Comparative biomechanical analysis of two techniques of radiolunate plate-fusion: oblique screw vs. parallel screws.

The purpose of this prospective randomized comparative biomechanical study on four pairs of human cadaveric forearms was to discern whether primary stability following plate arthrodesis differs from the position of the screws. Four wrists were randomly assigned to either group such that one wrist of each pair was fixed via parallel screws and the other via an oblique screw crossing the radius and the lunate. Under fluoroscopic guidance, passive extension and flexion of each wrist was performed using a spring balance. Traction force increased by 5 N at each step, ranging from 0 N to a maximum of 100 N. Fixation using a plate and oblique screw demonstrated lower recoverable deformation of the implant and a higher primary stability at the fusion site than parallel screws. The current investigators conclude that an oblique screw crossing radius and lunate increase primary stability which is consistent with the radiological results of comparable clinical trails.

Process optimized minimally invasive total hip replacement.

The purpose of this study was to analyse a new concept of using the the minimally invasive direct anterior approach (DAA) in total hip replacement (THR) in combination with the leg positioner (Rotex- Table) and a modified retractor system (Condor). We evaluated retrospectively the first 100 primary THR operated with the new concept between 2009 and 2010, regarding operation data, radiological and clinical outcome (HOOS). All surgeries were perfomed in a standardized operation technique including navigation. The average age of the patients was 68 years (37 to 92 years), with a mean BMI of 26.5 (17 to 43). The mean time of surgery was 80 min. (55 to 130 min). The blood loss showed an average of 511.5 mL (200 to 1000 mL). No intra-operative complications occurred. The postoperative complication rate was 6%. The HOOS increased from 43 points pre-operatively to 90 (max 100 points) 3 months after surgery. The radiological analysis showed an average cup inclination of 43° and a leg length discrepancy in a range of +/- 5 mm in 99%. The presented technique led to excellent clinic results, showed low complication rates and allowed correct implant positions although manpower was saved.

A standardized fracture reduction model for long bones--implication and evaluation in the femur.

Fractures of the femoral bone are frequent injuries with a wide range of affected individuals. New treatment strategies and technologies are being explored permanently. Their quality is biomechanically judged by the accuracy of the anatomical reduction. Malalignment of the fragments would have an eminent impact on the overall outcome and rehabilitation. To establish a method for investigations of the reduction results of femoral fractures, we developed a model, using a navigation system for taking measurement. The dynamic reference bases (DRBs) were mounted to the intact femoral bone and registered as the reference position. A special construction allowed removal and reattachment of the DRBs without provoking change in the DRB-bone system. The model was evaluated in its constancy. Translational deviations remained below 0.9 mm and rotational deviations below 0.3° after 40 repetitive reattachments. The model could prove to be valid and reliable. An application in long-bone trauma research is reasonable.

Electromagnetic induction heating of an orthopaedic nickel--titanium shape memory device.

Shape memory orthopaedic implants made from nickel-titanium (NiTi) might allow the modulation of fracture healing, changing their cross-sectional shape by employing the shape memory effect. We aimed to show the feasibility and safety of contact-free electromagnetic induction heating of NiTi implants in a rat model. A water-cooled generator-oscillator combination was used. Induction characteristics were determined by measuring the temperature increase of a test sample in correlation to generator power and time. In 53 rats, NiTi implants were introduced into the right hind leg. The animals were transferred to the inductor, and the implant was electromagnetically heated to temperatures between 40 and 60°C. Blood samples were drawn before and 4 h after the procedure. IL-1, IL-4, IL-10, TNF-α, and IFN-γ were measured. Animals were euthanized at 3 weeks. Histological specimens from the hind leg and liver were retrieved and examined for inflammatory changes, necrosis, and corrosion pits. Cytokine measurements and histological specimens showed no significant differences among the groups. We concluded that electromagnetic induction heating of orthopedic NiTi implants is feasible and safe in a rat model. This is the first step in the development of new orthopedic implants in which stiffness or rigidity can be modified after implantation to optimize bone-healing.

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.

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 degrees vs. 8.4 degrees ) and for varus/valgus alignment (1.1 degrees vs. 2.5 degrees ). 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.

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.

Three-dimensional measurement of femoral antetorsion: comparison to a conventional radiological method.

