Ralf Westphal

Robot-assisted Long Bone Fracture Reduction

The preferred treatment of femoral (thigh bone) shaft fractures nowadays is the minimally invasive technique of intramedullary nailing. However, in addition to its advantages, this technique also has a number of disadvantages, such as the frequent occurrence of malaligned fracture reductions and high X-ray exposure, especially to the operating team. The aim of our research is to overcome these shortcomings by utilizing modern techniques such as three-dimensional (3D) imaging, navigation, and robotics. In this paper we present the current state of our interdisciplinary research project. We first introduce a telemanipulated fracture reduction procedure, which is based on 3D imaging data. This set-up is improved one step further towards an automated fracture reduction procedure. Finally, two drilling tasks, namely the opening of the medullar cavity and the distal locking of the intramedullary nail, are presented, which are supported by automated X-ray-based image analysis and robot-assisted drill guidance. We show that high reduction accuracies can be achieved with our robotic system. Furthermore, the robot-assisted drill guidance achieves superior results with respect to increased precision and decreased X-ray exposure compared with the conventional procedure. We conclude that this surgical procedure benefits conspicuously from the support of robotic assistance systems and that further research and development in this field is worthwhile.

Robot-assisted fracture reduction: A preliminary study in the femur shaft

Reduction in femoral shaft fractures can be difficult to achieve with minimally invasive techniques. Malalignment and high intra-operative radiation exposure can result. The hypothesis was that robot-assisted fracture reduction could improve the quality of reduction while reducing the amount of radiation exposure. A robot system was developed that allows fracture manipulation with a joystick as input device. The system provides the surgeon with haptic and metric feedback. Fifteen synthetic femurs were broken and reduced by simulated open (group A) and closed techniques (group B). These techniques were compared with the robot-assisted reduction with (group C) and without (group D) haptic and metric information. An image intensifier was simulated with two orthogonal cameras. All reduction techniques showed minor malalignment. In group C, the alignment was: procurvatum/recurvatum 0.6° (0–2.0°); varus/valgus 0.8° (0–3.0°); and axial rotation 0.8° (0–3.1°). A significant difference was seen between the groups (two-way ANOVA, p<0.001). Axial rotation was significantly lower in group C than in group B (1.9°; p<0.001). The residual varus and valgus deviation was higher in group C compared with group A (0.4°, p=0.03). The median number of simulated radiographs was significantly less in group C (35) compared with group D (72; p<0.001) and group B (49; p=0.01). Robot-assisted fracture reduction of the femur provides high precision in alignment while reducing the amount of intraoperative imaging. Further research in this field is worthwhile.

Pose Estimation of Cylindrical Fragments for Semi-Automatic Bone Fracture Reduction

We present an approach for estimating the relative transformations between fragments of a broken cylindrical structure in 3d. To solve this problem, we first measure the orientation and position of the cylinder axes for each fragment by an adapted kind of Hough Transformation. The cylinder axes are an important feature for separation of fractured areas and for calculation of an initial reposition solution (constraining 4 DOFs). After these processing steps, we compute the relative transformations between corresponding fragments by using well-known surface registration techniques, like 2d depths correlation and the ICP (Iterative Closest Point) algorithm. One goal of our project is to use the proposed method for estimation of relative transformations between fragments of fractured long bones for computer aided and semi-automatic bone alignment and fracture reduction in surgery.

Robot‐assisted fracture reduction using three‐dimensional intraoperative fracture visualization: An experimental study on human cadaver femora

Closed fracture reduction can be a challenging task. Robot‐assisted reduction of the femur is a newly developed technique that could minimize potential complications and pitfalls associated with fracture reduction and fixation. We conducted an experimental study using 11 human cadaver femora with intact soft tissues. We compared robot‐assisted fracture reduction using 3D visualization with manual reduction, using 2D fluoroscopy. The main outcome measure was the accuracy of reduction. The manual reductions were done by an experienced orthopedic trauma surgeon, whereas the robot‐assisted reductions were done by surgeons of different experience. The robot‐assisted group showed significantly less postreduction malalignment (p < 0.05) for internal/external rotation (2.9° vs. 8.4°) and for varus/valgus alignment (1.1° vs. 2.5°). However, the reduction time was significantly (p < 0.01) longer (6:14 min vs. 2:16 min). The higher precision associated with robot‐assisted fracture reduction makes this technique attractive and further research and development worthwhile. In particular, less experienced surgeons may benefit from this new technique.

