Evaluation of the tensile strength of the human ureter--preliminary results

Mechanical characterization of porcine ureter for the evaluation of tissue-engineering applications

Introduction: Clinics increasingly require readily deployable tubular substitutes to restore the functionality of structures like ureters and blood vessels. Despite extensive exploration of various materials, both synthetic and biological, the optimal solution remains elusive. Drawing on abundant literature experiences, there is a pressing demand for a substitute that not only emulates native tissue by providing requisite signals and growth factors but also exhibits appropriate mechanical resilience and behaviour. Methods: This study aims to assess the potential of porcine ureters by characterizing their biomechanical properties in their native configuration through ring and membrane flexion tests. In order to assess the tissue morphology before and after mechanical tests and the eventual alteration of tissue microstructure that would be inserted in material constitutive description, histological staining was performed on samples. Corresponding computational analyses were performed to mimic the experimental campaign to identify the constitutive material parameters. Results: The absence of any damages to muscle and collagen fibres, which only compacted after mechanical tests, was demonstrated. The experimental tests (ring and membrane flexion tests) showed non-linearity for material and geometry and the viscoelastic behaviour of the native porcine ureter. Computational models were descriptive of the mechanical behaviour ureteral tissue, and the material model feasible. Discussion: This analysis will be useful for future comparison with decellularized tissue for the evaluation of the aggression of cell removal and its effect on microstructure. The computational model could lay the basis for a reliable tool for the prediction of solicitation in the case of tubular substitutions in subsequent simulations.

Mechanical characteristics of the ureter and clinical implications

The ureteric wall is a complex multi-layered structure. The ureter shows variation in passive mechanical properties, histological morphology and insertion forces along the anatomical length. Ureter mechanical properties also vary depending on the direction of tensile testing and the anatomical region tested. Compliance is greatest in the proximal ureter and lower in the distal ureter, which contributes to the role of the ureter as a high-resistance sphincter. Similar to other human tissues, the ureteric wall remodels with age, resulting in changes to the mechanical properties. The passive mechanical properties of the ureter vary between species, and variation in tissue storage and testing methods limits comparison across some studies. Knowledge of the morphological and mechanical properties of the ureteric wall can aid in understanding urine transport and safety thresholds in surgical techniques. Indeed, various factors alter the forces required to insert access sheaths or scopes into the ureter, including sheath diameter, safety wires and medications. Future studies on human ureteric tissue both in vivo and ex vivo are required to understand the mechanical properties of the ureter and how forces influence these properties. Testing of instrument insertion forces in humans with a focus on defining safe upper limits and techniques to reduce trauma are also needed. Last, evaluation of dilatation limits in the mid and proximal ureter and clarification of tensile strength anisotropy in human specimens are necessary.

Three Dimensional Printing Technology Used to Create a High-Fidelity Ureteroscopy Simulator: Development and Validity Assessment (Rein-3D-Print-UroCCR-39)

OBJECTIVE

To create and assess the validity of a high-fidelity, three dimensional (3D) printed, flexible ureteroscopy simulator resulting from a real case.

METHODS

A patient's CT scan was segmented to obtain a 3D model in .stl format, including the urinary bladder, ureter and renal cavities. The file was printed and a kidney stone was introduced into the cavities. The simulated surgery consisted of monobloc stone extraction. Nineteen participants split into 3 groups according to their level (6 medical students, 7 residents and 6 urology fellows) performed the procedure twice at a 1-month interval. They were rated according to a global score and a task-specific score, based on an anonymized, timed video recording.

RESULTS

Participants demonstrated a significant improvement between the 2 assessments, both on the global score (29.4 vs 21.9 points out of 35; P < .001) and the task-specific score (17.7 vs 14.7 points out of 20; P < .001) as well as procedure time (498.5 vs 700 seconds; P = .001). Medical students showed the greatest progress for the global score (+15.5 points (mean), P = .001) and the task-specific score (+6.5 points (mean), P < .001). 69.2% of participants considered the model as visually quite realistic or highly realistic and all of them judged it quite or extremely interesting for intern training purposes.

