The Dynamic Role of Buttress Reconstruction after Maxillectomy

Functional stability analyses of maxillofacial skeleton bearing cleft deformities

The symmetrically stable craniofacial bony structure supports the complex functions and delicate contour of the face. Congenital craniofacial deformities are often accompanied by bony defects and have been repetitively correlated with compromised dento-maxillary stability, but neither the extent nor the pattern of cleft-related maxillary instability has been explored in detail. Furthermore, it is largely unknown if the bony defect and related instability are correlated with secondary maxillary deformity common among patients with orofacial clefts. With the aid of finite element modeling, we studied the detailed relationship between cleft-related bony defect and maxillary stability under occlusal loading. Craniofacial models were generated based on cone-beam computed tomography data and loaded with mimicked bite forces along the axial axis of each tooth. Our data showed that all cleft models exhibited more asymmetrical deformations under mastication compared with the normal. Models with palatal cleft demonstrated greater asymmetry, greater dental arch contraction, and less maxillary protrusion compared to models with alveolar cleft only. For unilateral cleft models, alveolus on non-cleft side tended to be more protruded and lifted than the cleft side. For bilateral cleft models, the most prominent feature was the seriously contracted alveolar arch and curved and pitched premaxillae. These findings indicated cleft type-specific pattern of maxillary instability, which were largely in accordance with dentoalveolar morphological features among patients. Collectively, our study elucidated the detailed relationship between cleft bony defect and the pattern of maxillary instability, and suggested a prototype for studying the abnormal maxillary and dental arch growth among patients with craniofacial deformities.

BIOMECHANICAL ANALYSIS TO VERIFY THE BUTTRESS THEORY WHEN USING THE ANATOMICAL THIN TITANIUM MESH PLATE FOR ZYGOMATICOMAXILLARY COMPLEX BONE FRACTURE

Objective: The aim of this study was to investigate the biomechanics of the facial skeletal for understanding the buttress after fixation with standard and modified anatomical thin titanium mesh (ATTM) plates by finite element (FE) analysis. Methods: Standard ATTM (SATTM) plate designed as the “L”-shape anticipated to be fixed in the ZMC anterior maxilla and lateral buttress to increase the fixation screw anchoring strength and another modified ATTM (MATTM) plate with a protrusion in the medial side and a slot and barb design in the lateral side to enhance the zygomaticomaxillary/nasomaxillary buttresses and provide precise positioning to the ZMC segments were studied by the FE analysis under masticatory forces with 250[Formula: see text]N. Result: The FE simulation results indicated that the total displacement distribution of the maxillary for ZMC fracture fixation with MATTM plate was smaller than that of SATTM plate. Stress concentration was found at the frontal and alveolar processes of the maxillary bone for SATTM plate fixation. Local vector plots of the first principal stress near the frontal process of the maxillary and zygomaticofacial formen of the zygomatic indicated that the stress flow for MATTM plate fixation was relatively close to nasomaxillary buttress, and the zygomaticomaxillary buttress, respectively. Conclusions: This study concluded that “L”-shape ATTM plate designed with a protrusion in the medial side and a slot and barb design in the lateral side can enhance the zygomaticomaxillary/nasomaxillary buttresses under uniform occlusal condition.

DESIGN OF A MAXILLOFACIAL PROSTHESIS BASED ON TOPOLOGY OPTIMIZATION

The use of custom implants has recently gained increasing importance in craniofacial surgery in order to optimize preoperative planning and reduce operative time. The design of patient-specific implants plays an important role to restore craniofacial bone. Nevertheless, the design method has become the bottleneck. In this study, a new design method of a maxillofacial prosthesis based on the topology optimization was proposed to realize lightweight custom implants. At first, parametric predesign of the optimized model was carried out to ensure that the optimized model conformed to the main physiological anatomical structure and recover basic function structure. Then, the design region is defined under given load and boundary conditions. The material interpolation technique of SIMP with the penalization factor is adopted to get the final optimized 3D model. Finally, the experimental results verify that the method of topology optimization for the maxillofacial prosthesis proposed is efficient.

