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Cochlear implants are crucial for addressing severe-to-profound hearing loss, with the success of the procedure requiring careful electrode placement. This scoping review synthesizes the findings from 125 studies examining the factors influencing insertion forces (IFs) and intracochlear pressure (IP), which are crucial for optimizing implantation techniques and enhancing patient outcomes. The review highlights the impact of variables, including insertion depth, speed, and the use of robotic assistance on IFs and IP. Results indicate that higher insertion speeds generally increase IFs and IP in artificial models, a pattern not consistently observed in cadaveric studies due to variations in methodology and sample size. The study also explores the observed minimal impact of robotic assistance on reducing IFs compared to manual methods. Importantly, this review underscores the need for a standardized approach in cochlear implant research to address inconsistencies and improve clinical practices aimed at preserving hearing during implantation. [ABSTRACT FROM AUTHOR]

Purpose: The significance of atraumatic electrode array (EA) insertion in cochlear implant (CI) surgery is widely acknowledged, with consensus that forces due to EA insertion are directly correlated with insertion trauma. Unfortunately, the manual perception of these forces through haptic feedback is inherently limited, and techniques for in vivo force measurements to monitor the insertion are not yet available. Addressing this gap, we developed of a force-sensitive insertion tool capable of capturing real-time insertion forces during standard CI surgery. Methods: This paper describes the tool and its pioneering application in a clinical setting and reports initial findings from an ongoing clinical study. Data and experiences from five patients have been evaluated so far, including force profiles of four patients. Results: The initial intraoperative experiences are promising, with successful integration into the conventional workflow. Feasibility of in vivo insertion force measurement and practicability of the tool's intraoperative use could be demonstrated. The recorded in vivo insertion forces show the expected rise with increasing insertion depth. Forces at the end of insertion range from 17.2 mN to 43.6 mN, while maximal peak forces were observed in the range from 44.8 mN to 102.4 mN. Conclusion: We hypothesize that this novel method holds the potential to assist surgeons in monitoring the insertion forces and, thus, minimizing insertion trauma and ensuring better preservation of residual hearing. Future data recording with this tool can form the basis of ongoing research into the causes of insertion trauma, paving the way for new and improved prevention strategies. [ABSTRACT FROM AUTHOR]

PurposeThe significance of atraumatic electrode array (EA) insertion in cochlear implant (CI) surgery is widely acknowledged, with consensus that forces due to EA insertion are directly correlated with insertion trauma. Unfortunately, the manual perception of these forces through haptic feedback is inherently limited, and techniques for in vivo force measurements to monitor the insertion are not yet available. Addressing this gap, we developed of a force-sensitive insertion tool capable of capturing real-time insertion forces during standard CI surgery.MethodsThis paper describes the tool and its pioneering application in a clinical setting and reports initial findings from an ongoing clinical study. Data and experiences from five patients have been evaluated so far, including force profiles of four patients.ResultsThe initial intraoperative experiences are promising, with successful integration into the conventional workflow. Feasibility of in vivo insertion force measurement and practicability of the tool’s intraoperative use could be demonstrated. The recorded in vivo insertion forces show the expected rise with increasing insertion depth. Forces at the end of insertion range from 17.2 mN to 43.6 mN, while maximal peak forces were observed in the range from 44.8 mN to 102.4 mN.ConclusionWe hypothesize that this novel method holds the potential to assist surgeons in monitoring the insertion forces and, thus, minimizing insertion trauma and ensuring better preservation of residual hearing. Future data recording with this tool can form the basis of ongoing research into the causes of insertion trauma, paving the way for new and improved prevention strategies.

Introduction: In cochlear implant surgery, the insertion of the electrode array (EA) into the cochlea is critical as its implementation can influence the preservation of residual hearing. Insertion tests are the primary method for basic research on parameters influencing the insertion and help to further improve the design of EAs and surgical techniques. With automated insertion devices close to clinical application, a consensus on optimal insertion parameters is needed, which requires reliable testing methods. Moreover, the limited availability of EAs needs to be considered. We propose a test setup that provides high repeatability and flexibility for various research questions. Methods: Design requirements for multiple types of experiments such as variability of insertion speed or trajectory as well as cochlear geometry guided the computer aided design of the test bench. Moreover, repeated insertions with the same EA were supposed to be possible. To evaluate its functionality, insertion tests into a 3D printed cochlea model were performed and recorded. Results: The central components of the test bench are a linear actuator driving the EA and a goniometer changing the orientation of the target - a cochlea model or a specimen. A force sensor can be mounted below the target to measure forces in its frame of reference. The experimental results show high reproducibility of insertion forces for recurring trajectories with a single EA. Conclusion: The test bench enables reproducible insertion tests with a high number of repetitions and reduced EA usage. This allows a more detailed investigation of broadly discussed influences on the insertion such as the insertion speed or trajectory as well as cochlear geometry and can thereby drive future EA development.