CONCLUSION

Our 3D printed ureteroscopy simulator was able to enhance the progress of medical students who are new to endoscopy, whilst being valid and reasonably priced. It could become part of a training program in urology, in line with the latest recommendations for surgical education.

Comparison of shock wave lithotripsy and ureteroscopy in patients with proximal ureteral stones under the COVID-19 pandemic

PURPOSE

To compare the effectiveness, safety, and cost between ultrasound-guided shock wave lithotripsy (SWL) with an early second session protocol and ureteroscopy (URS) in patients with proximal ureteral stones using the propensity score matching (PSM) method based on a large prospective study.

METHODS

This prospective study was conducted in a tertiary hospital from June 2020 to April 2022. Patients who underwent lithotripsy (SWL or URS) for proximal ureteral stones were enrolled. The stone-free rate (SFR), complications, and cost were recorded. PSM analysis was performed.

RESULTS

A total of 1230 patients were included, of whom 81.1% (998) were treated with SWL and 18.9% (232) were treated with URS. After PSM, the SWL group had an equivalent SFR at one month (88.7 vs. 83.6%, P = 0.114) compared with the URS group. Complications were rare and comparable between the two groups, while the incidence of ureteral injuries was higher in the URS group compared with the SWL group (1.4 vs. 0%, P = 0.011). The hospital stay was significantly shorter (1 day vs. 2 days, P < 0.001), and the cost was considerably less (2000 vs. 25,053, P < 0.001) in the SWL group compared with the URS group.

CONCLUSION

This prospective PSM cohort demonstrated that ultrasound-guided SWL with an early second session protocol had equivalent effectiveness but better safety and lower cost compared with URS in the treatment of patients with proximal ureteral stones, whether the stones were radiopaque or radiolucent. These results will facilitate treatment decisions for proximal ureteral stones.

Ileal ureteral replacement for the management of ureteral avulsion during ureteroscopic lithotripsy: a case series

INTRODUCTION

To describe our initial experience with ileal ureteral replacement (IUR) for the management of ureteral avulsion (UA) during ureteroscopic lithotripsy.

METHODS

Between September 2010 and April 2021, ten patients received ileal ureteral replacement for ureteral avulsion during ureteroscopic lithotripsy. Anterograde urography and computed tomography urography (CTU) were applied to evaluate the lesion. Follow-up was performed with magnetic resonance urography and renal ultrasound as well as clinical assessment of symptoms. We retrospectively analysed the clinical data of ten patients treated with ileal ureteral replacement for the treatment of ureteral avulsion.

RESULTS

Four patients underwent open ileal ureteral replacement, two underwent laparoscopic ileal ureteral replacement, and four underwent robotic-assisted ileal ureteral replacement. The mean operative time (OT) was 310 min (range 191-530). The mean estimated blood loss (EBL) was 193 mL (range 10-1000). The mean length of the ileal graft was 21 cm (range 12-25). The median postoperative hospital time was 13 days (range 7-19). All surgeries were effectively completed, and no case required open conversion in laparoscopic and robotic-assisted surgeries. There was no obvious hydronephrosis according to contrast-enhanced computed tomography 3-dimensional reconstruction images without serious complications or progressive hydronephrosis during a median follow-up duration of 51 months (range 5-131), and the success rate was 100%.

CONCLUSIONS

Our initial results and experience showed that ileal ureteral replacement for the management of ureteral avulsion during ureteroscopic lithotripsy is safe and feasible.

Ureteral injury following anterior thoracolumbar spinal instrumented fusion for adolescent idiopathic scoliosis: a case report with CT angiography analysis of surgically relevant anatomy

PURPOSE

To report a rare ureteral injury following anterior spinal fusion for adolescent idiopathic scoliosis (AIS) that resulted in complete nephrectomy and to delineate the anatomical relationship between the proximal ureter and the anterior lumbar spine based on CT angiography (CTA).

