Accuracy of linear drilling in temporal bone using drill press system for minimally invasive cochlear implantation

Purpose

A minimally invasive approach for cochlear implantation involves drilling a narrow linear path through the temporal bone from the skull surface directly to the cochlea for insertion of the electrode array without the need for an invasive mastoidectomy. Potential drill positioning errors must be accounted for to predict the effectiveness and safety of the procedure. The drilling accuracy of a system used for this procedure was evaluated in bone surrogate material under a range of clinically relevant parameters. Additional experiments were performed to isolate the error at various points along the path to better understand why deflections occur.

Methods

An experimental setup to precisely position the drill press over a target was used. Custom bone surrogate test blocks were manufactured to resemble the mastoid region of the temporal bone. The drilling error was measured by creating divots in plastic sheets before and after drilling and using a microscope to localize the divots.

Results

The drilling error was within the tolerance needed to avoid vital structures and ensure accurate placement of the electrode; however, some parameter sets yielded errors that may impact the effectiveness of the procedure when combined with other error sources. The error increases when the lateral stage of the path terminates in an air cell and when the guide bushings are positioned further from the skull surface. At contact points due to air cells along the trajectory, higher errors were found for impact angles of \(45^{\circ }\) and higher as well as longer cantilevered drill lengths.

Conclusion

The results of these experiments can be used to define more accurate and safe drill trajectories for this minimally invasive surgical procedure.

     

Configuration optimization and experimental accuracy evaluation of a bone-attached,parallel robot for skull surgery

Purpose

Minimally invasive cochlear implantation is a novel surgical technique which requires highly accurate guidance of a drilling tool along a trajectory from the mastoid surface toward the basal turn of the cochlea. The authors propose a passive, reconfigurable, parallel robot which can be directly attached to bone anchors implanted in a patient’s skull, avoiding the need for surgical tracking systems. Prior to clinical trials, methods are necessary to patient specifically optimize the configuration of the mechanism with respect to accuracy and stability. Furthermore, the achievable accuracy has to be determined experimentally.

Methods

A comprehensive error model of the proposed mechanism is established, taking into account all relevant error sources identified in previous studies. Two optimization criteria to exploit the given task redundancy and reconfigurability of the passive robot are derived from the model. The achievable accuracy of the optimized robot configurations is first estimated with the help of a Monte Carlo simulation approach and finally evaluated in drilling experiments using synthetic temporal bone specimen.

Results

Experimental results demonstrate that the bone-attached mechanism exhibits a mean targeting accuracy of \((0.36\pm 0.12)\) mm under realistic conditions. A systematic targeting error is observed, which indicates that accurate identification of the passive robot’s kinematic parameters could further reduce deviations from planned drill trajectories.

Conclusion

The accuracy of the proposed mechanism demonstrates its suitability for minimally invasive cochlear implantation. Future work will focus on further evaluation experiments on temporal bone specimen.

     

Workflow and simulation of image-to-physical registration of holes inside spongy bone

Purpose

Mastoid cells as well as trabecula provide unique bone structures, which can serve as natural landmarks for registration. Preoperative imaging enables sufficient acquisition of these structures, but registration requires an intraoperative counterpart. Since versatile surgical interventions involve drilling into mastoid cells and trabecula, we propose a registration method based on endoscopy inside of these drill holes.

Methods

Recording of the surface of the inner drill hole yields bone-air patterns that provide intraoperative registration features. In this contribution, we discuss an approach that unrolls the drill hole surface into a two-dimensional image. Intraoperative endoscopic recordings are compared to simulated endoscopic views, which originate from preoperative data like computed tomography. Each simulated view corresponds to a different drill pose. The whole registration procedure and workflow is demonstrated, using high-resolution image data to simulate both preoperative and endoscopic image data.

Results

As the driving application is minimally invasive cochlear implantation, in which targets are close to the axis of the drill hole, Target Registration Error (TRE) was measured at points near the axis. TRE at increasing depths along the drill trajectory reveals increasing registration accuracy as more bone-air patterns become available as landmarks with the highest accuracy obtained at the center point. At the facial recess and the cochlea, TREs are (\(0.363\pm 0.169\)) mm and (\(0.553\pm 0.262\)) mm, respectively.