Purpose: Trauma that may be inflicted to the inner ear (cochlea) during the insertion of an electrode array (EA) in cochlear implant (CI) surgery can significantly decrease the hearing outcome of patients with residual hearing. Interaction forces between the EA and the cochlea are a promising indicator for the likelihood of intracochlear trauma. However, insertion forces have only been measured in laboratory setups. We recently developed a tool to measure the insertion force during CI surgery. Here, we present the first ex vivo evaluation of our tool with a focus on usability in the standard surgical workflow. Methods: Two CI surgeons inserted commercially available EAs into three temporal bone specimens. The insertion force and the orientation of the tool were recorded together with camera footage. The surgeons answered a questionnaire after each insertion to evaluate the surgical workflow with respect to CI surgery. Results: The EA insertion using our tool was rated successful in all 18 trials. The surgical workflow was evaluated to be equivalent to standard CI surgery. Minor handling challenges can be overcome through surgeon training. The peak insertion forces were 62.4 mN ± 26.7 mN on average. Peak forces significantly correlated to the final electrode insertion depth, supporting the assumption that the measured forces mainly correspond to intracochlear events and not extracochlear friction. Gravity-induced forces of up to 28.8 mN were removed from the signal, illustrating the importance of the compensation of such forces in manual surgery. Conclusion: The results show that the tool is ready for intraoperative use. In vivo insertion force data will improve the interpretability of experimental results in laboratory settings. The implementation of live insertion force feedback to surgeons could further improve residual hearing preservation. [ABSTRACT FROM AUTHOR]

Adhesive bonding, mechanical fastening, and snap-fit are all ways for attaching plastic components together. Snap-fit is employed to assemble plastic parts because it is an efficient, cost-effective, and fast joining technique. When it comes to snap-fits, you have two options: separable and inseparable. The term separable refers to the ability of the components to be dismantled successfully without breaking, whereas inseparable refers to the plastic parts being permanently attached. This investigation focuses on cantilever snap-fit since it is frequently used in the automotive, aerospace, and other sectors. Numerous aspects and parameters affect the functioning of snap-fits, notably on the forces of the insertion and retention. The parameters are the feature thickness (Tb), beam length (Lb), beam width (Wb), base radius (Rb), mounting (α) and dismounting angle (β). The forces required to attach and detach the snap-fits are thought to increase as the insertion and retention angles increase. The results can be seen that higher insertion and retention angle contributes to higher insertion and retention forces as portrayed from Set 7 with the value of 1.1052 N and -1.0214 N.

Cochlear implants are crucial for addressing severe-to-profound hearing loss, with the success of the procedure requiring careful electrode placement. This scoping review synthesizes the findings from 125 studies examining the factors influencing insertion forces (IFs) and intracochlear pressure (IP), which are crucial for optimizing implantation techniques and enhancing patient outcomes. The review highlights the impact of variables, including insertion depth, speed, and the use of robotic assistance on IFs and IP. Results indicate that higher insertion speeds generally increase IFs and IP in artificial models, a pattern not consistently observed in cadaveric studies due to variations in methodology and sample size. The study also explores the observed minimal impact of robotic assistance on reducing IFs compared to manual methods. Importantly, this review underscores the need for a standardized approach in cochlear implant research to address inconsistencies and improve clinical practices aimed at preserving hearing during implantation.

