Could rhombic-shaped miniplates be applicable for subcondylar fractures of the mandible? a biomechanical study

Abstract

AimMandibular condylar process fractures are the most common fractures in the maxillofacial region. Surgical treatment of condylar region fractures with miniplates and miniscrews has become more popular because it is a stable method that allows immediate function. The present study examined sheep hemimandibular subcondylar fracture models to evaluate the biomechanical properties of two different miniplate/screw system types used for surgical fixation of subcondylar fractures.MethodsExperimental standardized subcondylar fracture lines were examined in ten sheep hemimandibula models. Each segment was fixed with one of two fixation types: double straight miniplates with eight miniscrews or a single rhombic-shaped miniplate with five miniscrews. All models were mounted in a servohydraulic testing unit, and a continuous linear force was applied. Maximum force and displacement values were evaluated and statistically analyzed.ResultsThe rhombic-shaped miniplate group had statistically significantly lower values than the double straight miniplate group for the maximum force, work at maximum load, and hardness. There was no statistically significant difference between the two groups in terms of the displacement at the maximum load.ConclusionConsidering the advantages of rhomboid mini-plates, further clinical and mechanical studies are needed for their use in the surgical fixation of subcondylar fractures.

Keywords

Introduction

Condylar fractures account for 25–50% of all mandibular fractures.¹ Fractures in the mandibular condylar area were classified into three groups, according to the anatomical level of the fracture line. Intracapsular or condylar head fractures occur at a high level above the ligament; condylar neck fractures occur on the thin and narrow area just below the condyle head; subcondylar fractures begin from the sigmoid notch and run obliquely to the posterior border of the ramus or the masseteric tuberosity, including the condylar process.² This high incidence rate of condylar fractures is explained by the condylar area being the weakest portion of the mandible. Fractures of the condylar region occur mainly when the force applied to other regions of the mandible is distributed and transferred to this area.³ Due to the complex anatomy of the temporomandibular joint, as well as the surgical proximity of this area to the facial nerve, the maxillary artery, and many other important and vital structures, surgically managing subcondylar fractures and stabilizing the fragments present some challenges and risks.²
Fracture lines and degrees of fragment displacement vary according to the area of force exertion, the magnitude and direction of force, the patient’s occlusal position at the moment of impact, and individual anatomical features.2 Clinicians face several options and challenges when choosing functional, aesthetic, comfortable, and economical methods. When treating condyle fractures, occlusion, jaw movements, maxillofacial symmetry, and temporomandibular joint functions should be managed, reconstructed, or treated. The options depend on the opinions of clinicians; therefore, there is no consensus concerning the ideal method or material.^4-5
In 1976, the basic principles of functionally stable osteosynthesis using miniplates and miniscrews were defined. The main purpose of this method is to ensure a stable relationship between the fractured and mandibular segments to allow for immediate function. In 1980, internal fixation with miniplates and miniscrews in condyle fractures was reported for the first time in the literature.⁶ Since then, further information has been accumulated, indicating that internal rigid fixation via miniplates and miniscrews is the most advantageous treatment option for mandibular condylar neck and subcondylar fractures. Treatment outcomes in these areas have benefited considerably from different miniplate system designs.^7-9 Because of the small volume and thin neck of the condylar region, it is important that the clinician should choose the smallest, thinnest, and few materials that are possible to retain sufficient long-term resistance, success and comfort.^7,10-11 Many different miniplate types have been designed with varying shapes, sizes, and thicknesses for different indications and regions.¹² Three-dimensional mini-plates have become more popular owing to their ease of use, low volume coverage, and high-level mechanical properties.^12-13 Among these, a newly designed, rhombic-shaped, 3-dimensional (3D) osteosynthesis plate has been presented.¹⁴
Although both the straight and 3D fixation devices have advantages and are frequently used to surgically reduce subcondylar fractures, to the best of our knowledge, no published study has evaluated the biomechanical efficacy of the rhombic-shaped miniplate. Therefore, this study aimed to biomechanically evaluate the fixation resistance and stability of the newly designed miniplate/screw fixation method compared with the conventional double straight miniplate/screw method, both of which are used to surgically treat subcondylar fractures.

