Computer-assisted Navigation System Research Articles

Advances in Computer-Aided Technology for Total Knee Arthroplasty.

Technology such as computer-assisted navigation systems, robotic-assisted systems, and patient-specific instrumentation has been increasingly explored during the past decade in an effort to optimize component alignment and improve clinical outcomes. Computer-assisted navigation accurately restores mechanical-axis alignment, but clinical outcome data are inconsistent. Computer-assisted navigation gap balancing has shown early promise in establishing mechanical-axis alignment with improved functional outcomes. Robotic-assisted systems more accurately restore component alignment when compared with computer-assisted navigation, but clinical outcomes have yet to be determined. Patient-specific instrumentation does not consistently improve alignment, accuracy, or patient outcomes. Studies demonstrating implant survivorship, cost-efficiency, and improved clinical outcomes and patient satisfaction are needed. [Orthopedics. 2017; 40(6):338-352.].

The value of computer-assisted navigation for bone reconstruction after tumor resection.

This study was designed to evaluate the use of computer-assisted navigation with computed tomography (CT) images for bone reconstruction after resection in malignant bone tumor treatment. Forty-five patients with malignant bone tumors were recruited for this study. CT scan images in a computer-assisted navigation system were used to assist during the osteotomy, the pairing with allografts, and the monitoring of the allograft and joint lines to perform joint reconstruction. Our results show that osteotomy and allograft pairing were successful in all patients. The average duration of the osteotomy procedures was 46.8±12.3 min; and the average pairing time was 32.5±9.8 min. The anatomical registration points and the three-dimensional virtual CT images were successfully matched. The average error of registration was 0.36±0.09 mm. Also, the range of tumor resection and allograft osteotomy were successfully paired, with an average error of 0.11±0.03 mm. No complications such as unequal limbs length or joint deformities occurred after reconstruction. The average follow-up time was 11.6±3.9 months. The tumor recurrence rate was 11.1% (5/45) and the survival rate 95.6% (43/45). The average healing time for the allograft and host bone was 5.5±1.2 months and no unexpected internal fixations, fractures or joint collapses occurred. The average knee joint functionality MSTS score was 25.5±6.6 points. No significant differences were found in the length of tumor resection, rate of negative incision margin, duration of osteotomy or of pairing, registration error or allogeneic bone and defect matching error averages between those patients with tumor recurrence and those without it (p>0.05). Based on our results, the computer-assisted navigation system for bone reconstruction after malignant tumor resection allows for high precision during osteotomy, delivers a high success rate of pairing, results in great limb function and low complication rates, and is thus a highly successful and safe approach benefiting bone cancer patients.

Computer-assisted Minimally Invasive Transforaminal Lumbar Interbody Fusion May Be Better Than Open Surgery for Treating Degenerative Lumbar Disease.

This study was a retrospective review of prospectively collected clinical data. To evaluate the clinical and radiologic outcomes of computer-assisted minimally invasive spine surgery transforaminal lumbar interbody fusion (CAMISS-TLIF) and open TLIF for the treatment of 1-level degenerative lumbar disease. Minimally invasive TLIF is becoming increasingly popular; however, the limited space and high rate of hardware complications associated with this method are challenging to surgeons. Computer-assisted navigation has the potential to dynamically show the fine anatomic structures, which could theoretically facilitate minimally invasive spine procedures. Sixty-one patients underwent 1-level TLIF procedures (30, CAMISS-TLIF; 31, open TLIF). The computer-assisted navigation system was used for CAMISS-TLIF, whereas conventional fluoroscopy was used for open TLIF. Demographic, operative, visual analog scale, and Oswestry disability index data were collected. Screw insertion was assessed by computed tomography, and radiologic fusion based on Bridwell grading was evaluated 2 years after surgery by independent investigators. The CAMISS-TLIF group had significantly less blood loss, postoperative drain, need for transfusion, and initial postoperative back pain; earlier rehabilitation; and shorter postoperative hospitalization than the open TLIF group, whereas CAMISS-TLIF took longer surgical time than open TLIF. However, no significant differences between the 2 groups in visual analog scale scores and Oswestry disability index were observed at 3 months, 1 year, and 2 years postoperatively. A total of 93.33% and 73.39% of screws in the CAMISS and open groups, respectively, had no pedicle perforation (P=0.016), and the fusion rate was similar in both groups (P=0.787). Computer-assisted navigation facilitated minimally invasive spine surgery-TLIF. CAMISS-TLIF was superior to open TLIF for treating 1-level degenerative lumbar disease, although it required longer operation time in the initial stage. CAMISS-TLIF showed several benefits compared with open TLIF, including less intraoperative blood loss, postoperative drainage, and pain; earlier rehabilitation; and shorter postoperative hospitalization.