(1) Background: During a cochlear implant insertion, the mechanical trauma can cause residual hearing loss in up to half of implantations. The forces on the cochlea during the insertion can lead to this mechanical trauma but can be highly variable between subjects which is thought to be due to differing anatomy, namely of the scala tympani. This study presents a systematic investigation of the influence of different geometrical parameters of the scala tympani on the cochlear implant insertion force. The influence of these parameters on the insertion forces were determined by testing the forces within 3D-printed, optically transparent models of the scala tympani with geometric alterations. (2) Methods: Three-dimensional segmentations of the cochlea were characterised using a custom MATLAB script which parametrised the scala tympani model, procedurally altered the key shape parameters (e.g., the volume, vertical trajectory, curvature, and cross-sectional area), and generated 3D printable models that were printed using a digital light processing 3D printer. The printed models were then attached to a custom insertion setup that measured the insertion forces on the cochlear implant and the scala tympani model during a controlled robotic insertion. (3) Results: It was determined that the insertion force is largely unaffected by the overall size, curvature, vertical trajectory, and cross-sectional area once the forces were normalised to an angular insertion depth. A Capstan-based model of the CI insertion forces was developed and matched well to the data acquired. (4) Conclusion: By using accurate 3D-printed models of the scala tympani with geometrical alterations, it was possible to demonstrate the insensitivity of the insertion forces to the size and shape of the scala tympani, after controlling for the angular insertion depth. This supports the Capstan model of the cochlear implant insertion force which predicts an exponential growth of the frictional force with an angular insertion depth. This concludes that the angular insertion depth, rather than the length of the CI inserted, should be the major consideration when evaluating the insertion force and associated mechanical trauma caused by cochlear implant insertion. [ABSTRACT FROM AUTHOR]

Inner ear trauma caused by cochlear implantation is a severe clinical problem. It was shown that an electrode alginate coating can reduce the insertion forces in vitro. The grade of the alginate viscosity can be adjusted by using different metal ions for cross-linking the salts of the alginic acid. The aim was to investigate the stability and inner ear biocompatibility of alginate using different in vitro established cross-linkers.

Cochlear implants include an electrode array (EA) which needs to be inserted into the cochlea. Insertion tests using artificial cochlear models (ACM) or ex vivo specimens are widely used methods during EA development to characterize EA design properties, including insertion forces. Measured forces are directly linked to the orientation of the cochlear lumen with respect to the insertion axis of the test bench. While desired insertion directions in ACM experiments can be predefined by design, specimens are individually shaped and the cochlear lumen is embedded invisibly. Therefore, a new method for accurate, individual specimen positioning is required. A key element of the proposed method is a customizable pose setting adapter (PSA) used to adjust the specimen’s fine positioning. After rigid fixation of the specimen to a holder featuring spherical registration markers and subsequent cone beam computed tomography the desired insertion direction is planned. The planned data is used to calculate the individual shape of the PSA. Finally, the PSA is 3D printed and mounted between force sensor and specimen holder to correctly align the specimen to the test bench’s insertion axis. All necessary hard- and software have been developed including the specimen holder, a software for registration and trajectory planning, and a custom Matlab script whose output drives a parametric CAD file of the PSA. Positioning accuracy was determined in a first trial using 10 virtual trajectories and was found to be 0.23 ± 0.12 mm and 0.38 ± 0.17°. The presented stereotactic positioning procedure enables high repeatability in future ex vivo insertion experiments due to accurate, image-guided control of the insertion direction.

(1) Background: During a cochlear implant insertion, the mechanical trauma can cause residual hearing loss in up to half of implantations. The forces on the cochlea during the insertion can lead to this mechanical trauma but can be highly variable between subjects which is thought to be due to differing anatomy, namely of the scala tympani. This study presents a systematic investigation of the influence of different geometrical parameters of the scala tympani on the cochlear implant insertion force. The influence of these parameters on the insertion forces were determined by testing the forces within 3D-printed, optically transparent models of the scala tympani with geometric alterations. (2) Methods: Three-dimensional segmentations of the cochlea were characterised using a custom MATLAB script which parametrised the scala tympani model, procedurally altered the key shape parameters (e.g., the volume, vertical trajectory, curvature, and cross-sectional area), and generated 3D printable models that were printed using a digital light processing 3D printer. The printed models were then attached to a custom insertion setup that measured the insertion forces on the cochlear implant and the scala tympani model during a controlled robotic insertion. (3) Results: It was determined that the insertion force is largely unaffected by the overall size, curvature, vertical trajectory, and cross-sectional area once the forces were normalised to an angular insertion depth. A Capstan-based model of the CI insertion forces was developed and matched well to the data acquired. (4) Conclusion: By using accurate 3D-printed models of the scala tympani with geometrical alterations, it was possible to demonstrate the insensitivity of the insertion forces to the size and shape of the scala tympani, after controlling for the angular insertion depth. This supports the Capstan model of the cochlear implant insertion force which predicts an exponential growth of the frictional force with an angular insertion depth. This concludes that the angular insertion depth, rather than the length of the CI inserted, should be the major consideration when evaluating the insertion force and associated mechanical trauma caused by cochlear implant insertion.

