Digital skull anatomy of the Oligocene North American tortoise Stylemys nebrascensis with taxonomic comments on the species and comparisons with extant testudinids of the Gopherus-Manouria clade

The anatomy of North American tortoises is poorly understood, despite a rich fossil record from the Eocene and younger strata. Stylemys nebrascensis is a particularly noteworthy turtle in this regard, as hundreds of specimens are known from Oligocene deposits, and as this species is one of the earliest fossil turtles to have been described in the scientific literature. Since its initial description based on a shell, many specimens with more complete material have been referred to Stylemys nebrascensis. Here, we review and confirm the referral of an important historic specimen to Stylemys nebrascensis, which includes shell, non-shell postcranial, and skull material. This allows us to document unique skull features of Stylemys nebrascensis (e.g., an unusual 'poststapedial canal' that connects the posterior skull surface with the cavum acustico-jugulare) and to refer another well-preserved skull to the species. Based on computed-tomography scanning of these two skulls, we provide a detailed description of the cranial and mandibular osteology of Stylemys nebrascensis. Stylemys nebrascensis has a combination of plesiomorphic skull characteristics (e.g., retention of a medial jugal process) and derived traits shared with extant gopher tortoises (e.g., median premaxillary ridge) that suggest it may be a stem-representative of the gopher tortoise lineage. This supports the hypothesis that extant and fossil tortoises from North America form a geographically restricted clade that split from Asian relatives during the Paleogene.

Updated cranial and mandibular description of the Late Cretaceous (Maastrichtian) baenid turtle Saxochelys gilberti based on micro-computed tomography scans and new information on the holotype-shell association

Saxochelys gilberti is a baenid turtle from the Late Cretaceous Hell Creek Formation of the United States of America known from cranial, shell, and other postcranial material. Baenid turtles are taxonomically diverse and common fossil elements within Late Cretaceous through Eocene faunas. Detailed anatomical knowledge is critical to understanding the systematics and morphological evolution of the group. This is particularly important as baenids represent an important group of continental vertebrates that survived the mass extinction event associated with the Cretaceous/Paleogene boundary. High-resolution micro-computed tomography scanning of the holotype skull reveals additional anatomical details for the already well-known Saxochelys gilberti. This includes the revision of some anatomical statements from the original description, but also detailed knowledge on internal anatomical features of the braincase and the description of a well-preserved axis (cervical vertebra 2). Our new detailed description and previous work on the shell and postcrania make Saxochelys one of the best-described, nearly complete baenid turtles, which are often only known from either isolated shell or cranial material. A revised phylogenetic analysis confirms the position of Saxochelys gilberti as a derived baenid (Eubaeninae) more closely related to Baena arenosa than to Eubaena cephalica.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13358-023-00301-6.

Anterior supra-acetabular external fixation for tile C1 pelvic fractures: a digital anatomical study and a finite element analysis

OBJECTIVE

Investigating the anatomical characteristics of supra-acetabular screw corridor as well as comparing the biomechanical stability between semi- and full-length screw external fixations for Tile C1 pelvic fractures.

METHODS

50 male and 50 female uninjured pelvic CT data were converted into three-dimensional models and the supra-acetabular corridors were reconstructed by the Mimics software. The horizontal slice was redefined passing through the bilateral anterior inferior iliac spine and bilateral posterior superior iliac spine at the same time. On every horizontal slices, a 5 mm diameter virtual screw was placed along with the unilateral anterior narrowing to posterior narrowing of the supra-acetabular corridor, and the relevant parameters of the semi- and full-length screw fixations were measured from inferior to superior at an interval height of 2.5 mm until the width of the corridor was less than 5 mm. Thus, the insertion position was located, as well as the inclination angle ranges were measured. The same procedure was done on a bilateral supra-acetabular corridor for each patient. Last, a Tile C1 pelvic finite element model was simulated and fixed with either semi- or a full-length anterior supra-acetabular external fixator. A 500 N loading was tested on the model with three directions (cranial-caudal, anterior-posterior and lateral-medial) and the stiffness was determined by the max displacements.

RESULTS

The insertion points of supra-acetabular screw for 66% (66/100) of men and 78% (78/100) of women were located at the outer lower part of the anterior inferior iliac spine (AIIS) (p < 0.001). The medial inclination angles of the screw were 29.50 ± 4.05° for men and 28.00 ± 3.78° for women (p = 0.007). The cranial inclination angles of the screw were 29.40 ± 5.38° for men and 28.57 ± 6.01° for women (p = 0.306). The safe inclination angle ranges of the semi-length screw were 3°-6° bigger than the full-length screw. For semi-length corridor, the widths were 14.07 ± 2.39 mm for men and 11.29 ± 1.81 mm for women (p < 0.001) and the depths were 71.77 ± 5.96 mm for men and 69.26 ± 5.21 mm for women (p < 0.001). For full-length corridor, the widths were 10.61 ± 2.10 mm for men and 8.44 ± 2.03 mm for women (p < 0.001) and the depths were 133.37 ± 7.60 mm for men and 129.01 ± 8.12 mm for women (p < 0.001). In the finite element analysis, the max displacements of the pelvis under three loading modes (cranial-caudal, anterior-posterior and lateral-medial) for semi-length fixation were 0.772 mm, 0.409 mm and 0.331 mm and for full-length fixation were 0.727 mm, 0.385 mm and 0.262 mm.