METHODS

Thoracolumbar spine CTAs of children with AIS were reviewed. We measured the following relationships to the ureters: lateral-most aspect of vertebral body, anterior psoas at intervertebral disc/vertebral body levels, and lateral psoas at vertebral body level. Spine level at which the renal arteries originated from the aorta was identified. Distance from origin to corresponding vertebral body/intervertebral disc also was measured.

RESULTS

Forty-one girls and seven boys (mean age 12 years, range 7-18) were analyzed. Scoliosis lumbar convexity was left 94% and right 6%. From L1 to L4, ureter was identified within 1-2 cm of vertebral body. Distance between ureter and vertebral body and ureter and anterior psoas at intervertebral disc/vertebral body levels was less on left vs. right from L1 to L4 (p < 0.0001). Distance between ureter and lateral psoas was less on left vs. right from L1 to L2 (p = 0.0205; p = 0.0132) and greater on left vs. right from L3 to L4 (p = 0.0022; p = 0.0076). Renal artery originated at L1/L2 in > 50%. There was no difference in distance from renal artery origin to vertebral body/intervertebral disc (p = 0.4764).

CONCLUSION

Ureteral injury is a potentially morbid complication of anterior spine surgery. Injury can occur secondary to disrupted blood supply and mechanical tissue damage. Surgeons must clearly understand the juxta-spinal anatomy to limit dissection and modify retraction to reduce risk.

LEVEL OF EVIDENCE

Level IV.

Comparison of ureteroscopy (URS) complementary treatment after extracorporeal shock wave lithotripsy failure with primary URS lithotripsy with holmium laser treatment for proximal ureteral stones larger than10mm

Background

To compare ureteroscopy (URS) complementary treatment following extracorporeal shock wave lithotripsy (SWL) failure with primary URS lithotripsy for proximal ureteral stones > 10 mm, and try to find out acceptable number of SWL sessions followed by safe URS.

Methods

This was a retrospective study following approval from Medical Ethics Committee of People's Hospital of Chongqing Banan District. Patients (n = 340) who received URS in our hospital for stones > 10 mm from Jan 2015 to June 2020 were divided into two groups according to their previous SWL history. Group 1 consisted of 160 patients that underwent unsuccessful SWL before URS. Group 2 encompassed 180 patients without SWL before URS. Patient’s operative outcomes were compared. A logistic regression and receiver operator characteristics (ROC) were used to identify the acceptable number of SWL sessions prior to URS, regarding the intra-operative complications of URS.

Results

The group 1 required more surgery time (41.38 ± 11.39 min vs. 36.43 ± 13.36 min, p = 0.01). At the same time, more intra-operative (68.1% VS 22.8%, p < 0.05) and post-operative (35% VS 18.0%, p = 0.001) complications occurred in group 1. Need more hospital stay in group 1 (2.7 ± 1.2 days vs 1.6 ± 1.1 days, p < 0.05). More patients in group 1 need further URS (16.3% VS 8.9%, p = 0.029). After second URS, the SFR of URS in two groups was insignificant differences (82.5% VS 88.9%, p > 0.05). The median (25–75%) of SWL sessions before URS was 2 (1–3) in group 1. According to the results of logistic regression analysis, patients suffered more SWL failure have an increased risk of complications during URS (OR = 1.995, 95% CI: 1.636–2.434). ROC showed that the optimal number of SWL session followed by URS were 0.5, with a sensitivity of 67.7% and specificity of 71.5%. Intra-operative complication rates of URS treatment were higher in patients who suffered > 1 SWL failure (72.6% vs 57.4%, p = 0.047).

Conclusion

There was no acceptable number of SWL sessions that could be followed by URS with fewer intra-operative complications. Patients who underwent previous SWL were likely to suffer more intra-operative complications, the average operating time, hospitalization time, and needing further treatment, during URS treatment for proximal ureteral stones larger than 10 mm.