The aim of the study was to evaluate insertion forces during manual insertion of a straight atraumatic electrode in human temporal bones, and post-implantation histologic evaluation of the samples to determine whether violation of intracochlear structures is related to insertion forces. In order to minimize intracochlear trauma and preserve residual hearing during cochlear implantation, knowledge of the insertion forces is necessary. Ten fresh frozen human temporal bones were prepared with canal wall down mastoidectomy. All samples were mounted on a one-axis force sensor. Insertion of a 16-mm straight atraumatic electrode was performed from different angles to induce 'traumatic' insertion. Histologic evaluation was performed in order to evaluate intracochlear trauma. In 4 of 10 samples, dislocation of the electrode into scala vestibuli was observed. The mean insertion force for all 10 procedures was 0.003 ± 0.005 N. Insertion forces measured around the site of dislocation to scala vestibuli in 3 of 4 samples were significantly higher than insertion forces at the same location of the cochleae measured in samples without trauma ( p < 0.04). Mean force during the whole insertion process of the straight atraumatic electrode is lower than reported by other studies using longer electrodes. Based on our study, insertion forces leading to basilar membrane trauma may be lower than the previously reported direct rupture forces. [ABSTRACT FROM AUTHOR]

Tissue trauma is a frequent complication of cochlear implantation (CI) surgery, but the relationship between intracochlear trauma, electrode insertion forces, and surgeons' ability to perceive these forces is poorly understood. In this study, we simulated CI surgery using a benchtop apparatus to repeatedly apply small forces to the subjects' hands while reducing the variability in their hand movements. We used a psychophysical testing procedure to estimate the force perception thresholds of 10 otologic surgeons and found a median threshold of 20.4 mN. The results suggest that surgeons have the capability to sense at least some insertion forces and are likely to perceive severe trauma such as occurs when the electrode crosses from one scala to the other. [ABSTRACT FROM AUTHOR]

Background: The purpose of this study was to examine factors that could help reduce primary perforation during insertion of a framed intrauterine device (IUD) and to determine factors that contribute in generating enough uterine muscle force to cause embedment and secondary perforation of an IUD. The objective was also to evaluate the main underlying mechanism of IUD expulsion. Methods: We compared known IUD insertion forces for "framed" devices with known perforation forces in vitro (hysterectomy specimens) and known IUD removal forces and calculated a range of possible intrauterine forces using pressure and surface area. These were compared with known perforation forces. Results: IUD insertion forces range from 1.5 N to 6.5 N. Removal forces range from 1 N to 5.8 N and fracture forces from 8.7 N to 30 N depending upon device. Measured perforation forces are from 20 N to 54 N, and calculations show the uterus is capable of generating up to 50 N of myometrial force depending on internal pressure and surface area. Conclusion: Primary perforation with conventional framed IUDs may occur if the insertion pressure exceeds the perforation resistance of the uterine fundus. This is more likely to occur if the front end of the inserter/IUD is narrow, the passage through the cervix is difficult, and the procedure is complex. IUD embedment and secondary perforation and IUD expulsion may be due to imbalance between the size of the IUD and that of the uterine cavity, causing production of asymmetrical uterine forces. The uterine muscle seems capable of generating enough force to cause an IUD to perforate the myometrium provided it is applied asymmetrically. A physical theory for IUD expulsion and secondary IUD perforation is given. [ABSTRACT FROM AUTHOR]

