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.

Mutational Studies of Aldose Reductase to Trace a Transient Pocket Opening and to Explain Ligand Affinity Cliffs.

Human aldose reductase, a target for the development of inhibitors for preventing diabetic complications, displays a transient specificity pocket which opens upon binding with specific, potent inhibitors. We investigated the opening mechanism of this pocket by mutating leucine residues involved in the gate keeping mechanism to alanine. Two isostructural inhibitors distinguished only by a single nitro to carboxy group replacement, have a 1000-fold difference in their binding affinity to the wild type. This difference is reduced to 10-fold in the mutated variants as the nitro derivative loses in affinity but conserves binding to the open transient pocket. The affinity of the carboxylate analog is minimally altered but the analog binding preference changes from the closed to open state of the transient pocket. Differences in the solvation properties of ligands and the transient pocket as well as changes from induced fit to conformational selections provide an explanation for the altered behavior of the ligands with respect to their binding to the different variants.

Mechanical stability analysis of reference clamp fixation in computer-assisted spine surgery.

BACKGROUND: Pedicle screw misplacement is a common complication, while 7% may result in neurological complications. Computer-assisted navigation improves the rate of ideally placed screws. Inappropriate reference marker attachment can cause major problems in the outcome and duration of surgery. OBJECTIVE: To improve fixation of reference bases by comparing different designs of spine clamps and measuring their stability against the relevant thoracic and lumbar anatomy. METHODS: Force needed to dislocate the clamp from the processus spinosus using defined fixation of 0.79, 0.90 and 1.02 Nm torque was evaluated. Force transmission from clamp to the processus spinosus was also examined. Artificial thoracic and lumbar vertebral bodies were used for attaching spine clamps of three different designs. An instrument transmitted linear force onto the reference clamp and recorded the force when dislocation occurred. Another device determined transmitted force for each clamp utilizing 0.79, 0.90, 1.02, 1.13 and 1.24 Nm torque. RESULTS: L-clamp had the most stable fixation in lumbar section for every torque and developed the greatest forces. These transmitted forces were similar to the less stable Y-design. I-design created the smallest forces and had the most stable fixation for thoracic spine. The Y- and the L-design caused a notably high number of fractures. CONCLUSION: Great force leads to great stability, but also creates more fractures, favoring the use of smaller forces. Specific anatomy adaptation is important. Different clamp designs create different forces, while still differing in stability depending on their application in the thoracic or the lumbar spine.

Femoral malrotation following intramedullary nailing in bilateral femoral shaft fractures.

INTRODUCTION: This study was designed to evaluate the incidence of femoral malrotation in bilateral femoral shaft fractures. MATERIALS AND METHODS: All closed bilateral femoral shaft fractures in patients aged 18 or over treated between April 2000 and December 2009 were included in the current study. All patients received a postoperative CT-scan to estimate femoral antetorsion and leg length. All bilateral fractures were treated with intramedullary nailing on a radiolucent table. Retrospectively, all patients were analyzed according to the following parameters: (1) femoral antetorsion of both limbs and antetorsion difference in degrees, (2) femoral length discrepancy (cm), (3) incidence of femoral malrotation >15°, (4) revision rate due to femoral malrotation. RESULTS: A total of 24 patients (11 [45.8%] female; 13 [52.8%] male) with bilateral femoral shaft fractures were included in this study of average age 38 years (median 38 years, range 18-74 years). Clinically relevant malrotation (greater than 15°) was found in 10 cases (41.2%), whereas in 4 cases (40%) a revision surgery was required. DISCUSSION: Bilateral femoral shaft fractures are associated with a high incidence of clinically relevant femoral malrotation over 15°. Measurement of intraoperative femoral antetorsion in bilateral femoral shaft fractures is quite difficult and currently only feasible postoperatively.

Influence of femoral malrotation on knee joint alignment and intra-articular contract pressures.

