A biomechanical comparison of four different fixation methods for midshaft clavicle fractures

Transcription

1 Original Article A biomechanical comparison of four different fixation methods for midshaft clavicle fractures Proc IMechE Part H: J Engineering in Medicine 2016, Vol. 230(1) Ó IMechE 2015 Reprints and permissions: sagepub.co.uk/journalspermissions.nav DOI: / pih.sagepub.com Yang Chen, Yang Yang, Xinlong Ma, Weiguo Xu, Jianxiong Ma, Shaowen Zhu, Baoyi Ma and Dan Xing Abstract Clavicle fractures may occur in all age groups, and 70% 80% of clavicle fractures occur in the midshaft. Many methods for treating midshaft clavicular fractures have been reported and remain controversial. To provide some guidance for clinical treatment, 30 artificial polymethyl methacrylate models of the clavicle were sewn obliquely at the midshaft to simulate the most common type of clavicular fractures, and the fracture models were divided into five groups randomly and were fixed as follows: the reconstruction plates were placed at the superior position of the fracture model (R-S group), the reconstruction plates were placed at the anteroinferior position of the fracture model (R-AI group), the locking plates were placed at the superior position (L-S group), the locking plates were placed at the anteroinferior position (L-AI group); and the control models were unfixed (control group). The strain gauges were attached to the bone surface near the fracture fragments, and then, the biomechanical properties of the specimens were measured using the compression test, torsion test and three-point bending test. The results showed that plate fixation can provide a stable construct to help with fracture healing and is the preferred method in the treatment of clavicle fractures. The locking plate provides the best biomechanical stability when placed at the anteroinferior position, and this surgical method can reduce the operation time and postoperative complications; thus, it would be a better choice in clinical practice. Keywords Clavicle fracture, biomechanics, locking plate, reconstruction plate, fixation methods Date received: 28 December 2014; accepted: 21 September 2015 Introduction Compared with other bones, the location of the clavicle is superficial and there are few muscles to provide protection to this bone; thus, clavicle fractures are very common in clinical practice and account for 6% of all systemic fractures. 1 Clavicle fractures may occur in all age groups; among them, 70% 80% occurred in the middle third of the clavicle. 1 Many surgical methods of treating clavicle fractures have been reported, including the conservative treatment method. However, the incidence of nonunion and malunion in displaced clavicle fractures with conservative treatments has increased in recent years. 2,3 Zlowodzki et al. 4 reported that the incidence of nonunion in displaced clavicle fractures treated with the conservative method was 15.1%, while the nonunion incidence of plate fixation was only 2.2%. In clinical work, surgeons gradually realized that the intramedullary nail or Kirschner wire has a poor antirotation capability, leading to movement in the medullary cavity, 5 7 and some surgeons even reported that the dislocated Kirschner wire may puncture the trachea; 8 thus, intramedullary nail or Kirschner wire fixation was gradually eliminated in clinical practice. Meanwhile, with the improvement of materials and design, plate fixation has been accepted by many surgeons in treating displaced middle clavicle fractures. 9 However, for plate fixation, whether to choose the reconstruction plate or locking plate and where to place the plate remain controversial. Some scholars have Department of Orthopedics Institute, Tianjin Hospital, Tianjin, China Corresponding authors: Xinlong Ma, Department of Orthopedics Institute, Tianjin Hospital, 406, Jiefang Nan Street, Hexi District, Tianjin , China. cywonder050204@163.com Weiguo Xu, Department of Orthopedics Institute, Tianjin Hospital, 406, Jiefang Nan Street, Hexi District, Tianjin , China. keviin2007@gmail.com

2 14 Proc IMechE Part H: J Engineering in Medicine 230(1) reported that compared with the superior position, the anteroinferior position appears to cause fewer postoperative complications. 4 There were some advantages when the plate was placed at the anteroinferior position. First, due to the plate being placed at a relatively secluded location that does not affect the appearance of the clavicle site, secondary surgery to remove the plate may be avoided. Second, due to its special shape, the contact area of the plate and bone surface is relatively larger when the plate was placed at the anteroinferior position compared with the superior position, achieving better robustness. Third, this surgical approach can avoid injuring major neurovascular structures around the clavicle. Many scholars have reported that placing the plate at the anteroinferior aspect yielded excellent results In this study, identically synthetic clavicle models using a midshaft osteotomy were used to compare