Conclusion

This contribution demonstrates a new method for registration via endoscopic acquisition of small features like trabecula or mastoid cells for image-guided procedures. It has the potential to revolutionize bone registration because it requires only a preoperative dataset and intraoperative endoscopic exploration. Endoscopic recordings of at least 20 mm length and isotropic voxel sizes of 0.2 mm or smaller of the preoperative image data are recommended.

     

Validation of minimally invasive, image-guided cochlear implantation using Advanced Bionics, Cochlear, and Medel electrodes in a cadaver model

Purpose

Validation of a novel minimally invasive, image-guided approach to implant electrodes from three FDA-approved manufacturers—Medel, Cochlear, and Advanced Bionics—in the cochlea via a linear tunnel from the lateral cranium through the facial recess to the cochlea.

Methods

Custom microstereotactic frames that mount on bone-implanted fiducial markers and constrain the drill along the desired path were utilized on seven cadaver specimens. A linear tunnel was drilled from the lateral skull to the cochlea followed by a marginal, round window cochleostomy and insertion of the electrode array into the cochlea through the drilled tunnel. Post-insertion CT scan and histological analysis were used to analyze the results.

Results

All specimens ( $N=7$ ) were successfully implanted without visible injury to the facial nerve. The Medel electrodes ( $N=3$ ) had minimal intracochlear trauma with 8, 8, and 10 (out of 12) electrodes intracochlear. The Cochlear lateral wall electrodes (straight research arrays) ( $N=2$ ) had minimal trauma with 20 and 21 of 22 electrodes intracochlear. The Advanced Bionics electrodes ( $N=2$ ) were inserted using their insertion tool; one had minimal insertion trauma and 14 of 16 electrodes intracochlear, while the other had violation of the basilar membrane just deep to the cochleostomy following which it remained in scala vestibuli with 13 of 16 electrodes intracochlear.

Conclusions

Minimally invasive, image-guided cochlear implantation is possible using electrodes from the three FDA-approved manufacturers. Lateral wall electrodes were associated with less intracochlear trauma suggesting that they may be better suited for this surgical technique.     

Surgical planning tool for robotically assisted hearing aid implantation

Purpose

For the facilitation of minimally invasive robotically performed direct cochlea access (DCA) procedure, a surgical planning tool which enables the surgeon to define landmarks for patient-to-image registration, identify the necessary anatomical structures and define a safe DCA trajectory using patient image data (typically computed tomography (CT) or cone beam CT) is required. To this end, a dedicated end-to-end software planning system for the planning of DCA procedures that addresses current deficiencies has been developed.

Methods

   Efficient and robust anatomical segmentation is achieved through the implementation of semiautomatic algorithms; high-accuracy patient-to-image registration is achieved via an automated model-based fiducial detection algorithm and functionality for the interactive definition of a safe drilling trajectory based on case-specific drill positioning uncertainty calculations was developed.

Results

   The accuracy and safety of the presented software tool were validated during the conduction of eight DCA procedures performed on cadaver heads. The plan for each ear was completed in less than 20 min, and no damage to vital structures occurred during the procedures. The integrated fiducial detection functionality enabled final positioning accuracies of $0.15\pm 0.08$  mm.

Conclusions

   Results of this study demonstrated that the proposed software system could aid in the safe planning of a DCA tunnel within an acceptable time.     

Electromagnetic tracking system with reduced distortion using quadratic excitation

Purpose

Electromagnetic tracking systems, frequently used in minimally invasive surgery, are affected by conductive distorters. The influence of conductive distorters on electromagnetic tracking system accuracy can be reduced through magnetic field modifications. This approach was developed and tested.