Insertion of needle into tissue is influenced by the cutting edges and the needle tip geometry. In this paper, we aimed at investigating the relationship between the insertion forces and cutting edge geometry and general mathematical models of included and inclination angles for two different needle configurations. Two new geometries, one with parabolic cut and other with parabolic surface, cut with two bevel planes have been proposed along with the corresponding mathematical models to improve the cutting edge properties. Results show that parabolic needles after cutting with bevel planes have significantly improved cutting edge properties and are better than the other common needle configurations such as bevel cut. Simulation studies predicted that the deformation and stresses are slightly higher for proposed needle tip geometries than currently available topologies. However, the advantage of included and inclination angles reduce insertion forces thus optimization of medical needle design for the selected tip geometries is a trade-off between insertion forces and deflection in needle. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: To investigate the influence of alterations of the scala tympani environment and modifications of the surface of cochlear implant electrode arrays on insertion forces in vitro. Study Design: Research experimental study. Methods: Fibroblasts producing neurotrophic factors were cultivated on the surface of Nucleus 24 Contour Advance electrodes. Forces were recorded by an Instron 5542 Force Measurement System as three modified arrays were inserted into an artificial scala tympani model filled with phosphate-buffered saline (PBS). The recorded forces were compared to control groups including three unmodified electrodes inserted into a model filled with PBS (unmodified environment) or Healon (current practice). Fluorescence microscopy was used before and after the insertions to identify any remaining fibroblasts. Additionally, three Contour Advance electrodes were inserted into an artificial model, filled with alginate/barium chloride solution at different concentrations, while insertion forces were recorded. Results: Modification of the scala tympani environment with 50% to 75% alginate gel resulted in a significant decrease in the insertion forces. The fibroblast-coated arrays also led to decreased forces comparable to those recorded with Healon. Fluorescence microscopy revealed fully cell-covered arrays before and partially covered arrays after the insertion; the fibroblasts on the arrays' modiolar surface remained intact. Conclusions: Modifications of the scala tympani's environment with 50% to 75% alginate/barium chloride and of the cochlear implant electrode surface with neurotrophic factor-producing fibroblasts drastically reduce the insertion forces. As both modifications may serve future intracochlear therapies, it is expected that these might additionally reduce possible insertion trauma. [ABSTRACT FROM AUTHOR]

Objectives/Hypothesis: To assess the insertion forces and feasibility of insertion of a prototype electrode carrier coated with a flexible and biodegradable coating developed for lubrication and drug delivery. Study Design: Experimental study. Methods: Eight coated and eight uncoated electrode carriers were inserted into a scala tympani model by means of an insertion device, and forces produced during insertion were determined in near real time. The maximum insertion depths and insertion angle were determined. To test the handling and operability, five coated electrode carriers were implanted into human temporal bones. Additionally, the bones were processed undecalcified and the distribution of the coating material within the cochlea evaluated. Results: Insertion forces were markedly reduced in the group of coated electrode carriers for insertion depths above 15 mm. The insertions were less fitful and led to a higher maximum insertion angle. The insertion of the coated electrode carrier was feasible, and the coating material was evident up to the apical parts of the cochlea postimplantation. Conclusions: Coating of a cochlear implant electrode carrier may reduce insertion forces responsible for the surgical trauma. Loaded with active substances, the coating may help to deliver drugs to the apical parts of the cochlear where hair cells reside in patients with residual hearing. Laryngoscope, 2009 [ABSTRACT FROM AUTHOR]

Abstract-Substantial advancement in the understanding of the neuronal basis of behavior and the treatment of neurological disorders has been achieved via the implantation of various devices into the brain. To design and optimize the next generation of neuronal implants while striving to minimize tissue damage, it is necessary to understand the mechanics of probe insertion at relevant length scales. Unfortunately, a broad-based understanding of brain-implant interactions at the necessary micrometer scales is largely missing. This paper presents a generalizable description of the micrometer-scale penetration mechanics and material properties of mouse brain tissue in vivo. Cylindrical stainless steel probes were inserted into the cerebral cortex and olfactory bulb of mice. The effects of probe size, probe geometry, insertion rate, insertion location, animal age, and the presence of the dura and pia on the resulting forces were measured continuously throughout probe insertion and removal. Material properties (modulus, cutting force, and frictional force) were extracted using mechanical analysis. The use of rigid, incompressible, cylindrical probes allows for a general understanding of how probe design and insertion methods influence the penetration mechanics of brain tissue in vivo that can be applied to the quantitative design of most future implantable devices. [ABSTRACT FROM AUTHOR]

