Decontamination of a robot used to reprocess reusable surgical instruments

BACKGROUND

Using robots to handle medical devices in the decontamination area of the Central Sterile Supply Department (CSSD) can reduce risks and address staff shortages. The gripper design must allow reliable cleaning using standard CSSD procedures to avoid build-up of biofilms and possible cross-contamination between different instrument trays and the gripper's functionality. This study explores the design of the robot's gripper regarding cleanability, aiming to determine whether successful cleaning can be achieved even after prolonged drying for a working shift of 8 h.

METHODS

We optimized a gripper for cleanability and used it to assess the spread of different test soils depending on different forms of motion. Subsequently, we analysed the cleanability using sheep's blood as test soil, reprocessing the gripper in different assembly configurations after 4 and 8 h of drying, and measuring residual protein.

FINDINGS

Based on our investigations, we documented the spread of contamination depending on the type of motion of the gripper's components. Sheep's blood exhibited the highest dispersion among the test soils, permeating through thin crevices. Importantly, all samples displayed residual protein levels below the warning threshold, irrespective of drying time and gripper disassembly or cleaning position. Cleaning in a device-specific optimized position achieved results comparable to cleaning the disassembled individual components.

CONCLUSIONS

These findings indicate that cleaning even after one working shift of 8 h and without the labour-intensive disassembly of the gripper is feasible, supporting the future use of robots to handle contaminated medical devices in the CSSD decontamination area.

Non-invasive assessment of muscle compartment elasticity by pressure-related ultrasound in pediatric trauma: a prospective clinical study in 25 cases of forearm shaft fractures

BACKGROUND

Soft-tissue swelling after limb fractures in pediatric patients is well known to be a risk factor for developing acute compartment syndrome (ACS). Clinical assessment alone is uncertain in specific cases. Recently, we proposed a non-invasive ultrasound-based method to objectify muscle compartment elasticity for monitoring. We hypothesize a strong correlation between the soft-tissue swelling after stabilization of upper limb fractures and the compartment elasticity objectified with a novel ultrasound-based approach in pediatric trauma.

PATIENTS AND METHODS

In a prospective clinical study, children suffering forearm fractures but not developing an ACS were included. The muscle compartment elasticity of the m. flexor carpi ulnaris was assessed after surgical intervention by a non-invasive, ultrasound-based method resulting in a relative elasticity (RE in %) in both the control (healthy limb) and study group (fractured limb). Soft-tissue swelling was categorized in four different levels (0-3) and correlated with the resulting RE (%).

RESULTS

The RE in the study group (15.67%, SD ± 3.06) showed a significantly decreased level (p < 0.001) compared with the control (22.77%, SD ± 5.4). The categorized grade of soft-tissue swelling resulted in a moderate correlation with the RE (rs = 0.474).

CONCLUSIONS

The presented study appears to represent a novel approach to assess the posttraumatic pressure changes in a muscle compartment after fracture stabilization non-invasively. In this first clinical study in pediatric cases, our measurement method represents a low-cost, easy, and secure approach that has the potential to substitute invasive measurement of suspected ACS in muscle compartment conditions. Further investigations in lager cohorts are required to prove its daily clinical practicability and to confirm the expected reliability.

Non-invasive and reliable assessment of compartment elasticity by pressure related ultrasound: An in-vitro study

PURPOSE

The development of acute compartment syndrome is a serious threat to trauma patients. The clinical assessment alone is not reliable enough to determine the need for fasciotomy in many cases. The Physician´s assessment of the elasticity of the muscle compartment might be particularly important to objectively evaluate the pressure in this enclosed space. The purpose of this study was to determine the observer´s reproducibility, of compartment elasticity measurements by a novel ultrasonic approach.

METHODS

Increasing intra-compartmental pressures (ICP) were simulated in a water filled in-vitro model. Pressure related ultrasound was used to determine the relative elasticity (RE) of soft tissue compartments. A pressure transducing probe head was combined with the ultrasonic probe to obtain cross section views of the simulated compartment and to detect the amount of applied pressure by the observer. In this model, the compartment depth without compression (P₀) was set to be 100%. Changes of the compartment depth due to a probe pressure of 80 mmHg (P₈₀) were correlated to P₀ and an elasticity quotient as a value for RE (%) was calculated. Twelve blinded observers performed measurements for RE determination (%) under three pressure conditions. Reproducibility was calculated using intraclass correlation coefficient (ICC).

RESULTS

Measurements (n = 432) revealed that the RE (%) in the control group was 17,06% (SD+/-2,13), whereas the RE of the group ICP₃₀ significantly decreased to 12,66% (SD+/- 1,19) (p<0,001). The ICP₅₀ group revealed a further significant decrease to 8,43% (SD+/- 0,67) (p<0,001). Repeated measurement of RE and ICP showed a high level of correlation (spearman correlation coefficient: roh=0,922). A RE <14% resulted in a sensitivity of 96% and a specificity of 90,3% for diagnosis of an ICP >30 mmHg. ICC_inter was 0,986; 95%, CI: 0,977-0,992 (p<0,001).

DISCUSSION

The presented ultrasound-based approach reliably assesses the elasticity in a simulated compartment model. In this pioneer study investigating the inter- and intra-observer reproducibility, this method of measurement appears to be of low cost in addition to being an easy and secure approach that may have the potential to substitute invasive measurement. Further investigations are required to improve its feasibility and to confirm the reliability under clinical conditions.

