Three Dimensional Printing as a Tool For Anatomical Training in Lung Surgery.

Objective: Pulmonary anatomy is challenging, due to the high variability and its three-dimensional (3D) shape. While demands in thoracic oncologic surgery are increasing, the transition from open to thoracoscopic surgery is hampering anatomical understanding. This study analyzed the value of a 3D printed lung model in understanding and teaching anatomy. Methods: A 3D pulmonary model was created and tested among different levels of proficiency: 10 experienced surgeons, 10 fellow surgeons and 10 junior residents. They were tested in interpretation of anatomy based on thoracic CT-scans, either using the 3D model or a 2D anatomical atlas. Accuracy of the given answers, time to complete the task and the self-reported level of certainty were scored in each group. Results: In the experienced surgeons group there was no difference in between the 2D-model or 3D-model with a high rate of correct answers in both groups, and no differences in time or certainty. Fellow surgeons highly benefitted from the 3D-model with an improved accuracy from 26.6% to 70.0% (p = 0.001). Time to complete the task was shorter (207 versus 122 s, p < 0.0001) and participants were more secure (median of 4 versus 3, p = 0.007). For junior residents time to complete the task was shorter, the level of certainty was higher, but there was no improvement in accuracy. Conclusions: 3D printing may benefit in understanding anatomical relations in the complex anatomy of the bronchiopulmonary tree, especially for surgeons in training and could benefit in teaching anatomy. Supplementary Information: The online version contains supplementary material available at 10.1007/s40670-023-01807-x.

Entry Point Variation in the Osseous Fixation Pathway of the Anterior Column of the Pelvis-A Three-Dimensional Analysis.

Fractures of the superior pubic ramus can be treated with screw insertion into the osseous fixation pathway (OFP) of the anterior column (AC). The entry point determines whether the screw exits the OFP prematurely. This can be harmful when it enters the hip joint or damages soft tissues inside the lesser pelvis. The exact entry point varies between patients and can be difficult to ascertain on fluoroscopy during surgery. The aim of this study was to determine variation in the location of the entry point. A retrospective single center study was performed at a level 1 trauma center in the Netherlands. Nineteen adult patients were included with an undisplaced fracture of the superior pubic ramus on computer tomography (CT)-scan. Virtual three-dimensional (3D) models of the pelvises were created. Multiple screws were placed per AC and the models were superimposed. A total of 157 screws were placed, of which 109 did not exit the OFP prematurely. A universally reproducible entry point could not be identified. A typical crescent shaped region of entry points did exist and was located more laterally in females when compared to males. Three-dimensional virtual surgery planning can be helpful to identify the ideal entry points in each case.

Three-dimensional Surface Imaging for Clinical Decision Making in Pectus Excavatum.

To evaluate pectus excavatum, 3-dimensional surface imaging is a promising radiation-free alternative to computed tomography and plain radiographs. Given that 3-dimensional images concern the external surface, the conventional Haller index, and correction index are not applicable as these are based on internal diameters. Therefore, external equivalents have been introduced for 3-dimensional images. However, cut-off values to help determine surgical candidacy using external indices are lacking. A prospective cohort study was conducted. Consecutive patients referred for suspected pectus excavatum received a computed tomography (≥18 years) or plain radiographs (<18 years). The external Haller index and external correction index were calculated from additionally acquired 3-dimensional images. Cut-off values for the 3-dimensional image derived indices were obtained by receiver-operating characteristic curve analyses, using a conventional Haller index ≥3.25, and computed tomography derived correction index ≥28.0% as indicative for surgery. Sixty-one and 63 patients were included in the computed tomography and radiograph group, respectively. To determine potential surgical candidacy, receiver-operating characteristic analyses found an optimum cut-off of ≥1.83 for the external Haller index in both the computed tomography and radiograph group with a positive predictive value between 0.90 and 0.97 and a negative predictive value between 0.72 and 0.81. The optimal cut-off for the external correction index was ≥15.2% with a positive predictive value of 0.86 and negative predictive value of 0.93. The 3-dimensional image derived external Haller index and external correction index are accurate radiation-free alternatives to facilitate surgical decision-making among patients suspected of pectus excavatum with values of ≥1.83 and ≥15.2% indicative for surgery.

Validation of the OrthoGnathicAnalyser 2.0-3D accuracy assessment tool for bimaxillary surgery and genioplasty.

