Ten recommendations for sarcoma surgery: consensus of the surgical societies based on the German S3 guideline "Adult Soft Tissue Sarcomas".

PURPOSE: The evidence-based (S3) guideline "Adult Soft Tissue Sarcomas" (AWMF Registry No. 032/044OL) published by the German Guideline Program in Oncology (GGPO) covers all aspects of sarcoma treatment with 229 recommendations. Representatives of all medical specialties involved in sarcoma treatment contributed to the guideline. This paper compiles the most important recommendations for surgeons selected by delegates from the surgical societies. METHODS: A Delphi process was used. Delegates from the surgical societies involved in guideline process selected the 15 recommendations that were most important to them. Votes for similar recommendations were tallied. From the resulting ranked list, the 10 most frequently voted recommendations were selected and confirmed by consensus in the next step. RESULTS: The statement "Resection of primary soft tissue sarcomas of the extremities should be performed as a wide resection. The goal is an R0 resection" was selected as the most important term. The next highest ranked recommendations were the need for a preoperative biopsy, performing preoperative MRI imaging with contrast, and discussing all cases before surgery in a multidisciplinary sarcoma committee. CONCLUSION: The evidence-based guideline "Adult Soft Tissue Sarcomas" is a milestone to improve the care of sarcoma patients in Germany. The selection of the top ten recommendations by surgeons for surgeons has the potential to improve the dissemination and acceptance of the guideline and thus improve the overall outcome of sarcoma patients.

Tibial plateau fracture: does fracture classification influence the choice of surgical approach? A retrospective multicenter analysis.

PURPOSE: The role of classification systems for the choice of surgical approach and the management of tibial plateau fractures remains unclear. The purpose of this study was to investigate the potential of classification systems to choose the appropriate operative approach. Current surgical management strategies were investigated in a large multicenter assessment. METHODS: In this study, we retrospectively analyzed all patients with tibial plateau fractures that have received surgical treatment in one of the five Level I trauma facilities between 2012 and 2015. Fractures were classified in each center by a senior orthopedic surgeon using the AO/OTA and the Luo classification. Demographics, trauma mechanism, as well as the surgical approach were recorded. RESULTS: 538 patients (46.1% male, 53.9% female) were included. The anterolateral approach was used most frequently with 54.8% of all single approaches; 76.2% of all combined approaches used anterolateral as part of the approach. Combined approaches were used in 22.5% of the cases; a combination of the anterolateral and medial (10%), anterolateral, and posteromedial approach (5.8%) were used most frequently. The lowest number was found for the posterolateral (1.3%) and the combined approaches dorsal/anterolateral and medial/dorsal (1.7%, 1.1%). The AO/OTA classification showed a peak for 41.B2 (21.9%) and B3 (35.5%) fractures. Regarding the Luo classification, the dorsal column was involved in 45.7%. In contrast, only 14.7% of the surgical approaches used were able to address the dorsal tibial plateau potentially. CONCLUSION: The use of dorsal approach seems to be of minor importance than expected in daily clinical practice in this multicenter study. It was not possible to specify whether the AO/OTA or the Luo classification can reliably predict the choice of surgical approach. The operative treatment strategy of tibial plateau fractures seems to rather rely on the surgeons' experience, education, and preferences.

A Novel Shape Memory Plate Osteosynthesis for Noninvasive Modulation of Fixation Stiffness in a Rabbit Tibia Osteotomy Model.

UNLABELLED: 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, µCT, 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.

Transcutaneous electromagnetic induction heating of an intramedullary nickel-titanium shape memory implant.

PURPOSE: Inadequate mechanical stimuli are a major cause for nonunions following surgery for femoral and tibial shaft fractures. Adapting fixation rigidity during the course of fracture healing requires additional surgery. Nickel-titanium (NiTi) implants can change shape and rigidity by employing a temperature-dependent shape-memory effect. As a first step in the development of advanced intramedullary (IM) NiTi devices for fracture healing, this study aimed to test the feasibility and safety of transcutaneous electromagnetic induction heating of an IM NiTi implant in a rat model. METHODS: In 51 rats, NiTi implants were introduced into the left distal femur. Forty-four animals were transferred to an induction coil, and the implant was electromagnetically heated to temperatures between 40° and 60 °C Blood samples were drawn before and four hours after the procedure. Interleukin (IL)-1, IL-4, IL-10, tumour necrosis factor alpha (TNF-α) and interferon gamma (IFN-γ) were measured. Animals were sacrificed at three weeks. Histological specimens from the hind leg and liver were retrieved and examined for inflammatory changes, necrosis or corrosion pits. RESULTS: All animals successfully underwent the surgical procedure. Following transcutaneous induction heating, target temperature was confirmed in 37/44 rats. Postoperative controls showed no signs of undue limitations. Neither cytokine measurements nor histological specimens showed any significant differences between groups. There were no corrosion pits or necrosis. CONCLUSION: We conclude that electromagnetic induction heating of IM NiTi implants is feasible and safe in a rat femur model. These findings reflect a further step in the development of novel concepts for IM fracture fixation that might lead to better fracture healing, less patient discomfort and less need for surgical interventions.

