The effects of age and sex on the elastic mechanical properties of human abdominal fascia

The effect of breathing on the in vivo mechanical characterization of linea alba by ultrasound shearwave elastography

The most common surgical repair of abdominal wall hernia consists in implanting a mesh to reinforce hernia defects during the healing phase. Ultrasound shearwave elastography (SWE) is a promising non-invasive method to estimate soft tissue mechanical properties at bedside through shear wave speed (SWS) measurement. Combined with conventional ultrasonography, it could help the clinician plan surgery. In this work, a novel protocol is proposed to reliably assess the stiffness of the linea alba, and to evaluate the effect of breathing and of inflating the abdomen on SWS. Fifteen healthy adults were included. SWS was measured in the linea alba, in the longitudinal and transverse direction, during several breathing cycle and during active abdominal inflation. SWS during normal breathing was 2.3 [2.0; 2.5] m/s in longitudinal direction and 2.2 [1.9; 2.7] m/s in the transversal. Inflating the abdomen increased SWS both in longitudinal and transversal direction (3.5 [2.8; 5.8] m/s and 5.2 [3.0; 6.0] m/s, respectively). The novel protocol significantly improved the reproducibility relative to the literature (8% in the longitudinal direction and 14% in the transverse one). Breathing had a mild effect on SWS, and accounting for it only marginally improved the reproducibility. This study proved the feasibility of the method, and its potential clinical interest. Further studies on larger cohort should focus on improving our understanding of the relationship between abdominal wall properties and clinical outcomes, but also provide a cartography of the abdominal wall, beyond the linea alba.

Applied use of biomechanical measurements from human tissues for the development of medical skills trainers: a scoping review

OBJECTIVE

The objective of this review was to identify quantitative biomechanical measurements of human tissues, the methods for obtaining these measurements, and the primary motivations for conducting biomechanical research.

INTRODUCTION

Medical skills trainers are a safe and useful tool for clinicians to use when learning or practicing medical procedures. The haptic fidelity of these devices is often poor, which may be because the synthetic materials chosen for these devices do not have the same mechanical properties as human tissues. This review investigates a heterogeneous body of literature to identify which biomechanical properties are available for human tissues, the methods for obtaining these values, and the primary motivations behind conducting biomechanical tests.

INCLUSION CRITERIA

Studies containing quantitative measurements of the biomechanical properties of human tissues were included. Studies that primarily focused on dynamic and fluid mechanical properties were excluded. Additionally, studies only containing animal, in silico , or synthetic materials were excluded from this review.

METHODS

This scoping review followed the JBI methodology for scoping reviews and the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). Sources of evidence were extracted from CINAHL (EBSCO), IEEE Xplore, MEDLINE (PubMed), Scopus, and engineering conference proceedings. The search was limited to the English language. Two independent reviewers screened titles and abstracts as well as full-text reviews. Any conflicts that arose during screening and full-text review were mediated by a third reviewer. Data extraction was conducted by 2 independent reviewers and discrepancies were mediated through discussion. The results are presented in tabular, figure, and narrative formats.

RESULTS

Data were extracted from a total of 186 full-text publications. All of the studies, except for 1, were experimental. Included studies came from 33 countries, with the majority coming from the United States. Ex vivo methods were the predominant approach for extracting human tissue samples, and the most commonly studied tissue type was musculoskeletal. In this study, nearly 200 unique biomechanical values were reported, and the most commonly reported value was Young's (elastic) modulus. The most common type of mechanical test performed was tensile testing, and the most common reason for testing human tissues was to characterize biomechanical properties. Although the number of published studies on biomechanical properties of human tissues has increased over the past 20 years, there are many gaps in the literature. Of the 186 included studies, only 7 used human tissues for the design or validation of medical skills training devices. Furthermore, in studies where biomechanical values for human tissues have been obtained, a lack of standardization in engineering assumptions, methodologies, and tissue preparation may implicate the usefulness of these values.

CONCLUSIONS

This review is the first of its kind to give a broad overview of the biomechanics of human tissues in the published literature. With respect to high-fidelity haptics, there is a large gap in the published literature. Even in instances where biomechanical values are available, comparing or using these values is difficult. This is likely due to the lack of standardization in engineering assumptions, testing methodology, and reporting of the results. It is recommended that journals and experts in engineering fields conduct further research to investigate the feasibility of implementing reporting standards.

REVIEW REGISTRATION

Open Science Framework https://osf.io/fgb34.

Not deep enough: Modeling the effect of shallow placement of the DaVinci Xi "bariatric" long trocar on the muscular abdominal wall

INTRODUCTION

The DaVinci Xi Robotic Surgical System (Xi) long cannula (Intuitive Surgical Company, Sunnyvale, CA) provides five additional centimeters of distal length compared to the standard Xi trocar. The extra length allows the cannula to traverse prohibitively thick body wall tissue. Our aims are to quantitatively model the consequences of not preserving the rotational centerpoint of motion (RCM) at the muscular abdominal wall. This is an essential tenet in robotic surgery; it is violated with shallow placement of the long trocar. This leads to unchecked, unnoticed blunt widening of port sites by the robotic arm, increasing hernia risk.

METHODS

We begin with an exploration of the schematic of the Xi robotic arm as patented by Intuitive (U.S. Patent #5931832). We trigonometrically model the lateral displacement of the abdominal wall at the trocar site with respect to vertical trocar shallowness, instrument tip depth, and instrument tip lateral motion from neutral midline.

RESULTS

The rigid parallelogram movement structure of the Xi preserves the RCM at the thick black marker printed on every Xi cannula. By limitation of design, both long and standard trocars must have this marker at the exact same distance from their proximal end. The value ranges of our model parameters (presuming a reasonable maximum orientation angle of 45° from midline) are: trocar shallowness [1 cm, 7 cm]; instrument tip depth [0 cm, 20 cm]; instrument tip lateral movement [0.0 cm, 14.1 cm]. Abdominal wall displacement increased proportionally as each instrument tip parameter reached its maximum deviation from the orthogonal midline as described in the plot figure. Maximal wall displacement at maximal shallowness was approximately 7.0 cm.

CONCLUSION

Robotic surgery revolutionizes modern operation, particularly within bariatrics. However, the current Xi arm design disallows a true long trocar to be used safely without compromising the RCM, thereby risking hernia development.