Dynamically crosslinked polydimethylsiloxane-based polyurethanes with contact-killing antimicrobial properties as implantable alloplasts for urological reconstruction

A large population of patients is reported to suffer from urinary bladder-associated irreversible physiological disorders, rationalizing a continuous surge for structural and functional substitutes of urinary tissues, including ureters, bladder-wall, and urethra. The current gold standard for bladder reconstruction, an autologous gastrointestinal graft, is proven not to be an ideal substitute in the clinic. While addressing this unmet clinical need, a unique platform of antimicrobial polydimethyl siloxane-modified polyurethanes (TPU/PDMS) is designed and developed for its potential application as a urological implant. To the best of our knowledge, this study reports for the first time the successful integration of varying contents of PDMS within the molten polyurethane matrix using in situ crosslinking methodology. Thus, compatibilized binary blends possess clinically relevant viscoelastic properties to sustain high pressure, large distensions, and surgical manipulation. Furthermore, different chemical strategies are explored to covalently incorporate quaternized moieties, including 4-vinyl pyridine (4-VP), branched-polyethyleneimine (bPEI) as well as bPEI-grafted-(acrylic acid-co-vinylbenzyltriphenyl phosphonium chloride) (PAP), and counter urinary tract infections. The modified compositions, endowed with contact killing surfaces, reveal nearly three log reduction in bacterial growth in pathogenically infected artificial urine. Importantly, the antimicrobial TPU/PDMS blends support the uninhibited growth of mitochondrially viable murine fibroblasts, in a manner comparable to the medical-grade polyurethane. Collectively, the obtained results affirmed the newly developed polymers as promising biomaterials in reconstructive urology. STATEMENT OF SIGNIFICANCE: The clinical procedure for end-stage bladder disease remains replacement or augmentation of the bladder wall with a section of the patient's gastrointestinal tract. However, the absorptive and mucus-producing epithelium of intestinal segment is liable to short- and long-term complications. The dynamically crosslinked polydimethyl siloxane-based polyurethanes proposed herein, and the associated synthesis strategies to induce polycation grafted non-exhaustive contact-killing surfaces against uropathogents, have a significant clinical prospect in reconstructive urology. As an 'off-the-shelf' available alloplastic substitute, these blends offer the potential to circumvent the challenges associated with non-urinary autografts or scaffold based regenerative engineering and, thereby, shorten as well as simplify the surgical treatment. The targeted application has been conceived for a bladder patch to assist in various urinary diseases including, bladder carcinoma, refractory overactive bladder, interstitial cystitis, etc. However, given the ease of fabrication, moldability and the wide spectrum of mechanical properties that could be encompassed, these blends also present the possibility to be manifested into artificial ureteral or urethral conduits.

Controllable four axis extrusion-based additive manufacturing system for the fabrication of tubular scaffolds with tailorable mechanical properties

Many tubular tissues such as blood vessels and trachea can suffer long-segmental defects through trauma and disease. With current limitations in the use of autologous grafts, the need for a synthetic substitute is of continuous interest as possible alternatives. Fabrication of these tubular organs is commonly done with techniques such as electrospinning and melt electrowriting using a rotational collector. Current additive manufacturing (AM) systems do not commonly implement the use of a rotational axis, which limits their application for the fabrication of tubular scaffolds. In this study, a four axis extrusion-based AM system similar to fused deposition modeling (FDM) has been developed to create tubular hollow scaffolds. A rectangular and a diamond pore design were further investigated for mechanical characterization, as a standard and a biomimicry pore geometry respectively. We demonstrated that in the radial compression mode the diamond pore design had a higher Young's modulus (19,8 ± 0,7 MPa compared to 2,8 ± 0,5 MPa), while in the longitudinal tensile mode the rectangular pore design had a higher Young's modulus (5,8 ± 0,2 MPa compared to 0,1 ± 0,01 MPa). Three-point bending analyses revealed that the diamond pore design is more resistant to luminal collapse compared to the rectangular design. This data showed that by changing the scaffold pore design, a wide range of mechanical properties could be obtained. Furthermore, a full control over scaffold design and geometry can be achieved with the developed 4-axis extrusion-based system, which has not been reported with other techniques. This flexibility allow the manufacturing of scaffolds for diverse tubular tissue regeneration applications by designing suitable deposition patterns to match their mechanical pre-requisites.