Impact of an uncooperative passenger on the control of an externally guided self-balancing patient-transport system

Patient transport is a physically demanding task for paramedics. The risk of injuries is high and the early retirement rate in emergency medical services is among the highest compared to other industries. The aim of the SEBARES project is to reduce the workloads for paramedics by introducing a self-balancing patient-transport system with a stair climbing mechanism, which is externally guided by a paramedic. In an earlier study a prototype for flat terrain was set up with a sliding mode controller for the self-balancing mechanism. The performance of the prototype without a patient was evaluated in respect of the ergonomic requirements of the paramedic/user. Furthermore, a simulative study demonstrated a considerable impact of an uncooperative passenger on the self-stabilizing mechanism. Although control of self-stabilizing human transporters in general are well researched, possible negative influences of passengers are currently neglected during modelling and control design. For the described patient-transport application uncooperative behavior is very common. Therefore, this experimental study focuses on the impact of uncooperative patients on the dynamic behavior and influences on controller robustness. The prototype of the transport aid was adapted and 128 trials were conducted with 8 subjects who had to perform 4 different scenarios to simulate uncooperative passengers. The tasks were repeated with different parameter values to evaluate the robustness of a sliding mode controller. The results showed that increasing the robustness can reduce the average force on the paramedic's handle from 60 N to 35 N, while the passenger was performing cyclic movements of the upper body. However, a drawback of high robustness is the occurrence of chattering around the control reference. Further studies will consider adaptive controller design.

Impact of scapholunate dissociation on human wrist kinematics

Neither the complex motions of the scapholunate joint, nor the kinematic changes that occur as a result of injury to it, are fully understood. We used electromagnetic tracking within affected bones to evaluate the physiologic motions in the planes of flexion and extension, and of radial and ulnar deviation of human cadaver wrists, before and after complete transection of the scapholunate ligaments. Despite individual variance between each wrist, we were able to establish a pattern in the changes that occurred after scapholunate ligament injury. During the motions examined, the scaphoid showed an increase in translational deviation in almost all motion axes. In contrast, the movement of the lunate seemed to be impaired, especially in radial-ulnar deviation.

[Usability first. Model-based approach for the use-oriented risk analysis of medical devices]

Due to increasing automation, the number and complexity of technical components have increased in the medical context (e.g., in the clinic or in the home care sector) in recent years. Besides new effective and efficient therapeutic and diagnostic options, these devices entail a wide range of functions and very complex (often computer-based) user interfaces that may lead to human-induced risk potential. A systematic and early human risk analysis and a usability evaluation allow medical device manufacturers to identify and control risks within the human-machine interaction very efficiently. At the Department of Medical Engineering in the Helmholtz Institute for Biomedical Engineering at the RWTH Aachen University, a formal-analytical methodology and a corresponding software tool for prospective human-risk analysis and model-based usability evaluation has been developed. Based on a twofold approach, user interactive process sequences and their potential impacts on the overall process are identified and the resulting use-related risks are assessed. For this, the tasks are categorized (in system and user tasks) and modeled and temporally related within the framework of a high-level task analysis. Within a subsequent cognitive low-level task analysis, potentially critical parallel process sequences are then tested in order to detect a potential resource overload of the user. The subsequent corresponding human-risk analysis is developed according to a knowledge base (checklist) of taxonomies related to human error. The HiFEM (human-function effect modeling) methodology is universally applicable and can be used for the evaluation of human-computer interfaces as well as for the analysis of purely mechanical control interfaces and simple hand-held instruments (such as a scalpel and implant). In a comparative study, the HiFEM method clearly outperforms the classic FMEA (failure modes and effects analysis) process with regard to effectiveness, efficiency, learnability, and user satisfaction. Especially small and medium-sized enterprises that constitute the medical device industry can be supported by the new methodology in the context of risk management according to ISO 14971 as well as usability engineering in accordance with IEC 62366 and IEC 60601-1-6 as well as EN ISO 9241.

[Evaluation of biomechanical models for therapy planning of total hip arthroplasty - direct comparison of computational results with in vivo measurements]

A consideration of the patient-specific biomechanical situation in the context of the surgical planning of total hip arthroplasty is highly recommended and may have a positive impact on the therapeutic outcome. In current clinical practice, surgical planning is based on the status of the individual hip and its radiographic appearance. Several authors proposed different biomechanical modeling approaches for the calculation of the resultant hip force R on the basis of parameters gathered from plain radiography. The comparative study presented in this paper shows that the biomechanical models by Pauwels, Debrunner, Blumentritt and Iglič provide a good approximation of the magnitude of R when compared to the in vivo data from instrumented prostheses. In contrast, the Blumentritt model resulted in abnormally high values. However, the computational results for the orientation of R show a high variability of all modeling approaches and seem to depend more on the model used than on patient-specific parameters.

Myocardial effects of local shock wave therapy in a Langendorff model

OBJECTIVE

Applying shock waves to the heart has been reported to stimulate the heart and alter cardiac function. We hypothesized that shock waves could be used to diagnose regional viability.

METHOD

We used a Langendorff model to investigate the acute effects of shock waves at different energy levels and times related to systole, cycle duration and myocardial function.

RESULTS

We found only a small time window to use shock waves. Myocardial fibrillation or extrasystolic beats will occur if the shock wave is placed more than 15 ms before or 30 ms after the onset of systole. Increased contractility and augmented relaxation were observed after the second beat, and these effects decreased after prolonging the shock wave delay from 15 ms before to 30 ms after the onset of systole. An energy dependency could be found only after short delays (-15 ms). The involved processes might include post-extrasystolic potentiation and simultaneous pacing.

CONCLUSION

In summary, we found that low-energy shock waves can be a useful tool to stimulate the myocardium at a distance and influence function.