Methods

The voltage induced directly by the emitting coil in the sensing coil without additional influence by the conductive distorter depends on the first derivative of the voltage on the emitting coil. The voltage which is induced indirectly by the emitting coil across the conductive distorter in the sensing coil, however, depends on the second derivative of the voltage on the emitting coil. The electromagnetic tracking system takes advantage of this difference by supplying the emitting coil with a quadratic excitation voltage. The method is adaptive relative to the amount of distortion cause by the conductive distorters. This approach is evaluated with an experimental setup of the electromagnetic tracking system.

Results

In vitro testing showed that the maximal error decreased from 10.9 to 3.8 mm when the quadratic voltage was used to excite the emitting coil instead of the sinusoidal voltage. Furthermore, the root mean square error in the proximity of the aluminum disk used as a conductive distorter was reduced from 3.5 to 1.6 mm when the electromagnetic tracking system used the quadratic instead of sinusoidal excitation.

Conclusions

Electromagnetic tracking with quadratic excitation is immune to the effects of a conductive distorter, especially compared with sinusoidal excitation of the emitting coil. Quadratic excitation of electromagnetic tracking for computer-assisted surgery is promising for clinical applications.     

An automated insertion tool for cochlear implants with integrated force sensing capability

Purpose

Minimally invasive cochlear implantation and residual hearing preservation require both the surgical approach to the cochlea as well as the implant insertion to be performed in an atraumatic fashion. Considering the geometric limitations of this approach, specialized instrumentation is required to insert the electrode while preserving intracochlear membranes carrying the sensory hair cells.

Methods

An automated insertion tool for cochlear implants, which is capable of sensing insertion forces with a theoretical resolution of $30\,\upmu \mathrm{N}$ , is presented. In contrast to previous designs, the custom force sensor is integrated in the insertion mechanism. Moreover, a test bench for insertion studies under constant and reproducible boundary conditions is proposed. It is used to experimentally validate the force sensing insertion tool, which is achieved by comparing the acquired forces to a ground truth measurement. The results of insertion studies on both an acrylic cochlear phantom and temporal bone specimen are given and discussed.

Results

Results reveal that friction, occurring between the electrode carrier and the inside of the insertion tool guide tube, is likely to affect the force output of the proposed sensor. An appropriate method to compensate for these disturbances is presented and experimentally validated. Using the proposed approach to friction identification, a mean accuracy of $(4.0\pm 3.2)\, \hbox {mN}$ is observed.

Conclusions

The force information provided by the proposed, automated insertion tool can be used to detect complications during electrode insertion. However, in order to obtain accurate results, an identification of frictional forces prior to insertion is mandatory. The insertion tool is capable of automatically executing the appropriate trajectories.     

Cortical bone drilling and thermal osteonecrosis

Background

Bone drilling is a common step in operative fracture treatment and reconstructive surgery. During drilling elevated bone temperature is generated. Temperatures above 47 °C cause thermal osteonecrosis which contributes to screw loosening and subsequently implant failures and refractures.

Methods

The current literature on bone drilling and thermal osteonecrosis is reviewed. The methodologies involved in the experimental and clinical studies are described and compared.

Findings

Areas which require further investigation are highlighted and the potential use of more precise experimental setup and future technologies are addressed.

Interpretation

Important drill and drilling parameters that could cause increase in bone temperature and hence thermal osteonecrosis are reviewed and discussed: drilling speed, drill feed rate, cooling, drill diameter, drill point angle, drill material and wearing, drilling depth, pre-drilling, drill geometry and bone cortical thickness. Experimental methods of temperature measurement during bone drilling are defined and thermal osteonecrosis is discussed with its pathophysiology, significance in bone surgery and methods for its minimization.     

Neurosurgical craniotomy localization using a virtual reality planning system versus intraoperative image�Cguided navigation

Purpose

Accurate craniotomy placement is essential for frameless neuronavigation in minimally invasive neurosurgery. A craniotomy using virtual reality (VR) can be as accurate as neuronavigation.

Methods

We prospectively enrolled 48 patients that underwent minimally invasive cranial procedures planned using VR, followed by neuronavigation. First, craniotomies were planned using VR derived measurements. Second, frameless neuronavigation was applied to define the craniotomy. The locations of these paired craniotomies were compared. A correctly placed craniotomy was defined as one that enabled the surgeon to totally remove the pathology without need to enlarge the craniotomy intraoperatively.