the biomechanical properties of the locking plate and reconstruction plate following midshaft clavicle fracture treatment when they were placed at different positions to provide a theoretical reference for the clinical treatment of middle-third fractures of the clavicle. Figure 1. Illustrations demonstrating the location of strain gauges on the clavicle from an inferior view. Materials and methods Specimens and grouping A healthy volunteer (male, 24 years old) underwent a continuous spiral computed tomography (CT) of his clavicle, and then, the CT data were imported to mimic software to reconstruct the three-dimensional clavicle model. Next, the clavicle mould was made, and 30 polymethyl methacrylate (PMMA) clavicles were made to ensure that the biomechanical data came from uniform experimental samples. The 30 PMMA clavicle models were randomized and divided into five groups (six specimens in each group). In the control group, there was no intervention and the PMMA models remained intact; however, for the other four fracture groups, the PMMA clavicle models were subjected to middle-third oblique fractures by the same surgeon: in the R-S group, the 3.5-mm reconstruction plates were placed at the superior position of the fracture model; in the R-AI group, the 3.5-mm reconstruction plates were placed at the anteroinferior position of the fracture model; in the L-S group, the locking plates were placed at the superior position; and in the L-AI group, the locking plates were placed at the anteroinferior position. Strain gauge preparation The strain in all specimens was measured using electric constantan-foil strain gauges (Product Model: BE120-05AA-X30; Zhonghang Electronic Measuring Instruments CO., Ltd, Shaanxi, China) mounted on flexible phenolic-acetal backings. The strain gauges have a grid size of 0.50 mm mm, a grid resistance of O and a gauge factor of %. The Figure 2. The plates and orientation of the five groups. strain gauges were attached to the PMMA model surface by ethyl a-cyanoacrylate after the surface was processed with a steel file and acetone. 13 Colour-coded lead wires and strain gauges were connected using a connecting terminal. The nonbonded open-faced surface of the gauges and adjoining 1 2 cm of the lead wire were protected with a thin coat of silica gel and allowed to cure overnight. Based on the fracture line under the clavicle, the strain gauges were pasted at four locations: the upper left, upper right, lower left and lower right of the fracture line (Figure 1). In the measurement system, the signal of the strain gauge was sampled by the DHDAS-5929 Dynamic Signal Acquisition Analysis System (Donghua Automation Instrumentation Company, Jiangsu, China). Plate fixation of the fracture models The four fracture groups underwent plate fixation with reconstruction plates or locking plates according to the experiment design by an experienced orthopaedic surgeon, with three screws on both sides of the fracture line (Figure 2). Biomechanical test The denture acrylic and dental base acrylic resin liquid were mixed at a ratio of 20 g:40 ml to form PMMA to fix the specimens in the biomechanical testing system. The clavicle models were embedded by PMMA material and fixed in the specially designed square fixture

3 Chen et al. 15 Figure 4. Bending rigidity (N/mm) of the five groups as measured by axial compression test. Figure 3. The biomechanical test conducted by Instron 8874 servohydraulic biomechanical testing system: (a) axial compression test, (b) torsion test and (c) three-point bending test. the lowering speed of the indenter was 3 mm/min (Figure 3(c)). The specimens shared the same size; thus, the loading condition and distance between the three supported anvils remained constant. During the testing process, the load displacement data were recorded by MAXä software. The bending rigidity, torsional rigidity and maximum deflection value were generated from the load deformation curves. for the biomechanical test system. The Instron 8874 (Instron Corporation, Canton, MA) servohydraulic biomechanical testing system and the matched chucking appliance were used to perform the biomechanical tests: the axial compression, torsion and three-point bending tests. The system controller provides the exceptional control accuracy required for biomechanical testing, and the MAXä software can provide power and flexibility, including the generation of complex command waveforms and optimization of the data acquisition and storage. The strain values of all the samples were recorded by a DHDAS-5929 Dynamic Signal Acquisition Analysis System. The experimental parameters were explored according to the preliminary experiments and other literature, and the maximum load or displacement was set based on no damage to the PMMA clavicle models. In the axial compression test, specimens were placed vertically in the chucking appliance and were loaded with sinusoidal compression for 10 cycles at 0.25 Hz between 5 and 233 N (Figure 3(a)). The load was chosen according to a biomechanical test conducted by Iannotti et al. 14 The ranges of motion of the axial internal and external torsion were both 10, and the loading frequencies were all 0.25 Hz 15 (Figure 3(b)). In the compression test and torsion test, the first two loading cycles were used to eliminate the influence of the viscous tissue and control the experimental repeatability. Data were collected from the third cycle, and final biomechanical data were acquired from the average of the seventh, eighth and ninth cycles. 