An electromagnetic tracking method based on fast determination of the maximum magnetic flux density vector represented by two azimuth angles

In this paper, an electromagnetic tracking method based on fast determination of the maximum magnetic flux density vector (MMFDV) represented by two azimuth angles is proposed. The system designed to validate this method includes two magnetic sources and a 3-axis magnetic sensor. Each source consists of three mutual orthogonal coils. The main characteristic of this method is that the direction of MMFDV generated by a magnetic source can be determined as long as each coil of the source is excited once. Then the sensor can be located with a noniterative geometrical algorithm in real time. This method is easy to be implemented and can realize tracking in full coordinate space. Simulation and experimental results demonstrate a good performance of this method. It can be used as a part of computer-assisted navigation system in minimally invasive surgery after proper optimization.

Effects of reconstruction with unicondylar osteoarticular allografts with or without prosthesis for bone tumors around knee joint

Objective: To investigate the survival rate, function outcomes, and complications after using unicondylar osteoarticular allografts with or without prosthesis to reconstruct the knee joint for tumors located in distal femoral or proximal tibial uni-condyle. Methods: Twenty-two patients who underwent unicondylar osteoarticular allografts with or without prosthesis composite reconstructions from January 2007 to December 2015 in Department of Orthopaedic Surgery of Xi Jing Hospital, the Fourth Military Medical University were retrospectively reviewed. There were 14 males and 8 females and the mean age was 35 years(8-65 years). There were 12 malignent tumors and 10 aggressive benign tumors. The tumors were located in distal femur in 14 cases and proximal tibia in 8 cases. After tumor excision, the distal femur was reconstructed with unicondylar osteoallograft-prosthesis composite, and proximal tibial plate was reconstructed with unicondylar osteoarticular allograft with the help of computer-assisted navigation system. Function and radiograph were documented according to the Musculoskeletal Tumor Society (MSTS) functional scoring system and the International Society of Limb Salvage (ISOLS) radiographic scoring system. The median follow-up time was 60 months (5-116 months). Results: At the latest follow-up, 2 patients had amputation owing to local recurrence in 12 malignant tumors. Three patients had pulmonary metastasis and 1 patient died another 2 alive with disease. Kaplan-Meier analysis indicated that the disease-free survival rate was 73%. There was no recurrence and metastasis in 10 patients with giant cell tumor. The average MSTS score was 26 points and the radiographic score was 78%-94%(average 90%). The complications included superficial infection in 1 patient and screw broken in 1 patient. There was no broken or collapse allograft in all composite reconstruction patients but 6 cases in allograft reconstruction. Conclusions: Unicondylar osteoarticular allografts or prosthesis composite was feasible reconstruction for tumors in distal femoral uni-condyle. It could provide good functional outcomes and also prevent joint degeneration. Similarly, allograft reconstruction was also a reliable technique for proximal tibial defect.

