Evaluation of a Vertical Box Plating Technique for Mandibular Body Fractures and Retrospective Analysis of Patient Outcomes

Key Points

Question Does a vertically oriented box plate increase resistance to torsional forces and reduce complications in the treatment of mandibular body fractures?

Findings In this comparative study and retrospective medical record review of 84 patients, it was demonstrated that box plating for mandibular body fractures was associated with reduced neurosensory complications and operative time compared with traditional rigid internal fixation plating techniques.

Meaning Vertically oriented box plates may be a superior treatment option for the open reduction and internal fixation of mandibular body fractures.

Introduction

The primary goal of mandible fracture repair remains to establish preinjury occlusion, often with temporary maxillomandibular fixation using arch bars, bone screws, or skeletal wire.¹ Anatomical reduction of mandibular fragments is also a principal goal achieved using bone clamps, wires, and/or temporary internal fixation devices. The addition of implantable plates can reduce the necessity or time requirement of maxillomandibular fixation. Adequate fixation is of great importance in successful treatment and often includes the use of reconstructive plates.

The mainstay of current use of internal fixation plates involves the placement of these devices at the inferior or superior border perpendicular to the fracture. These plates were designed to prevent segmental distraction forces from causing failure in a 2-dimensional plane. However, some studies suggest that these plates may provide poor resistance to torsional or twisting forces, especially when there are multiple fracture sites.² In contrast, 3-dimensional, or box, plates use quadrangle geometry to provide additional stability in all dimensions, which offers better resistance against torque forces.³

Ellis,² when questioning how much strength is required in a plate to adequately fixate a mandible fracture, concluded that it was these torsional rotational forces that when not stabilized caused failure of fracture healing. An additional advantage of vertically oriented box plates is a smaller dissection field (Figure 1). In order to place inferior border horizontal plates, a wide field of dissection and exploration is required. To place vertically oriented box plates, a narrower field of dissection is required, potentially requiring a shorter operative time and potentially providing better periosteal support to the healing bone. In this study, vertically oriented box plates were biomechanically tested to measure degree of torsion resisted when compared with standard plates. Additionally, clinical data were reviewed to determine if vertically oriented box plates, which have multiple points of resistance to rotational torque forces, resulted in improved operating parameters, including shorter operative time and reduced failure rates.

Methods

Evaluation of the vertical box plate began with an analysis using biomechanical models. Synthetic mandible replicas (Stryker) were used to evaluate 6 monocortical mandibular body fracture configurations. A handsaw was used to simulate a body fracture, then different plating sets were applied to simulate the repair. Plating techniques of open reduction and internal fixation were performed as described by the Association for the Study of Internal Fixation.⁴ After reconstructive plates were applied, each mandible was subjected to torsional loading applied by a deflection beam torque wrench (Performance Tools) until the construct failed and caused malunion (Supplement). An external hex-headed bolt was also applied to the parasymphyseal region of the mandible for attachment to the torque wrench during force loading (Figure 1). Measurements were recorded for maximum torque sustained prior to deformation and loss of mandible alignment along fracture lines. Examiners were blinded to the plating configuration while taking measurements, and average torque values were recorded after 5 trials for each configuration.

A complementary examination of the vertically oriented box plate included a retrospective review that examined patient medical records at Jacobi Medical Center, a level 1 trauma center in Bronx, New York, from 2005 to 2018. The study was approved by the Montefiore Medical Center Institutional Review Board, which included a waiver for patient informed consent because the retrospective data were deidentified. Patients were selected if they had a coding in their electronic medical record for repair with open reduction and internal fixation of a mandibular body or parasymphyseal fracture. Patients who were operated on by either the plastic surgery, otorhinolaryngology, or oral and maxillofacial surgery teams were included. All of the vertical box plating applications were performed via an intraoral approach by the otorhinolaryngology team, while the traditional plating techniques were performed by all 3 surgical services. Patients were excluded if they were treated with a closed technique, had prior surgical treatment, or if a different segment of the mandible was fractured. Patients with multiple fractured segments were included. Medical records were reviewed for surgical approach, rate of complications, plating techniques, operative time, length of maxillomandibular fixation, and length of admission. The complications studied included malocclusion, nonunion, infection, neurosensory disturbance, and wound dehiscence. Operative time was defined as the time from when the patient entered the operating room to when they left. Length of admission was defined as number of postoperative days in the hospital.