INTRODUCTION: The standard treatment of femoral diaphyseal fractures is intramedullary nailing. Torsion error remains a largely unsolved problem. We hypothesized that femoral malrotation would change the coronal alignment of the lower extremity and the center of force (COF) in the tibiofemoral joint as compared to the native state. METHOD: Ten cadaveric legs were used. Intraarticularly placed sensor foil was used to measure contact pressures for each condyle. The resultant pressure of this two-force measurement was calculated as the COF for the joint. Mechanical axis was defined by the navigation system. Two novel devices were used: (1) to simulate bodyweight with leg attachment and fixation to the anterior pelvis and (2) to fix the femur at various degrees of malrotation. A mid-diaphyseal osteotomy was performed and the distal fragment was rotated both internally and externally in 5° increments to a maximum of 25°. COF and axial alignment were assessed at each step with application of a half-bodyweight specific to each specimen. RESULTS: Internal rotation resulted in valgus deviation of the mechanical axis and a shift in COF towards the lateral condyle (P < 0.05). External rotation caused varus deviation and switched COF towards the medial condyle (P < 0.05). This study shows that femoral malrotation has a significant effect on mechanical axis alignment and force vectors within the knee. Correlation with clinical outcomes is necessary and further research into minimizing such errors of torsion is warranted. CONCLUSION: Torsion errors are not merely cosmetic issues, but may result in further morbidity, such as varus or valgus deformity and shifting of the COF, which may lead to joint arthrosis.

Reliability of computer-assisted surgery as an intraoperative ruler in navigated high tibial osteotomy.

BACKGROUND: Computer-assisted surgery (CAS) can act as an intraoperative ruler in high tibial osteotomy (HTO) to visualize continuously the leg during surgery. QUESTIONS: The aim of the study is to evaluate the accuracy of CAS with respect to preoperative planning and postoperative deviation from the planned leg axis in HTO. In addition, the influence of surgeon experience as well as operation time and perioperative complications are analyzed. METHODS: A prospective multicenter study case series with follow-up at 6 weeks was performed in six centers. Medial open-wedge HTO with Tomofix(®) was done using computer assisted navigation technique with the Brainlab VV Osteotomy 1.0 module. RESULTS: Fifty-one patients with medial gonarthritis were treated with navigated HTO. The follow-up rate was 98%. The majority of HTO-CAS patients fell within the tolerated limit of ±3° for leg axis deviation, however, seven patients were reported with deviations outside of this range: three patients had deviations of >3°-4.5° and four patients >4.5°, respectively. Eight intraoperative complications were documented, partially resulting from technical problems associated with the navigation system. During the 6-week follow-up period, three postoperative complications were experienced, all not associated with navigation technology. CONCLUSIONS: In about 85% of cases, a perfect result in terms of deviation of the planned mechanical leg axis could be achieved. Computer assistance in HTO proved to be a helpful tool regarding intraoperative control of leg axis. LEVEL OF EVIDENCE: Level I, High quality prospective study (all patients were enrolled at the same preoperative planning point with ≥80% follow-up of enrolled patients).

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.

A customized modular reference array clamp for navigated spine surgery.

INTRODUCTION: The current authors have developed a modular system of reference array fixation which is tailored specifically to the spinal level being operated upon. They believe that this system may further increase the precision and accuracy of pedicle screw placement. MATERIALS AND METHODS: Two formalin-fixed whole body cadavers were used for this study. For cervical spine evaluation of the reference clamp, four odontoid screws (two per cadaver) for C1/C2-fusion and four lateral mass screws (two per cadaver) were implanted. Following navigated screw placement with 2D and 3D fluoroscopic verification, insertion of two lateral mass screws was performed. In the same way, lumbar and thoracic pedicle screws were implanted. Two pedicle screws were placed at two levels of the lumbar and two levels of the thoracic areas giving an overall of 16 screws implanted (8 cervical, 4 thoracic, and 4 lumbar). Postoperative evaluation involved comparison of postoperative 3D scans and preoperative planning images. A simple classification system was used for evaluation of any deviation from the planned trajectory. RESULTS: All pedicle screw placements were performed as planned without any technical problems. The reference array clamps remained in position at all the spinal levels at which they were employed with no loosening or displacement and no secondary damage to any of the spinous processes. Manual manipulation was performed but no displacement or slippage was observed. Image artefacts caused by the reference clamp were not significant as to obscure the area of interest. Both imaging modalities (Iso-C 3D and Vario 3D) generated sufficiently precise 3D images. There was no substantial difference in quality when those two systems were compared. DISCUSSION: Insufficient fixation of the reference clamp can lead to failure and complications. To date, no reference clamp systems have been developed specifically for navigated spine surgery. CONCLUSIONS: Stable reference array fixation is a critical step in navigated surgery. To date, the same reference clamps have been applied to the spinal anatomy as have been developed originally for the appendicular skeleton. The current investigators have developed a novel modular clamp and have demonstrated its efficacy in a cadaveric model.