Results

Using VR, the size and the position of the craniotomy were measured correctly in 47 of 48 cases (98%). In 44 of 48 cases (92%), neuronavigation identified the craniotomy site correctly. In cases where neuronavigation failed, minimally invasive surgery was successfully completed using preoperative VR surgery planning. No statistically significant difference was found between craniotomy localization using VR surgery planning or standard frameless neuronavigation (p?=?0.36).

Conclusion

The craniotomy for minimally invasive neurosurgical procedures can be identified accurately using VR surgery planning or neuronavigation. In cases of neuronavigation failure, VR surgery planning serves as an effective backup system to perform a minimally invasive operation.     

Image-based electrode array tracking for epicardial electrophysiological mapping in minimally invasive arrhythmia surgery

Purpose

Electrophysiological mapping is effective in realizing a precise minimally invasive arrhythmia surgery. Recently, an epicardial electrophysiological mapping system for minimally invasive arrhythmia surgery was reported. The system requires a small electrode array, a tracking system and a global mapping algorithm. The optical tracking system employed in the research requires line of sight and complicated configuration. This paper proposes a new tracking method for locating an electrode array.

Methods

We developed a small electrode array and optical markers. Center points of respective optical markers and the electrode array are tracked via an endoscopic stream and calculated in image space. The orientation of the electrode array is calculated using the dot product between the vector joining two center points of two upper optical markers and the vector joining two end points of the longest edge of the electrode array.

Results

Mean tracking errors of position and orientation of the electrode array were 0.51?mm and 0.64??, respectively. And the processing time was constant at 46?ms per frame. Our method could successfully track the electrode array on the epicardium during in vivo experiment and a global epicardial electrophysiological map was reconstructed from separately measured epicardial electrograms by the small electrode array.

Conclusions

An image-based tracking method for locating an electrode array was proposed. Tracking accuracy, processing time and applicability to surgical environment of our method proved to be acceptable. Consequently, our method enables the electrode array tracking system to be simplified with no separate tracking system.     

High-accuracy drilling with an image guided light weight robot: autonomous versus intuitive feed control

Purpose

Assistance of robotic systems in the operating room promises higher accuracy and, hence, demanding surgical interventions become realisable (e.g. the direct cochlear access). Additionally, an intuitive user interface is crucial for the use of robots in surgery. Torque sensors in the joints can be employed for intuitive interaction concepts. Regarding the accuracy, they lead to a lower structural stiffness and, thus, to an additional error source. The aim of this contribution is to examine, if an accuracy needed for demanding interventions can be achieved by such a system or not.

Methods

Feasible accuracy results of the robot-assisted process depend on each work-flow step. This work focuses on the determination of the tool coordinate frame. A method for drill axis definition is implemented and analysed. Furthermore, a concept of admittance feed control is developed. This allows the user to control feeding along the planned path by applying a force to the robots structure. The accuracy is researched by drilling experiments with a PMMA phantom and artificial bone blocks.

Results

The described drill axis estimation process results in a high angular repeatability (\(0.026^\circ \,\pm \,16^\circ \)). In the first set of drilling results, an accuracy of \((50\,\pm \,20\,\upmu {\mathrm {m}})\) at entrance and \((170\,\pm \,50\,\upmu {\mathrm {m}})\) at target point excluding imaging was achieved. With admittance feed control an accuracy of \((250\,\pm \,90\,\upmu {\mathrm {m}})\) at target point was realised. In a third set twelve holes were drilled in artificial temporal bone phantoms including imaging. In this set-up an error of \((20\,\pm \,15\,\upmu {\mathrm {m}})\) and \((165\,\pm \,80\,\upmu {\mathrm {m}})\) was achieved.

Conclusion

The results of conducted experiments show that accuracy requirements for demanding procedures such as the direct cochlear access can be fulfilled with compliant systems. Furthermore, it was shown that with the presented admittance feed control an accuracy of less then \(1\,\mathrm {mm}\) is achievable.