Single pulse analysis of intracranial pressure for a hydrocephalus implant

The intracranial pressure (ICP) waveform contains important diagnostic information. Changes in ICP are associated with changes of the pulse waveform. This change has explicitly been observed in 13 infusion tests by analyzing 100 Hz ICP data. An algorithm is proposed which automatically extracts the pulse waves and categorizes them into predefined patterns. A developed algorithm determined 88 %±8 % (mean ±SD) of all classified pulse waves correctly on predefined patterns. This algorithm has low computational cost and is independent of a pressure drift in the sensor by using only the relationship between special waveform characteristics. Hence, it could be implemented on a microcontroller of a future electromechanic hydrocephalus shunt system to control the drainage of cerebrospinal fluid (CSF).

Simplified detection of myocardial ischemia by seismocardiography. Differentiation between causes of altered myocardial function

Seismocardiography (SCG) is a noninvasive technique for recording cardiac vibrations. Changes in these waves have been correlated with chronic and acute alterations in myocardial function. This analysis is complex and clinical integration limited. The current study aimed to simplify the utilization of SCG by fast Fourier transformation for a reliable discrimination between different intra- and postoperative causes of hypotension (i.e., myocardial ischemia or hypovolemia). We operated on nine pigs and recorded SCG at baseline, at hypovolemia (occlusion of the inferior vena cava), and at ischemia (occlusion of the right coronary artery). In conclusion, SCG enables detection and differentiation of ischemia and hypovolemia as important causes of altered myocardial function during and after surgery. Thus, this simple and noninvasive diagnostic tool may be used intra- and postoperatively to identify patients at risk.

Electrical and Optical Properties of FeSi2 Layers

We fabricated α-FeSi2 and α-FeSi2 layers by using two methods: Ion Beam Synthesis (IBS) and Molecular Beam Allotaxy (MBA). In the latter technique a trapezoidal-shaped Fe profile was embedded in the Si matrix by codeposition of Si and Fe at temperatures of about 650°C. A rapid thermal anneal of the IBS and MBA samples at 1150°C for 10 s is necessary to obtain continuous α-FeSi2 layers. The Fe vacancy concentration of the α-FeSi2 layers was varied by a further anneal at lower temperatures. Resistivity measurements indicate a decrease of the resistivity with decreasing Fe vacancy concentration. The α-FeSi2 was transformed to a continuous β-FeSi2 layer by an anneal at 800°C for several hours. To investigate the nature of the band gap we performed absorption measurements at room temperature and 77 K. The analysis of the room temperature data revealed a direct transition at 0.84 eV and an additional indirect transition at 0.78 eV. At 77 K the direct transition shifts to ≈ 0.875 eV and the indirect to ≈ 0.86 eV.

Evaluation of a new computer-assisted surgical planning and navigation system based on two-dimensional fluoroscopy for insertion of a proximal femoral nail: an experimental study

Pertrochanteric femoral fractures are common and intramedullary nailing is an accepted method for their surgical treatment. Accurate placement of the implant is essential to ensure fixation. The conventional technique can require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on two-dimensional fluoroscopy for guide wire placement in the femoral neck has been developed, in order to perform intramedullary pertrochanteric fracture fixation using the proximal femoral nail (PFNA). The planning process was supported by a 'zero-dose C-arm navigation' system. The PFNA was inserted into 12, intact, femoral sawbones guided by the computer-based navigation, and into 12, intact, femoral sawbones using a conventional fluoroscopic-assisted technique. Guide wire and subsequent blade placement in the femoral neck was evaluated. The computer-assisted technique achieved a significant decrease in the number of required fluoroscopic images and in the number of guide wire passes. The obtained average blade placement accuracy in the femoral neck was equivalent to the conventional technique. The operation time was significantly longer in the navigation-assisted group. The addition of computer-assisted planning and surgical guidance to the intramedullary nailing of pertrochanteric femoral fractures offers a number of clinical benefits based on the results of this sawbone study. Further studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA introduction and with the goal of reducing operation time are indispensable before integration of this navigation system into clinical practice.

Evaluation of a fluoroscopy-based navigation system enabling a virtual radiation-free preview of X-ray images for placement of cannulated hip screws. A cadaver study

Accurate placement of cannulated screws is essential to ensure fixation of medial femoral neck fractures. The conventional technique may require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on 2D fluoroscopy for guide wire placement in the femoral neck has been developed to improve screw placement. The planning process was supported by a tool that enables a virtual radiation-free preview of X-ray images. This is called "zero-dose C-arm navigation". For the evaluation of the system, six formalin-fixed cadaveric full-body specimens (12 femurs) were used. The evaluation demonstrated the feasibility of fluoroscopically navigated guide wire and implant placement. Use of the novel system resulted in a significant reduction in the number of fluoroscopic images and drilling attempts while achieving optimized accuracy by attaining better screw parallelism and enlarged neck-width coverage. Operation time was significantly longer in the navigation assisted group. The system has yielded promising initial results; however, additional studies using fractured bone models and with extension of the navigation process to track two bone fragments must be performed before integration of this navigation system into the clinical workflow is possible, and these studies should focus on reducing the operation time.

[Evaluation of a 2D fluoroscopy-based navigation system for insertion of the dynamic hip screw (DHS): an experimental study]

PURPOSE

Dynamic hip screw (DHS) insertion for the fixation of lateral femoral neck fractures is an accepted surgical treatment method. A computer-assisted planning and navigation system based on 2D fluoroscopy has been developed for guidewire insertion in order to perform screw placement. The image acquisition process was supported by a radiation-saving procedure called "zero-dose C-arm navigation". The aim of this study was to evaluate this new system.

