Osteosynthesis using cannulated headless Herbert screws in mandibular angle fracture treatment: A new approach?

Comparison of Strengths of Mandibular Angle Fractures Following Different Plate Designs: A Human Cadaver Study

Study Design

This institutional cross-sectional study using cadaveric mandibles aimed to measure and compare the strengths of three plating designs utilized in osteosynthesis of mandibular angle fractures.

Objective

There have been prior studies on angle fracture fixation though few biomechanical studies on human cadaveric specimen. This study aims to directly compare the biomechanical strength of different plating designs to the mandibular angle fracture using a human cadaveric specimen substrate.

Methods

After receiving an angle osteotomy and either single plate, two plate, or 3D plate fixation, the specimens underwent biomechanical testing using the Instron 5565 mechanical testing unit. The primary outcomes measured were peak load at which permanent deformation started, displacement value at peak load, and load necessary for a specific amount of displacement at 1, 3, 5, and 7 mm.

Results

There were 15 hemi-mandibles in each group. Based on data analysis of all the specimens, there were no significant differences in the mandibular height, ramus width, mandibular thickness, angle height, and gonial angle between the hemimandibles.. This study demonstrated a statistically significant increased strength performance of the 3D plate over the single plate fixation and the 2-plate over the single plate fixation. The results between 2-plate and 3D plate were in similar values.

Conclusions

In terms of biomechanical strength, the 3D plate and two plate designs outperform the single plate design to mandibular angle fractures. There are various anatomical and patient specific situations that can aid in selection between them. In the absence of the favorable angle fracture and patient, biomechanical strength to the method of fixation selection needs to be considered.

The role of stiffness-matching in avoiding stress shielding-induced bone loss and stress concentration-induced skeletal reconstruction device failure

It is well documented that overly stiff skeletal replacement and fixation devices may fail and require revision surgery. Recent attempts to better support healing and sustain healed bone have looked at stiffness-matching of these devices to the desired role of limiting the stress on fractured or engrafted bone to compressive loads and, after the reconstructed bone has healed, to ensure that reconstructive medical devices (implants) interrupt the normal loading pattern as little as possible. The mechanical performance of these devices can be optimized by adjusting their location, integration/fastening, material(s), geometry (external and internal), and surface properties. This review highlights recent research that focuses on the optimal design of skeletal reconstruction devices to perform during and after healing as the mechanical regime changes. Previous studies have considered auxetic materials, homogeneous or gradient (i.e., adaptive) porosity, surface modification to enhance device/bone integration, and choosing the device's attachment location to ensure good osseointegration and resilient load transduction. By combining some or all of these factors, device designers work hard to avoid problems brought about by unsustainable stress shielding or stress concentrations as a means of creating sustainable stress-strain relationships that best repair and sustain a surgically reconstructed skeletal site. STATEMENT OF SIGNIFICANCE: Although standard-of-care skeletal reconstruction devices will usually allow normal healing and improved comfort for the patient during normal activities, there may be significant disadvantages during long-term use. Stress shielding and stress concentration are amongst the most common causes of failure of a metallic device. This review highlights recent developments in devices for skeletal reconstruction that match the stiffness, while not interrupting the normal loading pattern of a healthy bone, and help to combat stress shielding and stress concentration. This review summarises various approaches to achieve stiffness-matching: application of materials with modulus close to that of the bone; adaptation of geometry with pre-defined mechanical properties; and/or surface modification that ensures good integration and proper load transfer to the bone.

Assessment of CAD/CAM Customized V Pattern Plate Versus Standard Miniplates Fixation in Mandibular Angle Fracture (Randomized Clinical Trial)

Background

Mandibular angle is the most common site for fractures, accounting for 23-42% of all cases of mandibular fractures. A customized fixation system is designed directly for a specific patient, which reduces the time spent bending and fixing the plate during the operation. This study was designed to assess the effect of CAD/CAM customized V pattern plate versus standard miniplates fixation in mandibular angle fracture.

Materials and Methods

This prospective randomized clinical trial included 26 patients suffering from mandibular angle fracture. Patients were selected from Oral and Maxillofacial Surgery Department, Faculty of Dentistry, Cairo University and Ahmed Maher Teaching Hospital. Study group (13) needed open reduction and internal fixation by using CAD/CAM V plate with surgical guide, while control group (13) needed open reduction and internal fixation by using standard superior-inferior miniplate fixation. The patients were then followed up for one year postoperatively.

Results

It showed that there was a statistical difference between the study group and the control group regarding postoperative pain, occlusion, and maximal interincisal opening (p value < 0.05%). There was no statistical difference (p value > 0.05%) in the postoperative panoramic radiograph that was taken within the postoperative 1st week in both groups, while the increase in mean bone density was statistically significant (p value < 0.05%) from 6 months to one year postoperatively.

Conclusion

CAD/CAM customized V pattern plate is a suitable plate design because it offers sufficient stability for normal bone healing, the creation of an ideal occlusion, an early return to function, and adequate postoperative radiographic outcomes.

Trial Registration

It was registered at ClinicalTrials.gov. Registration number: NCT03761524. Registration date: 03.12.2018.