Review of In Vivo Bone Strain Studies and Finite Element Models of the Zygomatic Complex in Humans and Nonhuman Primates: Implications for Clinical Research and Practice

The craniofacial skeleton is often described in the clinical literature as being comprised of vertical bony pillars, which transmit forces from the toothrow to the neurocranium as axial compressive stresses, reinforced transversely by buttresses. Here, we review the literature on bony microarchitecture, in vivo bone strain, and finite-element modeling of the facial skeleton of humans and nonhuman primates to address questions regarding the structural and functional existence of facial pillars and buttresses. Available bone material properties data do not support the existence of pillars and buttresses in humans or Sapajus apella. Deformation regimes in the zygomatic complex emphasize bending and shear, therefore conceptualizing the zygomatic complex of humans or nonhuman primates as a pillar obscures its patterns of stress, strain, and deformation. Human fossil relatives and chimpanzees exhibit strain regimes corroborating the existence of a canine-frontal pillar, but the notion of a zygomatic pillar has no support. The emerging consensus on patterns of strain and deformation in finite element models (FEMs) of the human facial skeleton corroborates hypotheses in the clinical literature regarding zygomatic complex function, and provide new insights into patterns of failure of titanium and resorbable plates in experimental studies. It is suggested that the "pillar and buttress" model of human craniofacial skeleton function be replaced with FEMs that more accurately and precisely represent in vivo function, and which can serve as the basis for future research into implants used in restoration of occlusal function and fracture repair. Anat Rec, 299:1753-1778, 2016. © 2016 Wiley Periodicals, Inc.

A biomechanical study of relationship between sternum defect patterns and thoracic respiration

BACKGROUND

Various types of sternum defects are produced after the removal of thoracic tumors involving the sternum. The present study aims to elucidate the relationship between the defect patterns and their effects on thoracic respiration.

METHODS

Ten sets of finite element models were produced simulating thoraces of 10 persons and termed normal models. With each of the 10 normal models, the sternum was removed in six different ways to produce new models termed defect models. Defect models were categorized into hemi-superior (H-S), hemi-inferior (H-I), hemi-whole length (H-W), bilateral-superior (B-S), bilateral-inferior (B-I), and bilateral-whole length (B-W) defect types, depending on the locations of the defects. Respiratory movement was dynamically simulated with these models. The volume change the thoraces present during respiration was measured to evaluate the effectiveness of thoracic respiration. This value - defined as ΔV - was calculated and was compared between normal and defect models.

RESULTS

With H-W and B-W type models, ΔV dropped to around 20% of normal values. With H-S and B-S type models, ΔV dropped to around 50% of normal values. With H-I and B-I type models, ΔV presented values almost equivalent to those of normal models.

CONCLUSION

Effectiveness of thoracic respiration is seriously impaired when the whole length of the sternum is absent. Reconstruction of the defect is essential for these cases. However, since the upper part of the sternum is most important for effective thoracic respiration, priority should be placed on the upper part in performing reconstruction.

BIOMECHANICAL ANALYSIS OF THE APPLICATION OF ZYGOMA IMPLANTS FOR PROSTHESIS IN UNILATERAL MAXILLARY DEFECT

The objective of this research is to evaluate the biomechanical effect of zygomatic implant-supported obturator prostheses in unilateral maxillary defect. Based on CT data, four 3D numerical models were built. One model was a normal craniofacial complex (model 1) and other three models were structures with unilateral maxilla defect reconstructed using clasp-retained obturator prosthesis (model 2), one zygomatic implant-supported and clasp-retained prosthesis (model 3), two zygomatic implant-supported and clasp-retained prosthesis (model 4). Bilateral vertical loads of 300[Formula: see text]N were imposed and the stress and displacement distribution were calculated, analyzed and compared. The bilateral occlusal forces dispersed along the three-mechanical-pillar of the maxillofacial region and the displacement distributed symmetrically in model 1. Because of mechanical pillars break on the affected side, all occlusal forces were transferred by clasps and abutment teeth in model 2, which induced the increase in stress and displacement level. The zygomatic implant restored mechanical pillars and greatly reduced the stress and displacements levels in models 3 and 4. The stress and displacement distributions on clasps, bones, teeth and periodontal ligaments were more reasonable with the support of zygomatic implants. Therefore, the zygomatic implant-supported and clasp-retained prostheses were found to be more effective for unilateral maxillary defect reestablishment.