Two-stage multilevel en bloc spondylectomy with resection and replacement of the aorta.

OBJECTIVE: We report a case of multilevel spondylectomy in which resection and replacement of the adjacent aorta were done. Although spondylectomy is nowadays an established technique, no report on a combined aortic resection and replacement has been reported so far. METHODS: The case of a 43-year-old man with a primary chondrosarcoma of the thoracic spine is presented. The local pathology necessitated resection of the aorta. We did a two-stage procedure with resection and replacement of the aorta using a heart-lung machine followed by secondary tumor resection and spinal reconstruction. RESULTS: The procedure was successful. A tumor-free margin was achieved. The patient is free of disease 48 months after surgery. CONCLUSION: En bloc spondylectomy in combination with aortic resection is feasible and might expand the possibility of producing tumor-free margins in special situations.

Assessment of the accuracy of infrared and electromagnetic navigation using an industrial robot: Which factors are influencing the accuracy of navigation?

Our objectives were to detect factors that influence the accuracy of surgical navigation (magnitude of deformity, plane of deformity, position of the navigation bases) and compare the accuracy of infrared with electromagnetic navigation. Human cadaveric femora were used. A robot connected with a computer moved one of the bony fragments in a desired direction. The bases of the infrared navigation (BrainLab) and the receivers of the electromagnetic device (Fastrak-Pohlemus) were attached to the proximal and distal parts of the bone. For the first part of the study, deformities were classified in eight groups (e.g., 0 to 5(°)). For the second part, the bases were initially placed near the osteotomy and then far away. The mean absolute differences between both navigation system measurements and the robotic angles were significantly affected by the magnitude of angulation with better accuracy for smaller angulations (p < 0.001). The accuracy of infrared navigation was significantly better in the frontal and sagittal plane. Changing the position of the navigation bases near and far away from the deformity apex had no significant effect on the accuracy of infrared navigation; however, it influenced the accuracy of electromagnetic navigation in the frontal plane (p < 0.001). In conclusion, the use of infrared navigation systems for corrections of small angulation-deformities in the frontal or sagittal plane provides the most accurate results, irrespectively from the positioning of the navigation bases.

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.

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.

Computer-assisted antetorsion control prevents malrotation in femoral nailing: an experimental study and preliminary clinical case series.

MATERIALS AND METHODS: The effect of fluoroscopy-based navigation for femoral fracture reduction on the prevention of malrotation was examined in an experimental setting followed by a first case series. Eleven cadaver femurs were used. All femurs were reduced by closed methods. An optoelectronic navigation system was utilized to check for fragment reduction and alignment. Fluoroscopic control without navigation was used as the control group. The Six Sigma Analysis [offset capability index (C (pk)) = 1.3] was used to compare the probability of outliers of more than 15 degrees . In the clinical case series the same navigation tool was used in ten non-consecutive patients with femoral fractures. Torsional differences between both legs were measured postoperatively by CT scan. RESULTS: The highest malrotation in the navigated group was 7.0 degrees for the cadaver testings, while two femurs in the control group showed a difference of more than 10 degrees (10.3 degrees , 17.4 degrees). Only the navigated group showed a sufficient offset capability index (C (pk-navigated) = 1.83; C (pk-conventional) = 0.59). In the clinical series nine femurs were successfully reduced by navigation control. The average malrotation was 6.6 degrees . No patient had a torsional difference of more than 10 degrees. CONCLUSION: Navigated femoral nailing reduces the risk for outliers of postoperative torsional differences and might avoid revision surgery for malrotation. LEVEL OF EVIDENCE: IV.

Utility of intraoperative three-dimensional imaging at the hip and knee joints with and without navigation.

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.

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.

Navigated pedicle screw placement: experimental comparison between CT- and 3D fluoroscopy-based techniques.

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 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.

Navigated femoral nailing using noninvasive registration of the contralateral intact femur to restore anteversion. Technique and clinical use.

The difficulty in assessing femoral rotation during intramedullary nailing is well-established. Navigation systems allow the surgeon to detect and set the version of the injured leg at the desired angle. We report the first cases of navigated femoral nailing using noninvasive registration of the contralateral uninjured leg to determine the patient's anatomy. This allows the desired femoral rotation, which is that of the healthy femur, to be statically locked to precisely match the contralateral limb.

First clinical results and consequences of intraoperative three-dimensional imaging at tibial plateau fractures.

Anatomic reduction and appropriate implant placement is essential for optimal treatment of intraarticular tibial plateau fractures. Standard intraoperative fluoroscopy provides limited visualization of the reduction and hardware placement compared with pre- or postoperative three-dimensional (3-D) imaging modalities. As such, postoperative computed tomography has become a common procedure to evaluate the quality of the reduction and fixation. The Iso-C3D provides 3-D intraoperative imaging to dynamically assess the surgical reduction and fixation at different anatomic regions. We report on our first 19 clinical tibial plateau fractures scanned intraoperatively with the Iso-C3D. When compared with conventional c-arm images, the Iso-C3D scans demonstrated improved ability to identify articular malreduction and implant malposition.

