OBJECTIVES:To develop an accurate intraoperative method to estimate changes in intraarticular contact pressures during high tibial osteotomy (HTO).METHODS:Changes in knee alignment and pressure were monitored in real time in seven cadaver specimens that received HTO. Intraarticular contact pressure (N/mm2 ) in each knee compartment was estimated based on extraarticularly acquired data (leg alignment, correction, and ankle tilt) and based on the application of an axial force of half bodyweight (400-450 N).RESULTS:Contact pressure estimation was more accurate in the lateral compartment (R2  = 0.940) than in the medial compartment of the knee (R2  = 0.835). The optimism-corrected R2 was 0.936 for the lateral compartment and 0.821 for the medial compartment.CONCLUSIONS:We have established a framework for estimating the change in intraarticular contact pressures based on extraarticular data. This research could be helpful in generating appropriate algorithms to estimate joint alignment changes based on applied loads.

IntroductionThe field of robot-assisted fracture reduction has been developed by several research groups over more than one decade by now, with the main goals of increasing the fracture reduction accuracy. However, the influence of different reduction paths to patients’ physiology is not fully known yet. The aim of our study was to compare the impacts of a robot-assisted direct reduction path versus an artificially prolonged reduction path by measuring the cytokine responses in an in vivo rat model.Materials and methodsThirty-six male CD© rats were assigned into three groups with an external fixator and osteotomy on the left femur. Seven days later, the robot was attached and one group was reduced in a single attempt, while the other group underwent 10 attempts by the robot. The third group was the control group without reduction. Before, and as well as 6, 24 and 48h after the reduction process blood samples were collected. IL-1, IL-6, IL-10, IL-17, and MCP-1 concentrations where analysed via ELISA or cytometric bead assay. Muscle biopsies in the osteotomy area were collected 48h after the reduction process for histological analyses. Statistical significance was set at p≤0.05.ResultsAnalysis of the cytokines showed that the pro-inflammatory cytokine IL-6 of the Ten-Attempts reduction group significantly increased 6h after reduction compared to the control group. IL-6 further showed markedly elevated levels 6h after surgery in the Ten-Attempts reduction group compared to the Single-Attempt reduction group. On the anti-inflammatory side, IL-10 showed a significant decrease in the Ten-Attempts reduction group 6h after reduction compared to the Single-Attempt reduction and control group. Muscle biopsies showed a significant increase of pathological changes in both reduction groups and an increase in the severity of bleedings of the Ten-Attempts reduction group compared to the Single-Attempt reduction and control group.ConclusionA direct and gentle reduction procedure as feasible by the aid of a robot is preferable over a prolonged reduction in terms of cytokine response and tissue changes.

Nickel-titanium shape memory alloy (NiTi-SMA) implants might allow modulating fracture healing, changing their stiffness through alteration of both elastic modulus and cross-sectional shape by employing the shape memory effect (SME). Hypotheses: a novel NiTi-SMA plate stabilizes tibia osteotomies in rabbits. After noninvasive electromagnetic induction heating the alloy exhibits the SME and the plate changes towards higher stiffness (inverse dynamization) resulting in increased fixation stiffness and equal or better bony healing. In 14 rabbits, 1.0 mm tibia osteotomies were fixed with our experimental plate. Animals were randomised for control or induction heating at three weeks postoperatively. Repetitive X-ray imaging and in vivo measurements of bending stiffness were performed. After sacrifice at 8 weeks, macroscopic evaluation, µ CT, and post mortem bending tests of the tibiae were carried out. One death and one early implant dislocation occurred. Following electromagnetic induction heating, radiographic and macroscopic changes of the implant proved successful SME activation. All osteotomies healed. In the treatment group, bending stiffness increased over time. Differences between groups were not significant. In conclusion, we demonstrated successful healing of rabbit tibia osteotomies using our novel NiTi-SMA plate. We demonstrated shape-changing SME in-vivo through transcutaneous electromagnetic induction heating. Thus, future orthopaedic implants could be modified without additional surgery.

The purpose of this study was to evaluate the different temperature levels whilst drilling cemented and cementless hip prostheses implanted in bovine femora, and to evaluate the insulating function of the cement layer.

PURPOSE:The purpose of this study was to evaluate the different temperature levels while drilling solid materials and to compare different cooling solutions for possible temperature control. An additional purpose was to develop an internal cooling device which can be connected to routinely used manual drilling devices in trauma surgery.METHODS:Drilling was performed on a straight hip stem implanted in bovine femora without cooling, with externally applied cooling and with a newly developed internal cooling device. Temperature changes were measured by seven thermocouples arranged near the borehole. Additionally, thermographic scans were performed during drilling.RESULTS:Drilling without cooling leads to an immediate increase in temperature to levels of thermal osteonecrosis (over 200 °C). With externally applied cooling temperatures were decreased, but were still up to a tissue damaging 85 °C. Internally applied cooling led to a temperature decrease to tissue-preserving levels during the drilling procedure (24.7 °C).CONCLUSION:Internal cooling with HPC-drillers lowered the measured temperatures to non-tissue damaging temperatures and should avoid structural tissue damage.