Orthognathic surgery is a widely performed procedure to correct dentofacial deformities. Virtual treatment planning is an important preparation step. One advantage of the use of virtual treatment planning is the possibility to assess the accuracy of orthognathic surgery. In this study, a tool (OrthoGnathicAnalyser 2.0), which allows for quantification of the accuracy of orthognathic surgery, is presented and validated. In the OrthoGnathicAnalyser 2.0 the accuracy of the osseous chin can now be assessed which was not possible in the earlier version of the OrthoGnathicAnalyser. 30 patients who underwent bimaxillary surgery in combination with a genioplasty were selected from three different centers in the Netherlands. A pre-operative (CB)CT scan, virtual treatment planning and postoperative (CB)CT scan were required for assessing the accuracy of bimaxillary surgery. The preoperative and postoperative (CB)CT scans were aligned using voxel-based matching. Furthermore, voxel-based matching was used to align the pre-operative maxilla, mandible and rami towards their postoperative position whereas surface-based matching was used for aligning the pre-operative chin towards the postoperative position. The alignment resulted in a transformation matrix which contained the achieved translations and rotations. The achieved translations and rotations can be compared to planning values of the virtual treatment plan. To study the reproducibility, two independent observers processed all 30 patients to assess the inter-observer variability. One observer processed the patients twice to assess the intra-observer variability. Both the intra- and inter-observer variability showed high ICC values (> 0.92) and low measurement variations (< 0.673±0.684mm and < 0.654±0.824°). The results of this study show that the OrthoGnathicAnalyser 2.0 has an excellent reproducibility for quantification of skeletal movements between two (CB)CT scans.

Holographic Augmented Reality for DIEP Flap Harvest.

BACKGROUND: During a deep inferior epigastric perforator (DIEP) flap harvest, the identification and localization of the epigastric arteries and its perforators are crucial. Holographic augmented reality is an innovative technique that can be used to visualize this patient-specific anatomy extracted from a computed tomographic scan directly on the patient. This study describes an innovative workflow to achieve this. METHODS: A software application for the Microsoft HoloLens was developed to visualize the anatomy as a hologram. By using abdominal nevi as natural landmarks, the anatomy hologram is registered to the patient. To ensure that the anatomy hologram remains correctly positioned when the patient or the user moves, real-time patient tracking is obtained with a quick response marker attached to the patient. RESULTS: Holographic augmented reality can be used to visualize the epigastric arteries and its perforators in preparation for a deep inferior epigastric perforator flap harvest. CONCLUSIONS: Potentially, this workflow can be used visualize the vessels intraoperatively. Furthermore, this workflow is intuitive to use and could be applied for other flaps or other types of surgery.

A nonsurgical approach with repeated orthoptic evaluation is justified for most blow-out fractures.

OBJECTIVE: This study presents the results of an updated clinical protocol for orbital blow-out fractures, with a special emphasis on nonsurgical treatment and orthoptic evaluation of functional improvement. METHODS: A two-centre multidisciplinary prospective cohort study was designed to monitor the results of a clinical protocol by assessing ductions, diplopia, globe position, and fracture size. Patients underwent clinical assessment and orthoptic evaluation at first presentation and then at 2 weeks and 3/6/12 months after nonsurgical or surgical treatment. Outcome parameters were field of binocular single vision (BSV), ductions, degree of enophthalmos, a diplopia quality-of-life (QoL) questionnaire, and other sequelae or surgical complications. RESULTS: 46 of the 58 patients who completed the 3, 6 and/or 12-month follow-up received nonsurgical treatment. There was full recovery without diplopia or enophthalmos (>2 mm) in 45 of the 58 patients. The other 13 patients had limited diplopia, mainly in extreme upward gaze (average BSV 90). Five of those 13 patients did not experience impairment of diplopia in daily life. The average QoL score at the end of follow-up was 97. No patients developed late enophthalmos. CONCLUSION: This study showed that a high percentage of patients with orbital floor and/or medial wall fracture recovered spontaneously without lasting diplopia or cosmetically disfiguring enophthalmos. The conservative treatment protocol assessed here underlines the importance of orthoptic evaluation of functional parameters.

What is the value of 3D virtual reality in understanding acetabular fractures?