Recurrent shoulder instability among athletes: changes in quality of life, sports activity, and muscle function following open repair.

BACKGROUND: Recurrent anterior shoulder instability is a disabling condition in young athletes with possibly underestimated impact on quality of life and sports activity. Commonly used clinical scoring systems do not reflect the impairment of quality of life and sports activity. It was our aim to assess the return to preinjury levels of quality of life and sports activity as well as the changes in muscle function among competitive and recreational athletes. HYPOTHESIS: Patients suffering from post-traumatic recurrent shoulder instability have to adopt their participation in sports and therefore discover a reduction in quality of life. Open stabilization procedures are able to improve shoulder function and to reduce recurrence rates. However, return to preinjury shoulder function is not guaranteed. STUDY DESIGN: Retrospective longitudinal cohort study on 19 consecutive athletes with recurrent, post-traumatic shoulder instability. All patients were treated with an open, capsulo-labral repair. The minimum follow-up was 24 months. METHODS: Life quality (SF12) and sports activity data (Athletic Shoulder Outcome Scoring System) were retrospectively collected for the time before injury (time 1) and for the time with recurrent instability (time 2). Two years after surgical stabilization (time 3), we followed our patients with different clinical outcome scores, rotator surface EMG measurement, isokinetic muscle strength testing, and a radiological evaluation. This design of a three-step follow-up allowed for calculating the impact on quality of life and sports activity following the injury. RESULTS: Two years after surgery, the clinical scoring systems revealed good-to-excellent results in all patients. Quality of life physical component summary remained diminished by 9.2% despite the surgical procedure and was therefore significantly lower as compared to preinjury levels (p < 0.05). Sports activity was also significantly lower at the time of follow-up (p < 0.05). In this specific procedure, external rotation was not impaired postoperatively. EMG testing showed an overall reduction of muscle activity, however not significant. Isokinetic muscle strength was significantly diminished for external rotation and shoulder abduction. CONCLUSIONS: Open reconstruction procedures for recurrent shoulder instability can restore shoulder function and stability to near-normal values. Despite good-to-excellent clinical results, there is a significant impairment of quality of life and sports activity 2 years after surgery. Muscle activity and muscle strength are diminished. Recurrent shoulder instability remains a disabling condition to the young athlete. Future strategies have to emphasize restoration of quality of life, sports activity, and muscle function.

Forces and torques during fracture reduction: Intraoperative measurements in the femur.

Reduction is a crucial step in fracture treatment. We determined intraoperative peak forces and torques during fracture reduction in seven patients with eight fractures of the femoral shaft. All fractures were temporarily stabilized by external fixation. Force and torque measurements were performed during the subsequent intramedullary nailing procedure. A three-dimensional load cell was attached to the distal femur fragment using two Schanz screws. All forces and torques were registered on-line during the reduction process. The maximum resulting force was 411 N, the maximum resulting torque 74 N x m. The highest force was observed along the shaft axis with 396 N for distraction. The maximum torque value was measured around the frontal axis, being 74 N x m for antecurvature. These results may assist the development of new reduction techniques and devices.

Minimally invasive exchange tibial nailing for a broken solid nail: case report and description of a new technique.

We present a minimally invasive technique for the removal of a broken solid tibial nail. A special device was invented that minimizes the extraction difficulties. After minimal over-reaming, the device is slid in an antegrade fashion over the nail and locked. Retraction is safe and easy. This article is an illustrative case-presentation describing the device and the surgical technique.

Navigated intraoperative analysis of lower limb alignment.

INTRODUCTION: Accurate intraoperative assessment of lower limb alignment is crucial for the treatment of long bone fractures, implantation of knee arthroplasties and correction of deformities. During orthopaedic surgery, exact real time control of the mechanical axis is strongly desirable. The aim of this study was to compare conventional intraoperative analysis of the mechanical axis by the cable method with continuous, 3-dimensional imaging with a navigation system. MATERIALS AND METHODS: Twenty legs of fresh human cadaver were randomly assigned to conventional analysis with the cable method (n = 10) or navigated analysis with a fluoroscopy based navigation system (n = 10). The intersection of the mechanical axis with the tibia plateau was presented as percentage of the tibia plateau (beginning with 0% at the medial border and ending with 100% laterally). CT-scans were performed for all legs and the CT-values of the mechanical axis were compared to the measurements after cable method and navigation. Furthermore, the radiation time and dose area product of both groups for single analysis of the mechanical axis was compared. RESULTS: Conventional evaluation of the mechanical axis by the cable method showed 6.0+/-3.1% difference compared to the analysis by CT. In the navigated group the difference was 2.6+/-1.8% (P = 0.008). Radiation time and dose area product were highly significantly lower after conventional measurement. CONCLUSIONS: Navigated intraoperative evaluation of the mechanical axis offers increased accuracy compared to conventional intraoperative analysis. Furthermore, navigation provides continuous control not only of the mechanical axis, but also of the sagittal and transverse plane. Using the cable method, radiation exposure depends on the number of measurements and is lower compared to the navigation system for single intraoperative analysis of the mechanical axis, but may be higher in case of repeated intraoperative measurements.