Human feeding biomechanics: performance, variation, and functional constraints

The evolution of the modern human (Homo sapiens) cranium is characterized by a reduction in the size of the feeding system, including reductions in the size of the facial skeleton, postcanine teeth, and the muscles involved in biting and chewing. The conventional view hypothesizes that gracilization of the human feeding system is related to a shift toward eating foods that were less mechanically challenging to consume and/or foods that were processed using tools before being ingested. This hypothesis predicts that human feeding systems should not be well-configured to produce forceful bites and that the cranium should be structurally weak. An alternate hypothesis, based on the observation that humans have mechanically efficient jaw adductors, states that the modern human face is adapted to generate and withstand high biting forces. We used finite element analysis (FEA) to test two opposing mechanical hypotheses: that compared to our closest living relative, chimpanzees (Pan troglodytes), the modern human craniofacial skeleton is (1) less well configured, or (2) better configured to generate and withstand high magnitude bite forces. We considered intraspecific variation in our examination of human feeding biomechanics by examining a sample of geographically diverse crania that differed notably in shape. We found that our biomechanical models of human crania had broadly similar mechanical behavior despite their shape variation and were, on average, less structurally stiff than the crania of chimpanzees during unilateral biting when loaded with physiologically-scaled muscle loads. Our results also show that modern humans are efficient producers of bite force, consistent with previous analyses. However, highly tensile reaction forces were generated at the working (biting) side jaw joint during unilateral molar bites in which the chewing muscles were recruited with bilateral symmetry. In life, such a configuration would have increased the risk of joint dislocation and constrained the maximum recruitment levels of the masticatory muscles on the balancing (non-biting) side of the head. Our results do not necessarily conflict with the hypothesis that anterior tooth (incisors, canines, premolars) biting could have been selectively important in humans, although the reduced size of the premolars in humans has been shown to increase the risk of tooth crown fracture. We interpret our results to suggest that human craniofacial evolution was probably not driven by selection for high magnitude unilateral biting, and that increased masticatory muscle efficiency in humans is likely to be a secondary byproduct of selection for some function unrelated to forceful biting behaviors. These results are consistent with the hypothesis that a shift to softer foods and/or the innovation of pre-oral food processing techniques relaxed selective pressures maintaining craniofacial features that favor forceful biting and chewing behaviors, leading to the characteristically small and gracile faces of modern humans.

Designing patient-specific 3D printed craniofacial implants using a novel topology optimization method

Large craniofacial defects require efficient bone replacements which should not only provide good aesthetics but also possess stable structural function. The proposed work uses a novel multiresolution topology optimization method to achieve the task. Using a compliance minimization objective, patient-specific bone replacement shapes can be designed for different clinical cases that ensure revival of efficient load transfer mechanisms in the mid-face. In this work, four clinical cases are introduced and their respective patient-specific designs are obtained using the proposed method. The optimized designs are then virtually inserted into the defect to visually inspect the viability of the design . Further, once the design is verified by the reconstructive surgeon, prototypes are fabricated using a 3D printer for validation. The robustness of the designs are mechanically tested by subjecting them to a physiological loading condition which mimics the masticatory activity. The full-field strain result through 3D image correlation and the finite element analysis implies that the solution can survive the maximum mastication of 120 lb. Also, the designs have the potential to restore the buttress system and provide the structural integrity. Using the topology optimization framework in designing the bone replacement shapes would deliver surgeons new alternatives for rather complicated mid-face reconstruction.