BACKGROUND: Acetabular fractures are difficult to classify owing to the complex three-dimensional (3D) anatomy of the pelvis. 3D printing helps to understand and reliably classify acetabular fracture types. 3D-virtual reality (VR) may have comparable benefits. Our hypothesis is that 3D-VR is equivalent to 3D printing in understanding acetabular fracture patterns. METHODS: A total of 27 observers of various experience levels from several hospitals were requested to classify twenty 3D printed and VR models according to the Judet-Letournel classification. Additionally, surgeons were asked to state their preferred surgical approach and patient positioning. Time to classify each fracture type was recorded. The cases were randomized to rule out a learning curve. Inter-observer agreement was analyzed using Fleiss' kappa statistics (κ). RESULTS: Inter-observer agreements varied by observer group and type of model used to classify the fracture: medical students: 3D print (κ = 0.61), VR (κ = 0.41); junior surgical residents: 3D print (0.51) VR (0.54); senior surgical residents: 3D print (0.66) VR (0.52); junior surgeons: 3D print (0.56), VR (0.43); senior surgeons: 3D print (κ = 0.59), VR (κ = 0.42). Using 3D printed models, there was more agreement on the surgical approach (junior surgeons κ = 0.23, senior surgeons κ = 0.31) when compared with VR (junior surgeons κ = 0.17, senior surgeons 0.25). No difference was found in time used to classify these fractures between 3D printing and VR for all groups (P = 1.000). CONCLUSIONS: The Judet-Letournel acetabular classification stays difficult to interpret; only moderate kappa agreements were found. We found 3D-VR inferior to 3D printing in classifying acetabular fractures. Furthermore, the current 3D-VR technology is still not practical for intra-operative use.

Toward Holographic-Guided Surgery.

The implementation of augmented reality (AR) in image-guided surgery (IGS) can improve surgical interventions by presenting the image data directly on the patient at the correct position and in the actual orientation. This approach can resolve the switching focus problem, which occurs in conventional IGS systems when the surgeon has to look away from the operation field to consult the image data on a 2-dimensional screen. The Microsoft HoloLens, a head-mounted AR display, was combined with an optical navigation system to create an AR-based IGS system. Experiments were performed on a phantom model to determine the accuracy of the complete system and to evaluate the effect of adding AR. The results demonstrated a mean Euclidean distance of 2.3 mm with a maximum error of 3.5 mm for the complete system. Adding AR visualization to a conventional system increased the mean error by 1.6 mm. The introduction of AR in IGS was promising. The presented system provided a solution for the switching focus problem and created a more intuitive guidance system. With a further reduction in the error and more research to optimize the visualization, many surgical applications could benefit from the advantages of AR guidance.

Maxillofacial prosthetic rehabilitation: A survey on the quality of life.

STATEMENT OF PROBLEM: Maxillofacial prostheses, especially those supported by endosseous implants, are regarded as a viable, secure treatment for the reconstruction of facial defects to restore quality of life. The long-term quality of life of patients treated with facial prostheses with different retentive systems is unclear. PURPOSE: The purpose of this clinical study was to assess the long-term quality of life of patients treated with facial prostheses with different retentive systems over a 14-year period at a Dutch oral and maxillofacial surgery unit. MATERIAL AND METHODS: A total of 66 patients with facial prostheses were inventoried and categorized based on anatomic location and type of retention. A 62-item questionnaire was designed to survey the daily prosthetic use, care, quality, durability, longevity, and reliability of retention. Furthermore, issues relating to general satisfaction, self-image, and socialization frequency were addressed. RESULTS: Completed validated questionnaires were returned by 52 patients. Of the prosthetic replacements, 23% (n=12) were orbital, 33% (n=17) nasal, and 44% (n=23) auricular prostheses. The survey showed that a prosthetic reconstruction led to high satisfaction scores with regard to wearing comfort, anatomic fit, color, and anatomic form. A significant difference was shown for implant-retained facial prostheses, which provided enhanced retention and increased ease of placement and removal (Fisher exact test P=.01 and P=.04). Patients with nasal prostheses were less satisfied with the junction of their prostheses to the surrounding soft tissue and more aware of others noticing their prosthetic rehabilitation. Patients with auricular defects were less embarrassed (P=.01) by their prostheses. Although auricular prostheses were less frequently cleaned (P=.01), no significant difference was found in minor soft tissue complications between different anatomic locations and the various retentive systems. CONCLUSIONS: Implant-retained prostheses have advantages over adhesive-retained prostheses in terms of ease of handling. However, improvements in prosthetic material properties, including color stability and durability, are needed to increase the longevity of facial prostheses.

Applications and limitations of using patient-specific 3D printed molds in autologous breast reconstruction.