Navigated scaphoid screw placement using customized scaphoid splint: an anatomical study.

INTRODUCTION: Accuracy in navigated surgery depends on placement and registration of stable reference markers close to the anatomic region of interest. Navigation in small and complex anatomic regions, such as the scaphoid, is challenging due to difficulties in placing a stable reference marker. In the current paper, we describe the use of a customized wrist-positioning device "Scaph-splint" with a built-in reference marker that facilitates navigated scaphoid screw insertion in combination with a 3D imaging device. MATERIALS AND METHODS: Initial cadaveric feasibility study Five fresh-frozen cadaveric upper extremity specimens were utilized. Each specimen was secured onto the "Scaph-splint" with the wrist in about 90 degrees of extension. Using a 3D fluoroscope, a series of images were taken of the carpal bones and reconstructed in axial, sagittal, and coronal planes. Navigated planning and guidance of scaphoid drilling and screw placement was performed. Next, a repeat 3D scan was taken to analyze the drill canal. The accuracy of navigated scaphoid drilling, drilling trials, and any penetration of the scaphoid outside of the planned drill trajectory were evaluated. A grading scheme was used to assess the drilling accuracy: Grade 1 <1 mm deviation, Grade 2 <2 mm deviation, Grade 3 <3 mm. RESULTS: Scaphoid drilling was confirmed to be completely accurate (Grade 1) in two specimens, highly accurate (Grade 2) in two specimens, and accurate (Grade 3) in one specimen. No specimen required a repeat drilling of the scaphoid. In one specimen, the proximal scaphoid pole was perforated by the drill. No registration failures or loosening of the reference marker occurred. CONCLUSION: The use of the "Scaph-splint" enabled stabilization of the hand and wrist, thus adequately fixing the reference marker in relation to scaphoid for optimal navigation and screw placement without the need to directly penetrate the scaphoid with a reference marker. The use of 3D fluoroscopy further increased the accuracy and precision of scaphoid screw placement.

Intraoperative 3D imaging: value and consequences in 248 cases.

BACKGROUND: Intraoperative visualization of articular surfaces is technically demanding, and standard two-dimensional fluoroscopic imaging frequently does not provide adequate detail of nonplanar joints. New imaging modalities allow for intraoperative 3D visualization, which are useful in articular fractures. Purpose of this study was to evaluate the utility of 3D imaging in articular fracture reconstruction. METHODS: In a prospective cohort study, we evaluated 248 consecutive patients with intra-articular fractures. After fracture fixation using standard fluoroscopy, 3D imaging was performed intraoperatively using the Iso-C3D system for all patients. Surgeons filled out questionnaires regarding the utility and perceived accuracy of the 3D system. Postoperative CT scans were performed on approximately half of the patients. Main outcome measurements were based on the surgeons decision to immediately revise the articular reduction or implant position. The setup time for the system was recorded. For patients with postoperative CT scans, articular surface gaps of 2 mm or intra-articular hardware placement was again evaluated. RESULTS: In 19% of all cases, intraoperative image analysis resulted in immediate adjustment of the reduction or hardware exchange. These revisions were based on Iso-C3D views of the articular surface that were not visible using fluoroscopy. Of the 129 postoperative CT scans, five cases revealed a technical error of the joint reconstruction, and a secondary revision procedure was performed. CONCLUSION: In conclusion, the Iso-C3D was a valuable intraoperative tool, providing additional information about the articular surface compared with conventional fluoroscopy in a variety of anatomic regions.

Comparative study of different intraoperative 3-D image intensifiers in orthopedic trauma care.