     

A multimedia electronic patient record (ePR) system for image-assisted minimally invasive spinal surgery

Purpose

This paper presents the concept of bridging the gap between diagnostic images and image-assisted surgical treatment through the development of a one-stop multimedia electronic patient record (ePR) system that manages and distributes the real-time multimodality imaging and informatics data that assists the surgeon during all clinical phases of the operation from planning Intra-Op to post-care follow-up. We present the concept of this multimedia ePR for surgery by first focusing on image-assisted minimally invasive spinal surgery as a clinical application.

Methods

Three clinical phases of minimally invasive spinal surgery workflow in Pre-Op, Intra-Op, and Post-Op are discussed. The ePR architecture was developed based on the three-phased workflow, which includes the Pre-Op, Intra-Op, and Post-Op modules and four components comprising of the input integration unit, fault-tolerant gateway server, fault-tolerant ePR server, and the visualization and display. A prototype was built and deployed to a minimally invasive spinal surgery clinical site with user training and support for daily use.

Summary

A step-by-step approach was introduced to develop a multimedia ePR system for imaging-assisted minimally invasive spinal surgery that includes images, clinical forms, waveforms, and textual data for planning the surgery, two real-time imaging techniques (digital fluoroscopic, DF) and endoscope video images (Endo), and more than half a dozen live vital signs of the patient during surgery. Clinical implementation experiences and challenges were also discussed.     

Warning navigation system using real-time safe region monitoring for otologic surgery

Purpose We developed a surgical navigation system that warns the surgeon with auditory and visual feedback to protect the facial nerve with real-time monitoring of the safe region during drilling. Methods Warning navigation modules were developed and integrated into a free open source software platform. To obtain high registration accuracy, we used a high-precision laser-sintered template of the patient’s bone surface to register the computed tomography (CT) images. We calculated the closest distance between the drill tip and the surface of the facial nerve during drilling. When the drill tip entered the safe regions, the navigation system provided an auditory and visual signal which differed in each safe region. To evaluate the effectiveness of the system, we performed phantom experiments for maintaining a given safe margin from the facial nerve when drilling bone models, with and without the navigation system. The error of the safe margin was measured on postoperative CT images. In real surgery, we evaluated the feasibility of the system in comparison with conventional facial nerve monitoring. Results The navigation accuracy was submillimeter for the target registration error. In the phantom study, the task with navigation ( $0.7 \pm 0.25$ mm) was more successful with smaller error, than the task without navigation ( $1.37 \pm 0.39$ mm, $P<0.05$ ). The clinical feasibility of the system was confirmed in three real surgeries. Conclusions This system could assist surgeons in preserving the facial nerve and potentially contribute to enhanced patient safety in the surgery.     

Arthroskopisch gestütztes Frakturmanagement des oberen und unteren Sprunggelenks

Introduction

Fracture management of the ankle and calcaneus is a domain of open joint surgery; however, in certain cases there are strong arguments for a differentiated approach with arthroscopic control of surgery.

Methoden

The benefits of a minimally invasive procedure are reduced surgical soft tissue damage, detection and treatment of additional joint damage and direct visualization of fracture reduction. Surgical options are limited by severe soft tissue damage accompanying fractures.

Conclusion

Complex fractures with deep impressions of the joint surfaces and multiple fracture lines on the articular side will continue to be treated by conventional open surgery. The additional use of open arthroscopy allows a direct alignment control in such situations.     

A fluorolaser navigation system to guide linear surgical tool insertion

Purpose

Conventional navigation systems for minimally invasive orthopedic surgery require a secondary monitor to display guidance information generated with CT or MRI images. Newer systems use augmented reality to project surgical plans into binocular glasses. These surgical procedures are often mentally challenging and cumbersome to perform.

