Stryker Orthopaedic Modeling and Analytics (SOMA): A Review.

Due to the differences in bone morphology between demographics such as age, gender, body mass index, and ethnicity, the development of orthopaedic implants requires a large number of anatomical data from various patient populations. In an effort to assess these demographic variations, Stryker Orthopaedic Modeling and Analytics (SOMA) has been developed. SOMA is a suite of tools which utilizes a comprehensive database of computed tomography scans (CT-scans), plus associated three-dimensional (3D) bone models, allowing the user to assess population differences in bone morphology, bone density, and implant fit for the purposes of research and development. Several additional software tools are currently in development to further analyze bone density and have the potential to enhance component fit. These tools, in combination with the database, have been previously utilized for development of many implant designs and techniques in hip and knee arthroplasty, as well as in trauma surgery.

Three-Dimensional Mapping of Scapular Body, Neck, and Glenoid Fractures.

OBJECTIVES: The purpose of this study was to report patterns of scapular fractures and define them with a contemporary methodology. METHODS: . DESIGN: Retrospective study, 2015-2021. SETTING: Single, academic, Level 1 trauma center. PATIENT SELECTION CRITERIA: Consecutive patients ≥18 years, presenting with unilateral scapula fracture, with thin-slice (≤0.5-mm) bilateral computed tomography (CT) scans of the entirety of both the injured and uninjured scapulae. OUTCOME MEASURES AND COMPARISONS: Thin-slice (0.5-mm) CT scans of injured and normal scapulae were obtained to create three-dimensional (3D) virtual models. 3D modeling software (Stryker Orthopedics Modeling and Analytics, Stryker Trauma GmbH, Kiel, Germany aka SOMA) was used to create a 3D map of fracture location and frequency. Fracture zones were delineated using anatomic landmarks to characterize fracture patterns. RESULTS: Eighty-seven patients were identified with 75 (86%) extra-articular and 12 (14%) intra-articular fractures. The dominant fracture pattern emanated from the superior lateral border (zone E) to an area inferior to the spinomedial angle (zone B) and was present in 80% of extra-articular fractures. A second-most common fracture line propagated from the primary (most-common) line toward the inferior medial scapular border with a frequency of 36%. Bare zones (with 1 or no fractures present) were identified in 4 unique areas. Furthermore, intra-articular fractures were found to be heterogenous. CONCLUSIONS: The 3D fracture map created in this study confirmed that extra-articular scapular fractures occur in certain patterns with a relatively high frequency. Results provide greater insight into scapular fracture locations and may help to study prognosis of injury and improve treatment strategy including operative approaches and surgical tactics.

A comparison between Asians and Caucasians in the dimensions of the femoral isthmus based on a 3D-CT analysis of 1189 adult femurs.

INTRODUCTION: For successful intramedullary implant placement at the femur, such as nailing in unstable proximal femur fractures, the use of an implant that at least reaches or exceeds the femoral isthmus and yields sufficient thickness is recommended. A number of complications after intramedullary femoral nailing have been reported, particularly in Asians. To understand the anatomical features of the proximal femur and their ethnic differences, we aimed to accurately calculate the femoral isthmus dimensions and proximal distance of Asians and Caucasians. METHODS: In total, 1189 Asian and Caucasian segmented 3D CT data sets of femurs were analyzed. The individual femoral isthmus diameter was precisely computed to investigate whether gender, femur length, age, ethnicity or body mass index have an influence on isthmus diameters. RESULTS: The mean isthmus diameter of all femurs was 10.71 ± 2.2 mm. A significantly larger diameter was found in Asians when compared to Caucasians (p < 0.001). Age was a strong predictor of the isthmus diameter variability in females (p < 0.001, adjusted r2 = 0.299). With every year of life, the isthmus showed a widening of 0.08 mm in women. A Matched Pair Analysis of 150 female femurs showed a significant difference between isthmus diameter in Asian and Caucasian femurs (p = 0.05). In 50% of the cases the isthmus was found in a range of 2.4 cm between 16.9 and 19.3 cm distal to the tip of the greater trochanter. The female Asian femur differs from Caucasians as it is wider at the isthmus. CONCLUSIONS: In absolute values, the proximal isthmus distance did not show much variation but is more proximal in Asians. The detailed data presented may be helpful in the development of future implant designs. The length and thickness of future standard implants may be considered based on the findings.