BACKGROUND: Over the last years, several techniques have been proposed to improve the outcome of autologous breast reconstruction procedures. One of these innovations describes patient-specific, three-dimensional (3D) printed breast molds for intraoperative use based on 3D stereophotogrammetry. In this article, we want to share our preliminary experiences with producing such templates, its clinical possibilities and limitations in practice. METHODS: Patient-specific templates were designed based on 3D stereophotogrammetry images. The 3D template was fabricated using a 3D printer. During breast reconstruction, the autologous flap was placed inside the printed template to aid the surgeon in determining the shape and volume of the autologous flap creating the desired breast dimensions. Patients were 3D-photographed 6 to 9 months post-operatively. RESULTS: Three patients with unilateral breast reconstructions showed a width difference of 0.5 cm and mean volume difference of 211 ml between the reconstructed and contralateral breasts. In the three bilateral reconstructed patients, a mean difference in breast width and volume of respectively 0.5 cm and 16 ml was found. CONCLUSIONS: Patient-specific breast templates are inexpensive and relatively easy to design, while being practical and convenient to obtain insight in the dimensions of the desired breast during reconstruction, according to the operating surgeons. Patient selection is however critical, as patients must have sufficient donor volume and/or satisfying breast shape to be able to use the template to its full potential.Level of evidence: Level IV, therapeutic study.

Accuracy of Three Software Applications for Breast Volume Calculations from Three-Dimensional Surface Images.

BACKGROUND: Knowing breast volumes before certain surgeries helps the surgeon to obtain breast symmetry. Calculating breast volumes from three-dimensional surface images is possible with specialized software applications. However, limited data exist concerning the accuracy of such volume calculations. The purpose of this study was to investigate the accuracy of breast volume calculations performed with the 3D BreAST, 3dMD Vultus, and VECTRA software applications. METHODS: Twenty-six subjects who underwent 44 mastectomies were enrolled. Preoperative three-dimensional surface images were acquired with a VECTRA-XT stereophotogrammetry device. Breast volumes were calculated from these images with the three software applications. The mastectomy specimens were weighed to derive their actual volume and compared with the software calculations. RESULTS: For all three methods, a positive correlation between the breast volume and absolute calculation error was found (p < 0.001), but not for the errors as a percentage of the breast volume (p = 0.17, p = 0.80, and p = 0.42). The 3D BreAST, 3dMD Vultus, and VECTRA applications provided mean volume calculation errors of 21, 186, and -32 ml (p = 0.27, p < 0.001, and p = 0.14) or 2 ± 25, 48 ± 26, and -6 ± 27 percent of the breast volume (p = 0.67, p < 0.001, and p = 0.16), respectively. CONCLUSIONS: Despite that two applications calculated accurate mean breast volumes, all applications showed a high standard deviation in terms of the percentage of the breast volume. Therefore, the usefulness of absolute breast volume calculations from three-dimensional surface images seems limited. CLINICAL QUESTION/LEVEL OF EVIDENCE: Diagnostic, II.

Virtual Incision Pattern Planning using Three-Dimensional Images for Optimization of Syndactyly Surgery.

Syndactyly is a congenital condition characterized by fusion of the fingers. If not treated correctly during infancy, syndactyly may hinder the normal development of hand function. Many surgical techniques have been developed, with the main goal to create a functional hand with the smallest number of operative corrections. Therefore, exact preoperative planning of the reconstructive procedure is essential. An imaging method commonly used for preoperative planning is 3-dimensional (3D) surface imaging. The goal of this study was to implement the use of this technique in hand surgery, by designing a virtual planning tool for a desyndactylization procedure based on 3D hand images. A 3D image of a silicon syndactyly model was made on which the incision pattern was virtually designed. A surgical template of this pattern was printed, placed onto the silicon model and delineated. The accuracy of the transfer from the virtual delineation toward the real delineation was calculated, resulting in a mean difference of 0.82 mm. This first step indicates that by using 3D images, a virtual incision pattern can be created and transferred back onto the patient successfully in an easy and accurate way by using a template. Thereafter, 3D hand images of 3 syndactyly patients were made, and individual virtual incision patterns were created. Each pattern was transferred onto the patient by using a 3D printed template. The resulting incision pattern needed minor modifications by the surgeon before the surgery was performed. Further research and validation are necessary to develop the virtual planning of desyndactylization procedures.

The advantages of advanced computer-assisted diagnostics and three-dimensional preoperative planning on implant position in orbital reconstruction.