Experimental validation of 3D printed patient-specific implants using digital image correlation and finite element analysis

With the dawn of 3D printing technology, patient-specific implant designs are set to have a paradigm shift. A topology optimization method in designing patient-specific craniofacial implants has been developed to ensure adequate load transfer mechanism and restore the form and function of the mid-face. Patient-specific finite element models are used to design these implants and to validate whether they are viable for physiological loading such as mastication. Validation of these topology optimized finite element models using mechanical testing is a critical step. Instead of inserting the implants into a cadaver or patient, we embed the implants into the computer-aided skull model of a patient and, fuse them together to 3D print the complete skull model with the implant. Masticatory forces are applied in the molar region to simulate chewing and measure the stress-strain trajectory. Until recently, strain gages have been used to measure strains for validation. Digital Image Correlation (DIC) method is a relatively new technique for full-field strain measurement which provides a continuous deformation field data. The main objective of this study is to validate the finite element model of patient-specific craniofacial implants against the strain data from the DIC obtained during the mastication simulation and show that the optimized shapes provide adequate load-transfer mechanism. Patient-specific models are obtained from CT scans. The principal maximum and minimum strains are compared. The computational and experimental approach to designing patient-specific implants proved to be a viable technique for mid-face craniofacial reconstruction.

Not only "nurture", but also "nature", influence the outcome of zygoma repair

The present study aims to elucidate the relationship between preoperative deviation patterns of fractured zygomas and treatment outcomes. Forty-five randomly selected patients with tri-pod type zygoma fractures were classified into a medial rotation group and a lateral rotation group, depending on preoperative deviation patterns. A minimum of 6 months after the operation, symmetry of the cheek was evaluated by three plastic surgeons using a VAS system. The evaluated scores were compared between the two groups. Furthermore, simulation of postoperative secondary deformity was performed by applying hypothetically defined relapse forces on CAD models produced by referring to the CT data of 20 patients. The deviation values obtained by the simulation were compared between the two groups. The results demonstrate that VAS scores were higher for the lateral rotation group than for the medial rotation group and that the deviation values were higher for the medial rotation group than for the lateral rotation group. It is concluded that treatment outcomes of zygoma fractures are affected by preoperative deviation patterns. Cases with medial rotation are likely to present poorer outcomes than those with lateral rotation.

Biomechanical Analysis of the Effect of Intracranial Pressure on the Orbital Distances in Trigonocephaly

Objective

This biomechanical study aims to elucidate differences in how skulls with trigonocephaly, normal skulls, and postoperative trigonocephalic skulls respond to intracranial pressure and how this affects the orbital distances.

Materials and Methods

For 10 patients with trigonocephaly (8.2 ± 4.5 months), simulation models were produced based on the computed tomographic data of the skulls. These models were categorized as the Trigono group. For each model, a 15-mm Hg pressure was applied to the neurocranium to simulate the intracranial pressure. The interorbital distances expanded in response to the applied pressure. The amount of the change in the orbital distance was calculated using finite element analysis. The same processes were repeated for 10 models simulating normal skulls (the Control group) and postoperative trigonocephalic skulls (the Remodeled group). The changes in the orbital distance were compared among the three groups.

Results

The changes in the orbital distance were significantly smaller for the Trigono group than for the Control group. However, changes were significantly greater for the Remodeled group than for the Control group.

Conclusion

The expansion of interorbital distances in response to the cranial pressure is restricted in skulls with trigonocephaly. This restriction is eliminated by performing remodeling of the skull. These findings explain why spontaneous correction of hypotelorism occurs postoperatively in trigonocephaly.

In vivo bone strain and finite-element modeling of the craniofacial haft in catarrhine primates