Defining the Ideal "Nail Exit Path" of a Tibial Intramedullary Nail-A Computed Tomography Analysis of 860 Tibiae.

OBJECTIVES: To identify the ideal distal nail position in the distal tibia, using a computed tomography analysis. METHODS: Three-dimensional models of 860 left tibiae were analyzed using the Stryker Orthopaedic Modeling and Analytics software (SOMA, Stryker, Kiel, Germany). The nail axis was defined by 7 center points at the middle of the inner cortical boundary. The point where this line fell relative to the center of the tibial plafond in both the anteroposterior and mediolateral planes was calculated. RESULTS: The mean mediolateral offset of the tibial nail exit path was 4.4 ± 0.2 mm (95% confidence interval) lateral to the center of the tibial plafond. The mean anteroposterior offset of the tibial nail exit path was 0.6 ± 0.1 mm anterior to the center of the tibial plafond. CONCLUSIONS: We have presented an anatomic study analyzing the ideal nail exit path using computed tomography scans of 860 tibiae. We defined that the ideal nail exit path of a tibial nail is lateral with respect to the center of the tibial plafond. This is supported by previous clinical studies and has significant implications for preventing malalignment when treating distal tibial fractures with intramedullary nailing.

Bone morphology of the proximal femoral canal: ethnicity related differences and the influence on cementless tapered wedge stem designs.

BACKGROUND: Differences in proximal femoral morphology between ethnicities may have implications on the design of cementless tapered wedge stems. This study analyses the differences in Asian and Caucasian bone morphology as well as the related fit of various cementless tapered wedge stem designs. METHODS: A computed tomography database and modelling software was used to retrospectively analyse a total of 1345 femora. Ethnicity related comparisons as well as the fit of the stem designs were analysed. RESULTS: Statistically significant differences between canal shape of Caucasian and Japanese as well as non-Japanese Asians were observed. The fit of the stems within the femoral canal was highly dependent on the respective stem shape. CONCLUSIONS: The shape differences in stem designs had a larger influence on the fit within the femoral canal than the differences in ethnicity related to bone morphology.

The three-dimensional bone mass distribution of the posterior pelvic ring and its key role in transsacral screw placement.

To optimize the placement of iliosacral screws in osteoporotic bone it is essential to know where to find the best purchase. The aim of this study was to determine and visualize the distribution of bone mass in the posterior pelvic ring by using a color-coded thermal map, to differentiate the bone distribution patterns in normal pelvises and in pelvises with impaired bone density and to identify zones in S1 and S2 with particularly good bone quality, in both healthy and osteoporotic pelvises. A total of 324 pelvises were included. The bone density of the posterior pelvic ring, the fifth lumbar vertebral body (L5) and screw corridors S1 and S2 were visualized. Each individual pelvis was measured with a 3D automated program. Two groups were selected - patients with mean bone density in L5 of ≤100 HU (group 1, n = 52) and those with mean bone density >100 HU (group 2, n = 272). Color-coded thermal maps are presented of the bone density distribution in the pelvises. Bone density in L5 correlated significantly with S1 and S2; bone density was significantly higher in the S1 than in the S2 corridor (p < 0.001). Bone was denser in the posterior and upper parts of the S1 body. Bone density was significantly lower in group 2 than in group 1 (p < 0.001). The color-coded "thermal" maps of bone mass distribution can help surgeons to decide where sacroiliac screws are likely to find optimal purchase.