Robot Assisted Fracture Reduction

Reduction in femoral shaft fractures may be difficult to achieve with minimal invasive techniques. Malalignment and high intraoperative radiation exposures often results. Our hypothesis is that robot assisted fracture reduction may improve the precision of reduction while reducing the amount of radiation exposure. We present a telemanipulator system for robot assisted reduction of femoral shaft fractures. The telemanipulated reduction is performed with a 2 dof input device with haptical feedback based on intraoperatively acquired 3D imaging data. We performed a test series to measure achievable reduction accuracies on artificially broken human femur bones without soft tissues. Furthermore, we performed first tests for the reduction on complete human legs in 3D. It could be shown, that telemanipulated reduction of such fractures in 3D is yielding very good accuracies in an intuitive and efficient way. Robot assisted fracture reduction can improve the reduction accuracy and reduce the X-ray irradiation exposure to the patient and the OR staff.

A rat model for evaluating physiological responses to femoral shaft fracture reduction using a surgical robot.

The first step in treatment of displaced femoral shaft fractures is adequate reduction of the fracture fragments. Manually performed, reduction can be challenging, and is frequently associated with soft tissue damage, especially when repeated reduction attempts are made. The magnitude of local and systemic inflammatory responses caused by prolonged and repeated reduction maneuvers has not been fully established. We devised an operative technique utilizing a robotic reduction device for use in a rat. A femoral fracture was simulated by means of an osteotomy. The robot enabled reproduction of both manual and guided precision reductions, performed in a single path movement. An external fixator was designed specifically to manipulate the rat femur and also for fixation of the osteotomy region. First, reduction accuracy was assessed in eight femurs, then the quality of fixator placement and reduction accuracy was analyzed in 22 femurs. In the first case, 100% of the femurs were accurately reduced. In the second case, 91% had successful stable fixation and an accurate reduction was achieved in 86% of the specimens. We demonstrated the feasibility of a model of robot‐assisted fracture reduction that could be used to analyze the effects of reduction on the surrounding soft tissue via biochemical and histopathological means. A future aspect will be to evaluate whether the robot confers an advantage in fracture reduction versus the conventional technique, which would have significant implications for the use of robotic devices in orthopaedic surgery.

Robotic Cadaver Testing of a New Total Ankle Prosthesis Model (German Ankle System)

Background: An investigation was carried out into possible increased forces, torques, and altered motions during load-bearing ankle motion after implantation of two different total ankle prostheses. We hypothesized that the parameters investigated would not differ in relation to the two implants compared. Methods: We included two different ankle prostheses (Hintegra, Newdeal, Vienne, France; German Ankle System, R-Innovation, Coburg, Germany). The prostheses were implanted in seven paired cadaver specimens. The specimens were mounted on an industrial robot that enables complex motion under predefined conditions (RX 90, Stäubli, Bayreuth, Germany). The robot detected the load-bearing (30 kg) motion of the 100th cycle of the specimens without prostheses as the baseline for the later testing, and mimicked that exact motion during 100 cycles after the prostheses were implanted. The resulting forces, torques, and bone motions were recorded and the differences between the prostheses compared. Results: The Hintegra and German Ankle System, significantly increased the forces and torques in relation to the specimen without a prosthesis with one exception (one-sample-t-test, each p ≤ 0.01; exception, parameter lateral force measured with the German Ankle System, p = 0.34). The force, torque, and motion differences between the specimens before and after implantation of the prostheses were lower with the German Ankle System than with the Hintegra (unpaired t-test, each p ≤ 0.05). Conclusions: The German Ankle System prosthesis had less of an effect on resulting forces and torques during partial weightbearing passive ankle motion than the Hintegra prosthesis. This might improve function and minimize loosening during the clinical use.