MATERIALS AND METHODS

In the context of a sawbone study, we inserted dynamic hip screws. The procedure was performed under navigation control and in the conventional technique in 12 sawbones. Both procedures were performed in an open and closed technique.

RESULTS

The computer-assisted technique significantly reduced the number of intraoperative fluoroscopic images (open technique: -8.1 ± 0.5; p < 0.001 - closed technique: -12.3 ± 3.7; p < 0.001) and the number of guidewire passes (open technique: -1.3 ± 1.2; p < 0.05 - closed technique: -1.5 ± 1.2; p < 0,05). There was no difference with respect to precision in both groups. The operation time was significantly longer in the navigation-assisted groups (open technique: + 14.6 ± 5.4 min; p < 0.001 - closed technique: + 13 ± 3 min; p < 0.001).

CONCLUSION

The addition of computer-assisted planning and surgical guidance supported by "zero-dose C-arm navigation" may be useful for the fixation of lateral femoral neck fractures by the DHS as it reduces the amount of fluoroscopic images and requires fewer drill tracks. Further studies with the goal of reducing the operation time are necessary.

[Evaluation of a 2D fluoroscopy-based navigation system for insertion of femoral neck screws. An experimental study]

INTRODUCTION

The aim of this study was the evaluation of a new computer-assisted planning and navigation system based on 2D-fluoroscopy for guidewire insertion in order to perform cannulated screw placement into the femoral neck. The image acquisition process was supported by a radiation-saving procedure called Zero-dose C-arm navigation.

MATERIAL AND METHODS

In the context of a sawbone study, we performed insertion of 3 cannulated screws positioned under navigation control as well as using the conventional technique in 12 sawbones. Both procedures were performed using open and closed techniques.

RESULTS

The computer-assisted technique significantly reduced the amount of intraoperative fluoroscopic images (open technique: -14±3 images, closed technique: -29.4±6 images). Drilling attempts were reduced in the computer-assisted groups (open technique: -1.2±1 attempts, closed technique: -1.7±1.5 attempts) and the femoral neck area covered by the screws was greater in the navigation-assisted groups (open technique: +32.1±16.3 mm(2), closed technique: +32.6±14.9 mm(2)), There was no difference concerning parallelism of the screws or perforation of femoral neck or head. The operation time was significantly longer in the navigation-assisted groups (open technique: +24.2±2.1 min, closed technique: +22.8±5.8 min).

CONCLUSION

The addition of computer-assisted planning and surgical guidance supported by Zero-dose C-arm navigation can be useful for the fixation of medial femoral neck fractures with cannulated screws. Further studies with the goal of reducing the operation time are indispensable before integrating this navigation system into the clinical workflow.

Silicon Surface Chemistry By IR Spectroscopy in the Mid- To Far-IR Region: H2O And Ethanol On Si(100)

The technique of external reflection infrared (IR) spectroscopy is used to study silicon surface chemistry. External reflection is enhanced by implanting a buried cobalt silicide layer in silicon to act as an infrared reflector. The preparation of clean well-ordered surfaces from the ion implanted substrates is demonstrated. The reactions of water and ethanol with Si(100) are investigated.

Trackerless ultrasound-integrated bone cement detection using a modular minirobot in revision total hip replacement

Medical robots are superior to freehand manipulation if an accurate, precise, and time-efficient implementation of a preplanned intervention is required. In the first part of this contribution a new modular minirobot for automatic ultrasound-based bone cement detection followed by subsequent cement milling in revision total hip replacement is presented. A minirobot integrated ultrasound module eliminates the need for external position tracking (e.g. by an optical system) as well as patient registration since the scanned contours can be directly provided within the robot's coordinate system. Further, the modular minirobot concept allows kinematics, workspace, and mechanical parameters to be easily adapted to the requirements of related or even new surgical applications. In the experimental part, the impact of ultrasound module integration on the implementation of optimized scanning strategies is investigated and evaluated in a laboratory set-up. As wave mode conversion and refraction artefacts due to angular sound incidence influence the detection accuracy, the transducer alignment can be optimized with respect to the number of degrees of freedom (DOFs) provided by the minirobot. A model-based scanning approach using two degrees of freedom (2DOFs), three degrees of freedom (3DOFs), and four degrees of freedom (4DOFs) respectively is presented. For automated scanning path calculation, a 2DOF distal-proximal prescan has been performed to estimate the principal components of the cement cavity's geometry using either a model-based or a statistical approach. In a cadaver study, the model-based approach consistently outperformed the statistical approach. The 3DOFs and 4DOFs scanning strategies yielded a significantly higher scanning accuracy if compared with the 2DOFs approach whereas the 3DOFs approach represents a trade-off between system complexity and detection accuracy.

Robot- and computer-assisted craniotomy (CRANIO): From active systems to synergistic man—machine interaction

Computer and robot assistance in craniotomy/craniectomy procedures is intended to increase precision and efficiency of the removal of calvarial tumours, enabling the preoperative design and manufacturing of the corresponding implant. In the framework of the CRANIO project, an active robotic system was developed to automate the milling processes based on a predefined resection planning. This approach allows for a very efficient milling process, but lacks feedback of the intra-operative process to the surgeon. To better integrate the surgeon into the process, a new teleoperated synergistic architecture was designed. This enables the surgeon to realize changes during the procedure and use their human cognitive capabilities. The preoperative planning information is used as guidance for the user interacting with the system through a master—slave architecture. In this article, the CRANIO system is presented together with this new synergistic approach. Experiments have been performed to evaluate the accuracy of the system in active and synergistic modes for the bone milling procedure. The laboratory studies showed the general feasibility of the new concept for the selected medical procedure and determined the accuracy of the system. Although the integration of the surgeon partially reduces the efficiency of the milling process compared with a purely active (automatic) milling, it provides more feedback and flexibility to the user during the intra-operative procedure.