PURPOSE: The aim of our study was to produce a 3-D reconstruction of a CT dataset and compare it to the conventional method, with that same dataset, in terms of precision and the influence of femoral positioning. METHODS: A mechanical support was developed to rigidly fix the femur in a designated position. After measuring the real AT, a CT scan with different femur positions was performed. Eight cadaveric specimens were utilized for this study. Each examination was performed twice and the mean value was recorded. The Jend method was chosen as the conventional mode for femoral antertorsion measurement. In the 3-D reconstruction, the angle between the femoral neck and trailing edge of the femoral condyles was measured. RESULTS: Measurement of the AT by 3-D reconstruction (0.8 degrees ) was significantly better than the conventional method after (3.0 degrees ; P = 0.016). The positioning of the femur influences measurement of the femoral AT angle by conventional method measurement whereas evaluation using the 3-D reconstruction was more independent of femoral positioning. CONCLUSION: 3-D reconstruction enables precise determination of the femoral AT angle, and is independent of femoral positioning as conventional methods seem to be. In clinical practice, 3-D reconstruction may allow a greater understanding of the femoral AT angle post fracture reduction and internal fixation. However, we believe the 3-D method of measuring the AT-angle can potentially optimize the patient's treatment outcome by allowing the orthopaedic surgeon to measure the femoral AT-angle more precisely after femoral fracture reduction.

3D visualized robot assisted reduction of femoral shaft fractures: evaluation in exposed cadaveric bones.

The main problems in intra-medullary nailing of femoral shaft-fractures are leg-length discrepancies and rotational differences with an incidence of 2-18% and 20-40% respectively. These may lead to severe postoperative sequelae such as additional correctional operations and difficult rehabilitation. Insufficient visualization can be considered the main reason for these complications. Finally, retention of the fragments in the correct alignment before nail insertion is difficult. To overcome these problems we established a robotic telemanipulator system to support the reduction process. It was evaluated in 30 fractures of embalmed human femora. Specially programmed software used an image-dataset which was acquired by an isocentric 3D fluoroscope. For visualization, a surface projection was generated. Localization and tracking of the fragments and the robot-arm as well as accuracy measurement was performed by using an optical navigation system. Manipulation was controlled via a force-feedback joystick. This way, collisions of the fragments were transmitted back to the surgeon. At the end of the reduction the robot could rigidly retain the fragments' position.

Radiolunate fusion in the rheumatoid wrist via three point fixation with a mini-titanium-T-plate and oblique screw.

PURPOSE: Traditional surgical techniques for radiolunate arthrodesis typically result in an unsatisfactory primary stability. Thus cast immobilisation is implemented until bone healing is complete. Nonunion and implant dislocation are frequent complications. METHODS: Eighteen patients (20 wrists) with rheumatoid disease who had undergone a radiolunate arthrodesis procedure using a mini-titanium-T-plate with an oblique screw were examined. The high primary stability of this fusion depends on three point fixation. RESULTS: Complete bone healing was achieved in all wrists. Dislocation of a screw occurred in one wrist which subsequently healed in mild dislocation. Grip strength improved in 12 hands with pain relief in 19 wrists. 18 patients rated the result of the operation as "very good" or "good" and would agree to have the operation again. CONCLUSION: The mini-titanium-T-plate with oblique screw achieves high primary stability via three point fixation of the lunate at the radius. Thus, postoperative immobilisation in a cast is unnecessary. The procedure is well tolerated by patients with a high satisfaction rating.

Rotational stability of femoral osteosynthesis in femoral fractures - navigated measurements.

Rotational malalignment after intramedullary nailing of femoral fractures is common, and symptoms occur when malrotation reaches 15 degrees . Intraoperative measurement of rotation remains difficult, and multiple techniques have been described to address this. Regardless of the method used, rotational toggling may occur between the interlocking screws and the screw holes. We hypothesized that a clinically significant amount of rotation may occur with standard statically locked intramedullary nails. Mid-shaft diaphyseal fractures were created in 24 cadaveric femurs. Specimens were divided into 4 groups, and were stabilized with a statically locked intramedullary nail, a dynamically locked intramedullary nail, a compression plate, and a locking plate. Six additional femurs were kept intact as a control group. Specimens were mounted in a custom holding jig, which stabilized the constructs proximally and allowed free rotation distally. A computer navigation system was applied, and the femoral anteversion was measured. 4 N-m of internal and external torque was applied, and the change in version was measured. The statically locked nails rotated 14.2 degrees , and the dynamically locked group rotated 15.7 degrees . Both intramedullary nail groups showed significantly greater rotation than the plated groups. The compression plate specimens rotated 6.5 degrees on average, and the locked plate group rotated 3.8 degrees . Intramedullary femoral nailing with static or dynamic interlocking allows 15 degrees of rotation of the femur around the nail under physiologic load. This may exacerbate intraoperative errors in determining and setting rotation. Angular stable plates or nails may minimize this problem.

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.