Application of a computer-assisted surgical navigation system in temporomandibular joint ankylosis surgery: a retrospective study

This retrospective study evaluated the effect of surgical computer-assisted navigation in temporomandibular joint (TMJ) ankylosis gap arthroplasty. Eighteen patients (25 sides) with bony ankylosis who underwent surgical treatment under computer-assisted navigation (navigation group) from May 2011 to April 2013 were assessed, along with 19 such patients (25 sides) treated without computer-assisted navigation (non-navigation group) from March 2009 to April 2011. The navigation group patients underwent surgery with the preservation of ≥3mm bone thickness in the skull base and anterior wall of the external auditory canal. Postoperatively, computed tomography (CT) was used to measure the residual bone thickness in the skull base and anterior wall of the external auditory canal. Maximum mouth opening (MMO) changes were evaluated at >1 year of follow-up. Postoperative CT measurements showed that the lowest skull base thickness in the navigation group was significantly lower than that in the non-navigation group (3.86±1.95mm vs. 6.01±3.07mm, P=0.009). The lowest thicknesses of the anterior wall of the external auditory canal were similar in the two groups. Postoperative follow-up showed similar average MMO in the two groups. Therefore, with the navigation system, TMJ ankylosis gap arthroplasty can achieve more extensive removal of the ankylosed bone, at least towards the skull base, under the premise of ensuring a safety distance of 3mm.

Application of a Computer-Assisted Navigation System (CANS) in the Delayed Treatment of Zygomatic Fractures: A Randomized Controlled Trial

The delayed treatment of zygomatic complex (ZMC) fracture presents a difficult challenge to surgeons. The aim of this study was to compare the treatment effects of delayed surgery of ZMC fractures with and without a computer-assisted navigation system (CANS). In this observer-blinded single-site randomized clinical trial, patients with unilateral ZMC fracture were included and randomized 1:1 to delayed treatment with or without CANS. The primary outcome measurement was the absolute bilateral differences of the ZMC eminence and width based on computed tomographic (CT) measurements 48 to 72hours after surgery. One hundred three patients with unilateral ZMC fracture without immediate treatment were enrolled, and 78 were randomized to each group. Postoperative CT measurements showed that the bilateral difference in ZMC eminence was significantly less for the navigation group than for the control group (1.24 vs 2.22mm; P < .001). The bilateral difference in ZMC width was not significantly different between the 2 groups (0.94 vs 1.36mm; P= .061). The percentage of patients exhibiting a morphologically symmetrical face (bilateral differences ≤2mm in ZMC eminence and width) was 71.8% (28 of 39) for the navigation group and 35.9% (14 of 39) for the control group (P= .001). Photogrammetry showed that the average difference between the postoperative CT data and the preoperative design was smaller in the navigation group (1.30 vs 2.40mm; P= .012). Use of CANS improved ZMC symmetry in patients with unilateral ZMC fracture who had delayed treatment by allowing for more accurate implementation of the preoperative plan.

Advantages of computer-assisted navigation system in open-wedge high tibial osteotomy

Advantages of computer-assisted navigation system in open-wedge high tibial osteotomy

Prospects of Robot-Assisted Mandibular Reconstruction with Fibula Flap: Comparison with a Computer-Assisted Navigation System and Freehand Technique.

Background Function and aesthetics have a significant impact on the quality of life in patients undergoing mandibular reconstructive surgery, but achieving satisfactory results remain challenging. The aim of the study is to investigate the feasibility and accuracy of robot-assisted mandibular reconstruction with fibula flap in comparison to that with a computer-assisted navigation system and the freehand technique. Methods Experimental procedures (15 phantom studies and 6 animal experiments) were performed with a custom three-arm robotic system automatically, under the guidance of a computer-assisted navigation system, and by the freehand technique, respectively. The accuracy of the reconstruction was assessed by comparison between the preoperative and postoperative three-dimensional surface virtual models. Results All procedures were successfully performed. In the phantom study, the mean deviation of the fibula implant was 1.221, 1.581, and 2.313 mm, respectively, with the robotic system, the navigation system, and the freehand technique; in the animal experiment the corresponding figures were 1.7697, 1.7847, and 2.0815 mm, respectively. The mean deviation of the proximal mandibular ramus was 1.0420, 1.0532, 1.8800 mm with the robotic system, computer-assisted navigation system, and freehand technique, respectively, and the mean deviation of the distal mandibular segment was 1.1645, 2.7198, and 2.8445 mm, respectively. Conclusions The robotic system is feasible, efficient, and reliable for mandibular reconstruction. The accuracy of the fibula implant orientation with the robotic system was comparable to that with navigation system and superior to that with the freehand technique.