Materials and Methods

This study was approved by the local ethic committee of Mersin University (No. E-728620. Date: 2018-05-14). Based on related research, the ideal sample size was calculated using G* Power software (Ver.3.1.9.2) to ensure adequate power for the study. Five samples were required in each group, with 5% significance and 80% power.
Experimental and standardized subcondylar fractures were created by removing the coronoid process of ten sheep hemimandible models (Figure 1). The specimens were divided into two fixation groups of five samples each. In one group, double non-locking, four-holed titanium miniplates with eight miniscrews (2 × 5 mm) were applied, and in the other group, single rhombic-shaped titanium non-locking miniplates with five miniscrews (2 × 5 mm) were applied (KLS Martin, Tuttlingen, Germany). The positions of the miniplates and miniscrews were standardized and the plates were shaped. Then, the fragments were fixed according to their groups (Figure 2).
With the help of a fixation device, all hemimandibles were mounted from the corpus region in a servo-hydraulic testing unit (Lloyd Universal Testing Machine, AMETEK, Inc., Hampshire, England) inclined 15° to inferior on the sagittal plane and 10° to lateral on the coronal plane. This positioning was intended to mimic chewing forces on the condyle according to the method defined by Ziccardi et al.¹⁵ A wedge-shaped apparatus was applied to the condylar process and preloaded with 10N. Subsequently, a continuous linear force of 10 mm/min was applied. In all models, straight forces were applied until deformation was observed in miniscrews or miniplates. The displacement and force values were digitally recorded by software integrated into the servohydraulic device. Statistical analyses were performed using IBM SPSS Statistics (Ver.22.0). Data were tested for normality using the Shapiro–Wilk test. Differences between the groups were analyzed using independent t-tests. The level of significance was set at P<0.05.Ethical ApprovalEthics Committee approval for the study was obtained. This study was approved by the Ethics Committee of Mersin University (Date: 14.05.2018, Decision No: E-728620)

Results

Table 1 presents the maximum load (N), displacement at maximum load (mm), and stiffness (N/m) values for the rhombic plate and double straight plate groups in the biomechanical tests.
Table 2 provides the mean, standard deviation, standard error, and comparison results between the groups for the maximum load, displacement on maximum load, and stiffness values. These results showed a significant difference (P=0.002) in the maximum load and stiffness. However, there was no statistically significant difference between the groups in terms of the displacement on maximum load values (P>0.05).

Discussion

Fracture fixation methods have been evaluated in vitro using two basic methods. In one method, finite element analysis, the complex structure is divided into many simpler, smaller elements and nodes. Therefore, the entire structure may be exposed to virtual forces in the software, and the force distributions, load bearing, and stress zones maybe evaluated objectively and digitally.^13,16-17 The other method involves biomechanical evaluation via a simulation model, prepared with human cadavers, animal bones, or synthetic replica models. One portion of the model was fixed to the testing device, and the vertical load was adjusted to the other portion of the model, which was not fixed. Thus, the shear and compression forces and displacement values of the free ends of the fixed models can be measured using a computer-aided device.^14,18 For this study, the authors chose the biomechanical cantilever beam testing method described by Ziccardi et al.¹⁵ which is highly preferred in the extant literature.
Evidence suggests that a single plate would not be sufficiently stable; therefore, two plates are required to achieve stable fixation.^8,19 However, two straight miniplates (the conventional method) require eight miniscrews, and the necessary materials have a large volume, given the thickness of the condylar region. For this region, there are various three-dimensional designs including trapezoid, deltoid, rhombic-shaped, strut, 9-hole trapezoid, and lambda, etc.^12,20 Recently, a newly designed, rhombic-shaped, 3D miniplate system using five miniscrews has been developed. In a finite element analysis study, which evaluated the displacement values of biting load in a therhombic-shaped miniplate used for mandibular subcondylar fracture, the displacement values were reported as falling between 0.27mm and 1.10 mm.²¹ In another finite element analysis study, Abdelwahab et al. compared a rhombic-shaped miniplate to a single straight miniplate and to a double straight mini plate in a mandible subcondylar fracture model. Virtual displacement values were measured as 1.06 mm for the single straight miniplate, 0.20 mm for the double straight miniplate, and 0.40 mm for the rhombic miniplate. The study results suggested that in cases where the thickness of the condyle neck was limited, a single straight miniplate would be unsuccessful; however, a rhombic-shaped miniplate could be biomechanically successful and reliable and could provide appropriate healing.
Halawani et al.²² reported the clinical results of rhombic-shaped miniplates used for subcondylar and condylar neck fractures in 20 patients. The rhombic miniplates were clinically and radiologically stable and showed satisfactory osteosynthesis. In a randomized controlled clinical trial among 20 patients, Ashor et al.²³ compared rhombic miniplates to double straight miniplates for the treatment of high-level subcondylar fractures, but there were no statistically significant radiological or clinical differences between the groups. The authors suggested that rhombic miniplates could be used because they are advantageous in the presence of thin bones, are easier to apply, reduce operating time, and have economic advantages.
In a similar study planned in parallel to the present study, Achour et al.¹⁴ compared five different methods, including rhombic and double straight miniplate groups. They reported that rhombic-shaped miniplates provided a lower maximum force compared to double straight miniplates; however, there was no statistically significant difference in displacement in the lateromedial or anteroposterior directions. These results were consistent with the present findings; however, force magnitudes differed between the studies because the researchers employed different models (sheep vs. pig).