16 In the three-point bending test, the specimens were compressed to fail and Statistical methods The SPSS 17.0 statistical package was used for data analysis, and data are expressed as the mean 6 standard deviation. Significant differences were determined by one-way analysis of variance (ANOVA) followed (where significant) by Scheffe s post hoc test to identify significant pair-wise differences, and p \ 0.05 was considered statistically significant. As strain values have no unit, absolute values were used in the statistics, and the sign represents the direction of force. Results The biomechanical tests of all of the specimens were completed, and there was no data loss. In the axial compression test, the average bending rigidities of the L-AI group and R-AI group were and N/mm, respectively, whereas the average bending rigidities of the L-S group and R-S group were and N/mm, respectively; the average bending rigidity of the control group was N/mm (Figure 4). The differences among the five groups were statistically significant. Analysis from the perspective of the placement location of plates revealed that the bending rigidity of groups with the plate placed at the anteroinferior position was larger than that of groups with the plate placed at the superior position (p = 0.030). The average torsional rigidities of internal rotation in the control group, L-AI group, R-AI group, L-S group and R-S group were 0.72, 0.73, 0.74, 0.71 and 0.76 Nm/deg, respectively (Figure 5), and the

4 16 Proc IMechE Part H: J Engineering in Medicine 230(1) Figure 5. Torsional rigidity (Nm/deg) of the five groups in external and internal rotation test. differences among the five groups were not statistically significant (P = 0.279). Similarly, the average torsional rigidities of external rotation in the control group, L- AI group, R-AI group, L-S group and R-S group were 0.77, 0.73, 0.74, 0.71 and 0.76 Nm/deg, respectively (Figure 5), and the differences among the five groups were not statistically significant (P = 0.349). In the three-point bending test, the maximum deflection values of the four fixation groups were all larger than those of the control group. The average maximum deflection values of internal rotation in the control group, L-AI group, R-AI group, L-S group and R-S group were 8.75, 16.07, 13.08, and mm, respectively. Analysis from the perspective of the placement position revealed that the differences in the maximum deflection between groups with the plate placed at the anteroinferior position and groups with the plate placed at the superior position were not statistically significant. However, the maximum deflection values of the locking plate groups were larger than those of the reconstruction plate groups (p = 0.018) (Figure 6). The strain values of each resistance strain gauge were recorded by the DHDAS-5929 Dynamic Signal Acquisition Analysis System during the three types of biomechanical tests (Figure 7). The strain values of the four fixation groups were less than those of the control group, and the differences were statistically significant (p \ 0.05). Among the four fixation groups, the strain values of the L-AI group were the smallest, followed by those of the R-AI group and L-S group. Additionally, the strain values of the R-S group were the largest among the four fixation groups, but the differences among them were not statistically significant (p. 0.05). Discussion The clavicle has a complex three-dimensional shape, accompanied by many ligaments and muscles that are attached to it. The exact load acted on the clavicle Figure 6. Maximum deflection value (mm) of the five groups. when it is fractured is difficult to calculate and remains unclear. The load acted on the clavicle would vary not only with the degree and specific site of the fracture but also with age, body habitus and the activity and function of the shoulder joint. The clavicle bears axial compressive, torsional and bending loads and is considered the shoulder s supporting structure. Therefore, all of these loading modes would be taken into consideration when the fixation method for clavicle fractures is evaluated. Thus, in this study, we used the above three loading modes in biomechanical tests to evaluate the effects of different types of plates and plate location. The results showed that the plates placed at the anteroinferior position had a similar anti-torsion effect to the plates placed at the superior position and a stronger bending stiffness than plates placed at the superior position. The bending forces acting on the clavicle were borne by plates that were