Soft Tissue Hybrid Model for Real-Time Simulations.

In this article, a recent formulation for real-time simulation is developed combining the strain energy density of the Spring Mass Model (SMM) with the equivalent representation of the Strain Energy Density Function (SEDF). The resulting Equivalent Energy Spring Model (EESM) is expected to provide information in real-time about the mechanical response of soft tissue when subjected to uniaxial deformations. The proposed model represents a variation of the SMM and can be used to predict the mechanical behavior of biological tissues not only during loading but also during unloading deformation states. To assess the accuracy achieved by the EESM, experimental data was collected from liver porcine samples via uniaxial loading and unloading tensile tests. Validation of the model through numerical predictions achieved a refresh rate of 31 fps (31.49 ms of computation time for each frame), achieving a coefficient of determination R2 from 93.23% to 99.94% when compared to experimental data. The proposed hybrid formulation to characterize soft tissue mechanical behavior is fast enough for real-time simulation and captures the soft material nonlinear virgin and stress-softened effects with high accuracy.

Educative Hybrid Intervention as a Strategy for Reintegration to the Clinical Courses of Undergraduate Students in COVID-19 Pandemic.

The SARS-CoV-2 pandemic generated the need to modify the current clinical educational model with the challenge of promoting safety and the continuity of clinical education through the use of virtual platforms. Since clinical training in hospital institutions cannot be substituted, a strategic training plan was developed to guarantee protection, safety, and academic continuity for students upon returning to clinical clerkships. The objective of this project was to develop and evaluate the impact of a massive hybrid training plan as an educative strategy to give the theoretical and practical knowledge required for the safe return of undergraduate students to their respective clinical activities in the context of this pandemic. An academic program was designed through a massive hybrid strategy to train 616 undergraduate students studying clinical cycles by presential, virtual, synchronous, and asynchronous activities. To know the program's impact, a study based on an initial evaluation and a final evaluation was carried out to evaluate the acquisition of the critical knowledge and skills of the program. A significant difference was found between the means of the initial and final evaluations (p <0.001), as well as a high impact of the intervention (d 1.6). Significant improvements in the areas of COVID-19 initial management (p <0.001) and personal protective equipment use (p <0.001) were seen in the post-test when compared to the initial evaluation. Both a quantitative and a qualitative analysis were carried out, finding positive results on the course design, quality of didactic resources, and instructors' performance. Massive hybrid training is an effective strategy to facilitate the reintegration of undergraduate students into their face-to-face clinical rotations.

LAPKaans: Tool-Motion Tracking and Gripping Force-Sensing Modular Smart Laparoscopic Training System.

Laparoscopic surgery demands highly skilled surgeons. Traditionally, a surgeon's knowledge is acquired by operating under a mentor-trainee method. In recent years, laparoscopic simulators have gained ground as tools in skill acquisition. Despite the wide range of laparoscopic simulators available, few provide objective feedback to the trainee. Those systems with quantitative feedback tend to be high-end solutions with limited availability due to cost. A modular smart trainer was developed, combining tool-tracking and force-using employing commercially available sensors. Additionally, a force training system based on polydimethylsiloxane (PDMS) phantoms for sample stiffness differentiation is presented. This prototype was tested with 39 subjects, between novices (13), intermediates (13), and experts (13), evaluating execution differences among groups in training exercises. The estimated cost is USD $200 (components only), not including laparoscopic instruments. The motion system was tested for noise reduction and position validation with a mean error of 0.94 mm. Grasping force approximation showed a correlation of 0.9975. Furthermore, differences in phantoms stiffness effectively reflected user manipulation. Subject groups showed significant differences in execution time, accumulated distance, and mean and maximum applied grasping force. Accurate information was obtained regarding motion and force. The developed force-sensing tool can easily be transferred to a clinical setting. Further work will consist on a validation of the simulator on a wider range of tasks and a larger sample of volunteers.

Laparoscopic partial splenectomy for congenital splenic cyst in a pediatric patient: Case report and review of literature.

Non-parasitic splenic cysts (NPSC) are a rare condition that makes difficult to know their true incidence and represent 10% of all benign splenic cysts, they can be either congenital with the presence of epithelial lining that originate from invagination of the capsular mesothelial lining or post-traumatic with absence of epithelial lining. We present our management of a splenic congenital cyst in a pediatric patient. A 10-year-old female patient presented to the clinic complaining with a 3-week abdominal pain at the left upper quadrant. An ultrasound showed an enlarged spleen with a thinned walled cystic image on the lower pole of 5cm. An abdominal CT confirmed the presence of a splenic cyst at the lower pole of the spleen of 5cm in diameter. Three-port laparoscopic partial splenectomy was done isolating and dividing the lower splenic artery and vein and the lower pole of the spleen with a vessel sealing device. Management of a non-parasitic splenic cyst is controversial: cystectomy, fenestration, percutaneous drainage and sclerotherapy have been previously described, most of them aiming to preserve spleen function and avoiding overwhelming post-splenectomy infection. Partial splenectomy seems the most effective one in terms of preserving spleen function and avoiding recurrence.

Design Concepts of Polycarbonate-Based Intervertebral Lumbar Cages: Finite Element Analysis and Compression Testing.

This work explores the viability of 3D printed intervertebral lumbar cages based on biocompatible polycarbonate (PC-ISO® material). Several design concepts are proposed for the generation of patient-specific intervertebral lumbar cages. The 3D printed material achieved compressive yield strength of 55 MPa under a specific combination of manufacturing parameters. The literature recommends a reference load of 4,000 N for design of intervertebral lumbar cages. Under compression testing conditions, the proposed design concepts withstand between 7,500 and 10,000 N of load before showing yielding. Although some stress concentration regions were found during analysis, the overall viability of the proposed design concepts was validated.

Influence of PEEK Coating on Hip Implant Stress Shielding: A Finite Element Analysis.

Stress shielding is a well-known failure factor in hip implants. This work proposes a design concept for hip implants, using a combination of metallic stem with a polymer coating (polyether ether ketone (PEEK)). The proposed design concept is simulated using titanium alloy stems and PEEK coatings with thicknesses varying from 100 to 400 µm. The Finite Element analysis of the cancellous bone surrounding the implant shows promising results. The effective von Mises stress increases between 81 and 92% for the complete volume of cancellous bone. When focusing on the proximal zone of the implant, the increased stress transmission to the cancellous bone reaches between 47 and 60%. This increment in load transferred to the bone can influence mineral bone loss due to stress shielding, minimizing such effect, and thus prolonging implant lifespan.

Irrigation with bupivacaine at the surgical bed for postoperative pain relief after laparoscopic cholecystectomy.

PURPOSE: The aim of this study was to evaluate the effect of bupivacaine irrigated at the surgical bed on postoperative pain relief in laparoscopic cholecystectomy patients. METHODS: This study included 60 patients undergoing elective laparoscopic cholecystectomy who were prospectively randomized into 2 groups. The placebo group (n=30) received 20cc saline without bupivacaine, installed into the gallbladder bed. The bupivacaine group (n=30) received 20cc of 0.5% bupivacaine in at the same surgical site. Pain was assessed at 0, 6, 12, and 24 hours by using a visual analog scale (VAS). RESULTS: A significant difference (P=.018) was observed in pain levels between both groups at 6 hours postoperatively. The average analgesic requirement was lower in the bupivacaine group, but this did not reach statistical significance. CONCLUSIONS: In our study, the use of bupivacaine irrigated over the surgical bed was an effective method for reducing pain during the first postoperative hours after laparoscopic cholecystectomy.