Symmetry Matching of the Medial Acetabular Surface-A Quantitative Analysis in View of Patient-Specific Implants.

OBJECTIVE: To quantify intrapelvic surface symmetry in reference to a preshaped suprapectineal acetabular implant. METHODS: In this cross-sectional study, an anatomically preshaped acetabular fracture implant was fitted on 3D surface models of 516 pelvises from a preexisting bone database using a software tool for automated implant fitting (SOMA, Stryker Orthopaedic Modeling and Analytics) of a CAD model of the implant. The distances between bone and the reference implant were measured at 2310 reference points for each hemipelvis. RESULTS: The average distance between the left hemipelvis and the plate was 1.98 mm (median, 10% percentile: 1.45, 90% percentile: 2.78) and 2.0 mm (median, 10% percentile: 1.45, 90% percentile: 2.92) between the right hemipelvis and the plate. There was no significant difference between the 2 hemipelvises (median absolute pairwise delta: 0.25 mm; 10% percentile: 0.04, 90% percentile: 0.82; Wilcoxon, P = 0.064). CONCLUSIONS: With regard to the periacetabular surface of the inner pelvis, the pelvis can be considered sufficiently symmetric for using the mirrored contralateral hemipelvis as a template for patient-specific implants in acetabular fracture fixation.

New Design Process for Anatomically Enhanced Osteosynthesis Plates.

This study evaluated the implementation and effectiveness of an iterative process aimed to quantify and enhance the anatomical fit of an osteosynthesis plate design for the fifth metacarpal bone regarding a defined shape-based acceptance criterion (SAC) while complying with basic clinical requirements and engineering limitations. The process was based on employing virtual tools (a database of individual three-dimensional bone models, statistical analysis of the bone geometry, and proprietary software tools) to evaluate conformity between plate designs and bone shape. The conformity was quantified by the mean distance between plate and bone (MBP). The enhancement was completed when the median MBP of the population was below the SAC threshold. This was fulfilled by the third plate design (two enhancement iterations). The intentionally abstract enhancement process may serve as a guideline for development of plate designs for other indications. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1508-1517, 2019.

Comparison of 2 versus 3 dimensional fracture mapping strategies for 3 dimensional computerized tomography reconstructions of scapula neck and body fractures.

Fracture mapping has been used in the understanding of injury patterns in different bones. To our knowledge, there are no applications of this technique using three-dimensional (3D) morphologic fracture characteristics. Previously, scapula fractures were mapped by transferring information from 3D computed tomography to a two-dimensional (2D) template. Cole et al. determined that 3D Computerized Tomography (CT) scans were more reliable compared to plain radiographs in terms of scapular angulation, translation, and glenopolar angle measurements. Thus, we hypothesized that if there is a difference between fracture lines drawn in 3D and in 2D, then the 3D mapping would yield more accurate fracture patterns. We completed a retrospective, comparative study (evidence level III) utilizing CT imaging from a single center scapular registry. We studied ten patients with scapula fractures in whom bilateral CT scans were obtained. Fractures were mapped both two and three-dimensionally, and we measured deviations between the fracture lines that were drawn with each approach. The measured deviations ranged from 10.4 mm to 28.0 mm when comparing 2D versus 3D techniques, with the mean deviation being 4.0 mm and 10.4 mm, respectively. Half of the 2D renderings possessed hidden fracture lines that were later revealed on 3D imaging. Three-dimensional renderings were more accurate when compared to 2D fracture mapping methods. This more accurate technique will allow for better understanding of 3D morphology and provide a basis for future fracture mapping in any bone. Accurate mapping is important because surgical approach, reduction, fixation, and implant design and selection are based on fracture patterns. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:265-271, 2018.

A numeric approach for anatomic plate design.