Editor's note: This paper was commissioned for this Image Guided Surgery special issue, but has been published in an earlier issue. It can be found in Proc. IMechE, Part H: J. Engineering in Medicine, 2010, 224(H3), 441–452. DOI: 10.1243/09544119JEIM596.

[Evaluation of the efficiency of the zero-dose-C-arm navigation approach]

BACKGROUND

The efficiency and success of computer-assisted fluoroscopic navigation systems mainly depend on the quality of the process of image acquisition: obtaining the correct view of anatomic structures, relative orientation of multiplanar X-ray images and the necessary amount of radiation dose. These systems may be optimised by using a system called zero-dose c-arm navigation (ZDCAN). We investigate whether the available computer-assisted systems may be used to navigate the c-arm before image acquisition to obtain X-ray images with maximised accuracy and minimal radiation exposure.

METHODS

Based on position data of an optical tracking system combined with statistical deformable bone models, ZDCAN is able to generate a real-time preview of expected X-ray images of the lower extremities without using radiation. We performed a cadaver study on six full-body specimens comparing the zero-dose approach to conventional positioning of the c-arm in order to evaluate efficiency and accuracy. Eight users acquired two perpendicular X-ray images of the hip, the knee and the femoral diaphysis.

RESULTS

The number of X-ray images required to get a satisfying picture could be reduced to seven using the zero-dose approach; the conventional approach needed 11 images. The mean time did not differ significantly. Regarding the image quality, using ZDCAN quasi-orthogonality could be reached while the conventional approach showed a large variation of the relative orientation.

CONCLUSION

Using ZDCAN, the amount of radiation can be reduced by requiring less X-ray images as well as reaching better accuracy.

Evaluation of deformable models for femoral neck surgery

OBJECTIVE

Using fluoroscopic images alone, it is difficult to guarantee that screws are positioned within the femoral head and neck. This study evaluates whether the introduction of deformable 3D models limiting the planning and navigation space is a helpful approach to minimizing the incidence of misplaced screws, thereby enhancing patient safety.

BACKGROUND

Even though a screw may appear to lie within the femoral head and neck on fluoroscopic images, this may not, in fact, be the case. This is a particular problem for interventions such as fixation of a slipped femoral head or osteosynthesis of the femoral neck, where screws must be set close to the cortical bone without penetrating the joint or injuring the cortex of the femoral neck.

METHODS

A system was developed which permits computer-based planning and navigation of screws for femoral neck fracture fixation based on fluoroscopic images. Different approaches were employed which either a) make use of a deformable model adapted to the femoral head/neck, constraining the screw positions within this model; or b) allow the user to position the screws with or without geometrical constraints on the X-rays while maintaining parallelism of the screws. All designs were evaluated and compared by 7 test users using integral projection X-rays calculated from the CT dataset. Results were checked using a 3D model of the bone, also calculated from the CT dataset.

RESULTS

Positioning screws using the deformable model resulted in a significantly smaller distribution of screw tip locations and no penetrations into the hip joint, in contrast to the other approaches where up to 11% of screws were misplaced.

CONCLUSIONS

Constraining the planning and navigation space by means of a deformable model allows better control of screw positioning and thus increases the chances of a successful intervention. In particular, CAS systems allowing for virtual fluoroscopy should consider supporting this planning approach.

Evaluation of a new fluoroscopy-based navigation system in the placement of the femoral component in hip resurfacing

Prosthesis-specific mechanical alignment instruments for the precise and reproducible positioning of the femoral component constitute one of the major improvements in modern hip resurfacing prostheses. However, mechanical failure of the femoral component is mostly attributable to the surgical technique, and in particular to notching of the femoral neck. In order to evaluate a novel computer-assisted fluoroscopy-based planning and navigation system, six DUROMTM hip resurfacing prostheses were implanted into artificial femurs by means of computer-assisted fluoroscopy-based navigation and prosthesis-specific mechanical alignment instruments. Subsequently, the planning and navigation system was tested within the scope of a cadaver study on three fixed whole-body preparations (six femurs). The average difference between planned and actual angle of the prosthesis was 0±0.7° for fluoroscopy-based navigation versus 6.5±7.8° for the in-vitro use of the prosthesis-specific mechanical alignment instruments, and 1±1.4° for fluoroscopic navigation in the cadaver study. The average discrepancy between planned and actual anterior offset was −1.2±1.2 mm versus 0.8±4 mm, and 0.3±2.2 mm in the cadaver study, and the time required for the total of five planning and navigation steps was 17.2±1.5 min versus 14±0.8 min and 20.2±2.5 min respectively. No notching of the femoral neck occurred under fluoroscopy nor under conventional treatment. During in-vitro studies, use of the computer-assisted fluoroscopy-based planning and navigation system resulted in enhanced accuracy compared with conventional prosthesis-specific mechanical alignment instruments. The system has yielded initial promising results within the scope of the cadaver study.