INTRODUCTION: Recently, isocentric C-arm fluoroscopy (Iso-C 3D) has been introduced as a precise imaging modality for intraoperative evaluation and management of fractures and osteosyntheses. The Siemens Iso-C 3D collects multiple fluoroscopic images during a 190-degree arc of rotation around the anatomic region of interest and reconstructs them into sagittal, axial, and coronal planes. Like the Iso-C 3D, the new Ziehm Vario 3D imaging system reconstructs images in multiple planes, but only requires a 136-degree arc of rotation. The purpose of this study was to compare the image quality and range of applicability of these two imaging systems. METHODS: All the tests were performed on a human cadaver. In the first part of the experiment, different bones and joints were scanned in their native condition using both the Iso-C 3D and Vario 3D. In the second part of the experiment, scans were performed in the same anatomic regions after simulated fractures and subsequent fixation. In some cases, suboptimal placement of hardware was intentionally undertaken. Direct visualization of the fracture construct and in certain cases computed tomographic (CT) imaging served as the gold standard. The scans from both imaging systems were analyzed using a DICOM viewer by five orthopedic trauma surgeons randomized and blinded to the study. The evaluation was based on the overall image quality, delineation of cancellous and cortical bone, delineation of joint surfaces, presence of artifacts, visualization quality of intra-articular incongruities, quality of reduction and implant positioning, and clinical applicability of the scan. These items were rated using a visual analog scale and a points system. A total of 55 3D scans were made and evaluated. RESULTS: There was no significant difference between the two imaging systems in terms of the overall image quality, delineation of cancellous and cortical bone, and the presence of artifacts. The delineation of joint surfaces was significantly better visualized with the Iso-C 3D. Furthermore, Iso-C 3D scans demonstrated a higher overall clinical applicability than Vario 3D images. However, the Vario 3D was able to provide superior quality with scans of the shoulder joint and the adipose tissue. There was no significant difference in the visualization of intra-articular incongruities, quality of reduction, and implant positioning. CONCLUSION: Although the Iso-C 3D imaging system was superior in delineating the joint surfaces, the image quality, and the overall clinical applicability, the study revealed that both devices provided 3D images with sufficient quality to the surgeon to assess clinically relevant questions, including the quality of fracture reduction and implant positioning. On the other hand, the Ziehm Vario 3D is capable of doing scans of the shoulder area, which could not be taken with the Siemens Iso-C 3D because of the isocentric design.

Intraoperative 3D imaging in calcaneal fracture care-clinical implications and decision making.

BACKGROUND: In operative calcaneal fracture care malposition of screws and joint line incongruity frequently remain unrecognized using fluoroscopy intraoperatively, and are frequently only recognized on postoperative computed tomography scans. The purpose of this study was to analyze the feasibility and utility of a new C-arm-based three-dimensional imaging technology for calcaneal trauma care. METHODS: The C-arm-based three- dimensional imaging device (ISO-C-3D) was used in 32 patients during a 2-year period. Patients were indicated for open reduction and internal fixation using standard techniques and fluoroscopy. After reduction and implant placement was determined to be correct, the ISO-C-3D procedure was performed. The time for setup and use, and the consequences were recorded. An assessment was obtained from the surgeon regarding the feasibility and the adequacy and quality of the data provided, using a Visual Analog Scale. RESULTS: The average total time required for ISO-C-3D use was 610 seconds. The information obtained from the scan led the surgeon to alter the reduction or screw placement during the procedure in 41% of the patients. Surgeons rating according to a Visual Analog Scale: feasibility 9.5, accuracy and quality 9.2, clinical benefit 8.2. CONCLUSION: Intraoperative three- dimensional visualization with the ISO-C-3D provides important information in the operative treatment of calcaneal fractures which cannot always be obtained from plain films or standard fluoroscopy alone. The use of the device adds minimal time to the overall procedure, and was found to be extremely useful in evaluating reduction and implant position intraoperatively in calcaneal fractures.

Estimation of pretraumatic femoral antetorsion in bilateral femoral shaft fractures.