Osteosynthesis plate designs with high levels of anatomical compliance have been demonstrated to have numerous clinical benefits. The purpose of this paper is to introduce a systematic numeric approach for anatomic plate design on the example of the distal medial tibia. The advantage of using numeric approaches for plate design is to gain objective and complete anatomical input as opposed to cadaveric investigations with limited sample sizes. A recent development in this area is a proprietary technology called SOMA which is based on a large database of 3D bone models generated from thin-slice computer tomographic scans plus associated software tools. In this paper, one of these associated software tools is described which automatically assesses the anatomic fit of osteosynthesis plates based on a large database of bone models. As an example, this tool was applied to assess the mean plate to bone distance of distal medial tibia plates, when fitted onto 444 Caucasian and 310 Asian 3D bone models respectively. The analyses revealed differences in the anatomical compliance of plates from different generations and manufacturers. The anatomical compliance of SOMA designed plates was statistically significantly better compared to all other plates in all groups "Short", "Intermediate" and "Long" and for both ethnicities "Caucasian" and "Asian" (P<0.001). The study has shown that using an underlying database with accompanying computational tools such as SOMA can be a powerful and efficient approach towards the development and advancement of osteosynthesis plates in trauma surgery, ultimately resulting in plates with high levels of anatomical compliance and potential clinical benefits.

Bone microarchitecture of the tibial plateau in skeletal health and osteoporosis.

BACKGROUND: Impaired bone structure poses a challenge for the treatment of osteoporotic tibial plateau fractures. As knowledge of region-specific structural bone alterations is a prerequisite to achieving successful long-term fixation, the aim of the current study was to characterize tibial plateau bone structure in patients with osteoporosis and the elderly. METHODS: Histomorphometric parameters were assessed by high-resolution peripheral quantitative computed tomography (HR-pQCT) in 21 proximal tibiae from females with postmenopausal osteoporosis (mean age: 84.3 ±â€¯4.9 years) and eight female healthy controls (45.5 ±â€¯6.9 years). To visualize region-specific structural bony alterations with age, the bone mineral density (Hounsfield units) was additionally analyzed in 168 human proximal tibiae. Statistical analysis was based on evolutionary learning using globally optimal regression trees. RESULTS: Bone structure deterioration of the tibial plateau due to osteoporosis was region-specific. Compared to healthy controls (20.5 ±â€¯4.7%) the greatest decrease in bone volume fraction was found in the medio-medial segments (9.2 ±â€¯3.5%, p < 0.001). The lowest bone volume was found in central segments (tibial spine). Trabecular connectivity was severely reduced. Importantly, in the anterior and posterior 25% of the lateral and medial tibial plateaux, trabecular support and subchondral cortical bone thickness itself were also reduced. CONCLUSION: Thinning of subchondral cortical bone and marked bone loss in the anterior and posterior 25% of the tibial plateau should require special attention when osteoporotic patients require fracture fixation of the posterior segments. This knowledge may help to improve the long-term, fracture-specific fixation of complex tibial plateau fractures in osteoporosis.

Femoral antecurvation-A 3D CT Analysis of 1232 adult femurs.

INTRODUCTION: For optimal treatment of femoral fractures, it is essential to understand the anatomical antecurvation of the human femur. Recent clinical studies have highlighted the problem of distal anterior encroachment or even perforation of the nail tip. The aim of this study was to accurately describe the femoral antecurvation in a large cohort. Another objective was to identify the most important influences on femoral antecurvation, such as age, femur length, gender and ethnicity. METHODS: A three dimensional modelling and analytical technology was applied for the analysis of 1,232 femurs. Individual femoral antecurvation was precisely computed to determine whether gender, femur length, age, ethnicity or body mass index influence the radius of curvature (ROC). RESULTS: The calculated mean ROC for all femurs was 943 mm. The lowest ROC of 826 mm was found in female Asian femurs. A regression analysis demonstrated that age and femur length could predict the variability of the curvature, with femoral length as most powerful predictor. A matched pair subgroup analysis between Asians and Caucasians could not show any significant differences of ROC values. CONCLUSIONS: The mean radius of the femoral antecurvation may be smaller than previously reported revealing a significant mismatch between the actual individual anatomy and existing implants. In opposite to existing literature, this study suggests, that antecurvation differences between various ethnicities may exclusively be attributed to differences in femoral length and age. The findings of this study may be found helpful in the development of novel designs for intra- and extramedullary implants.

