relat Res. 1987;216:109–19.

Journal

Journal of Orthopaedic Surgery and Research – Springer Journals

Published: Dec 1, 2017

Keywords: orthopedics; surgical orthopedics

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