Case report series: management of complete ureteral avulsion with review of the relevant literature

Background

Endoscopic operations and ureteroscopy have become the first choice for ureteral calculi and ureter-related operations. The ratios of the complications, which are mostly iatrogenic, range between 9 and 11%. Total ureteral avulsion during URS is quite rare with a prevalence of 0–0.3%. We present three total ureteral avulsions we experienced in our clinic during the last 2 years and their treatment.

Case presentation

During the last 2 years, we experienced three total ureteral avulsions: one of these occurred in our clinic and the other two occurred in an external center and were referred to us. In two cases, the omental flap was rotated after ureteral reimplantation and the ureter was completely wrapped inside the omental flap. In the third case, boari flap was formed from the bladder. Due to the presence of extrarenal wide renal pelvis, anastomosis was made with boari flap after a y–v flap was rotated on the renal pelvis. D-J stents of the patients were removed at the end of 3 months. Although there was mild hydronephrosis, parenchymal thinning and a significant decrease in functions were not observed. Ureteral avulsion of the patients was successfully managed without the need for nephrectomy.

Conclusion

Ureteral avulsion management is an extremely difficult condition for both the surgeon and the patient. So, the most important thing is to prevent ureteral avulsion. Ureteroplasty and omental flap treatment are applicable methods with quite successful results for complete ureteral avulsions.

Boari-Flap reconstrution due to a total ureteral avulsion in a patient with ipslateral ureterolithiasis and contralateral renal nodule

The ureteral avulsion during ureterolithotripsy (URS) occurs due to the sudden movement of the optical device or endoscopic extractor either in its removal or insertion, associated with a probable previous lesion in the ureter wall, causing a vital fragility area. A 52-year-old male patient with, an obstructive calculus of 9 mm was found in the left middle ureter, and a heterogeneous hypervascular nodule located in the right kidney, suggesting neoplasia. During procedure with rigid ureteroscopy with ureteroscope removal, due to the pressure of the device and tissue fragility, there was total ureter avulsion.

In vitro study of age-related changes in human ureteral failure properties according to region, direction, and layer

Knowledge of the capacity of the ureteral wall to withstand urodynamic or external stresses is essential to understand ureteral injury and rupture that mostly occur following trauma, but may also be secondary to obstructive uropathy. It has clinical significance as well in the prevention of iatrogenic injury, for example, during ureteroscopy, but no information is available with regard to the age-related failure properties and regional differences have not been systematically described. Uniaxial tensile testing was performed on 166 ureteral rings and strips from 21 humans free of overt urologic disease; histological evaluation was performed. The degree of layer participation to the intact wall failure stress (=tissue strength), peak elastic modulus (=stiffness), and failure stretch (=extensibility) was assessed by examining layer-specific ruptures in the stress-stretch data. Failure stress at and peak elastic modulus before the first (muscle/adventitial) rupture correlated inversely less with age ( p < 0.05 in few regions/directions) than failure stress at the second (mucosal) rupture ( p < 0.05 in the middle and lower ureter), consistent with the decreased mucosal thickness in ≥50-year-old subjects. Failure stretch at both ruptures did not correlate with age ( p > 0.05 in most regions/directions), paralleling elastin content. Correlations with age were more significant in females than males. Failure stress at the second rupture point was higher ( p < 0.05) distally in <50-year-old but not in ≥50-year-old subjects, justified by the increased collagen distally in the former. Directional differences in failure stretches ( p < 0.05 at all ages/regions/genders) were justified by preferentially axial collagen reinforcement. The presented results may establish the foundation for computational models of iatrogenic/accidental ureteral trauma.

