Improvement of the insertion axis for cochlear implantation with a robot-based system

A method for accurate and reproducible specimen alignment for insertion tests of cochlear implant electrode arrays

PURPOSE

The trajectory along which the cochlear implant electrode array is inserted influences the insertion forces and the probability for intracochlear trauma. Controlling the trajectory is especially relevant for reproducible conditions in electrode insertion tests. Using ex vivo cochlear specimens, manual alignment of the invisibly embedded cochlea is imprecise and hardly reproducible. The aim of this study was to develop a method for creating a 3D printable pose setting adapter to align a specimen along a desired trajectory toward an insertion axis.

METHODS

Planning points of the desired trajectory into the cochlea were set using CBCT images. A new custom-made algorithm processed these points for automated calculation of a pose setting adapter. Its shape ensures coaxial positioning of the planned trajectory to both the force sensor measuring direction and the insertion axis. The performance of the approach was evaluated by dissecting and aligning 15 porcine cochlear specimens of which four were subsequently used for automated electrode insertions.

RESULTS

The pose setting adapter could easily be integrated into an insertion force test setup. Its calculation and 3D printing was possible in all 15 cases. Compared to planning data, a mean positioning accuracy of 0.21 ± 0.10 mm at the level of the round window and a mean angular accuracy of 0.43° ± 0.21° were measured. After alignment, four specimens were used for electrode insertions, demonstrating the practical applicability of our method.

CONCLUSION

In this work, we present a new method, which enables automated calculation and creation of a ready-to-print pose setting adapter for alignment of cochlear specimens in insertion test setups. The approach is characterized by a high level of accuracy and reproducibility in controlling the insertion trajectory. Therefore, it enables a higher degree of standardization in force measurement when performing ex vivo insertion tests and thereby improves reliability in electrode testing.

Cochlear Implantation: The use of OTOPLAN Reconstructed Images in Trajectory Identification

OBJECTIVES

This study aimed to define the best electrode trajectory line in cochlear implant (CI) surgery using the OTOPLAN (otology planning software) reconstructed 3D model and to investigate the surgical distance of the retro-facial approach as a direct access to the round window.

METHODS

Computed tomography (CT) scans of the normal temporal bone were included for analysis in this study. OTOPLAN reconstruction was used to build 3D models with specific ear structures for study analysis.

RESULTS

Twenty-five scans were included; the average age at the time of CT scan was 6.8±12 years. Twelve scans (48%) were right-sided and thirteen (52%) were left-sided. The best trajectory line to the round window was identified in all scans. The retro-facial approach was the optimal approach for 52% of cases (13/25). In all scans, the safe distance from the facial nerve were in favor of the retro-facial approach (P = 0.0011).

CONCLUSION

The OTOPLAN reconstructed imaging provided a good analysis of the retro-facial approach and helped in planning the surgical trajectory line towards the round window. Additionally, calculation of the surgical distance can help the surgeon compare the retro-facial approach to the standard facial recess for preoperative planning. These findings may help in robotic surgery.

Imaging of the human cochlea using micro-computed tomography before and after cochlear implantation: comparison with cone-beam computed tomography

PURPOSE

Analysis of cochlear structures and postoperative temporal bone (TB) imaging are gaining importance in the evaluation of cochlear implantation (CI°). Our aims were to explore the microarchitecture of human cochlea using micro-computed tomography (μCT), analyze electrode's placement inside cochlea after CI°, and compare pre-/post-implantation μCT scans with cone-beam CT (CBCT) scans of same TBs.

METHODS

Cadaveric TBs were scanned using μCT and CBCT then underwent CI° using straight electrodes. Thereafter, they underwent again μCT and CBCT-imaging.

RESULTS

Ten TBs were studied. μCT allowed visualization of scala tympani, scala vestibuli, basilar membrane, osseous spiral lamina, crista fenestrae, and spiral ligament. CBCT showed same structures except spiral ligament and crista fenestrae. After CI°, μCT and CBCT displayed the scalar location and course of electrode array within the cochlea. There were 7 cases of atraumatic electrode insertion and 3 cases of insertion trauma: basilar membrane elevation, electrode foldover with limited migration into scala vestibuli, and electrode kinking with limited migration into scala vestibuli. Insertion trauma was not correlated with cochlea's size or crista's maximal height but with round window membrane diameter. Resolution of μCT was higher than CBCT but electrode artifacts were similar.

