Guillaume Kazmitcheff

Friction force measurement during cochlear implant insertion: application to a force-controlled insertion tool design

Hypothesis The aim of the study was to evaluate force profiles during array insertion in human cochlea specimens and to evaluate a mechatronic inserter using a 1-axis force sensor. Background Today, the surgical challenge in cochlear implantation is the preservation of the anatomic structures and the residual hearing. In routine practice, the electrode array is inserted manually with a limited sensitive feedback. Materials and Methods Hifocus 1J electrode arrays were studied. The bench test comprised a mechatronic inserter combined to a 1-axis force sensor between the inserter and the base of the array and a 6-axis force sensor beneath the cochlea model. Influence of insertion tube material, speed (0.15, 0.5, and 1.5 mm/s) and lubricant on frictions forces were studied (no-load). Different models were subsequently evaluated: epoxy scala tympani model and temporal bones. Results Frictions forces were lower in the plastic tube compared with those in the metal tube (0.09 ± 0.028 versus 0.14 ± 0.034 at 0.5 mm/s, p < 0.001) and with the use of hyaluronic acid gel. Speed did not influence frictions forces in our study. Insertion force profiles provided by the 1- and 6-axis force sensors were similar when friction forces inside the insertion tool (no-load measurements) were subtracted from the 1-axis sensor data in the epoxy and temporal bone models (mean error, 0.01 ± 0.001 N). Conclusion Using a sensor included in the inserter, we were able to measure array insertion forces. This tool can be potentially used to provide real-time information to the surgeon during the procedure.

Definition of Metrics to Evaluate Cochlear Array Insertion Forces Performed with Forceps, Insertion Tool, or Motorized Tool in Temporal Bone Specimens

Introduction. In order to achieve a minimal trauma to the inner ear structures during array insertion, it would be suitable to control insertion forces. The aim of this work was to compare the insertion forces of an array insertion into anatomical specimens with three different insertion techniques: with forceps, with a commercial tool, and with a motorized tool. Materials and Methods. Temporal bones have been mounted on a 6-axis force sensor to record insertion forces. Each temporal bone has been inserted, with a lateral wall electrode array, in random order, with each of the 3 techniques. Results. Forceps manual and commercial tool insertions generated multiple jerks during whole length insertion related to fits and starts. On the contrary, insertion force with the motorized tool only rose at the end of the insertion. Overall force momentum was 1.16 ± 0.505 N (mean ± SD, n = 10), 1.337 ± 0.408 N (n = 8), and 1.573 ± 0.764 N (n = 8) for manual insertion with forceps and commercial and motorized tools, respectively. Conclusion. Considering force momentum, no difference between the three techniques was observed. Nevertheless, a more predictable force profile could be observed with the motorized tool with a smoother rise of insertion forces.

Validation method of a middle ear mechanical model to develop a surgical simulator.

Ossicular surgery requires a high dexterity for the manipulation of the fragile and small middle ear components. Currently, the only efficient technique for training residents in otological surgery is through the use of temporal bone specimens, where any existing surgical simulator does not provide useful feedback. The objective of this study was to develop a finite-element model of the human ossicular chain dedicated to surgical simulation and to propose a method to evaluate its behavior. A model was developed based on human middle ear micromagnetic resonance imaging. The mechanical parameters were determined according to published data. To assess its performance, the middle ear transfer function was analyzed. The robustness of our model and the influence of different middle ear components were also evaluated at low frequency by static force pressure simulations. The mechanical behavior of our model in nominal and pathological conditions was in good agreement with published human temporal bone measurements. We showed that the cochlea influences the transfer function only at high frequency and could be omitted from a surgical simulator. In addition, surgeons were able to manipulate the validated middle ear model with a real-time haptic feedback. The computational efficiency of our approach allowed real-time interactions, making it suitable for use in a training simulator.

Damage to inner ear structure during cochlear implantation: Correlation between insertion force and radio-histological findings in temporal bone specimens