oriented like a universal beam with the narrow side paralleled with these forces; thus, the plates can provide the maximum inertia in the area moment to counter the bending moment. Iannotti et al. 14 thought that the plate placed at the superior position could provide better fracture rigidity, construct stiffness and strength in torsional and axial loading than one placed at the anterior position. However, our results showed that there were no significant differences in the torsional test between the two types of placement locations. We found that the plates with an anteroinferior position would provide stronger rigidity in bending force, although the plates with a superior position could produce tension band-like effects on the clavicle with the bending force load. Iannotti et al. compared the bending rigidity of clavicle fractures with cadaver models whose ages were years. The large range of age may lead to the inconstant quality of bone, which may influence the biomechanical test results. In this study, we used PMMA clavicle models manufactured by the same mould to ensure uniform experimental samples and avoid interference of the results arising from different

5 Chen et al. 17 Figure 7. Strain values (me) of the five groups during the three kinds of biomechanical tests: (a) the torsion test of internal rotation, (b) the three-point bending test, (c) the torsion test of external rotation and (d) the axial compression test. a: control group; b: locking plate placed in anteroinferior position; c: reconstruction plate placed in anteroinferior position; d: locking plate placed in superior position; e: reconstruction plate placed in superior position. samples. 17 There were no fracture gaps in our osteotomy models; thus, the biomechanical tests were mainly influenced by plate structures and placement positions. However, a transverse osteotomy with nondisplacement could supply an inherent stability in bending, possibly exerting an influence on the results of the bending test. Wolff s law states that bone will adapt to the load. If the load increases, the bone will remodel itself over time to become stronger to resist the load, and the internal architecture undergoes adaptive changes. In other words, growth speed and the direction of bone cells are closely related to stress. Skedros et al. 18 investigated the regeneration and reconstruction force of calcaneus cortical bone, and they found that osseous tissue could generate functional adaptation in response to stress. In other words, stress can make the osseous tissue develop in a certain direction, taking the form of cortical bone, which advocates that stress becomes thinner and cortical bone with principal compressive stress becomes thicker. Huiskes et al. 19 conducted research to explain this phenomenon. They found that with a low stress stimulus, bone strain decreased and bone metabolism would gradually turn into bone resorption; thus, cortical bone becomes progressively thinner. Additionally, a high stress stimulus could increase bone strain and bone metabolism gradually turns into bone formation; thus, cortical bone becomes progressively thicker. Shen et al. 20 measured the clavicle thickness in different parts by CT, and they found that the middle shaft and anteroinferior side had the thickest bone cortex. The outcome indicated that the middle shaft and anteroinferior side in the clavicle bear more stress than other parts under physiological activity. Therefore, the treatment with the plate placed at the anteroinferior side would make the fixation very stable, and the stress distribution in the clavicle was in line with that under physiological activity. The secondary purpose of this study was to evaluate whether the locking plate or reconstruction plate has a better effect on midshaft clavicle fractures. The technology of the locking plate was a revolution in treating difficult orthopaedic problems, such as osteoporotic fractures, comminuted fractures and bone defects. In

6 18 Proc IMechE Part H: J Engineering in Medicine 230(1) this study, we found that traditional reconstruction plates were biomechanically adequate when the fracture site could be fixed stably by the bone-to-bone contact. In torsional tests, the locking plate placed at the anteroinferior position displayed similar biomechanical properties with the reconstruction plate placed at the superior position, probably because the torsion activity was exerted through the centre of the fracture site. However, when the clavicle was osteoporotic or when no contact was present, the locking plate could still provide advantageous biomechanical properties to ensure the fixation effect. The three-point bending tests showed that the locking plates had better biomechanical properties in resisting compressive stress than traditional reconstruction plates. The strain values of the fixation groups were lower than those of the control group, and the differences were statistically significant, indicating that plate fixation could bear more stress, which was conducive to the early healing of fractures. Many studies 3,21 reported that the incidence rate of bone nonunion and malunion in the middle clavicle fractures with the expectant treatment gradually increased in recent years. Additionally, a related meta-analysis showed that the nonunion rate of clavicle fractures with expectant treatment was 5.9%; in displaced clavicle fractures, the nonunion rate can increase to 15.1%. 