CONCLUSIONS

μCT was accurate in visualizing cochlear structures, and course and scalar position of electrode array inside cochlea with any possible trauma to cochlea or array. CBCT offers a good alternative to μCT in clinical practice for cochlear imaging and evaluation of CI°, with lower radiation and higher resolution than multi-slice CT. Difficulties related to non-traumatic CI° are multifactorial.

Robotics and cochlear implant surgery: goals and developments

PURPOSE OF REVIEW

Cochlear implantation (CI) is a viable option for patients with severe sensorineural hearing loss. Advances in CI have focused on minimizing cochlear trauma to improve hearing preservation outcomes, and in doing so expanding candidacy to patients with useful cochlear reserve. Robotics holds promise as a potential tool to minimize intracochlear trauma with electrode insertion, improve surgical efficiency, and reduce surgical complications. The purpose of this review is to summarize efforts and advances in the field of robotic-assisted CI.

RECENT FINDINGS

Work on robotics and CI over the past few decades has explored distinct surgical aspects, including image-based surgical planning and intraoperative guidance, minimally invasive robotic-assisted approaches mainly through percutaneous keyhole direct cochlear access, robotic electrode insertion systems, robotic manipulators, and drilling feedback control through end effector sensors. Feasibility and safety have been established and many devices are undergoing clinical trials for clinical adoption, with some having already achieved approval of national licensing bodies.

SUMMARY

Significant work has been done over the past two decades that has shown robotic-assisted CI to be feasible and safe. Wider clinical adoption can potentially result in improved hearing preservation and quality of life outcomes to more CI candidates.

Suitable Electrode Choice for Robotic-Assisted Cochlear Implant Surgery: A Systematic Literature Review of Manual Electrode Insertion Adverse Events

Background and Objective

The cochlear implant (CI) electrode insertion process is a key step in CI surgery. One of the aims of advances in robotic-assisted CI surgery (RACIS) is to realize better cochlear structure preservation and to precisely control insertion. The aim of this literature review is to gain insight into electrode selection for RACIS by acquiring a thorough knowledge of electrode insertion and related complications from classic CI surgery involving a manual electrode insertion process.

Methods

A systematic electronic search of the literature was carried out using PubMed, Scopus, Cochrane, and Web of Science to find relevant literature on electrode tip fold over (ETFO), electrode scalar deviation (ESD), and electrode migration (EM) from both pre-shaped and straight electrode types.

Results

A total of 82 studies that include 8,603 ears implanted with a CI, i.e., pre-shaped (4,869) and straight electrodes (3,734), were evaluated. The rate of ETFO (25 studies, 2,335 ears), ESD (39 studies, 3,073 ears), and EM (18 studies, 3,195 ears) was determined. An incidence rate (±95% CI) of 5.38% (4.4-6.6%) of ETFO, 28.6% (26.6-30.6%) of ESD, and 0.53% (0.2-1.1%) of EM is associated with pre-shaped electrodes, whereas with straight electrodes it was 0.51% (0.1-1.3%), 11% (9.2-13.0%), and 3.2% (2.5-3.95%), respectively. The differences between the pre-shaped and straight electrode types are highly significant (p < 0.001). Laboratory experiments show evidence that robotic insertions of electrodes are less traumatic than manual insertions. The influence of round window (RW) vs. cochleostomy (Coch) was not assessed.

Conclusion

Considering the current electrode designs available and the reported incidence of insertion complications, the use of straight electrodes in RACIS and conventional CI surgery (and manual insertion) appears to be less traumatic to intracochlear structures compared with pre-shaped electrodes. However, EM of straight electrodes should be anticipated. RACIS has the potential to reduce these complications.