Background: Because chondrocytes are responsible for articular cartilage matrix synthesis and maintenance, reduced chondrocyte viability could compromise graft survival, healing, and clinical outcome. Hypothesis: Typical forces used in osteochondral grafting reduce the viability of the chondrocytes in the graft. Study Design: Controlled laboratory study. Methods: Osteochondral grafting was performed in 4 fresh-frozen cadaver knees (n = 16 per knee). Impact force was measured during extrusion of the donor graft from the harvester into the recipient site, seating the graft flush with the articular surface of the surrounding cartilage using a tamp, and recessing the graft surface below the recipient articular surface. The magnitudes of forces measured during cadaver surgery (200, 400, and 800 N) were reproduced using a drop-tower apparatus on 80 fresh osteochondral grafts harvested from knee blocks provided by tissue banks. Cell viability and glycosaminoglycan release in media were measured at 48 hours after injury. Results: Forces were relatively low (range, 124-356 N) during graft extrusion from the harvester into the recipient defect or during flush seating (range, 191-418 N) of the graft. Attempts to recess the graft generated significantly greater force (range, 147- 685; P < .01). When the donor graft length was 2 mm longer than the depth of the recipient hole, the mean impact force generated was even higher (range, 240-1114 N) than the force seen in a donor graft of equal length. No reduction in viability was seen at 200-N and 400-N impacts. However, a significant decrease in chondrocyte viability was seen in the group impacted with 800 N (only 50% of cells were viable, compared with 91% in the sham group; P < .01). Glycosaminoglycan levels in culture media did not correlate significantly with insertion force. Conclusion: Typical graft insertion forces did not significantly reduce chondrocyte viability. However, increased graft length relative to the depth of the recipient hole and attempts to recess the graft generated higher forces, which reduced chondrocyte viability. Clinical Relevance: Any theoretical benefits of cancellous bone compaction that may occur in grafts that are recessed or are longer than the recipient holes must be balanced against the potential reduction in chondrocyte viability. [ABSTRACT FROM AUTHOR]

Accurate needle insertion into soft, inhomogeneous tissue is of practical interest because of its importance in percutaneous therapies. In procedures that involve multiple needle insertions such as transrectal ultrasound‐guided prostate brachytherapy, it is important to reduce tissue deformation before puncture and during needle insertion. In order to reduce this deformation, we have studied the effect of different trajectories for a 2‐DOF (degrees of freedom) robot performing needle insertion in soft tissue. To obtain an optimum trajectory, we have compared tissue indentation and frictional forces for different trajectories. According to the results of our experiments, infinitesimal force per tissue displacement is a useful parameter for online trajectory update. In addition, the results show that axial rotation can reduce tissue indentation before puncture and frictional forces after puncture. Our proposed position/force controller is shown to provide considerable improvement in performance with regard to minimizing tissue deformation before puncture. [ABSTRACT FROM AUTHOR]

To enable authentic interfacing with neuronal structures in the brain, preventing alterations of tissue during implantation of devices is critical. By transiently implanting oxygen microsensors into rat cortex cerebri for 2 h, substantial and long lasting (>1 h) hypoxia is routinely generated in surrounding tissues; this hypoxia is linked to implantation generated compressive forces. Preferential loss of larger neurons and reduced metabolic components in surviving neurons indicates decreased viability one week after such hypoxic, compressive implantations. By devising an implantation method that relaxes compressive forces; magnitude and duration of hypoxia generated following such an implantation are ameliorated and neurons appear similar to naïve tissues. In line with these observations, astrocyte proliferation was significantly more pronounced for more hypoxic, compressive implantations. Surprisingly, astrocyte processes were frequently found to traverse cellular boundaries into nearby neuronal nuclei, indicating injury induction of a previously not described astrocyte-neuron interaction. Found more frequently in less hypoxic, force-relaxed insertions and thus correlating to a more beneficial outcome, this finding may suggest a novel protective mechanism. In conclusion, substantial and long lasting insertion induced hypoxia around brain implants, a previously overlooked factor, is linked to significant adverse alterations in nervous tissue. [ABSTRACT FROM AUTHOR]

Ureteral access sheaths (UAS) vary in their ability to resist buckling forces. We evaluated the forces utilized during simulated placement of a UAS. A model UAS (21F OD, 9F ID) was made of polyolefin material. Mounted to the distal tip of the catheter was a spring (7/32″ × 1″ × 0.28″ wire thickness). When simulating catheter insertion, the spring was placed in contact with an Extech™ 475040 Digital Force Gauge to measure the peak compression force (Newton). Three repetitions of the task were performed by practicing urologists ( n = 8) and urology residents ( n = 5). Participants were instructed to “Push until you feel a level of resistance that would make you stop if you were putting in a real ureteral access sheath”. Urologists applied a maximum force of 6.55 ± 0.45 N while urology residents applied a maximum force of 4.84 ± 0.64 N. There was a significant difference in the forces applied between the two groups ( P = 0.035). No significant difference in the variance (ranges or spread) of forces applied by the urologists and residents were identified ( P = 0.11). One-way analysis of variance demonstrated no differences in the force applied between the first, second and third attempt ( P = 0.80). Quantifying the insertion forces used during placement of a UAS will facilitate the design of UAS and provides information critical to the design of ureteroscopic simulators. Understanding the range of forces used by experienced urologists will help establish competency parameters for professionals in training. [ABSTRACT FROM AUTHOR]