&NA; Cochlear implant insertion should be as least traumatic as possible in order to reduce trauma to the cochlear sensory structures. The force applied to the cochlea during array insertion should be controlled to limit insertion‐related damage. The relationship between insertion force and histological traumatism remains to be demonstrated. Twelve freshly frozen cadaveric temporal bones were implanted with a long straight electrodes array through an anterior extended round window insertion using a motorized insertion tool with real‐time measurement of the insertion force. Anatomical parameters, measured on a pre‐implantation cone beam CT scan, position of the array and force metrics were correlated with post‐implantation scanning electron microscopy images and histological damage assessment. An atraumatic insertion occurred in six cochleae, a translocation in five cochleae and a basilar membrane rupture in one cochlea. The translocation always occurred in the 150‐ to 180‐degree region. In the case of traumatic insertion, different force profiles were observed with a more irregular curve arising from the presence of an early peak force (30 ± 18.2 mN). This corresponded approximately to the first point of contact of the array with the lateral wall of the cochlea. Atraumatic and traumatic insertions had significantly different force values at the same depth of insertion (p < 0.001, two‐way ANOVA), and significantly different regression lines (y = 1.34x + 0.7 for atraumatic and y = 3.37x + 0.84 for traumatic insertion, p < 0.001, ANCOVA). In the present study, the insertion force was correlated with the intracochlear trauma. The 150‐ to 180‐degree region represented the area at risk for scalar translocation for this straight electrodes array. Insertion force curves with different sets of values were identified for traumatic and atraumatic insertions; these values should be considered during motorized insertion of an implant so as to be able to modify the insertion parameters (e.g axis of insertion) and facilitate preservation of endocochlear structures. Graphical abstract Figure. No caption available. HighlightsTwelve human cadaveric temporal bones were cochlear implanted at constant speed of insertion.Insertion forces during cochlear implantation were correlated with inner ear structure traumatism.Two different functions were identified for traumatic and atraumatic insertions.The control of the insertion force could reduce the risk of insertion‐related damage.

Effect of embedded dexamethasone in cochlear implant array on insertion forces in an artificial model of scala tympani.

Hypothesis Loading otoprotective drug into cochlear implant might change its mechanical properties, thus compromising atraumatic insertion. This study evaluated the effect of incorporation of dexamethasone (DXM) in the silicone of cochlear implant arrays on insertion forces. Background Local administration of DXM with embedded array can potentially reduce inflammation and fibrosis after cochlear implantation procedure to improve hearing preservation and reduce long-term impedances. Methods Four models of arrays have been tested: 0.5-mm distal diameter array (n = 5) used as a control, drug-free 0.4-mm distal diameter array (n = 5), 0.4-mm distal diameter array with 1% eluded DXM silicone (n = 5), and 0.4-mm distal diameter array with 10% eluded DXM silicone (n = 5). Via a motorized insertion bench, each array has been inserted into an artificial scala tympani model. The forces were recorded by a 6-axis force sensor. Each array was tested seven times for a total number of 140 insertions. Results During the first 10-mm insertion, no difference between the four models was observed. From 10- to 24-mm insertion, the 0.5-mm distal diameter array presented higher insertion forces than the drug-free 0.4-mm distal diameter arrays, with or without DXM. Friction forces for drug-free 0.4-mm distal diameter array and 0.4-mm distal diameter DXM eluded arrays were similar on all insertion lengths. Conclusion Incorporation of DXM in silicone for cochlear implant design does not change electrode array insertion forces. It does not raise the risk of trauma during array insertion, making it suitable for long-term in situ administration to the cochlea.

Registration of a Validated Mechanical Atlas of Middle Ear for Surgical Simulation

This paper is centered on the development of a new training and rehearsal simulation system for middle ear surgery. First, we have developed and validated a mechanical atlas based on finite element method of the human middle ear. The atlas is based on a microMRI. Its mechanical behavior computed in real-time has been successfully validated. In addition, we propose a method for the registration of the mechanical atlas on patient imagery. The simulation can be used for a rehearsal surgery with the geometrical anatomy of a given patient and with mechanical data that are validated. Moreover, this process does not necessitate a complete re-built of the model.

Super paramagnetic nanoparticles delivery through a microcatheter by solenoids

In order to design a drug delivery system to the human cochlea, a magnetic pump driving Fe3O4 super paramagnetic nanoparticles (MNP) attachable to a drug was evaluated. Such a device could be inserted into the cochlea by a minimally invasive technique. In this study, the effect of a magnetic field generated by solenoids coiled around a 1 mm diameter catheter filled with 200 nm MNP was studied. Results showed that, particles can be concentrated at different locations of the catheter for a precise delivery at different cochlear locations. The particles could also be driven between 2 solenoids 50 mm apart with 150 mA which is compatible with current sources in available cochlear implants.

Haptic Rendering on Deformable Anatomical Tissues with Strong Heterogeneities

This paper is focus on the development of a haptic rendering method to simulate interactions with heterogeneous deformable materials, such as anatomical components. Indeed, the strong heterogeneities of the biological tissues involves numerical and real-time issues to simulate the deformations and the mechanical interactions between the organs and the surgical tools. In this paper, we propose a new haptic algorithm adapted to the modeling of heterogeneous biological tissues, based on non-linear finite element model. The central contribution is the use of a triple asynchronous approach: one loop at low rate, which computes a preconditionner that solves the numerical conditioning problems; a second at intermediate rate, to update the model of the biological simulation; and the haptic loop which provides the feedback to the user at high rate. Despite of the desynchronization, we show that the calculation of haptic forces remains accurate compared to the model. We apply our method to a challenging microsurgical intervention of the human middle ear. This surgery requires a delicate gesture in order to master the applied forces.