First Study in Men Evaluating a Surgical Robotic Tool Providing Autonomous Inner Ear Access for Cochlear Implantation

Image-guided and robot-assisted surgeries have found their applications in skullbase surgery. Technological improvements in terms of accuracy also opened new opportunities for robotically-assisted cochlear implantation surgery (RACIS). The HEARO^® robotic system is an otological next-generation surgical robot to assist the surgeon. It first provides software-defined spatial boundaries for orientation and reference information to anatomical structures during otological and neurosurgical procedures. Second, it executes a preplanned drill trajectory through the temporal bone. Here, we report how safe the HEARO procedure can provide an autonomous minimally invasive inner ear access and the efficiency of this access to subsequently insert the electrode array during cochlear implantation. In 22 out of 25 included patients, the surgeon was able to complete the HEARO^® procedure. The dedicated planning software (OTOPLAN^®) allowed the surgeon to reconstruct a three-dimensional representation of all the relevant anatomical structures, designate the target on the cochlea, i.e., the round window, and plan the safest trajectory to reach it. This trajectory accommodated the safety distance to the critical structures while minimizing the insertion angles. A minimal distance of 0.4 and 0.3 mm was planned to facial nerve and chorda tympani, respectively. Intraoperative cone-beam CT supported safe passage for the 22 HEARO^® procedures. The intraoperative accuracy analysis reported the following mean errors: 0.182 mm to target, 0.117 mm to facial nerve, and 0.107 mm to chorda tympani. This study demonstrates that microsurgical robotic technology can be used in different anatomical variations, even including a case of inner ear anomalies, with the geometrically correct keyhole to access to the inner ear. Future perspectives in RACIS may focus on improving intraoperative imaging, automated segmentation and trajectory, robotic insertion with controlled speed, and haptic feedback. This study [Experimental Antwerp robotic research otological surgery (EAR2OS) and Antwerp Robotic cochlear implantation (25 refers to 25 cases) (ARCI25)] was registered at clinicalTrials.gov under identifier NCT03746613 and NCT04102215.

Robotics, automation, active electrode arrays, and new devices for cochlear implantation: A contemporary review

In the last two decades, cochlear implant surgery has evolved into a minimally invasive, hearing preservation surgical technique. The devices used during surgery have benefited from technological advances that have allowed modification and possible improvement of the surgical technique. Robotics has recently gained popularity in otology as an effective tool to overcome the surgeon's limitations such as tremor, drift and accurate force control feedback in laboratory testing. Cochlear implantation benefits from robotic assistance in several steps during the surgical procedure: (i) during the approach to the middle ear by automated mastoidectomy and posterior tympanotomy or through a tunnel from the postauricular skin to the middle ear (i.e. direct cochlear access); (ii) a minimally invasive cochleostomy by a robot-assisted drilling tool; (iii) alignment of the correct insertion axis on the basal cochlear turn; (iv) insertion of the electrode array with a motorized insertion tool. In recent years, the development of bone-attached parallel robots and image-guided surgical robotic systems has allowed the first successful cochlear implantation procedures in patients via a single hole drilled tunnel. Several other robotic systems, new materials, sensing technologies applied to the electrodes, and smart devices have been developed, tested in experimental models and finally some have been used in patients with the aim of reducing trauma in cochleostomy, and permitting slow and more accurate insertion of the electrodes. Despite the promising results in laboratory tests in terms of minimal invasiveness, reduced trauma and better hearing preservation, so far, no clinical benefits on residual hearing preservation or better speech performance have been demonstrated. Before these devices can become the standard approach for cochlear implantation, several points still need to be addressed, primarily cost and duration of the procedure. One can hope that improvement in the cost/benefit ratio will expand the technology to every cochlear implantation procedure. Laboratory research and clinical studies on patients should continue with the aim of making intracochlear implant insertion an atraumatic and reversible gesture for total preservation of the inner ear structure and physiology.