OBJECTIVE: To describe a system for measurement of the pretraumatic femoral antetorsion angle post-bilateral femoral shaft fracture with the use of new imaging software which allows segmentation and three dimensional (3D) reconstruction of DICOM (digital imaging and communications in medicine) images. MATERIAL AND METHODS: This case involved a 20-year-old patient with bilateral femoral shaft fractures. Following initial clinical examination, CT scans of both femurs were performed. Subsequently, the DICOM datasets were uploaded to the new software tool. Following segmentation and 3D reconstruction, pretraumatic femoral antetorsion angles were determined. RESULTS: Femoral antetorsion was described and assessed in two ways by referring to the intersection of the posterior condylar plane and (1) a line drawn between the center of the femoral head and femoral neck, (2) a line drawn between the centers of the femoral head and greater trochanter. Using these definitions, values for femoral antetorsion were found to be, respectively, 20 degrees at the right fracture site and 19 degrees on the left site, and 33 degrees bilaterally. DISCUSSION: The investigators describe in this current technical report the use of new imaging software which enables the calculation of femoral AV following reduction of virtual fracture fragments which are created from standard DICOM images. We believe that this 3D reconstruction method of measuring the antetorsion angle can be integrated into a regular treatment algorithm and may potentially optimize clinical outcomes.

Navigated femoral anteversion measurements: general precision and registration options.

INTRODUCTION: Intraoperative reduction of femoral fractures can result in rotational malalignment. Navigation modules allow fluoroscopy-based femoral anteversion (AV) measurements; however, their clinical feasibility has not been fully evaluated. An important technical consideration when obtaining navigated femoral rotational alignment is the necessity for orthogonal navigated fluoroscopic images. METHODS: The current investigators hypothesized that there would be a critical imaging angle between the fluoroscopic images which optimized the acquisition of accurate rotational measurements. Following initial testing in plastic femora, 14 intact human cadaveric femora were subjected to CT and navigated fluoroscopic assessment of AV. The navigated registration process included the following test series: Standard perpendicular AP and lateral imaging at a 90 degrees angle; planar rotation of the lateral fluoroscopy position perpendicular to the axis of femoral neck and angled to the AP position at 75 degrees, 60 degrees, and 50 degrees; inlet and outlet imaging of the axis of the femoral neck at angles of 10 degrees, 20 degrees, and 30 degrees. For all setups, the difference between the AV angle of the navigation system and the CT-measured angle was calculated. RESULTS: Results revealed no relevant differences between CT and navigated determination of plastic femora (1.5 degrees). No significant deviations of cadaver femora with 90 degrees angle imaging (mean 2.00 degrees, range 0.00 degrees-4.33 degrees), 75 degrees angle imaging (mean 1.95 degrees, range 0.00 degrees-3.33 degrees) and 60 degrees imaging (mean 2.00 degrees, range 0.00 degrees-3.33 degrees) were found. However, significant deviations were found for the navigated 50 degrees angled imaging technique (mean 5.02 degrees, range 2.33 degrees-7.67 degrees). CONCLUSION: These data demonstrated that the femoral AV angle can be calculated accurately by using two navigated fluoroscopic images when a minimum angle of 60 degrees is utilized between the angled fluoroscopic images for the registration process. A difference of <60 degrees does not allow for accurate navigated measurements.

An internet based learning tool in orthopaedic surgery: preliminary experiences and results.

Today universities can offer a variety of educational resources to their students through the internet. These may include lecture notes, PowerPoint presentations, or even an entire recording of a lecture in video format. At the Hannover Medical School (Hannover, Germany), the Trauma Surgery Department in collaboration with the Institute of Medical Informatics has developed an alternative method of "E-learning". We created a web-based multimedia resource center for Trauma Surgery using the Content-Management-System (CMS) Schoolbook application, which was initially developed by the Institute of Medical Informatics. The so called "Trauma Surgery Schoolbook" was first adopted in October of 2005 and has since been used and evaluated by medical students at our institution. The evaluation results for the academic year 2005/06 are reported in this paper. The majority of students enrolled in the Trauma Surgery rotation utilized the Schoolbook, which they regarded as a helpful and effective study tool. Our students embraced the possibility of being able to prepare for lectures and use the Schoolbook for independent home studying purposes. Over time, there was a steady increase in the utilization of the Schoolbook by the students from 67% in the first trimester to 93% in the third trimester. The majority of the surveyed students (79.6%) found the Schoolbook to be constructive and helpful. 8.1% did not have any opinion, and only 12.3% found it to not be helpful. The instructors also found this web-based training program to be both constructive and practical, and were able to utilize its multimedia components to complement their lectures. Overall, our experience with this computer-aided learning program demonstrated that web-based technologies can improve the quality of medical education, benefiting both the students and the instructors.

