[Improvement of registration accuracy for navigated-control drill in mastoidectomy (autopilot)]. / Der Einfluss von unterschiedlichen Registrierverfahren auf die Genauigkeit der navigiert-kontrollierten Fräse (Safety Assistance-Funktion) für die Mastoidektomie.

BACKGROUND: The goal of this study is the improvement of the surgical accuracy of a navigate-controlled drill for mastoidectomy in a lab test. METHODS: For lab tests an artificial model of the temporal bone with color-coded injury identification of the facial nerve (solution of 0.5 mm) was used. Two different registration methods were examined: (group 1) navigation bow with 4 integrated markers at the upper jaw; (group 2) landmark registration with 4 titanium micro screws. An optical navigation system was used. The targets were illustrated by 3 titanium screws within the range of the planum mastoideum. The accuracy of the navigate-controlled drill in drilling the planned cavity were evaluated at 20 temporal bone models. The measurement of the registration accuracy was evaluated by deviation between the target screw and the calculated position in the navigation system. The evaluation of the resulted cavities was done by 5 senior surgeons with the help of the microscope. RESULTS: The registration accuracy shows a maximum deviation between the real position and the calculated position of 1,73 MM in group of 1 and 0.93 MM in group 2. In group 1 the nerve was hurt in 5/20 cases and a maximum deviation of - 1.5 mm (Std 0.25 mm) (drilled beyond the nerve) was measured. In group 2 the nerve was not hurt, a maximum deviation of 0.5 mm (too early stopped before the nerve) was measured. CONCLUSIONS: Significantly better results of the registration and drilling accuracy show up in group group 2. Thus the preconditions for clinical use are fulfilled.

Surgery on the lateral skull base with the navigated controlled drill employed for a mastoidectomy (pre clinical evaluation).

Patients who are treated with a mastoidectomy usually suffer from an inflammation of the petrosal bone. The intervention is a time consuming landmark based surgery and usually performed with a powered drill. Delicate risk structures must be respected. Navigated Control (NC) describes the control for a power driven instrument which is controlled by a surgeon and additionally controlled according to the position of the instrument relatively to a deliberated position known from a preoperatively segmented work space which excludes risk structures. The force of a drill can be regulated by the principle of NC. Following results were received: 1. Risk structure segmentation is feasible 2. The drill and a phantom can be registered. 3. With NC the resection is faster, more accurate and with no risk structures damage. 4. The phantom is suitable.

[Clinical efficiency and the influence of human factors on ear, nose, and throat navigation systems]. / Ist der Vorteil eines Navigationssystems in der HNO-Chirurgie messbar? Ein Konzept zur Evaluation ergonomischer und chirurgischer Erfolgsparameter.

BACKGROUND: The aim of this study was to evaluate the Navibase navigation system for ear, nose, and throat (ENT) surgery. A new methodology for evaluating surgical and human factors is developed. PATIENTS AND METHODS: The evaluation is based on 102 ENT surgical applications, including 89 cases of functional endoscopic sinus surgery (FESS). The evaluation of surgical and human factors was performed by seven ENT surgeons. To evaluate surgical performance, level of quality (LOQ) in the 89 cases of FESS was determined, comparing the surgeon's own impressions with those of the navigation system on a scale from 0 to 100 and further comparing them with clinical results. Intraoperative changes in surgical strategy were documented. The human factors of total confidence (trust), situation awareness, skill set requirement and workload shift were recorded as level of reliance (LOR). RESULTS: The maximum deviation amounted to 1.93 mm. Averaging the quality of information resulted in an LOQ of 63.59. Every second application of the navigation system (47.9%) led to a change in surgical strategy. Total confidence showed a positive evaluation of 3.35 points in LOR. CONCLUSION: Application-relevant information relevant to the application beyond only technical details permits comparison with other assisting systems.

[Improved accuracy and precision of the automated shaver (navigated control) in functional endoscopic sinus surgery]. / Verbesserte Umsetzung der Resektionsgrenzen in der Nasennebenhöhlenchirurgie mit dem navigiert-kontrollierten Shaver.

BACKGROUND: The feasibility of a navigate-controlled Shaver for the paranasal sinus surgery was proven in an initial study. Deficits showed up in the conversion of the planed cavity. Goal of this study is (1) the development and evaluation of a FESS demonstrator for the investigations to the surgical accuracy and (2) the evaluation of the resulting surgical accuracy for registration and conversion of the work space with an improved rigidity of the Shaver and a completely revised study design. METHODS: As a demonstrator for the navigate-controlled resection of a volume through the Shaver a two-piece plastic head with an anatomical head and soft tissue model was designed. The investigation of the surgical accuracy takes place with 417 measurements to 4 different fiducial markers on the demonstrator head. The measurements for the deviation of the resulting cavity from the planned volume was realised with a work space by 24 x 24 x 30 mm. The 5 walls of the cavity were seized with 80 measuring points for each level and thus altogether 2000 measured values (5 models x 5 levels x 200 points). RESULTS: The described demonstrator showed itself suitable for the close-to-application attempts to the surgical accuracy. The maximum deviation A (max) indicated position of the Shaver from the reference value amounted to 1,93 mm. The maximum average value of the exceeding of a planned cavity amounts to 1,62 mm. CONCLUSIONS: Based on these results a virtual safety passage of 2.00 mm is sufficient. The study refers the clinical serviceability of the navigate-controlled Shaver in paranasal sinus surgery.