Electrical impedance guides electrode array in cochlear implantation using machine learning and robotic feeder

Cochlear Implant provides an electronic substitute for hearing to severely or profoundly deaf patients. However, postoperative hearing outcomes significantly depend on the proper placement of electrode array (EA) into scala tympani (ST) during cochlear implant surgery. Due to limited intra-operative methods to access array placement, the objective of the current study was to evaluate the relationship between EA complex impedance and different insertion trajectories in a plastic ST model. A prototype system was designed to measure bipolar complex impedance (magnitude and phase) and its resistive and reactive components of electrodes. A 3-DoF actuation system was used as an insertion feeder. 137 insertions were performed from 3 different directions at a speed of 0.08 mm/s. Complex impedance data of 8 electrode pairs were sequentially recorded in each experiment. Machine learning algorithms were employed to classify both the full and partial insertion lengths. Support Vector Machine (SVM) gave the highest 97.1% accuracy for full insertion. When a real-time prediction was tested, Shallow Neural Network (SNN) model performed better than other algorithms using partial insertion data. The highest accuracy was found at 86.1% when 4 time samples and 2 apical electrode pairs were used. Direction prediction using partial data has the potential of online control of the insertion feeder for better EA placement. Accessing the position of the electrode array during the insertion has the potential to optimize its intraoperative placement that will result in improved hearing outcomes.

Robotics for Cochlear Implantation Surgery: Challenges and Opportunities

OBJECTIVES

Recent advancements in robotics have set forth a growing body of evidence for the clinical application of the robotic cochlear implantation (RCI), with many potential benefits. This review aims to summarize these efforts, provide the latest developments in this exciting field, and explore the challenges associated with the clinical implementation of RCI.

DATA SOURCES

MEDLINE, PubMed, and EMBASE databases.

STUDY SELECTION

A search was conducted using the keywords "robotics otolaryngology," "robotic cochlear implant," "minimally-invasive cochlear implantation," "minimally-invasive mastoidectomy," and "percutaneous cochlear implant" with all of their synonyms. Literature selection criteria included articles published in English, and articles from 1970 to present.

RESULTS

The use of robotics in neurotology is a relatively new endeavor that continues to evolve. Robotics is being explored by various groups to facilitate in the various steps of cochlear implant surgery, including drilling a keyhole approach to the middle ear for implants, inner ear access, and electrode insertion into the cochlea. Initial clinical trials have successfully implanted selected subjects using robotics.

CONCLUSIONS

The use of robotics in cochlear implants remains in its very early stages. It is hoped that robotics will improve clinical outcomes. Although successful implants with robots are reported in the literature, there are some challenges that need to be addressed before this approach can become an acceptable option for the conventional cochlear implant surgery, such as safety, time, efficiency, and cost. However, it is hoped that further advancements in robotic technology will help in overcoming these barriers leading to successful implementation for clinical utility.

Atraumatic Insertion of a Cochlear Implant Pre-Curved Electrode Array by a Robot-Automated Alignment with the Coiling Direction of the Scala Tympani

INTRODUCTION

Electrode array translocation is an unpredictable event with all types of arrays, even using a teleoperated robot in a clinical scenario. We aimed to compare the intracochlear trauma produced by the HiFocus™ Mid-Scala (MS) electrode array (Advanced Bionics, Valencia, CA, USA) using a teleoperated robot, with an automated robot connected to a navigation system to align the pre-curved tip of the electrode array with the coiling direction of the scala tympani (ST).

METHODS

Fifteen freshly frozen temporal bones were implanted with the MS array using the RobOtol® (Collin, Bagneux, France). In the first group (n = 10), the robot was teleoperated to insert the electrode array into the basal turn of the ST under stereomicroscopic vision, and then the array was driven by a slow-speed hydraulic insertion technique with an estimated placement of the pre-curved electrode tip. In the second group (n = 5), 3 points were obtained from the preoperative cone-beam computed tomography: the 2 first defining the ST insertion axis of the basal turn and a third one at the center of the ST at 270°. They provided the information to the automated system (RobOtol® connected with a navigation system) to automatically align the electrode array with the ST insertion axis and to aim the pre-curved tip toward the subsequent coiling of the ST. After this, the electrode array was manually advanced. Finally, the cochleae were obtained and fixed in a crystal resin, and the position of each electrode was determined by a micro-grinding technique.

RESULTS

In all cases, the electrode array was fully inserted into the cochlea and the depth of insertion was similar using both techniques. With the teleoperated robotic technique, translocations of the array were observed in 7/10 insertions (70%), but neither trauma nor array translocation occurred with automated robotic insertion.