For the dichotomous outcomes, Pearson χ² tests were used to test the null hypothesis of equal occurrence probabilities in the 2 groups. For the count of complications, the Mann-Whitney U test was used. Time in the operating room was also considered an outcome because it affects the cost of providing treatment. The distributions of operative time were displayed as graphs of Kaplan-Meier time-to-event estimates, and the hypothesis of equal operative time distributions was tested with the log-rank test. A multivariate analysis of operative time was carried out using a Cox proportional hazards model, verifying the proportional hazards assumption with Cox-Snell residuals and graphical inspection.

Results

There were 84 distinct patients who accounted for 91 fractures that met eligibility criteria for this study. For patients with multiple fractures, 1 procedure per patient was selected at random for analysis. Of the total patients, 76 (91%) were men (Table 1). The mean (SD) age was 29.7 (12.0) years. All 8 female patients received the traditional plating technique. Of the 76 men, 18 received the vertical box plating technique. Overall 65 (77%) patients had multiple mandible fractures, but these additional fractures did not meet study eligibility criteria. The prevalence of such additional fractures was roughly similar in both treatment groups: 83% (n = 15 of 18) among those receiving vertical box plating and 76% (n = 50 of 66) among those receiving traditional plating.

The otolaryngology team treated 23 (27%) fractures, 5 with traditional plating and 18 with vertical box plating; the plastic surgery team treated 16 (19%) fractures, all with traditional plating; and the oral and maxillofacial surgery team treated 45 (54%) fractures, all with traditional plating. Patients were assigned randomly to surgical services for treatment based on a rotating sequential trauma call pool at the hospital. All 18 patients who received box plating and 27 of the 66 patients who received traditional plating were plated with 1 plate. The remaining 39 patients who received traditional plating required 2 plates. All patients received antibiotics except 2 (11%) patients who had box plated fractures and 3 (5%) patients who had traditional plated fractures. All 18 patients treated with vertical box plating required an intraoral approach. Of the patients with traditionally plated fractures, 54 (82%) were treated intraorally, 5 (8%) extraorally, and 7 (11%) with a combined approach.

A disparity was observed in postoperative neurosensory disturbance and occurred in 25 (38%) patients treated with traditional plating and 0 patients treated with box plating (P = .002) (Table 2). Similarly, measurements of any complication occurred in 41 (62%) patients treated with traditional plating and 6 (33%) patients treated with box plating (relative risk, 0.54; 95% CI, 0.27-1.06; P = .03). The median number of complications in the traditionally plated group was 1.0 (interquartile range, 2.0) and 0.0 (interquartile range, 1.0) in the vertical box group (P = .02). The rates of postoperative malocclusion, nonunion, reoperation, postoperative infection, facial nerve injury, unfavorable scarring, and wound dehiscence were not individually shown to be lower with any significance based on plating technique.

Differences in operative time were also observed with a median operative time in the traditionally plated group of 134 minutes, while the box plated group was 70 minutes (P < .001) (Figure 2). Operative time was further evaluated with a multivariate analysis using a Cox proportional hazards model, verifying the proportional hazards assumption with Cox-Snell residuals and graphical inspection.

In the biomechanical comparative analysis, plating using only a single miniplate resulted in deformation at the fracture line with less than 2.5 inch-pounds (<0.28 newton meters [N · m]) of torque resistance (Table 3). Greater resistance was seen using a 6-hole miniplate and a tension band, sustaining forces of 3.75 (0.42 N · m) and 5 inch-pounds (0.56 N · m) prior to deformation using a 1-mm and 1.5-mm miniplate, respectively. Up to 150% greater resistance than single plating was seen using a vertical box plate measuring 7.5 inch-pounds (0.85 N · m) prior to deformation and a box plate measuring 6.25 inch-pounds (0.71 N · m).

Discussion

Surgical management of mandibular body fractures is still fraught by complications such as malunion, infection, and nerve injury.⁵ A recent article by Ellis² concluded that the most important force causing mandibular fracture complications was the unchecked torsional force that standard horizontal plating only partially addresses. Although that article suggested more rigid plating as a potential solution, further analysis has suggested that multiple vertical points of fixation along a fracture line would more efficiently address the problem. Farmand^6,7 published on his experiences using box plates, which he called 3-D plates, and noted strong resistance to torsional forces, compact form, and lack of major complications. The strength of his plate was based on a geometrically closed quadrangular shape providing a stable configuration in 3 dimensions, not by its thickness or length. Accordingly, we found in a biomechanical fracture model that a plate oriented to provide multiple points of fixation perpendicular to a mandibular body fracture line would better resist torsional forces applied to the fracture. Furthermore, the retrospective clinical study demonstrated lower complication rates and shorter operative time when comparing vertical fixation with conventional techniques.