Computer-based anatomy a prerequisite for computer-assisted radiology and surgery.

RATIONALE AND OBJECTIVES: The aim of the study is to show the possibilities opened up by three-dimensional (3D) computer-based models of the human body for education in anatomy, training of radiological and endoscopic examinations, and simulation of surgical procedures. MATERIALS AND METHODS: Based on 3D data sets obtained from the Visible Human and/or clinical cases, virtual body models are created that provide an integrated spatial and symbolic description of the anatomy by using interactive color/intensity-based segmentation, ray casting visualization with subvoxel resolution, a semantic network for knowledge modeling, and augmented QuickTime VR (Apple Computer, Inc, Cupertino, CA) movies for presentation. RESULTS: From these models, various radiological, endoscopic, or haptic manifestations of the body can be derived. This is shown with examples from anatomy teaching, correlation of x-ray images with 3D anatomy for education in radiology, gastrointestinal endoscopy, correlation of ultrasound images with 3D anatomy in endoscopic ultrasonography, and simulation of drilling in temporal bone surgery. CONCLUSION: The presented models provide a means for realistic training in interpretation of radiological and endoscopic images of the human body. Furthermore, certain surgical procedures may be simulated realistically. Used as a complement to the current curriculum, these models have the potential to greatly decrease education times and costs.

Full circle: 3D femoral mapping demonstrates age-related changes that influence femoral implant positioning.

The geometry of the femur is important in the final position of an intramedullary implant; we hypothesised that the femoral geometry changes with age and this may predispose the elderly to anterior mal-positioning of these implants. We used CT DICOM data of 919 intact left femora and specialist software that allowed us to defined landmarks for measurement reference - such as the linea aspera - on a template bone that could be mapped automatically to the entire database. We found that older (>80 years) cortical bone is up to 1.5 mm thinner anteriorly and 2 mm thinner posteriorly than younger (<40 years) bone but the rate of change of posterior to anterior cortex thickness is greater in the older bone. We also found the isthmus in the elderly to be more distal and less substantial than in the younger bone. This study has demonstrated femoral geometry changes with age that may explain our perception that the elderly are at increased risk for anterior mal-positioning of intramedullary implants.

Determination of Femoral Neck Angle and Torsion Angle Utilizing a Novel Three-Dimensional Modeling and Analytical Technology Based on CT Datasets.

INTRODUCTION: Exact knowledge of femoral neck inclination and torsion angles is important in recognizing, understanding and treating pathologic conditions in the hip joint. However, published results vary widely between different studies, which indicates that there are persistent difficulties in carrying out exact measurements. METHODS: A three dimensional modeling and analytical technology was used for the analysis of 1070 CT datasets of skeletally mature femurs. Individual femoral neck angles and torsion angles were precisely computed, in order to establish whether gender, age, body mass index and ethnicity influence femoral neck angles and torsion angles. RESULTS: The median femoral neck angle was 122.2° (range 100.1-146.2°, IQR 117.9-125.6°). There are significant gender (female 123.0° vs. male 121.5°; p = 0.007) and ethnic (Asian 123.2° vs. Caucasian 121.9°; p = 0.0009) differences. The median femoral torsion angle was 14.2° (-23.6-48.7°, IQR 7.4-20.4°). There are significant gender differences (female 16.4° vs. male 12.1°; p = 0.0001). Femoral retroversion was found in 7.8% of the subjects. CONCLUSION: Precise femoral neck and torsion angles were obtained in over one thousand cases. Systematic deviations in measurement due to human error were eliminated by using automated high accuracy morphometric analysis. Small but significant gender and ethnic differences were found in femoral neck and torsion angles.