CONCLUSION

We have successfully tested an automated insertion system (robot + navigation) that could accurately align a pre-curved electrode array to the axis of the basal turn of the ST and its subsequent coiling, which reduced intracochlear insertion trauma and translocation.

In-Vitro Study of Speed and Alignment Angle in Cochlear Implant Electrode Array Insertions

OBJECTIVE

The insertion of the electrode array is a critical step in cochlear implantation. Herein we comprehensively investigate the impact of the alignment angle and feed-forward speed on deep insertions in artificial scala tympani models with accurate macro-anatomy and controlled frictional properties.

METHODS

Motorized insertions (n=1033) were performed in six scala tympani models with varying speeds and alignment angles. We evaluated reaction forces and micrographs of the insertion process and developed a mathematical model to estimate the normal force distribution along the electrode arrays.

RESULTS

Insertions parallel to the cochlear base significantly reduce insertion energies and lead to smoother array movement. Non-constant insertion speeds allow to reduce insertion forces for a fixed total insertion time compared to a constant feed rate.

CONCLUSION

In cochlear implantation, smoothness and peak forces can be reduced with alignment angles parallel to the scala tympani centerline and with non-constant feed-forward speed profiles.

SIGNIFICANCE

Our results may help to provide clinical guidelines and improve surgical tools for manual and automated cochlear implantation.

Robot-based assistance in middle ear surgery and cochlear implantation: first clinical report

PURPOSE

Middle ear surgery may benefit from robot-based assistance to hold micro-instruments or an endoscope. However, the surgical gesture performed by one hand may perturb surgeons accustomed to two-handed surgery. A robot-based holder may combine the benefits from endoscopic exposure and a two-handed technique. Furthermore, tremor suppression and accurate tool control might help the surgeon during critical surgical steps. The goal of this work was to study the safety of an otological robot-based assistant under clinical conditions in a limited series of patients.

METHODS

The RobOtol system has been used as an endoscope or a micro instrument holder for this series. Eleven cases were operated on with the robot as an endoscope holder for chronic otitis. Twenty-one cases were operated on with the robot as a micro-instrument holder for otosclerosis (9 cases), transtympanic tube placement (2 cases), or cochlear implantation (10 cases).

RESULTS

No complications related to the robot manipulation occurred during surgery nor in postoperative. In the chronic otitis group, all perforations were sealed and 3-month postoperative pure-tone average air-bone gap (PTA ABG) was 15 ± 2.6 dB. In the otosclerosis group, 1-month post-op PTA ABG was 10 ± 1 dB. For cochlear implantation cases, a scala tympani insertion, a vestibular scala translocation occurred and a full scala vestibuli insertion was observed in 7, 2 and 1 case, respectively.

CONCLUSION

The RobOtol system has reached the clinical stage. It could be used safely and with accurate control as an endoscope holder or a micro instrument holder in 32 cases.

Comparison of the Surgical Techniques and Robotic Techniques for Cochlear Implantation in Terms of the Trajectories Toward the Inner Ear

OBJECTIVES

The ideal outcome of cochlear implant surgery involves the insertion of the array inside the scala tympani of the cochlea with the least mechanical trauma. Recently, round window insertion and the direction in which the cochlea is approached have gained attention in this respect. The Angles of Cochlear Approach (ACA) can be defined with a plane in the plane of the basal turn, termed the in-plane angle, and the plane orthogonal to this plane, termed the out-plane angle. The aim of this study was to compare the trajectory angles for different surgical techniques of Veria, suprameatal, pericanal, and multiple posterior tympanotomy (PT) approaches, including an optimal trajectory that is simulated for robotic surgery.

MATERIALS AND METHODS

The trajectories of these surgical techniques were simulated on the same high-resolution computed tomography scan. The simulated trajectory angles were analyzed with dedicated software for medical images, defining the ACA and distances to critical otological structures.

RESULTS

The ACA are the smallest for surgical techniques that pass thought the PT. However, performing a surgical PT can include variability in the ACA, ranging from almost 0° to 20.8° in an out-plane angle, depending on how close a surgeon would approach the facial nerve. The Veria, Suprameatal approach (SMA), and peri-canal approaches have larger ACA and minimal distances to the ossicular chain and the ear canal. The maximum distance to the facial nerve and the widest out-plane angle is observe with a pericanal approach. The optimal PT approach refers to the trajectory without collisions and with the best possible ACA that can be planned.