Establishing navigated control in head surgery.

Navigated Control (NC) describes an additional control for a tracked power driven instrument within a preoperatively segmented work space. In head surgery the authors first implemented NC in functional endoscopic sinus surgery (FESS). Recently the feasibility of NC for surgery on the petrosal bone is evaluated. NC in FESS and in petrosal bone surgery may reduce the risk of comorbidity and the time effort compared to the conventional surgical interventions.

[Accuracy and precision in the evaluation of computer assisted surgical systems. A definition]. / Genauigkeit und Präzision in der Bewertung von chirurgischen Navigations- und Assistenzsystemen. Eine Begriffsbestimmung.

Accuracy represents the outstanding criterion for navigation systems. Surgeons have noticed a great discrepancy between the values from the literature and system specifications on one hand, and intraoperative accuracy on the other. A unitary understanding for the term accuracy does not exist in clinical practice. Furthermore, an incorrect equality for the terms precision and accuracy can be found in the literature. On top of this, clinical accuracy differs from mechanical (technical) accuracy. From a clinical point of view, we had to deal with remarkably many different terms all describing accuracy. This study has the goals of: 1. Defining "accuracy" and related terms, 2. Differentiating between "precision" and "accuracy", 3. Deriving the term "surgical accuracy", 4. Recommending use of the the term "surgical accuracy" for a navigation system. To a great extent, definitions were applied from the International Standardisation Organisation-ISO and the norm from the Deutsches Institut für Normung e.V.-DIN (the German Institute for Standardization). For defining surgical accuracy, the terms reference value, expectation, accuracy and precision are of major interest. Surgical accuracy should indicate the maximum values for the deviation between test results and the reference value (true value) A(max), and additionally indicate precision P(surg). As a basis for measurements, a standardized technical model was used. Coordinates of the model were acquired by CT. To determine statistically and reality relevant results for head surgery, 50 measurements with an accuracy of 50, 75, 100 and 150 mm from the centre of the registration geometry are adequate. In the future, we recommend labeling the system's overall performance with the following specifications: maximum accuracy deviation A(max), precision P and information on the measurement method. This could be displayed on a seal of quality.

[Navigated control: a new concept in computer assisted ENT-surgery]. / Navigated Control: Ein neues Konzept für die Computer-Assistierte-HNO-Chirurgie.

This work conceived and evaluates a mechatronical system for ORL-surgery by example of a Shaver for Functional Endoscopic Sinus Surgery controlled by navigation. The Shaver is automatically on/off-regulated depending on the current position in relation to the planned working space. This working space is defined on the basis of the individual CT data. Within this area the Shaver reacts to the signal of the surgeon (foot pedal). If the Shaver leaves the working space, an interruption of the drive regulation to the Shaver takes place. The evaluation of the planning software based on 32 patient CT-data sets. The registration accuracy in a anatomical model was examined on 451 measurements of endonasal attached titanium screws. The conversions of the working space were evaluated at 5 different technical models. The average time for segmenting the working space was found at 4.23 minutes per case. An average registration accuracy of the Shaver of 1.08 mm resulted. The pre-defined cavity was to be cleared away without restrictions. The preoperative determined work-space was converted by 3.1 mm over all levels. The study proves the feasibility of a mechatronical assistant system by the example of the navigate-controlled Shaver in paranasal sinus surgery. Contrary to conventional CAS solutions redundancy and cognitive discharge of the surgeon are considered in this conception. We see numerous applications according to the explained principle for power-control of instruments in ORL-surgery in the future such as drilling, high frequency surgery or laser.

Navigated control in functional endoscopic sinus surgery.

This study designs and evaluates a mechatronic system to assist ENT surgery, taking as an example a navigation controlled shaver as used in paranasal sinus surgery. The on/off status of the shaver is regulated automatically, depending on the current position of the shaver tip. The working space for the navigation controlled shaver is planned preoperatively as a three-dimensional model and is based on the individual patient's CT data. Within this area the shaver reacts to signals from the surgeon. If the tip of the shaver moves outside the predefined working space, the shaver's automatic drive control is interrupted by an electrical pulse. The planning software was evaluated using CT data sets from 32 patients. The accuracy of the registration was analysed on an anatomical model with the aid of 451 measurements on titanium screws attached endonasally, whilst the implementation of the working space was evaluated on 5 technical models. The average time taken for segmenting the working space was found to be 4.23 minutes. The average accuracy of the shaver registration was 1.08 mm. The selected cavity was to be resected without any restrictions. The preoperatively determined working space was implemented with a mean deviation of 3.1 mm over all levels. The study proves the feasibility of a mechatronic assistance system taking as an example the navigation controlled shaver used in paranasal sinus surgery. In contrast to isolated CAS solutions, this conceptual approach provides for the redundancy of the surgeon and eases their cognitive burden. We can foresee numerous applications in ENT surgery of the future following the principle presented here, in the control systems of power tools such as cutters, high frequency scalpels and lasers.