Conclusion

For subcondylar fractures of the mandible, rhombic-shaped plates showed statistically significantly lower results for maximum force and stiffness compared to double straight plates, which is the conventional treatment method. On the other hand, there were no statistically significant differences between the groups in terms of displacement. Considering this situation as well as the other advantages of rhombic-shaped miniplates (e.g., less volume coverage, fewer necessary miniscrews, and easier surgical application), they may serve as a clinically convenient treatment option for the surgical fixation of subcondylar fractures. This in vitro study should be supported by clinical case reports, case series, and randomized controlled trials for widespread clinical use.

Declarations

References

1. Bhutia O, Kumar L, Jose A, et al. Evaluation of facial nerve following open reduction and internal fixation of subcondylar fracture through retromandibular transparotid approach. Br J Oral Maxillofac Surg. 2014;52(3):236-240. doi:10.1016/j.bjoms.2013.12.002
   Article · PubMed · Google Scholar
2. Hackenberg B, Lee C, Caterson EJ. Management of subcondylar mandible fractures in the adult patient. J Craniofac Surg. 2014;25(1):166-171. doi:10.1097/scs.0000000000000498
   Article · PubMed · Google Scholar
3. Menon S, Sinha R. Gap arthroplasty for mandibular condyle dislocation and impaction into the middle cranial fossa. J Oral Maxillofac Surg. 2008;66(11):2390-2393. doi:10.1016/j.joms.2008.01.064
   Article · PubMed · Google Scholar
4. Ezhilarasi S, Katrolia R. IMF after ORIF in maxillofacial fractures: case report and literature review. Traumaxilla. 2022;4(1-3):32-34. doi:10.1177/26323273211073785
   Article · PubMed · Google Scholar
5. Minervini G, Franco R, Marrapodi MM, et al. Conservative treatment of temporomandibular joint condylar fractures: a systematic review conducted according to PRISMA guidelines and the Cochrane Handbook for Systematic Reviews of Interventions. J Oral Rehabil. 2023;50(9):886-893. doi:10.1111/joor.13497
   Article · PubMed · Google Scholar
6. El Sayed AGA, Ghanem AA, Al Mansi YA, Elhadidi YN, Abd El Wahab El Kassaby M. The use of combined microplate and miniplate in the fixation of mandibular fractures: a randomized clinical trial. J Craniofac Surg. 2023;10(1):1097-1099. doi:10.1097/scs.0000000000009527
   Article · PubMed · Google Scholar
7. Haim D, Mller A, Leonhardt H, et al. Biomechanical study of the delta plate and the TriLock Delta condyle trauma plate. J Oral Maxillofac Surg. 2011;69(10):2619-2625. doi:10.1016/j.joms.2011.01.002
   Article · PubMed · Google Scholar
8. Darwich MA, Albogha MH, Abdelmajeed A, Darwich K. Assessment of the biomechanical performance of 5 plating techniques in fixation of mandibular subcondylar fracture using finite element analysis. J Oral Maxillofac Surg. 2016;74(4):794.e1-794.e8. doi:10.1016/j.joms.2015.11.021
   Article · PubMed · Google Scholar
9. Ellis E, Kellman RM, Vural E. Subcondylar fractures. Facial Plast Surg Clin North Am. 2012;20(3):365-382. doi:10.1016/j.fsc.2012.05.002
   Article · PubMed · Google Scholar
10. Omezli MM, Torul D, Polat ME, Dayi E. Biomechanical comparison of osteosynthesis with poly-L-lactic acid and titanium screw in intracapsular condylar fracture fixation: an experimental study. Niger J Clin Pract. 2015;18(5):589-593. doi:10.4103/1119-3077.158946
    Article · PubMed · Google Scholar