Volume cutting for virtual petrous bone surgery.

A profound knowledge of anatomy and surgical landmarks of the temporal bone is a basic necessity for any otologic surgeon. Because this knowledge, so far, has been mostly taught by limited temporal bone drilling courses, our objective was to create a system for virtual petrous bone surgery that allows the realistic simulation of specific laterobasal surgical approaches. A major requirement was the development of an interactive drill-like tool, together with a new technique for realistic visualization of simulated cut surfaces. The system is based on a volumetric, high-resolution model of the temporal bone, derived from CT. Interactive volume cutting methods using a new multivolume scheme have been developed. In this scheme, cut regions are modeled independently in additional data volumes using voxelization techniques. The voxelization is adapted to successive cutting operations as needed for the simulation of a drill-like tool. A new visualization technique was developed for artifact-free rendering of sharp edges, as formed by the intersection of a cut and an object surface. The new multivolume visualization technique allows high-quality visualization of interactively generated cut surfaces. This is a necessity for a realistic simulation of petrous bone surgery. Our system therefore facilitates comprehension of the complex morphology, and enables the recognition of surgical landmarks, which is most important if injury to delicate organs (e.g., the facial nerve or auditory ossicles) is to be avoided. The system for virtual petrous bone surgery allows the simulation of specific surgical approaches with high-quality visualization. The user can learn about the complex three-dimensional anatomy of the temporal bone from the viewpoint of a real otosurgical procedure.

Virtual reality: a new paranasal sinus surgery simulator.

OBJECTIVES/HYPOTHESIS: Virtual surgical training systems are of growing value. Current prototypes for endonasal sinus surgery simulation are very expensive or lack running stability. No reliable system is available to a notable number of users yet. The purpose of this work was to develop a dependable simulator running on standard PC hardware including a detailed anatomic model, realistic tools and handling, stereoscopic view, and force feedback. STUDY DESIGN: Descriptive. METHODS: A three-dimensional voxel model was created based on a high-resolution computed tomography study of a human skull, from which the bony structures were segmented. The mucosa and organs at risk were added manually. The model may be manipulated with virtual surgical tools controlled with a low-cost haptic device, which is also used to adjust microscopic or endoscopic views. Visualization, haptic rendering, and tissue removal are represented with subvoxel resolution. RESULTS: The handling of the model is convincing. The haptic device provides a realistic feeling regarding the interaction between tool tip and anatomy. Three-dimensional orientation and the look and feel of virtual surgical interventions get close to reality. CONCLUSIONS: The newly developed system is a stable, fully operational simulator for sinus surgery based on standard PC hardware. Besides the limitations of a low-cost haptic device, the presented system is highly realistic regarding anatomy, visualization, manipulation, and the appearance of the tools. It is mainly intended for gaining surgical anatomy knowledge and for training navigation in a complex anatomical environment. Learning effects, including motor skills, have yet to be quantified.

Virtual dental surgery as a new educational tool in dental school.

PURPOSE: The virtual environment of the Voxel-Man simulator that was originally designed for virtual surgical procedures of the middle ear has been adapted to intraoral procedures. To assess application of the simulator to dentistry, virtual apicectomies were chosen as the pilot-test model. METHODS: A group of 53 dental students provided their impressions after virtual simulation of apicectomies in the Voxel-Man simulator. RESULTS: Fifty-one of the 53 students recommended the virtual simulation as an additional modality in dental education. The students indicated that the force feedback (e.g. simulation of haptic pressure), spatial 3D perception, and image resolution of the simulator were sufficient for virtual training of dental surgical procedures. CONCLUSION: The feedback from dental students involved in this pilot-test has encouraged our interdisciplinary group to continue further development of the simulator with the goal of creating new training strategies in dental and medical education.