Hypotheses regarding patterns of stress, strain and deformation in the craniofacial skeleton are central to adaptive explanations for the evolution of primate craniofacial form. The complexity of craniofacial skeletal morphology makes it difficult to evaluate these hypotheses with in vivo bone strain data. In this paper, new in vivo bone strain data from the intraorbital surfaces of the supraorbital torus, postorbital bar and postorbital septum, the anterior surface of the postorbital bar, and the anterior root of the zygoma are combined with published data from the supraorbital region and zygomatic arch to evaluate the validity of a finite-element model (FEM) of a macaque cranium during mastication. The behavior of this model is then used to test hypotheses regarding the overall deformation regime in the craniofacial haft of macaques. This FEM constitutes a hypothesis regarding deformation of the facial skeleton during mastication. A simplified verbal description of the deformation regime in the macaque FEM is as follows. Inferior bending and twisting of the zygomatic arches about a rostrocaudal axis exerts inferolaterally directed tensile forces on the lateral orbital wall, bending the wall and the supraorbital torus in frontal planes and bending and shearing the infraorbital region and anterior zygoma root in frontal planes. Similar deformation regimes also characterize the crania of Homo and Gorilla under in vitro loading conditions and may be shared among extant catarrhines. Relatively high strain magnitudes in the anterior root of the zygoma suggest that the morphology of this region may be important for resisting forces generated during feeding.

Sensitivity Analysis of a Validated Subject-Specific Finite Element Model of the Human Craniofacial Skeleton

Developing a more complete understanding of the mechanical response of the craniofacial skeleton (CFS) to physiological loads is fundamental to improving treatment for traumatic injuries, reconstruction due to neoplasia, and deformities. Characterization of the biomechanics of the CFS is challenging due to its highly complex structure and heterogeneity, motivating the utilization of experimentally validated computational models. As such, the objective of this study was to develop, experimentally validate, and parametrically analyse a patient-specific finite element (FE) model of the CFS to elucidate a better understanding of the factors that are of intrinsic importance to the skeletal structural behaviour of the human CFS. An FE model of a cadaveric craniofacial skeleton was created from subject-specific computed tomography data. The model was validated based on bone strain measurements taken under simulated physiological-like loading through the masseter and temporalis muscles (which are responsible for the majority of craniofacial physiologic loading due to mastication). The baseline subject-specific model using locally defined cortical bone thicknesses produced the strongest correlation to the experimental data ( r2 = 0.73). Large effects on strain patterns arising from small parametric changes in cortical thickness suggest that the very thin bony structures present in the CFS are crucial to characterizing the local load distribution in the CFS accurately.

Topological optimization for designing patient-specific large craniofacial segmental bone replacements

Restoring normal function and appearance after massive facial injuries with bone loss is an important unsolved problem in surgery. An important limitation of the current methods is heuristic ad hoc design of bone replacements by the operating surgeon at the time of surgery. This problem might be addressed by incorporating a computational method known as topological optimization into routine surgical planning. We tested the feasibility of using a multiresolution three-dimensional topological optimization to design replacements for massive midface injuries with bone loss. The final solution to meet functional requirements may be shaped differently than the natural human bone but be optimized for functional needs sufficient to support full restoration using a combination of soft tissue repair and synthetic prosthetics. Topological optimization for designing facial bone tissue replacements might improve current clinical methods and provide essential enabling technology to translate generic bone tissue engineering methods into specific solutions for individual patients.

Inferior meatal antrostomy impairs dynamic stability of the orbital walls

OBJECTIVES

The medial wall of the maxillary sinus, or the bony buttress, plays an important role in supporting the orbital floor. Since part of the bony buttress is removed in the inferior meatal antrostomy (IMA), it is expected that the IMA makes the orbital floor likely to develop serious fractures in traumatic situations. We conducted the present study to elucidate the effect of the IMA on the vulnerability of the orbital floor.

METHODS

After producing CAD (Computer Assisted Design) models simulating twelve skulls, we performed simulation antrostomy for each of the twelve CAD models in both the middle meatus and the inferior meatus. According to the site of the antrostomy, the models were categorized as the MMA (middle meatal antrostomy) or IMA groups. We then applied an impact on the orbital region of each model. Using the finite element method, we calculated the area of the orbital wall fracture induced by the impact. Then we compared the area of the orbital wall fractures between the MMA and IMA groups.

RESULTS

The orbital wall fracture areas were significantly greater in the IMA group than in the MMA group.

CONCLUSIONS

The patients who underwent IMA are likely to develop serious orbital fractures if their orbits receive traumatic impacts. Hence, surgeons should be prudent in their indications for IMA.