Robot- and computer-assisted craniotomy (CRANIO): From active systems to synergistic man—machine interaction

Computer and robot assistance in craniotomy/craniectomy procedures is intended to increase precision and efficiency of the removal of calvarial tumours, enabling the preoperative design and manufacturing of the corresponding implant. In the framework of the CRANIO project, an active robotic system was developed to automate the milling processes based on a predefined resection planning. This approach allows for a very efficient milling process, but lacks feedback of the intra-operative process to the surgeon. To better integrate the surgeon into the process, a new teleoperated synergistic architecture was designed. This enables the surgeon to realize changes during the procedure and use their human cognitive capabilities. The preoperative planning information is used as guidance for the user interacting with the system through a master—slave architecture. In this article, the CRANIO system is presented together with this new synergistic approach. Experiments have been performed to evaluate the accuracy of the system in active and synergistic modes for the bone milling procedure. The laboratory studies showed the general feasibility of the new concept for the selected medical procedure and determined the accuracy of the system. Although the integration of the surgeon partially reduces the efficiency of the milling process compared with a purely active (automatic) milling, it provides more feedback and flexibility to the user during the intra-operative procedure.

Computer- und Robotertechnik für die bildgeführte Orthopädische Chirurgie (Computer and Robot Technology for Image guided Orthopaedic Surgery)

Seit einigen Jahren hält die Computer- und auch Robotertechnologie in der Orthopädischen Chirurgie Einzug, wird jedoch teilweise sehr kontrovers diskutiert. Wo liegen Vorteile und Probleme der Automatisierungstechnik für den chirurgischen Einsatz? In diesem Beitrag sollen Möglichkeiten und Techniken im Überblick dargestellt werden. Entwicklungspotentiale insbesondere im Hinblick auf robotische Unterstützungssysteme sollen am Beispiel des CRIGOS-Parallelrobotersystems aufgezeigt werden.

[Functionality and accuracy of a fluoroscopic navigation system in the placement of the femoral component for hip resurfacing - a cadaver study]

INTRODUCTION

Resurfacing arthroplasty represents an alternative method to total hip replacement especially for the young and active patient. The main reasons for early implant failure are mal-positioning of the femoral component and notching of the femoral neck during femoral head preparation.

MATERIAL AND METHODS

In the context of a cadaver study of formalin-fixed cadaveric full body specimens 6 DUROM -Hip-Resurfacing prosthesis have been implanted under navigation control. The aim of the study was an evaluation of the functionality and accuracy of the computer-assisted planning and navigation system on the basis of a navigation module library from Surgitaix AG Aachen, Germany.

RESULTS

The main angulation error between planning (135.2 +/- 3.6 degrees ) and navigation (136.2 +/- 2.8 degrees ) was 1.9 +/- 1.1 degrees , the main anterior offset error between planning (2.2 +/- 1.3 mm) and navigation (2.7 +/- 2.3 mm) was 1.2 +/- 1.9 mm. The main distance error between planning and navigation was 2.7 +/- 1.3 mm. The mean time for all five planning and navigation steps was 20.2 +/- 2.5 min. Against the background of a acetabular bone-saving approach in all 6 cases the smallest possible femoral component could be implanted.

CONCLUSION

The computer-assisted fluoroscopic planning and navigation system for hip resurfacing showed within the scope of this cadaver study first promising results. The system approaches a practicable intraoperative planning with a high accuracy in operative implementation. Nevertheless, the potential benefit has to be evaluated in further clinical studies, especially from the perspective of a possible integration of this navigation system into the clinical work-flow. Further studies should consider a fluoroscopic-assisted range of motion assessment under consideration of an additional cup-module to enhance the postoperative range of motion after hip resurfacing procedures.

[Soft-tissue management in primary knee arthroplasty: common techniques, navigation and force-sensing devices]

Soft-tissue management is essential for the outcome in total knee arthroplasty. In combination with osseous resections and component positioning, correction of the underlying ligamentous dysbalance should yield a stable joint throughout the flexion arc. Different "philosophies" with regard to technique, timing and tactics in ligament balancing are described. So far, surgeons have not been provided with standardised devices that allow the objective measurement of this complex issue. Moreover, knowledge concerning the "ideal" soft-tissue stability following knee arthroplasty is still sparse. As part of the scientific project "OrthoMIT" (minimal invasive orthopaedic therapy) an approach to combine conventional soft-tissue management with navigation and force-sensing devices should be realized technically. The aim is to develop an instrument for the objective measurement of soft-tissue management in scientific and clinical applications.

Computer-assisted single- or double-cut oblique osteotomies for the correction of lower limb deformities

Corrective osteotomy interventions on lower extremities are widely accepted procedures for restoring axial alignment of lower limbs. However, some studies reveal failure rates of up to 70 per cent in a 10 year time frame, which indicates that the success of corrective osteotomies depends on multiple factors. Based on a comprehensive review of error sources among conventional correction osteotomy interventions, a novel approach was developed in order to reduce these error sources among all clinical working steps (deformity determination, planning, and intra-operative realization). The article describes the implemented methodology for realizing optimal correction osteotomies based on a six-dimensional or 12-dimensional optimization module for single- and double-cut oblique osteotomies. The results show that the realized planning and navigation concept enables reduction in the error sources among the clinical working steps of correction osteotomy interventions.

[Correction osteotomies near the knee and navigation: state of the art within the scope of the "OrthoMIT" project for the development of an integrated platform for smart interventional orthopaedic surgery and traumatology]

INTRODUCTION

"OrthoMIT--minimal invasive orthopaedic therapy" is a project to develop an integrated platform for less invasive operative procedures in hip, knee and spine surgery, supported by the German Federal Ministry for Education and Research (BMBF). Twenty-seven industrial and clinical partners under the management of the Orthopaedic Department of the University Hospital Aachen (Prof. Dr. F. U. Niethard) intend to develop in 10 subprojects innovative aspects and modules of the "OrthoMIT" system.