4 The nonunion rate of fixation with the plate was only 2.2%. This is consistent with the results of this study. Conclusion This study demonstrated that among the four fixation groups, the locking plates placed at the anteroinferior position showed the best biomechanical properties. Moreover, the locking plates can address complicated orthopaedic conditions, and plates placed at the anteroinferior position can avoid neurovascular complications and have a better appearance. The locking plate placed at the anteroinferior position is a good treatment method for clavicle fractures and can be widely applied in clinical practice. Acknowledgements Y.C. and Y.Y. contributed equally to this work. Declaration of Conflicting Interests The author(s) declared no potential conflicts of interest with respect to the research, authorship and/or publication of this article. Funding The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by grants from the National Natural Science Foundation of China (No ) and the Scientific and Technological Project of Tianjin Public Health Bureau (No. 12KG120). References 1. Von Unger S and Jupiter JB. The treatment of midshaft clavicle nonunion with bone defect. Tech Shoulder Elbow Surg 2007; 8: Lazarides S and Zafiropoulos G. Conservative treatment of fractures at the middle third of the clavicle: the relevance of shortening and clinical outcome. J Shoulder Elbow Surg 2006; 15(2): Andermahr J and Schifer G. Intrameduallary nail and clavicle fracture. Tech Shoulder Elbow Surg 2008; 9: Zlowodzki M, Zelle BA, Cole PA, et al. Treatment of acute midshaft clavicle fractures: systematic review of 2144 fractures: on behalf of the Evidence-Based Orthopaedic Trauma Working Group. J Orthop Trauma 2005; 19(7): Lyons FA and Rockwood CJ. Migration of pins used in operations on the shoulder. J Bone Joint Surg Am 1990; 72(8): Boehme D, Curtis RJ, Dehaan JT, et al. Non-union of fractures of the mid-shaft of the clavicle. Treatment with a modified Hagie intramedullary pin and autogenous bone-grafting. J Bone Joint Surg Am 1991; 73(8): Manske DJ and Szabo RM. The operative treatment of mid-shaft clavicular non-unions. J Bone Joint Surg Am 1985; 67(9): Adbenoor J, Mantoura J and Nahas A. Cervicothoracic pin migration following open reduction and pinning of a clavicular fracture: a case report. East J Med 2000; 5(1): Robinson CM, Goudie EB, Murray IR, et al. Open reduction and plate fixation versus nonoperative treatment for displaced midshaft clavicular fractures: a multicenter, randomized, controlled trial. J Bone Joint Surg Am 2013; 95(17): Collinge C, Devinney S, Herscovici D, et al. Anteriorinferior plate fixation of middle-third fractures and nonunions of the clavicle. J Orthop Trauma 2006; 20(10): Kloen P, Sorkin AT, Rubel IF, et al. Anteroinferior plating of midshaft clavicular nonunions. J Orthop Trauma 2002; 16(6): Verborgt O, Pittoors K, Van Glabbeek F, et al. Plate fixation of middle-third fractures of the clavicle in the semiprofessional athlete. Acta Orthop Belg 2005; 71(1): Nagata H, Schendel MJ, Transfeldt EE, et al. The effects of immobilization of long segments of the spine on the adjacent and distal facet force and lumbosacral motion. Spine 1993; 18(16): Iannotti MR, Crosby LA, Stafford P, et al. Effects of plate location and selection on the stability of midshaft clavicle osteotomies: a biomechanical study. J Shoulder Elbow Surg 2002; 11(5): Partal G, Meyers KN, Sama N, et al. Superior versus anteroinferior plating of the clavicle revisited: a mechanical study. J Orthop Trauma 2010; 24(7): Jia H, Zhu S, Ma J, et al. A biomechanical study of the recovery in spinal stability of flexion/extension and

7 Chen et al. 19 torsion after the resection of different posterior lumbar structures in a sheep model. Proc IMechE, Part H: J Engineering in Medicine 2013; 227(8): Xinlong M, Yang Y, Jianxiong M, et al. Comparison of mechanical properties of polymethyl methacrylate of different mixing ratios. J Med Eng Technol 2011; 35(1): Skedros JG, Mason MW and Bloebaum RD. Modeling and remodeling in a developing artiodactyl calcaneus: a model for evaluating Frost s Mechanostat hypothesis and its corollaries. Anat Rec 2001; 263(2): Huiskes R, Ruimerman R, van Lenthe GH, et al. Effects of mechanical forces on maintenance and adaptation of form in trabecular bone. Nature 2000; 405(6787): Shen JW, Tong PJ and Qu HB. A three-dimensional reconstruction plate for displaced midshaft fractures of the clavicle. J Bone Joint Surg Br 2008; 90(11): Lazarides S and Zafiropoulos G. Conservative treatment of fractures at the middle third of the clavicle: the relevance of shortening and clinical outcome. J Shoulder Elbow Surg 2006; 15(2):