Experimental evaluation of relapse-risks in operated zygoma fractures

OBJECTIVES

Prevention of relapse, or postoperative dislocation, of the fixed zygoma is necessary to achieve optimal results in the treatment of zygoma fractures. Assuming that the occurrence of intensified stresses on mastication at the screw-bone interface (SBI) constitutes the essential cause of the relapse, we evaluated the stresses for three different fixation methods-fixation at the frontal process (FP), inferior orbital rim (IOR), and zygomatico-maxillary buttress (ZMB).

METHODS

We used 10 computer-aided design (CAD) models simulating zygoma fractures in the experiment. For each CAD model, we fixed the fractured zygoma with four screws and one mini-plate at the FP, IOR, or ZMB. After applying a 5.5kg force simulating mastication, we calculated the intensity and distribution patterns of the stresses occurring at the SBIs of the fixation screws using the finite element method. Thereby, we evaluated dynamic stability of the fixed zygoma for each of the three fixation methods.

RESULTS

Greater stresses occur at the SBIs with IOR fixation than at those with FP and ZMB fixation. Although the stresses occurring at the SBIs on mastication demonstrated evenly distributed patterns with the FP and ZMB fixation, the stresses demonstrated concentration on one screw with the IOR fixation.

CONCLUSIONS

The fixed zygoma is more likely to cause relapse with the IOR fixation than with the FP or ZMB fixation. Hence, in performing zygoma fixation at the IOR, care should be taken to minimize the likelihood of postoperative relapse that is caused by skewed distribution of the stresses on the fixation screws.

The Structural Implications of a Unilateral Facial Skeletal Cleft: A Three-Dimensional Finite Element Model Approach

Objective:

For children born with a unilateral facial skeletal cleft, oral motor function is impaired and skeletal development and growth are asymmetrical with regard to the midsagittal plane. This study was designed to verify that a unilateral skeletal cleft and its dimensions (i.e., depth and width) affect the severity of the asymmetric stress and strain distribution within the maxilla.

Methods:

A three-dimensional finite element model of a normal maxilla was developed from pediatric, subject-specific computerized tomography scan data. A clefting pattern then was introduced to simulate varying degrees of deformity in geometry, with the bone properties and boundary conditions held constant. The asymmetric index was introduced to quantify the asymmetrical stress and strain distribution within the maxilla with regard to the midsagittal plane.

Results:

The unilateral skeletal cleft led to a nonuniform, asymmetric stress and strain distribution within the maxilla: intensified on the noncleft side and weakened on the cleft side. As the depth of the unilateral cleft increased, the stress and strain distribution became increasingly asymmetric as measured by the asymmetric index. In contrast, the width of the cleft had minimal effect on the asymmetrical stress and strain distribution.

Interpretation/conclusion:

These results implied that a child born with a unilateral cleft would be expected to have an asymmetric skeletal development between the noncleft and the cleft sides as a consequence of an asymmetric functional loading pattern.

Stress distribution on the thorax after the Nuss procedure for pectus excavatum results in different patterns between adult and child patients

OBJECTIVE

In the Nuss procedure, in which the deformed thorax is forcibly corrected by insertion of correction bars, considerable stresses occur on the patient's thorax. We performed the present study to elucidate how stress patterns on the thorax after this procedure differ between child and adult patients.

METHODS

Eighteen patients with pectus excavatum, constituting a child group (n = 10) and an adult group (n = 8), were included in the study. After a 3-dimensional computer-assisted design model was produced with computed tomographic data from each patient, simulation of the Nuss procedure was performed on the model. Then the stresses occurring on each thorax were calculated using the finite element method. The stresses were compared between the child and adult groups in terms of intensity on each rib and the distribution patterns over the whole thorax.

RESULTS

With all 12 ribs, significantly greater stress occurred in the adult group than stress in the child group. Although the stresses occurring on the thorax demonstrated concentrated patterns in the child group, widely distributed patterns were observed in the adult group.