MATERIALS AND METHODS

Within the project and amongst other procedures, joint-preserving correction osteotomies have been analysed to develop planning and navigation tools on the basis of improved and less invasive surgery. Therefore, the reproducibility and validity of the conventional methods were investigated and compared with the technical possibilities in computer-guided planning and navigated surgery for correction osteotomies of the upper extremities. Clinical needs, necessary innovative aspects and modules were defined out of these consolidated findings and passed on to the industrial partners of the "OrthoMIT" project to develop innovative techniques in the field of planning and navigation.

CONCLUSION

The present article reports in a concise way about the essentials of the available current techniques in correction osteotomies of the upper extremities with the main focus being placed on navigation.

Analysis of Surgical Management of Calvarial Tumours and First Results of a Newly Designed Robotic Trepanation System

This study was performed to evaluate the surgical strategy in patients with calvarial tumours, in order to design and modify a robot-assisted trepanation system. A total of 75 patients underwent craniectomy for the treatment of calvarial tumours during the 10-year period from 1993 to 2002. The patients' complaints, the size, location and histology of the tumour, and the various cranioplasty techniques used were analysed retrospectively. In a second procedure several craniectomies at typical locations according to the study's results were performed in a laboratory setting using a hexapod robotic tool, constructed at the Helmholtz-Institute, RWTH Aachen University, and plastic model heads. The workflow was documented and the reproducibility and the accuracy of the procedure were registered. A total of 83 surgical procedures were performed on 75 patients. The majority (87 %) of lesions treated surgically were located in the frontal, temporal and anterior parts of the parietal region. Histological examination revealed benign lesions in 66 % of the patients and dural involvement in 46 %. According to these results craniectomies were performed using the robotic system. Mean positioning accuracy of the robotic system while milling was 0.24 mm, with a standard deviation of 0.04 mm, and maximum error under 1 mm. Craniectomies leaving a 1-mm layer of the tabula interna intact to ensure a healthy dura were performed in several regions successfully. The majority of calvarial tumours, requiring surgical treatment in our patients, were located in cosmetically relevant areas in which drilling can be carried out with the robotic trepanation system. Consequently, the surgical approach had to be planned carefully in order to achieve a good cosmetic outcome.

Robot- and computer-assisted craniotomy: resection planning, implant modelling and robot safety

BACKGROUND

In cases of cranial tumour, manual resection of the cancerous tissue can be very stressful and time-consuming, due to the adhesion of the subjacent dura mater. Computer-assisted planning, navigation and robotic craniotomy, with optional skull reconstruction using customized implants, are of increasing clinical interest in craniofacial and neurosurgery.

METHODS

Using preoperative computed tomography (CT) images, an automatic segmentation of the tumour is performed, followed by resection planning. The skull reconstruction is performed using computer-assisted implant modeling and manufacturing. Risk analysis of the robot-guided intervention led to the development of a new hexapod robot system.

RESULTS

Results from registration and robot accuracy on plastic and Anatomical skull are shown. The concept of a stand-alone safety system is presented to supervise the robot during the intervention. The entire process from preoperative CT scan to intraoperative robot assisted removal of tumourous bone is shown in laboratory and anatomical trials.

CONCLUSION

The laboratory and anatomy studies conducted so far provided a substantial basis for further improvement of the system's integration in the surgical workflow and the final approval of the system for initial clinical studies.

Identification of milling parameters for manual cutting of bicortical bone structures

Within the framework of the development of a new neurosurgical robot system, parameters of conventional manual neurosurgical bone milling had to be determined. These results were used as a reference for the design and validation of the robotic versus manual milling task. Bovine scapulae were used for the tests because their bicortical structure is similar to the bone structure of the skull. The exercise was to cut defined geometries that had been registered on the bone prior to the start of the milling operation. The geometries had to be milled with a depth of 3 mm, which corresponded to the radius of the ball of the cutter. Different parameters like tool position, rotary speed, temperature, forces and time were registered. Eleven experienced neurosurgeons with practical experience of 80-1200 skull operations participated in this study. First results show a large variation in depth along the line. The lateral deviation was up to 5 mm, the depth error up to 2.5 mm, the tool temperature was 22 degrees C to 65 degrees C, and rotary speed varied from 15,000 to 80,000 rpm. Registered forces had maxima of 16 N in the feed direction and 21 N normal to the surface; average forces were approximately 1-2 N.

Intraoperative 3D-Rekonstruktion des PMMA-Köchers zur computerassistierten Revisionshüftendoprothetik auf Basis von 2D-Röntgen-Bildgebung

AIM

Computer-assisted cement removal out of the femoral medullary canal requires the exact definition of the plug's shape within a 3D coordination system. Aiming at a sufficiently precise reconstruction based on segmentation of just a few 2D X-ray images a special mathematic procedure is needed for automatic surface interpolation. The geometric specification of the resulting virtual model should take into account the characteristic geometry of the navigated tools in order to achieve the best possible removal.

METHOD

Studies were performed on anatomic specimens of entire human femora, that underwent cemented THA before being cut every 5 mm. The cross-sections were scanned at the high resolution of 600 dpi. Segmentation of the cement was performed with the help of a virtual deformable template and was both used for simulation of X-ray projections from various points of view and for validation of the reconstructed 3D model. By this means systematic errors such as those possible during X-ray acquisition, tracking or segmentation could be avoided and the precision of the procedure could be measured exclusively.