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.

[Navigated percutaneous placement of iliosacral screws using intra-operative three-dimensional imaging].

OBJECTIVE: To investigate the effect of a new technique of navigated percutaneous placement of iliosacral screws using intra-operative three-dimensional (3D) imaging. METHODS: Sixteen patients with hip fracture were placed in supine position. After the reference marker was fixed on the iliac crest, a 3-D C-arm navigation system was used intra-operatively to obtain 3D images that were transferred to the navigation system by an automatic. Registration process to calculate the length of screw and direction to insert it. A navigated pointer defined the entry point, while navigated percutaneous drilling was done accordingly with a navigated drill bit in combination with a navigated drill sleeve under permanent dynamic control on the navigation screen without further intra-operative fluoroscopic imaging. A control intra-operative 3D scan was used to observe the position of the screws, while for didactic reasons another postoperative CT scan was done. RESULTS: Twenty screws were successfully inserted into the first sacral vertebral bodies of the 16 patients. No additional intra-operative and postoperative complications occurred. The average operation time was 80 minutes and the average intra-operative radiation time was 1.13 minutes. Four patients underwent bilateral iliosacral fixation with longer operation time (152 minutes) and radiation time (1.56 minutes). The post-operative 3D scanning showed good results. No screws penetrated into the sacral canal or foramen. The reduction of fracture or dislocation and the position of iliosacral screws were all judged satisfactory. CONCLUSION: Compared with the conventional fluoroscopy method, navigated percutaneous placement of iliosacral screws under intra-operative 3D imaging reduces the radiation time and improves the accuracy. It is feasible and useful though there are some disadvantages such as the inferior image quality compared to CT scan, prolonged operation time and higher overall cost.

Improved accuracy of navigated drilling using a drill alignment device.

Drilling procedures are common in orthopedic surgery and are one specific task that may be aided by computer-assisted navigation. However, the inherent flexibility of drill bit bending may make this the limiting factor in achieving acceptable accuracy when using these systems. We designed an alignment device that was fit to a standard orthopedic drill that allowed an extension of the stabilizing point of a drill bit. In foam blocks with a similar density as cancellous bone, 208 total navigated drilling trials were performed, using four different sized drill bits (2.5, 3.2, 3.5, and 4.5 mm) with and without the alignment device. Drilling tracts of 80 mm were made towards an intended target on the other side of the block. Reduction in deviation from the intended target was significantly improved with the use of the guide, ranging from 33% to 45% for the four drill sizes. For the trails using the alignment device, the 2.5-mm drill bit was significantly less accurate than the three larger drills. Our results demonstrate that the use of external devices to augment drill bit stabilization can improve drilling accuracy. This may have particular importance when using navigation systems to drill into small anatomic confines.

Experimental validation of noninvasive referencing in navigated procedures on long bones.

Navigation procedures in orthopedic surgery require fixation of reference markers to the anatomic region of interest. Inadequate fixation might lead to micromotion or loosening of the reference marker, consequently causing registration failures or errors in navigation. Osseous rigid fixation is usually achieved by minimally invasive Schanz screws or pins. The goal of this study was to evaluate a non invasive external fixation device, a headband so far used in cranial navigation, as an alternative invasive fixation technique to reference markers in the femur. A common navigation system with an adapted trauma software application was used to track the positions of the soft tissue-attached headband relative to an invasive reference marker on the femur during manipulations of the thigh. Relative translative and rotational movements of the headband were measured during defined movements of the hip and knee and manipulations of the headband itself. The results revealed high translative and rotational movements, up to 6 mm and 3 degrees , respectively, due to minor manipulations of the affected lower extremity. Noninvasive soft tissue fixation with a headband does not allow rigid fixation for accurate navigated registration or operative procedures at the femur. Necessary intraoperative movements or manipulations would cause substantial registration failures. Invasive fixation techniques with screws or pins are still the method of choice.

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.