CONCLUSIONS

The stresses that occur on the thorax after the Nuss procedure take different patterns between children and adults in terms of intensity and distribution. The differences should be taken into consideration in managing postoperative pain after the Nuss procedure.

Appropriate diameter for screws to fix the maxilla following Le Fort I osteotomy: An investigation utilizing finite element analysis

BACKGROUND

After Le Fort I osteotomy, there is sometimes a secondary deformity (relapse), with the lower segment deviating from the intraoperatively fixed position. It is hyopothesized that the structural stability of the reconstructed maxilla is affected by the diameter of the fixation screws. The present study aims to elucidate the relationship between the diameters of the screws and the structural stability of the maxilla after Le Fort I osteotomy.

METHODS

3D models were produced on a workstation from 20 dry skulls and a Le Fort I operation was simulated on them. The upper and lower segments of the divided maxilla in each of the 20 models were connected using four plates and 16 screws. Five different diameters of the fixation screws were tested. Thus altogether 100 models were produced. A 180N load was applied to the molar region for each model. Using finite element analysis, the resultant stresses and deviations of the lower segments were calculated. Finally, referring to these values, the relationships between screw diameters and stability of the lower segment were evaluated.

RESULT

The stability of the lower segment was greatest when the diameter of the fixation screws was equal to the thickness of the bone at each fixation site.

CONCLUSION

In performing Le Fort I osteotomy, it is recommended that bone thickness is measured at each fixation site in advance, and the diameter of the fixation screws matched accordingly; thereby optimum stability of the reconstructed maxilla can be anticipated.

Combination of Costal Cartilage Graft and Rib-Latissimus Dorsi Flap

In secondary reconstruction of the maxilla, skeletal reconstruction as well as soft tissue augmentation is required to obtain a good contour. We present a new strategy for combining a costal cartilage graft with a rib-latissimus dorsi flap. We used this method to treat a 39-year-old man who had previously undergone total maxillectomy. First, a vascularized rib, elevated together with a latissimus dorsi flap, was fixed between the middle of the maxilla and the edge of the zygomatic arch. The small defects that could not be reconstructed with the rib only were reconstructed with a costal cartilage graft. The patient did not develop any postoperative infection or flap necrosis. Thirteen months after the secondary reconstruction, he presented with a good contour of the cheek. Our method was effective for the reconstruction of a complex skeletal defect of the maxilla.

Effectiveness of Additional Transmalar Kirschner Wire Fixation for a Zygoma Fracture

BACKGROUND

The purpose of this study was to verify the effectiveness of transmalar Kirschner wire fixation as additional fixation for the treatment of zygoma fractures.

METHODS

The authors compared two methods for zygoma fixation at the frontozygomatic suture from both theoretical and clinical viewpoints: miniplate fixation (plate fixation) and miniplate fixation with an additional transmalar Kirschner wire fixation (wire plus plate fixation). For the theoretical study, the authors produced zygoma fractures on 20 skull simulation models; these were generated on the basis of computed tomographic data of actual dry skulls. In their simulation surgery, they fixed the fractured zygoma with the above-mentioned two fixation methods, producing 20 plate fixation models and 20 wire plus plate fixation models. A 10-kgf load was then applied on the fractured zygoma in the anteroposterior and superoinferior directions. Finally, the stresses around the fixation screws and the deviation of the zygoma were calculated using finite element analysis. For the clinical study, the authors compared the postoperative zygoma alignment based on computed tomography of six patients treated with plate fixation and eight patients treated with wire plus plate fixation using a visual analogue scale.

RESULTS

In the theoretical study, the wire plus plate fixation models demonstrated a significant decrease in both the stresses around the screws and the deviation of the fractured bone compared with the plate fixation models. In the clinical study, the visual analogue scale scores for the wire plus plate fixation group were significantly higher than those for the plate fixation group.

CONCLUSION

Because the additional transmalar Kirschner wire fixation can effectively increase the stability of the fractured zygoma that has been fixed with one miniplate, it should be recommended as an effective technique for the treatment of complicated zygoma fractures.