AIM:To develop new fixation techniques for the treatment of periprosthetic fractures using intraprosthetic screw fixation with inserted threaded liners.METHODS:A Vancouver B1 periprosthetic fracture was simulated in femur prosthesis constructs using sawbones and cemented regular straight hip stems. Fixation was then performed with either unicortical locked-screw plating using the less invasive stabilization system-plate or with intraprosthetic screw fixation using inserted liners. Two experimental groups were formed using either prostheses made of titanium alloy or prostheses made of cobalt chrome alloy. Fixation stability was compared in an axial load-to-failure model. Drilling was performed using a specially invented prosthesis drill with constantly applied internal cooling.RESULTS:The intraprosthetic fixation model with titanium prostheses was superior to the unicortical locked-screw fixation in all tested devices. The intraprosthetic fixation model required 10 456 N ± 1892 N for failure and the unicortical locked-screw plating required 7649 N ± 653 N (P < 0.05). There was no significant difference between the second experimental group and the control group.CONCLUSION:Intraprosthetic screw anchorage with special threaded liners enhances the primary stability in treating periprosthetic fractures by internal fixation.

This article shows an approach to change the properties of an orthopaedic shape memory implant within biological tissue, using contactless induction heating. Due to inducing the one way-memory effect, triggered by the rise of temperature within the implant, the geometry and hence the mechanical properties of the implant itself, are altered. The power uptake of the implant, depending on the induction parameters as well as on its position within the induction coil, is shown. Thermographic measurements are carried out in order to determine the surface temperature distribution of the implant. In order to simulate biological tissue, the implant was embedded in agarose gel. Suitable heating parameters, in terms of a short heating process in combination with a reduced heat impact on the surrounding environment, were determined.

BACKGROUND Use of the proximal part of the femur in total hip arthroplasty enables preservation of the distal femur for later revisions. To use this advantage, different types of short-stem prosthesis have been developed in recent years. Although cementless hip arthroplasty is not common in the treatment of canine osteoarthritis, the use of cementless short-stems might be an alternative therapy. The new cementless short-stem prosthesis called Spiron® is self-tapping, and is constructed with a conical shape with threads. We measured the relative motion in the bone/prosthesis interface with specified loads in the femora of dogs to investigate two aspects: the primary stability of two systems of uncemented prosthesis with different principles of anchoring, and the theoretical use of the Spiron® in dog bone. We measured the cyclic behaviour (i.e., reversible, elastic), subsidence (i.e., irreversible, plastic, migration) and maximal applied load. METHODS Twenty-four pairs of fresh femur bones from adult German shepherd dogs were used. After measuring the total bone mineral density (TBMD), 16 bones were used in each of the short-stem prosthesis group (group A), the Zweymuller prosthesis group (group B), and the no-prosthesis control group (group C). Micromotion between bone and prostheses was measured for 16,200 N axial load steps, beginning with 200 N and increasing to 3000 N (1600 cycles/femur). Simple analysis of variance and non-parametric tests were used to compare the groups. RESULTS The Spiron prosthesis had significantly less motion in the bone/prosthesis interface compared with the Zweymuller prosthesis. CONCLUSIONS The new principle of anchoring of the Spiron short-stem prosthesis may provide higher primary stability compared with conventional techniques. The findings of this study support the assumption that the use of the Spiron prosthesis to treat osteoarthritis in the dog is feasible.

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.

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.

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 establishthe optimal starting point cancause 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 specialsoftwarein 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 pointusing 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 ofthe entry-point in antegrade femoral nailingis 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.

Intraoperative three-dimensional imaging in orthopaedic trauma care has achieved greater importance over the last few years in some specialized hospital centers. For various types of peripheral-extremity trauma, clinical studies have confirmed, on the basis of three-dimensional information, an intraoperative revision rate ranging from 7% to 19%. Three-dimensional C-arm imaging may be used to achieve adequate intraoperative information about the quality of fracture reduction, residual steps, and correct implant placement, and this technique has been described for use in both the hip joint (for acetabular fractures, isolated femoral head [Pipkin-type] fractures, three-dimensional navigated sacroiliac screw or acetabular column screw placements, and, less frequently, for navigated drilling of tumors or osteochondral lesions) and the knee joint (for tibial plateau fractures, complex distal femoral condylar fractures, and navigated targeting of osteochondral lesions in combination with the use of preoperative magnetic resonance imaging scans). Major limitations of this technology include increased intraoperative time requirements, limited image quality compared with that of computed tomographic scans, cost, specific positioning techniques, and the need for radiolucent operating-room tables. Although prospective studies have yet to be conducted, the ways in which the surgeon will benefit from the use of intraoperative three-dimensional imaging are apparent, but indications for combined three-dimensional C-arm navigated procedures at the hip and knee joint are still limited. Future directions may include the use of digital flat-panel detectors and even robotic-controlled C-arm motion.