Biofunctional Glycol-Modified Polyethylene Terephthalate and Thermoplastic Polyurethane Implants by Extrusion-Based Additive Manufacturing for Medical 3D Maxillofacial Defect Reconstruction

This work addresses the topic of extrusion-based additive manufacturing (filament-based material extrusion) of patient-specific biofunctional maxillofacial implants. The technical approach was chosen to overcome the shortcomings of medically established fabrication processes such as a limited availability of materials or long manufacturing times. The goal of the work was a successful fabrication of basic implants for defect reconstruction. The underlying vision is the implants' clinic-internal and operation-accompanying application. Following a literature search, a material selection was conducted. Digitally prepared three-dimensional (3D) models dealing with two representative mandible bone defects were printed based on the material selection. An ex-vivo model of the implant environment evaluated dimensional and fitting traits of the implants. Glycol-modified PET (PETG) and thermoplastic polyurethane (TPU) were finally selected. These plastics had high cell acceptance, good mechanical properties, and optimal printability. The subsequent fabrication process yielded two different implant strategies: the standard implant made of PETG with a build-up rate of approximately 10 g/h, and the biofunctional performance implant with a TPU shell and a PETG core with a build-up rate of approximately 4 g/h. The standard implant is meant to be intraoperatively applied, as the print time is below three hours even for larger skull defects. Standard implants proved to be well fitting, mechanically stable and cleanly printed. In addition, the hybrid implant showed particularly cell-friendly behavior due to the chemical constitution of the TPU shell and great impact stability because of the crack-absorbing TPU/PETG combination. This biofunctional constellation could be used in specific reconstructive patient cases and is suitable for pre-operative manufacturing based on radiological image scans of the defect. In summary, filament-based material extrusion has been identified as a suitable manufacturing method for personalized implants in the maxillofacial area. A further clinical and mechanical study is recommended.

Herbert Cannulated Bone Screw Osteosynthesis in Anterior Mandibular Fracture Treatment: A Comparative Study With Lag Screw and Miniplate

PURPOSE

The Herbert bone screw (HBS) is a successful and minimally invasive method of fracture fixation that is used routinely in orthopedic surgery. The aim of this study was to evaluate the clinical and radiographic performances of the HBS in the treatment of anterior mandibular fractures and compare it with the common and established treatment modalities, the lag screw (LS) and the 2.0-mm miniplate (MP).

MATERIALS AND METHODS

This study implemented a randomized clinical trial and enrolled a sample of patients with anterior mandibular fractures. The primary predictor variable was treatment group categorized as HBS, LS, or MP fixation of the fracture. Primary outcome variables were the presence of interfragmentary mobility and radiodensitometric appraisal of fracture healing progression. The secondary outcome was the postoperative clinical evaluation. Other variables collected were grouped into demographic, fracture location, and intraoperative clinical data. All recorded data were documented, tabulated, computed, and analyzed. Statistical significance was set at the 5% level.

RESULTS

Twenty-one patients were selected and randomly allocated to 1 of 3 groups based on the fixation modality used. There were no relevant differences in demographic data for the 3 groups. There were no statistically relevant differences in clinical evaluation outcomes. However, there was a statistically significant difference in the gain of mean postoperative bone density between the HBS and MP groups (P = .012) and between the LS and MP groups (P = .045), but not between the HBS and LS groups.

CONCLUSION

Cannulated HBS osteosynthesis provides a successful and minimally invasive treatment modality for the management of anterior mandibular fractures.

A customized fixation plate with novel structure designed by topological optimization for mandibular angle fracture based on finite element analysis

Background

The purpose of this study was to design a customized fixation plate for mandibular angle fracture using topological optimization based on the biomechanical properties of the two conventional fixation systems, and compare the results of stress, strain and displacement distributions calculated by finite element analysis (FEA).

Methods

A three-dimensional (3D) virtual mandible was reconstructed from CT images with a mimic angle fracture and a 1 mm gap between two bone segments, and then a FEA model, including volume mesh with inhomogeneous bone material properties, three loading conditions and constraints (muscles and condyles), was created to design a customized plate using topological optimization method, then the shape of the plate was referenced from the stress concentrated area on an initial part created from thickened bone surface for optimal calculation, and then the plate was formulated as “V” pattern according to dimensions of standard mini-plate finally. To compare the biomechanical behavior of the “V” plate and other conventional mini-plates for angle fracture fixation, two conventional fixation systems were used: type A, one standard mini-plate, and type B, two standard mini-plates, and the stress, strain and displacement distributions within the three fixation systems were compared and discussed.

Results

The stress, strain and displacement distributions to the angle fractured mandible with three different fixation modalities were collected, respectively, and the maximum stress for each model emerged at the mandibular ramus or screw holes. Under the same loading conditions, the maximum stress on the customized fixation system decreased 74.3, 75.6 and 70.6% compared to type A, and 34.9, 34.1, and 39.6% compared to type B. All maximum von Mises stresses of mandible were well below the allowable stress of human bone, as well as maximum principal strain. And the displacement diagram of bony segments indicated the effect of treatment with different fixation systems.

Conclusions

The customized fixation system with topological optimized structure has good biomechanical behavior for mandibular angle fracture because the stress, strain and displacement within the plate could be reduced significantly comparing to conventional “one mini-plate” or “two mini-plates” systems. The design methodology for customized fixation system could be used for other fractures in mandible or other bones to acquire better mechanical behavior of the system and improve stable environment for bone healing. And together with SLM, the customized plate with optimal structure could be designed and fabricated rapidly to satisfy the urgent time requirements for treatment.