CONCLUSION

The outer lower part of AIIS is recommended as an insertion point of the supra-acetabular screw with about 30° medial and cranial inclination angles, and the semi-length screw is safer for placing and has satisfactory biomechanical stability by compared with a full-length screw.

Evaluation of Child-Friendly Augmented Reality Tool for Patient-Centered Education in Radiology and Bone Reconstruction

The use of augmented reality (AR) has a rich history and is used in a number of fields. Its application in healthcare and anatomy education is developing considerable interest. However, although its popularity is on the rise, its use as an educational and practical tool has not been sufficiently evaluated, especially with children. Therefore, this study presents the design, development and evaluation of an educational tablet-based application with AR functionality for children. A distal radius fracture was chosen, as it is one of the more common fractures in the younger age group. Following a standardized software engineering methodology, we identified functional and non-functional requirements, creating a child-friendly tablet based AR application. This used industry standard software and incorporated three-dimensional models of a buckle fracture, object and image target marker recognition, interactivity and educational elements. In addition, we surveyed children at the Glasgow Science Centre on its usability, design and educational effectiveness. Seventy-one children completed a questionnaire (25 also underwent a short structured interview). Overall, the feedback was positive relating to entertainment value, graphic design, usability and educational scope of the application. Notably, it was shown to increase user understanding of radiology across all age groups following a trial of the application. This study shows the great potential of using digital technologies, and more particularly augmented information, in engaging future generations in science from a young age. Creation of educational materials using digital technologies, and evaluating its effectiveness, highlights the great scope novel technology could have in anatomical education and training.

A digital anatomic investigation of the safe triangle areas for L1-5 percutaneous minimally invasive discectomy

PURPOSE

To reconstruct the three-dimensional safe triangle areas at L1-5 based on the computed tomography digital data, analyze the safe scopes for the puncture location and angles, and provide anatomic references for percutaneous lumbar discectomy.

METHODS

Computed tomography data from patients and control group were imported from the database and anatomical reference parameters were measured in Mimics software. The rebuilt model was rotated clockwise along the M-axis to measure the inscribed circle radius of the safe triangle at different angles. Based on the outer diameter of the largest cannula, the safe angles were calculated. The distances between points on the projection of safe triangle-inscribed circle and the upper lumbar spinous process were measured. Similarly, while the safe triangle was on the left side, the model was contra-rotated to measure all the parameters.

RESULTS

There was no significant difference between the patient and control group in both the least distance between the selected anatomical reference locations and the safe triangle-inscribed circle radius at L4-5. According to the series which had a largest cannula of 2.5 mm, the safe puncture angles increased with the descending disc levels. The optimal angles were 40°-45° for L1-2, 45°-50° for L2-3, 50° for L3-4, and 55° for L4-5 separately. The differences between genders in the distances of paired reference points were significant.

CONCLUSIONS

Individual safe localization of the percutaneous puncture could be obtained by analyzing the three-dimensional relationship between the puncture localization and anatomical landmarks.

Distribution of iliac veins posterior to the common iliac artery bifurcation related to pelvic lymphadenectomy: A digital in vivo anatomical study of 442 Chinese females

OBJECTIVES

To investigate the distribution of iliac veins posterior to common iliac artery bifurcation (CIAB) for pelvic lymphadenectomy.

METHODS

After IRB approval was obtained, computer tomography angiography data of 442 female pelvises were acquired. After vascular three-dimensional (3D) reconstructions, the structural types, frequencies and diameters of iliac veins immediately posterior to CIAB were investigated and measured. To quantify iliac vein courses, linear distances and their distances on sagittal, coronal and vertical axes from CIAB to external/internal iliac veins confluence (EIIVC) were geometrically measured.

RESULTS

There were five structural types of iliac veins distribution immediately posterior to CIAB: common iliac vein (CIV, 13.8%), no occurrence of great vein (N, 71.27%, 0), EIIVC (1.58%) and external iliac vein (EIV, 13.35%) on the left side, while confluence of common iliac veins (CCIV, 8.82%), CIV (77.38%), N (1.58%, 0), EIIVC (6.11%), and EIV (6.11%) on right. The venous diameters immediately posterior to CIAB in "CCIV", "CIV" and "EIIVC" were significantly larger than that in "EIV" (P<0.05). Their linear distances and their distances on each axis from CIAB to external/internal iliac veins confluence (EIIVC) from CIAB to EIIVC were obtained.

CONCLUSIONS

In this study, we presented new distribution of iliac veins posterior to CIAB, including structural types, frequencies, venous diameters immediately posterior to CIAB, and their quantified courses from CIAB to EIIVC. It could help surgeons reduce the risk of vascular injury, hemorrhage or transfusion in pelvic lymphadenectomy.