Method

A comprehensive surgical navigation system for direct guidance while minimizing radiation exposure was designed and built. System accuracy was evaluated using in vitro needle insertion experiments. The fluoroscopic-based navigation technique is combined with an existing laser guidance technique. As a result, the combined system is capable of surgical planning using two or more X-ray images rather than CT or MRI scans. Guidance information is directly projected onto the patient using two laser beams and not via a secondary monitor.

Results

We performed 15 in vitro needle insertion experiments as well as 6 phantom pedicle screw insertion experiments to validate navigation system accuracy. The planning accuracy of the system was found to be 2.32?mm and 2.28°, while its overall guidance accuracy was found to be 2.40?mm and 2.39°. System feasibility was demonstrated by successfully performing percutaneous pin insertion on phantoms.

Conclusion

Quantitative and qualitative evaluations of the fluorolaser navigation system show that it can support accurate guidance and intuitive surgical tool insertion procedures without preoperative 3D image volumes and registration processes.     

Arthroskopie bei proximaler Humerusfraktur

Introduction

Arthroscopy has become an established treatment option for proximal humeral fractures.

Methods

Isolated and combined fractures of the greater and lesser tuberosity can be refixed using various arthroscopic techniques. Furthermore two and three part fractures of the proximal humerus can be treated by all-arthroscopic intramedullary nailing. In addition to the advantages of minimally invasive surgery, fracture and implant positioning can be optimized and controlled arthroscopically and relevant intra-articular concomitant pathologies can also be diagnosed and treated. Moreover, arthroscopy has proven to be beneficial as a revision tool for unsatisfactory courses of proximal humeral fracture treatment.

Conclusion

This review presents innovative arthroscopic treatment modalities for proximal humeral fractures. Surgical techniques are described, potential advantages compared to open procedures are outlined and first clinical results are demonstrated.     

Validation of four prognostic scores in patients with cancer admitted to Brazilian intensive care units: results from a prospective multicenter study

Objective

The aim of the present study was to validate the Simplified Acute Physiology Score II (SAPS II) and 3 (SAPS 3), the Mortality Probability Models III (MPM₀-III), and the Cancer Mortality Model (CMM) in patients with cancer admitted to several intensive care units (ICU).

Design

Prospective multicenter cohort study.

Setting

Twenty-eight ICUs in Brazil.

Patients

Seven hundred and seventeen consecutive patients (solid tumors 93%; hematological malignancies 7%) included over a 2-month period.

Interventions

None.

Measurements and main results

Discrimination was assessed by area under receiver operating characteristic (AROC) curves and calibration by Hosmer–Lemeshow goodness-of-fit test. The main reasons for ICU admission were postoperative care (57%), sepsis (15%) and respiratory failure (10%). The ICU and hospital mortality rates were 21 and 30%, respectively. When all 717 patients were evaluated, discrimination was superior for both SAPS II (AROC = 0.84) and SAPS 3 (AROC = 0.84) scores compared to CMM (AROC = 0.79) and MPM₀-III (AROC = 0.71) scores (P < 0.05 in all comparisons). Calibration was better using CMM and the customized equation of SAPS 3 score for South American countries (CSA). MPM₀-III, SAPS II and standard SAPS 3 scores underestimated mortality (standardized mortality ratio, SMR > 1), while CMM tended to overestimation (SMR = 0.48). However, using the SAPS 3 for CSA resulted in more precise estimations of the probability of death [SMR = 1.02 (95% confidence interval = 0.87–1.19)]. Similar results were observed when scheduled surgical patients were excluded.

Conclusions

In this multicenter study, the customized equation of SAPS 3 score for CSA was found to be accurate in predicting outcomes in cancer patients requiring ICU admission.     

E-Health and telemedicine

Purpose

To compare the accuracy of a navigation system for oral implantology using either a head-mounted display (HMD) or a monitor as a device for visualization.