RESULTS

With increasing number of X-rays the distance from the reconstructed 3D model to the original could continuously be reduced. Using only two x-rays a maximum error was measured with 6.5 mm, whereas 5 pictures taken from different angles showed to be enough to ensure an error below 1 mm in the distal part of the femur. By the use of 6 or more pictures no significant improvement could be attained.

CONCLUSION

The innovative procedure is essential for future 2D image-based fluoroscopic navigation of PMMA removal and bears the options of computer-controlled and robotic material working, respectively.

[Minaro--new approaches for minimally invasive roentgen image based hip prosthesis revision]

The main objective of the MINARO project (Minimal Invasive NAvigation and RObotics) is the development of a modular intraoperative planning system for fluoroscopy based total hip revision surgery. Especially the distal cement removal can be a challenging problem. To avoid exhaustive x-ray imaging a navigation system should be used, nevertheless, the three-dimensional shape of the bone cement remains unclear. Our approach in the MINARO-project is to reconstruct the real shape of the bone cement by using just a few x-ray projections. First results show, that the reconstruction has an RMS-Error smaller than 0.5 mm using 6 x-ray projections.

[Adaptive planing model for osteosynthesis of femoral neck fracture]

To investigate how surgeons can be supported in planning of screws for femoral neck fracture fixation reducing incidents of misplaced screws, a system was developed which makes use of a deformable model to be adapted to the femoral head/neck. The accuracy and usability of the system was checked against planning support systems mimicking the conventional positioning of screws within bi-planar x-rays. All designs were evaluated and compared by N = 7 test user. Checking the rate of misplaced screws a) at the femoral neck yielded rates of 8% or up to 42%, b) at the femoral head yielded rates of 0% or up to 11% for model-based or conventional planning, respectively. It is thus suggested to constrain the planning and navigation space by means of deformable models of the bone.

[Development of a compact, semi-robotic platform for an electronic surgical microscope]

In the context of the development of a new, electronic microscope for surgical interventions a semirobotic motion platform for the spatial placement and fixation of a stereoscopic camera is currently being developed. Based on an inquiry about the medical, technical and user-requirements, different phases and characteristics concerning frequency, workspace, speed and accuracy of camera movement during an intervention have been specified. To meet these requirements, a differentiated concept for the platform has been developed including a serial structure for manual pre-positioning, a parallel robot for motor-movement during surgical work and different user-interfaces for suitable robot-control.

[Technical principles for removal of femoral bone cements in hip prosthesis implant revision]

As the removal of femoral bone cement is one of the most challenging tasks in cemented total Hip Revision, a lot of different technical devices have been developed to aid the surgeon. All of their pros and cons are partly consequences of the specific system-design but mainly arise from the basic physical principles used. The known methods and devices as well as their data-handling have therefore been analysed, reduced to their principles according to the criteria of systematic engineering design and systematized in order to provide a better comparability and starting point for the development of new devices.

[Empirical studies of the reliability of surgical navigation systems]

A number of studies demonstrate the clinical relevance of systems for computer assisted surgery (CAS systems). As however studies on human error in medicine indicate, reliability of the results strongly depends on aspects of usability and error tolerance of the system. This paper presents studies which aim to assess these aspects of reliability of CAS systems. In a clinical study, interaction with a CAS system by 16 expert and novice surgeons was observed and assessed. From 133 recorded incidents 41% were rated to have significant impact on the clinical result or to inhibit successful completion of the task, which indicates a low degree of error tolerance of the system. These findings are supported by the results obtained from questionnaire, were learnability and error tolerance were judged to be not sufficient.

[Developing authoring tools for web-based multi-media orthopedics education modules]

In the framework of the EC-Project VOEU ("Virtual Orthopaedic European University"), authoring tools have been developed to support the implementation of online interactive courses for multimedia orthopaedic educational modules. Based on the pedagogical concept of case-based, problem-oriented learning, different user-interaction scenarios and Learning Objects (LOs) were analyzed and developed. Each LO acts as an interactive dialogue presenting one kind of question with certain rules and interactions. The multimedia course content entailing anamnesis, diagnosis and therapy is managed in a database and can be adaptively generated as certain LO with the help of Active Server Pages (ASPs). As an example, an interactive course on Developmental Dislocation of Hip has been implemented.

[CRANIO--development of a system for computer- and robot-assisted craniotomy]

In the framework of the DFG project CRANIO, we are dealing with the problems of computer-assisted planning and robot-assisted realization of craniotomy, with optional skull reconstruction. A CT dataset was obtained from a phantom skull model and basic operation planning as well as different registration methods were performed. As one option it is possible to mill a contour on the skull or even to remove the entire area with a robot-guided microsurgical milling tool. In this context, work space tests were performed with a hexapod parallel robot. The milling of any contour geometry could be realized with different tool angles using the existing CRIGOS robot system without additional axes.

[Visual user guidance for registration based on A-mode ultrasound]

In this study we investigate the use of an A-Mode ultrasound probe tracked by a mechanical localizer system (MicroScribe 3D) for non-invasive transcutaneous palpation and registration of bone surface points. A CT of a femur-model has been scanned and subsequently processed by segmentation and 3D-reconstruction. During the ultrasound registration, a computer based assistance tool helped guiding the alignment of the ultrasound probe. Three different modes of registration have been compared. Process times for registration have been recorded and compared. The results for using an A-Mode ultrasound system demonstrate a translation RMS accuracy of 0.58 mm. Mean ultrasound registration time has been measured to 108 sec. for palpation of 10 bone surface points of distal part of femur.