The preferred treatment of femoral shaft fractures nowadays is the minimally invasive technique of intramedullary nailing. However, besides its advantages, this technique also has a number of drawbacks like the frequent occurrence of malaligned fracture reductions and high X-ray exposures, especially to the operating team. The aim of our research is to overcome these shortcomings by utilizing 3D imaging and surgical navigation techniques in combination with a robot assisted reduction procedure. Even though telemanipulated reductions as developed in our earlier work can achieve high accuracies for simple fracture types, we show how reductions of more complex fractures can benefit from the developed automated methods by ensuring high reduction accuracies and attaining gentle reduction trajectories. We outline a system, which automatically computes the desired target poses of the fragments from 3D imaging data and focus on the algorithms, which plan reduction paths complying with soft-tissue constraints. In addition we propose how to automatically execute these plans by means of hybrid (position and force/torque) controlled skill primitives. In a feasibility study we finally show the applicability of this approach.

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.

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.

Fractures of the human thigh bone, the femur, are commonly caused by high-energy injury mechanisms, like traffic accidents, predominantly in young males or by low-energy mechanisms, like falling, in elderly females (Martinet et al., 2000; Zlowodzki et al., 2006). With approximately 37 per 100,000 persons per year this is an extremely frequently encountered injury (Arneson et al., 1988; Zlowodzki et al., 2006). In 1999 334,410 patients with fractures of the lower extremities have been counted in Germany1. 144,659 of which had fractures of the thigh bone. After subtracting fractures in the proximal (hip side) femur, 25,695 patients remain with fractures in the femoral shaft (the middle, diaphyseal) region to which this work is dedicated. Today, the treatment of choice for femur shaft fractures preferred by many surgeons is the minimal invasive technique of intramedullary nailing, which has been established as a standard technique for a definite stabilizing treatment in diaphyseal fractures of the lower extremities (Kempf et al., 1985; Krettek et al., 1996; Krettek, 2001; Winquist et al., 1984). The complete process of intramedullary nailing is shown as a sketch in figure 1. The process starts with the opening of the medullary cavity. A small soft tissue cut of about 5 cm has to be placed at the proximal end of the femur. In extension of the femoral shaft, the bone's cavity has to be opened. This is achieved with a surgical drill. Now the intramedullary nail is inserted into the bone's medullary cavity until it reaches the fracture region. Subsequently the two major bone fragments are aligned accordingly to their correct anatomical position. For this the distal (knee side) fracture segment is moved by the surgeon by means of a socalled Schanz' screw, whereas the proximal fracture segment is hold in its position by means of a second Schanz' screw. According to (Ruedi & Murphy, 2000), this form of manipulation is called “joystick” reduction. When the fracture segments are finally aligned correctly, the intramedullary nail is further inserted. Finally the nail is locked with the bone by means of lateral screws. During the final insertion and the locking of the nail, the correct retention, which means maintaining the correct segment positions, has to be ensured. The whole process is supervised by means of X-ray imaging. A detailed description of this surgical procedure can be found in (Ruedi & Murphy, 2000).

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.

Objective: Even with CT-based navigation, the misplacement rate for pedicle screws is reported to be as high as 10%. Using fluoroscopy-based 3D navigation, misplacement rates of 1.7 to 6% occur. The purpose of this study was to compare the accuracy of CT-based and Iso-C-based navigation in an experimental context.Methods: A foam spine model and the SurgiGATE(R) navigation system were used. First, a determination of point accuracy measured the difference between the real positions of markers placed on selected vertebrae and their positions as determined by the navigation system. In the verification mode, the pointer is placed exactly on the markers displayed on the monitor screen, and the deviation of the pointer tip and marker is measured in reality using a caliper. Secondly, pedicle accuracy was measured using pre-drilled holes for pedicle screws. A trajectory was planned into the visible hole and the navigated pointer was placed.Results: The measured accuracy for the markers showed a statistically significant difference between the results with CT and Iso-C navigation for one of six markers placed on the vertebra. Iso-C-based navigation demonstrated a lower mean deviation of 0.5 mm, compared to 1 mm with CT-based navigation. The deviation within the pre-drilled holes was lower when using the Iso-C3D scan. Using Iso-C3D navigation, 76.6% of the measurements showed no deviation at the entrance point, compared with 43% when using CT-based navigation. Also, with Iso-C3D navigation, 78.3% of the inserted pedicle awls hit the defined trajectories in the pre-drilled holes correctly, compared to 66.6% with CT-based navigation.Conclusion: The overall image-to-reality accuracy for CT- and Iso-C-based navigation was assessed in the described experimental setup. An apparent tendency towards higher accuracy with Iso-C-based navigation was evaluated; however, the differences were not significant.