The biomechanical experiment in the present study demonstrated that the vertical plate was able to provide torque resistance at a level equal to or greater than that of the traditional 2 horizontal plates. Although the traditional plates provided resistance to horizontal distraction, the vertical plate had better torque resistance. The subsequent retrospective review complemented the results from the biomechanical model by demonstrating that the vertically oriented box plate was associated with a lower risk of any complication in the outcomes analysis (62% vs 33.3%; 95% CI, 0.27-1.06; P = .03). The overall rate of complications in this study was in line with rates that have previously been reported in the literature.⁸ Additionally in the analyses, the vertical box plating technique was also associated with a markedly lower incidence of postoperative neurosensory disturbance. We believe that this may be because of the vertical nature of the plate, which decreases the lateral extent of subperiosteal dissection needed to apply the plate as compared with the larger horizontal plates. As such, less nerve “skeletonization” is required, thereby decreasing the risk to the mental nerve. All of the other rates of individual complication outcomes were lower in the vertical box plate group except for the rate of reoperation, but none met statistical significance. The relative increased rate of reoperation in the vertical box group included a case where a patient requested to have the plates removed as a requirement to serve in the military and a second patient who requested electively to have the plate removed. The study was not sufficiently powered to show a decrease in complications such as malunion and malocclusion independently, though overall the lower rate of any complication in the vertical box group was significant.

The study also demonstrated that placement of the vertical box plate was associated with an decrease in operative time (median time, 133 minutes for traditional plating vs 70 minutes for vertical box plating; P < .001). This reduction is beneficial not only for the efficiency of the surgeon, but also, importantly, for patient safety and to reduce hospital costs. Although a full cost comparison is outside the scope of this study, it must be noted that traditional plating techniques often call for multiple plating configurations while the vertical box is applied as a single plate, which further leads to lower costs.

A review of the literature reveals previous studies with similar conclusions, including a prospective study of 28 patients by Sadhwani and colleagues,⁹ which compared outcomes between 2-mm miniplates and box plates for parasymphyseal fractures. The group with the horizontal miniplates had increased complications, including postoperative mobility, malunion, and infection as compared with the group treated with box plates. Another prospective study by Barde and colleagues³ also showed that operative time was significantly reduced with box plating as compared with traditional horizontal plating, but they were unable to show any significant differences in outcomes. In a recent meta-analysis by Wusiman and colleagues¹⁰ comparing box vs standard miniplates for mandible fractures, the authors were able to show a significant decrease in complication rates with the use of box plates. They included 17 studies, including 9 randomized controlled trials, and demonstrated that the use of box miniplates in the fixation of mandibular fractures decreases the risk of postoperative complications by 52%.

Limitations

Because this study had both a laboratory and a retrospective medical record review arm, we attempted to minimize the limitations that either study type inherently maintains. However, this combined approach to evaluating a technique still has limitations both clinically and biomechanically. In the laboratory testing, there is limited extrapolation to clinical scenarios owing to the isolated and controlled laboratory setting in which the plating was performed. The experiment tested application of torsion in a single axis (rotating the segments along the axis of the mandible body) while in practice there are certainly multiple angles of force applied at the fracture line. We attempted to limit bias by running each plate configuration 5 times and recording the torque measurements on video. We also blinded the investigators to the plating configuration being tested during calculation of the maximum torque values. The point of maximal torsion was measured just before misalignment at the fracture line based on visual cues, which were subjective.

An intrinsic limitation of this study is that it is a retrospective review and not a randomized clinical trial. A direct comparison of vertical box plating vs traditional plating would require randomization. This study also included a limited sample size. Owing to the fact that the novel plating technique was only used by a single department, there is a possibility of additional confounding variables beyond plate shape. Multiple comparisons were carried out, so there is appreciable risk that these findings constitute type 1 errors. More importantly, the selection of plating technique was strongly associated with patient attributes, surgical team, and other aspects of treatment in this nonrandomized study. The ability to separate the influence of the plating technique from these other influences on outcomes was limited. Our best effort in this regard led to the conclusion that the separate influence of the plating technique on complication rates itself is probably close to zero and could not be estimated precisely enough to establish its direction. In our attempt to limit surgical team bias, both otolaryngology and oral and maxillofacial surgery team members were involved in data collection and analysis. One finding that seems robust is that the vertical plating technique is strongly associated with reduced operative time. This finding remains quite strong even in the multivariate Cox analysis, which also permitted adjustment for surgical team.

Conclusions

Vertical box plating for mandibular body fractures provided increased torque resistance at the fracture line in biomechanical testing and decreased complications and cost in a retrospective medical chart review compared with traditional plating techniques. Further randomized prospective studies are needed to demonstrate if improved resistance to rotational torsion translates to improvement in clinical outcomes.