Hands-on robotic distal interlocking in intramedullary nail fixation of femoral shaft fractures

INTRODUCTION Intramedullary nailing has become the gold standard in the treatment of femoral shaft fractures. This procedure involves the placement of distal interlocking bolts using the freehand technique. Accurate placement of distal interlocks can be a challenging task, especially in inexperienced hands. Misplacement of distal interlocking bolts can lead to iatrogenic fracture, instability of the bone-implant construct, or even malalignment of the extremity. Repeated drilling attempts increase radiation exposure and can cause additional bony and soft tissue trauma. We hypothesize that robot-guided placement of distal interlocks is more accurate, precise, and efficient than the freehand technique. METHODS A custom-designed drill guide was mounted onto the arm of an industrial robot. We developed a special device to secure a generic block (Synbone, Malans, Switzerland) into which an intramedullary nail could be inserted in a standardized way. A metric scale allowed later measurements of the drillings. Digital images were taken from each side of the block for analysis of the drilling trajectories. The fluoroscope was adjusted to obtain perfect circles of the distal interlocking holes. The number of images necessary to achieve this was recorded. The axis was recognized automatically by using the differences in contrast between the matrix of the generic bone and the implant (intramedullary nail). The drill trajectories were then computed. The robot with the mounted drill-guide automatically moved onto the calculated trajectory. The surgeon then executed the drilling. We performed 40 robot assisted drillings in generic blocks. Freehand drilling served as our control group. RESULTS Analysis of the digital images revealed a mean deviation of 0.94 mm and 2.7° off the ideal trajectory using robotic assistance. In 100% of the cases (n = 40), the distal locking hole was hit. A mean of 8.8 images was acquired. After manual drilling, 92.5% of the distal interlocks were hit. A mean deviation of 3.66 mm and 10.36° was measured. A mean of 23.4 fluoroscopic images were needed. The differences between the two methods were statistically significant. CONCLUSION Robot-guided drilling increases the accuracy and precision of distal interlocking while reducing irradiation. Considering economical and logistical aspects, this application should be integrated with robot-guided fracture reduction.

Effect of medial opening wedge high tibial osteotomy on intraarticular knee and ankle contact pressures

High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by shifting the center of force towards the lateral compartment. Previous studies have documented the effects of HTO on the biomechanics of the knee. However, the effects of the procedure on the contact pressures within the ankle joint have not been as well described. Seven cadavers underwent an HTO procedure with sequential 5° valgus realignment of the leg up to 15° of correction. An axial force of up to 550 N was applied and the intraarticular pressure was recorded. Minor valgus realignment of the proximal tibia does not significantly alter the biomechanics of the ankle. However, moderate‐to‐large changes in proximal tibial alignment result in significantly decreased tibiotalar contact surface area and in changes in intraarticular ankle pressures. These findings are clinically relevant, as they provide a biomechanical rationale for the diagnosis and treatment of ankle symptoms in the setting of lower limb malalignment or after alignment correction procedures.

Robotized access to the medullary cavity for intramedullary nailing of the femur

INTRODUCTION The insertion site for an antegrade femoral intramedullary nail in the treatment of a femoral shaft fracture has traditionally been performed using a free-hand technique. An inappropriate starting point can result in suboptimal nail insertion leading to malreduction, or iatrogenic fracture. Furthermore, repeated attempts to establish the optimal starting point can cause additional soft tissue trauma and radiation exposure. In the following study we compared a robot-guided technique with the standard free-hand technique for establishing the entry point of an antegrade femoral nail. We hypothesized that the robot-guided technique is more reliable and efficient. METHODS A custom-made drill-guide was mounted onto the arm of an industrial robot. Two orthogonal fluoroscopic images were acquired from the proximal femur of five cadaveric human specimens. Images were processed with a special software in order to create an enhanced contour-recognition map from which the bone axes were automatically calculated. The drilling trajectory was computed along the extension of the bone-axis. The robot then moved the drill-guide on this trajectory toward the entry point. The drilling was then performed by the surgeon. In the control group, five cadaveric human femora were utilized to manually establish the starting point using the free-hand technique. RESULTS 100% of the intramedullary cavities were successfully accessed with both the robot-guided and the manual techniques. In the manual technique repositioning of the drill was necessary in three out of five cases. The mean number of acquired fluoroscopic images was significantly reduced from 11.6 (manual) to 4 (robot-guided). CONCLUSION Robot-assisted drilling of the entry-point in antegrade femoral nailing is more reliable and requires fewer radiographic images than the free hand technique. Yet, based on economical and logistical considerations, its application will probably only be accepted when a concomitant application for fracture reduction is available.