CONCLUSION

Different surgical approaches yield important differences in the ACA. PT allows better ACA with maximum distances to the critical structures. However, the optimal PT trajectory simulated for robotic keyhole surgery is a further improvement on the trajectories through the facial recess.

Cochlear Implantation With a Novel Long Straight Electrode: the Insertion Results Evaluated by Imaging and Histology in Human Temporal Bones

HYPOTHESIS

To evaluate the insertion results of a novel straight array (EVO) by detailed imaging and subsequent histology in human temporal bones (TB).

BACKGROUND

The main focuses of modern cochlear implant surgery are to prevent damage to the intracochlear structures and to preserve residual hearing. This is often achievable with new atraumatic electrode arrays in combination with meticulous surgical techniques.

METHODS

Twenty fresh-frozen TBs were implanted with the EVO. Pre- and postoperative cone beam computed tomography scans were reconstructed and fused for an artifact-free representation of the electrode. The array's vertical position was quantified in relation to the basilar membrane on basis of which trauma was classified (Grades 0-4). The basilar membrane location was modeled from previous histologic data. The TBs underwent subsequent histologic examination.

RESULTS

The EVOs were successfully inserted in all TBs. Atraumatic insertion (Grades 0-1) were accomplished in 14 of 20 TBs (70%). There were three apical translocations, and two basal translocations due to electrode bulging. One TB had multiple translocations. The sensitivity and specificity of imaging for detecting insertion trauma (Grades 2-4) was 87.5% and 97.3.0%, respectively.

CONCLUSION

Comparable insertion results as reported for other arrays were also found for the EVO. Insertion trauma can be mostly avoided with meticulous insertion techniques to prevent bulging and by limiting the insertion depth angle to 360 degrees. The image fusion technique is a reliable tool for evaluating electrode placement and is feasible for trauma grading.

Cochlear Implant Insertion Axis Into the Basal Turn: A Critical Factor in Electrode Array Translocation

HYPOTHESIS

An inappropriate insertion axis leads to intracochlear trauma during cochlear implantation (CI).

BACKGROUND

Few studies assessed the relationship between the insertion axis and the electrode scalar location.

METHODS

Preimplantation cone-beam CT (CBCT) was performed on 12 human temporal bones. In five temporal bones, an optimal insertion axis was planned, due to the impossibility to attain the ST centerline from the posterior tympanotomy, because of facial canal position. In the seven other temporal bones, an inaccurate insertion axis was intentionally planned (optimal axis+15 degrees). Automated CI array insertion according to the planned axis was performed with a motorized insertion tool driven by a navigated robot-based arm. The cochlea and basilar membrane were segmented from the preimplantation CBCT and the array segmented from the postimplantation CBCT to construct a merged final three-dimensional (3D) model. Microscopical and 3D analysis were performed to determine the intracochlear trauma at the level of each electrode.

RESULTS

A good agreement was observed in determining electrode position between microscopic analysis and the 3D model (Cohen's kappa k = 0.67). The angle of approach to the ST centerline was associated with the number of electrodes inserted into the ST (r = -0.65, p = 0.02, [95% CI -0.90 to -0.11] Spearman's rank correlation).

CONCLUSION

A 3D reconstruction model was effective in determining the array position in the cochlea scalae. Our data indicate that the angle of approach to the ST centerline is a critical factor in intracochlear trauma. Additional studies should be conducted to assess the importance of the insertion axis with other array designs.

An Optimized Robot-Based Technique for Cochlear Implantation to Reduce Array Insertion Trauma

OBJECTIVE

To compare the intracochlear trauma induced by optimized robot-based and manual techniques with a straight electrode array prototype inserted at different lengths.

STUDY DESIGN

Experimental study.

SETTING

Robot-based otologic surgery laboratory.