A three-dimensional (3D) two-way coupled fluid-structure interaction (FSI) study of peristaltic flow in obstructed ureters

Obstruction in the ureter flow path is one of the most common problems in urinary-related diseases. As the ureter transports the urine using the expansion bolus created by the peristaltic pulses, an obstruction in its path can cause unwanted backflow and can also result in damage to the wall. But in order to understand this further, and specifically to quantify and parametrize the effect of the obstruction in the ureter, a detailed study investigating various level of obstructions in peristaltic ureter flow is necessary. In the current study, full 3D numerical simulations of peristalsis in an obstructed ureter are carried out using a finite element solver along with a two-way coupling between the fluid and structural domain with the arbitrary Eulerian-Lagrangian method. Analysis of the results shows that the larger the obstruction, the higher the wall shear stress and pressure gradient in the fluid. In addition, the amount of backflow increases with increase in the obstruction.

Vesicoureteral reflux and the extracellular matrix connection

Primary vesicoureteral reflux (VUR) is a common pediatric condition due to a developmental defect in the ureterovesical junction. The prevalence of VUR among individuals with connective tissue disorders, as well as the importance of the ureter and bladder wall musculature for the anti-reflux mechanism, suggest that defects in the extracellular matrix (ECM) within the ureterovesical junction may result in VUR. This review will discuss the function of the smooth muscle and its supporting ECM microenvironment with respect to VUR, and explore the association of VUR with mutations in ECM-related genes.

Soft 3D-Printed Phantom of the Human Kidney with Collecting System

Organ models are used for planning and simulation of operations, developing new surgical instruments, and training purposes. There is a substantial demand for in vitro organ phantoms, especially in urological surgery. Animal models and existing simulator systems poorly mimic the detailed morphology and the physical properties of human organs. In this paper, we report a novel fabrication process to make a human kidney phantom with realistic anatomical structures and physical properties. The detailed anatomical structure was directly acquired from high resolution CT data sets of human cadaveric kidneys. The soft phantoms were constructed using a novel technique that combines 3D wax printing and polymer molding. Anatomical details and material properties of the phantoms were validated in detail by CT scan, ultrasound, and endoscopy. CT reconstruction, ultrasound examination, and endoscopy showed that the designed phantom mimics a real kidney’s detailed anatomy and correctly corresponds to the targeted human cadaver’s upper urinary tract. Soft materials with a tensile modulus of 0.8–1.5 MPa as well as biocompatible hydrogels were used to mimic human kidney tissues. We developed a method of constructing 3D organ models from medical imaging data using a 3D wax printing and molding process. This method is cost-effective means for obtaining a reproducible and robust model suitable for surgical simulation and training purposes.

Ureteroscopy in proximal ureteral stones after shock wave lithotripsy failure: Is it safe and efficient or dangerous?

INTRODUCTION

We assessed the effectiveness of ureteroscopy (URS) in proximal ureteral stones performed after shock wave lithotripsy (SWL) failure, and determined outcomes in terms of success rate, complications, and operation time.

METHODS

We analyzed data of patients with previous unsuccessful SWL (Group I) and the ones that did not have SWL or URS before (Group II) for proximal ureteral stones between December 2007 and August 2014. Group I included 346 patients who underwent complementary URS and Group II 209 patients who underwent primary URS. Success rates, operation time and complications were compared between groups.

RESULTS

Success rates of complementary and primary URS were 78.9% and 80.9%, respectively. The difference in success rates was not statistically significant between groups (p = 0.57). The complication rates of complementary URS was 12.1%, and 9.5% in primary URS (p = 0.49). No statistically significant differences were noted in terms of gender, age, stone size and side, or lithotripter type between groups. The mean operation time and need for balloon dilatation were higher in complementary URS group compared to the primary URS group, and the difference was statistically significant (p < 0.05).

CONCLUSIONS

Complementary URS may be used safely after SWL failure in proximal ureteral stones. Its success rate and morbidities are similar to primary URS, except for longer operation time and an increased need for balloon dilatation.