Methods

Drilling experiments in plastic mandibles were performed by seven investigators supported by a navigation system using an HMD. A set of drilling experiments was carried out using a traditional monitor setup as standard of reference. Prior to the experiments, CT scans of the mandibles were performed. Positions of the boreholes were determined with the planning software Mimics $^{\circledR }$ . In order to find the correct positions of the boreholes, individuals had to match two pairs of crosshairs. By an infrared tracking device, the navigation system was able to spot the artificial jaw and the angular piece of the drill allowing for the navigation. After the experiments, a second CT scan was acquired: (i) to identify the beginning and the end of the boreholes, (ii) to compare the positions of the planned implant and the boreholes and (iii) to calculate the deviations.

Results

Overall deviation of the starting point of the borehole was $1.24 \pm 0.84\,\mathrm{mm}$ for the HMD and $1.12 \pm 0.68\,\mathrm{mm}$ for the monitor, $2.68 \pm 1.65\,\mathrm{mm}$ of the end point of the borehole for the HMD and $2.46 \pm 1.34\,\mathrm{mm}$ for the monitor. The mean deviation of the axis was $4.68^{\circ }\pm 3.7^{\circ }$ for the HMD and $4.53^{\circ }\pm 4.17^{\circ }$ for the monitor.

Conclusions

As overall accuracies do not differ significantly, the two methods seem to be equal. Personal skills seem to be crucial as the results show remarkable differences among the test persons. The results of our study demonstrate that the use of an HMD has no major drawbacks compared to the monitor setting. The striking advantage is that the surgeon is no longer obliged to turn his head away from the operation site during navigation, as all data relevant for the procedure are superimposed on the image of the real world in his field of view.     

Investigating the performance of a wrist stabilization device for image-guided percutaneous scaphoid fixation

Purpose   

Conventional navigated surgery relies on placement of a reference marker on the anatomy of interest. However, placement of such a marker is not readily feasible in small anatomic regions such as the scaphoid bone of the wrist. This study aimed to develop an alternative mechanism for patient tracking that could be used to perform navigated percutaneous scaphoid fixation.

Methods   

A prototype wrist stabilization device was developed to immobilize the scaphoid relative to a reference marker attached to the device. A position measurement system and 3D fluoroscopy were used to study the accuracy and limitations of wrist stabilization during simulated clinical usage with a cadaver specimen. Reference markers mounted on the device were used to measure intra-device motion. Radiometallic beads implanted in the scaphoid were used to measure patient-device motion. Navigated planning and guidance of scaphoid fixation were performed in five cadaver and eight “ideally immobilized” plastic specimens. Postoperative 3D fluoroscopy was used to assess the accuracy of navigated drilling.

Results   

The average intra-device motion was 1.9 mm during load application, which was elastically recovered upon release of the load. Scaphoid motion relative to the reference marker was predominately rotational with an average displacement of 1.25 mm and $2.0^{\circ }$ . There was no significant difference in the accuracy of navigated drilling between the cadaver specimens and the ideally immobilized group.

Conclusions   

The prototype wrist stabilization device meets the criteria for effective wrist stabilization. This study provides insight concerning proper use of the device to minimize scaphoid displacement and design recommendations to improve immobilization.     

A predictive bone drilling force model for haptic rendering with experimental validation using fresh cadaveric bone

Purpose

Bone drilling simulators with virtual and haptic feedback provide a safe, cost-effective and repeatable alternative to traditional surgical training methods. To develop such a simulator, accurate haptic rendering based on a force model is required to feedback bone drilling forces based on user input. Current predictive bone drilling force models based on bovine bones with various drilling conditions and parameters are not representative of the bone drilling process in bone surgery. The objective of this study was to provide a bone drilling force model for haptic rendering based on calibration and validation experiments in fresh cadaveric bones with different bone densities.

Methods

Using a commonly used drill bit geometry (2 mm diameter), feed rates (20–60 mm/min) and spindle speeds (4000–6000 rpm) in orthognathic surgeries, the bone drilling forces of specimens from two groups were measured and the calibration coefficients of the specific normal and frictional pressures were determined.

Results

The comparison of the predicted forces and the measured forces from validation experiments with a large range of feed rates and spindle speeds demonstrates that the proposed bone drilling forces can predict the trends and average forces well.

Conclusion

The presented bone drilling force model can be used for haptic rendering in surgical simulators.