SUBJECTS AND METHODS

A prototype array was inserted at different insertion lengths (21 and 25 mm) in 20 temporal bones. The manual insertion was performed with a microforceps. The optimized approach consisted of an optimal axis insertion provided by a robot-based arm controlled by a tracking system, with a constant speed of insertion (0.25 mm/s) achieved by a motorized insertion tool. The electrode position was determined at the level of each electrode by stereomicroscopic cochlea section analysis.

RESULTS

A higher number of electrodes correctly located in the scala tympani was associated with the optimized approach ( P = .03, 2-way analysis of variance). Regardless of the insertion technique used, the array inserted at 25 mm allowed complete insertion of the active stimulating portion of the array in all cases. Insertion depth was greater when the array was inserted to 25 mm versus 21 mm ( P < .001, 2-way analysis of variance). The optimized insertion was associated with less trauma than that from manual insertion regardless the length of the inserted array ( P = .04, 2-way analysis of variance).

CONCLUSION

Compared with a manual insertion, intracochlear trauma could be reduced with array insertion performed on an optimal axis by using motorized insertion and by applying a constant insertion speed.

Planning nonlinear access paths for temporal bone surgery

PURPOSE

Interventions at the otobasis operate in the narrow region of the temporal bone where several highly sensitive organs define obstacles with minimal clearance for surgical instruments. Nonlinear trajectories for potential minimally invasive interventions can provide larger distances to risk structures and optimized orientations of surgical instruments, thus improving clinical outcomes when compared to existing linear approaches. In this paper, we present fast and accurate planning methods for such nonlinear access paths.

METHODS

We define a specific motion planning problem in [Formula: see text] with notable constraints in computation time and goal pose that reflect the requirements of temporal bone surgery. We then present [Formula: see text]-RRT-Connect: two suitable motion planners based on bidirectional Rapidly exploring Random Tree (RRT) to solve this problem efficiently.

RESULTS

The benefits of [Formula: see text]-RRT-Connect are demonstrated on real CT data of patients. Their general performance is shown on a large set of realistic synthetic anatomies. We also show that these new algorithms outperform state-of-the-art methods based on circular arcs or Bézier-Splines when applied to this specific problem.

CONCLUSION

With this work, we demonstrate that preoperative and intra-operative planning of nonlinear access paths is possible for minimally invasive surgeries at the otobasis.

Influence of electrode array stiffness and diameter on hearing in cochlear implanted guinea pig

During cochlear implantation, electrode array translocation and trauma should be avoided to preserve residual hearing. The aim of our study was to evaluate the effect of physical parameters of the array on residual hearing and cochlear structures during insertion. Three array prototypes with different stiffnesses or external diameters were implanted in normal hearing guinea pigs via a motorized insertion tool carried on a robot-based arm, and insertion forces were recorded. Array prototypes 0.4 and 0.4R had 0.4 mm external diameter and prototype 0.3 had 0.3 mm external diameter. The axial stiffness was set to 1 for the 0.4 prototype and the stiffnesses of the 0.4R and 0.3 prototypes were calculated from this as 6.8 and 0.8 (relative units), respectively. Hearing was assessed preoperatively by the auditory brainstem response (ABR), and then at day 7 and day 30 post-implantation. A study of the macroscopic anatomy was performed on cochleae harvested at day 30 to examine the scala location of the array. At day 7, guinea pigs implanted with the 0.4R array had significantly poorer hearing results than those implanted with the 0.3 array (26±17.7, 44±23.4, 33±20.5 dB, n = 7, vs 5±8.7, 1±11.6, 12±11.5 dB, n = 6, mean±SEM, respectively, at 8, 16 and 24 kHz, p<0.01) or those implanted with the 0.4 array (44±23.4 dB, n = 7, vs 28±21.7 dB, n = 7, at 16 kHz, p<0.05). Hearing remained stable from day 7 to day 30. The maximal peak of insertion force was higher with the 0.4R array than with the 0.3 array (56±23.8 mN, n = 7, vs 26±8.7 mN, n = 6). Observation of the cochleae showed that an incorrectly positioned electrode array or fibrosis were associated with hearing loss ≥40 dB (at 16 kHz). An optimal position in the scala tympani with a flexible and thin array and prevention of fibrosis should be the primary objectives to preserve hearing during cochlear implantation.

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

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.