OBJECTIVE: Advanced three-dimensional (3D) diagnostics and preoperative planning are the first steps in computer-assisted surgery (CAS). They are an integral part of the workflow, and allow the surgeon to adequately assess the fracture and to perform virtual surgery to find the optimal implant position. The goal of this study was to evaluate the accuracy and predictability of 3D diagnostics and preoperative virtual planning without intraoperative navigation in orbital reconstruction. METHODS: In 10 cadaveric heads, 19 complex orbital fractures were created. First, all fractures were reconstructed without preoperative planning (control group) and at a later stage the reconstructions were repeated with the help of preoperative planning. Preformed titanium mesh plates were used for the reconstructions by two experienced oral and maxillofacial surgeons. The preoperative virtual planning was easily accessible for the surgeon during the reconstruction. Computed tomographic scans were obtained before and after creation of the orbital fractures and postoperatively. Using a paired t-test, implant positioning accuracy (translation and rotations) of both groups were evaluated by comparing the planned implant position with the position of the implant on the postoperative scan. RESULTS: Implant position improved significantly (P < 0.05) for translation, yaw and roll in the group with preoperative planning (Table 1). Pitch did not improve significantly (P = 0.78). CONCLUSION: The use of 3D diagnostics and preoperative planning without navigation in complex orbital wall fractures has a positive effect on implant position. This is due to a better assessment of the fracture, the possibility of virtual surgery and because the planning can be used as a virtual guide intraoperatively. The surgeon has more control in positioning the implant in relation to the rim and other bony landmarks.

Rating Nasolabial Aesthetics in Unilateral Cleft Lip and Palate Patients: Cropped Versus Full-Face Images.

OBJECTIVE: To determine if cropping facial images affects nasolabial aesthetics assessments in unilateral cleft lip patients and to evaluate the effect of facial attractiveness on nasolabial evaluation. DESIGN: Two cleft surgeons and one cleft orthodontist assessed standardized frontal photographs 4 times; nasolabial aesthetics were rated on cropped and full-face images using the Cleft Aesthetic Rating Scale, and total facial attractiveness was rated on full-face images with and without the nasolabial area blurred using a 5-point Likert scale. SETTING: Cleft Palate Craniofacial Unit of a University Medical Center. PATIENTS: Inclusion criteria: nonsyndromic unilateral cleft lip and an available frontal view photograph around 10 years of age. EXCLUSION CRITERIA: a history of facial trauma and an incomplete cleft. Eighty-one photographs were available for assessment. MAIN OUTCOME MEASURES: Differences in mean CARS scores between cropped versus full-face photographs and attractive versus unattractive rated patients were evaluated by paired t test. RESULTS: Nasolabial aesthetics are scored more negatively on full-face photographs compared to cropped photographs, regardless of facial attractiveness. (Mean CARS score, nose: cropped = 2.8, full-face = 3.0, P < .001; lip: cropped = 2.4, full-face = 2.7, P < .001; nose and lip: cropped = 2.6, full-face = 2.8, P < .001). CONCLUSION: Aesthetic outcomes of the nasolabial area are assessed significantly more positively when using cropped images compared to full-face images. For this reason, cropping images, revealing the nasolabial area only, is recommended for aesthetical assessments.

Integration of digital dental casts in cone beam computed tomography scans-a clinical validation study.

OBJECTIVES: Images derived from cone beam computed tomography (CBCT) scans lack detailed information on the dentition and interocclusal relationships needed for proper surgical planning and production of surgical splints. To get a proper representation of the dentition, integration of a digital dental model into the CBCT scan is necessary. The aim of this study was to validate a simplified protocol to integrate digital dental models into CBCT scans using only one scan. MATERIALS AND METHODS: Conventional protocol A used one combined upper and lower impression and two CBCT scans. The new protocol B included placement of ten markers on the gingiva, one CBCT scan, and two separate impressions of the upper and lower dentition. Twenty consecutive patients, scheduled for mandibular advancement surgery, were included. To validate protocol B, 3-dimensional reconstructions were made, which were compared by calculating the mean intersurface distances obtained with both protocols. RESULTS: The mean distance for all patients for the upper jaw is 0.39 mm and for the lower jaw is 0.30 mm. For ten out of 20 patients, all distances were less than 1 mm. For the other ten patients, all distances were less than 2 mm. CONCLUSIONS: Mean distances of 0.39 and 0.30 mm are clinically acceptable and comparable to other studies; therefore, this new protocol is clinically accurate. CLINICAL RELEVANCE: This new protocol seems to be clinically accurate. It is less time consuming, gives less radiation exposure for the patient, and has a lower risk for positional errors of the impressions compared to other integration protocols.