11. Laughlin RM, Block MS, Wilk R, Malloy RB, Kent JN. Resorbable plates for the fixation of mandibular fractures: a prospective study. J Oral Maxillofac Surg. 2007;65(1):89-96. doi:10.1016/j.joms.2005.10.055
    Article · PubMed · Google Scholar
12. Sikora M, Chęciński M, Nowak Z, et al. The use of titanium 3D miniplates in the surgical treatment of fractures of the mandibular condyle: a systematic review and meta-analysis of clinical trials. J Clin Med. 2021;10(3):3604-3628. doi:10.3390/jcm10163604
    Article · PubMed · Google Scholar
13. Ergezen E, Akdeniz SS. Evaluation of stress distribution of 4 different fixation systems at high- and low-level subcondylar fractures on a nonhomogeneous finite element model. J Oral Maxillofac Surg. 2020;78(4):1596.e1-1596.e12. doi:10.1016/j.joms.2020.04.017
    Article · PubMed · Google Scholar
14. Ben Achour A, Meißner H, Teicher U, et al. Biomechanical evaluation of mandibular condyle fracture osteosynthesis using the rhombic 3-dimensional condylar fracture plate. J Oral Maxillofac Surg. 2019;77(9):1868.e1-1868.e15. doi:10.1016/j.joms.2019.04.020
    Article · PubMed · Google Scholar
15. Ziccardi VB, Schneider RE, Kummer FJ. Wurzburg lag screw plate versus 4-hole miniplate for the treatment of condylar process fractures. J Oral Maxillofac Surg. 1997;55:602-607. doi:10.1016/s0278-2391(97)90492-4
    Article · PubMed · Google Scholar
16. Ataol M, Kilinc A, Saruhan N, Gundogdu M. Finite element analysis of 2 different implants applicable for vertical bone deficiency at the maxillary sinus. J Biomater Tissue Eng. 2019;9(3):315-321. doi:10.1166/jbt.2019.1978
    Article · PubMed · Google Scholar
17. Aquilina P, Chamoli U, Parr WCH, Clausen PD, Wroe S. Finite element analysis of 3 patterns of internal fixation of fractures of the mandibular condyle. Br J Oral Maxillofac Surg. 2013;51(2):326-331. doi:10.1016/j.bjoms.2012.08.007
    Article · PubMed · Google Scholar
18. Bayram B, Araz K, Uckan S, Balcik C. Comparison of fixation stability of resorbable versus titanium plates and screws in mandibular angle fractures. J Oral Maxillofac Surg. 2009;67(8):1644-1648. doi:10.1016/j.joms.2009.03.011
    Article · PubMed · Google Scholar
19. Ashour EM. Open reduction and internal rigid fixation of unilateral displaced subcondylar fractures using a single trapezoidal plate versus the traditional 2 miniplates: a comparative study. Egypt Dent J. 2021;67(4):2939-2960. doi:10.21608/edj.2021.76518.1636
    Article · PubMed · Google Scholar
20. Ganguly A, Mittal G, Garg R. Comparison between 3D delta plate and conventional miniplate in treatment of condylar fracture: a randomized clinical trial. J Craniomaxillofac Surg. 2021;49(11):1026-1034. doi:10.1016/j.jcms.2021.01.026
    Article · PubMed · Google Scholar
21. Kozakiewicz M, Świniarski J. Finite element analysis of newly introduced plates for mandibular condyle neck fracture treatment by open reduction and rigid fixation. Dent Med Probl. 2017;54:319-326. doi:10.17219/dmp/78913
    Article · PubMed · Google Scholar
22. El-Halawani GN, Ayad SS, Darwish SA, Hassan SR. Evaluation of rhombic 3-dimensional plate in treatment of mandibular subcondylar fractures in adult patients from Alexandria. Alex Dent J. 2017;42(1):56-61.
    PubMed · Google Scholar
23. Ashor MH, Salah AM, Shindy MI, et al. Clinical and radiographic outcomes of rhomboid plate in management of subcondylar fractures: prospective randomized controlled trial. Egypt J Oral Maxillofac Surg. 2018;9(1):1-5. doi:10.21608/omx.2018.5620
    Article · PubMed · Google Scholar

Tables