Validation of 3D documentation of palatal soft tissue shape, color, and irregularity with intraoral scanning.

OBJECTIVES: The purpose of this study was to assess the feasibility of 3D intraoral scanning for documentation of palatal soft tissue by evaluating the accuracy of shape, color, and curvature. MATERIALS AND METHODS: Intraoral scans of ten participants' upper dentition and palate were acquired with the TRIOS® 3D intraoral scanner by two observers. Conventional impressions were taken and digitized as a gold standard. The resulting surface models were aligned using an Iterative Closest Point approach. The absolute distance measurements between the intraoral models and the digitized impression were used to quantify the trueness and precision of intraoral scanning. The mean color of the palatal soft tissue was extracted in HSV (hue, saturation, value) format to establish the color precision. Finally, the mean curvature of the surface models was calculated and used for surface irregularity. RESULTS: Mean average distance error between the conventional impression models and the intraoral models was 0.02 ± 0.07 mm (p = 0.30). Mean interobserver color difference was - 0.08 ± 1.49° (p = 0.864), 0.28 ± 0.78% (p = 0.286), and 0.30 ± 1.14% (p = 0.426) for respectively hue, saturation, and value. The interobserver differences for overall and maximum surface irregularity were 0.01 ± 0.03 and 0.00 ± 0.05 mm. CONCLUSIONS: This study supports the hypothesis that the intraoral scan can perform a 3D documentation of palatal soft tissue in terms of shape, color, and curvature. CLINICAL RELEVANCE: An intraoral scanner can be an objective tool, adjunctive to the clinical examination of the palatal tissue.

Should Virtual Mirroring Be Used in the Preoperative Planning of an Orbital Reconstruction?

PURPOSE: Mirroring has been used as a diagnostic tool in orbital wall fractures for many years, but limited research is available proving the assumed symmetry of orbits. The purpose of this study was to evaluate volume and contour differences between orbital cavities in healthy humans. MATERIALS AND METHODS: In this cross-sectional study, the left and right orbital cavities of a consecutive sample of patients' computed tomograms were measured. Inclusion criteria were patients with no sign of orbital or sinus pathology or fracture. Outcome variables were differences in volume and contour. Descriptive statistics and Student paired t test were used for data analysis of orbital volume and distance maps were used for analysis of orbital contour. RESULTS: The sample was composed of 100 patients with a mean age of 57; 50% were men. The total mean orbital volume was 27.53 ± 3.11 mL. Mean difference between cavities was 0.44 ± 0.31 mL or 1.59% (standard deviation [SD], 1.10%). The orbital contour showed high similarity, with an absolute mean left-versus-right difference of 0.82 mm (SD, 0.23 mm). CONCLUSION: The authors hypothesize that the measured differences between right and left orbital volumes and contours are clinically minor. In consequence, the use of mirroring tools as part of preoperative planning in orbital reconstruction is legitimate with the aim of simulating the pre-traumatized anatomy.

Natural variation of the zygomaticomaxillary complex symmetry in normal individuals.

OBJECTIVE: The study aim was to investigate variations in the symmetry of the zygomaticomaxillary complex (ZMC) in normal individuals. METHOD: Computed tomography datasets of 200 individuals without facial fractures were analyzed using a validated three-dimensional analysis technique. The absolute average distance (AD) and 90th percentile distance (NPD) were calculated, representing respectively the overall and maximum symmetry between bilateral ZMCs. RESULTS: The mean AD and NPD of the total study group was 0.9 ± 0.3 mm (95% CI 0.3-2.3) and 1.7 ± 0.5 mm (95% CI 0.5-3.9), respectively. The mean AD and NPD in males were 1.0 ± 0.3 mm (95% CI 0.28-2.34) and 1.9 ± 0.5 mm (95% CI 0.5-3.9) versus 0.8 ± 0.3 mm (95% CI 0.4-1.7) and 1.6 ± 0.5 mm (95% CI 0.8-2.9), respectively, for females. A statistically significant difference between male and female was found for both AD and NPD (p < 0.01). The male population <40 years had a mean AD and NPD of 1.0 ± 0.3 mm and 1.8 ± 0.5 mm, which was not statistically significant when compared with males >40 years. CONCLUSION: The naturally occurring anatomic variation in ZMC symmetry described in this study is proposed as a benchmark for evaluating the amount of preoperative displacement and postoperative reduction of ZMC in trauma cases.