Evaluation of a surgical interface for robotic cryoablation task using an eye-tracking system

Computer-assisted navigation systems coupled with surgical interfaces (SIs) are providing doctors with tools that are safer for patients compared to traditional methods. Usability analysis of the SIs that guides their development is hence important. In this study, we record the eye movements of doctors and other people with no medical expertise during interaction with an SI that directs a simulated cryoablation task. There are two different arrangements for the layout of the same SI, and the goal is to evaluate whether one of these arrangements is ergonomically better than the other. We use several gaze related statistics some of which are employed in an SI design context for the first time. Even though the performance and gaze related analysis reveals that the two arrangements are comparable in many respects, there are also differences. Specifically, one arrangement leads to more saccades along the vertical and horizontal directions, lower saccade amplitudes in the crucial phase of the task, more locally clustered and yet globally spread viewing. Accordingly, that arrangement is selected for future use. The present study provides a proof of concept for the integration of novel gaze analysis tools developed for scene perception studies into the interface development process. Two arrangements for a surgical interface (SI) are developed using design principles.Doctors & laypeople perform SI-guided simulated cryoablation while gaze is recorded.Saccades in cardinal directions are more likely with one arrangement.Spatial fixation distributions at different temporal scales support the same arrangement.Design and evaluation with eye movements measures produce better SIs.

Does meniscus removal affect ACL-deficient knee laxity? An in vivo study.

The purpose of the present study was to determine, in vivo, the effect of different types of meniscectomy on an ACL-deficient knee. Using a computer-assisted navigation system, 56 consecutive patients (45 men and 11 women) were subjected to a biomechanical testing with Lachman test (AP30), drawer test (AP90), internal/external rotation test, varus/valgus rotation test and pivot-shift test. The patients were divided into three groups according to the status of the medial meniscus. Group BH, 8 patients with bucket-handle tear of medial meniscus underwent a subtotal meniscectomy; Group PHB, 19 patients with posterior horn body of medial meniscus tear underwent a partial meniscectomy; and Group CG with isolated ACL rupture, as a control group, with 29 patients. A significant difference in anterior tibial translation was seen at 30 grades and in 90 grades between BH and PHB groups compared to the CG. In response to pivot-shift test, no significant differences in terms of AREA and POSTERIOR ACC were found among the three groups (n.s). Concerning the anterior displacement of the pivot shift a statistically significant differences among the three tested groups was found. The present study shows that meniscal defects significantly affect the kinematics of an ACL-deficient knee in terms of anterior tibial translation under static and dynamic testing.

Computer-assisted stereotaxic navigation improves the accuracy of mechanical alignment and component positioning in total knee arthroplasty.

This study reports on a novel computer-assisted stereotaxic navigation (CASN) system that attempts to combine the accuracy of computer navigation with familiarity of conventional methods. We hypothesize that CASN would improve mechanical alignment and component positioning when compared to conventional instrumentation. 145 patients (192 knees) retrospectively matched for age, BMI, gender and pre-operative scores, underwent total knee arthroplasty (TKA) using CASN (n=92) or conventional instrumentation (n=100). Pre- and post-operative radiological alignment [Acceptable ranges: mechanical axis (MA) 0°±3°, coronal femoral-component angle (CFA) and coronal tibia-component angle (CTA) 90°±3°] and clinical outcomes (Knee Society Scores, Oxford Knee Score and Short Form-36) at 6months were examined. The CASN group had significantly improved mean MA (1.9°±1.4°, versus 2.8°±2.0° in the conventional group, p=0.001), CFA (1.6°±1.3°, versus 2.1°±1.5° in the conventional group, p=0.035) and CTA (1.6°±1.2°, versus 2.1°±1.5° in the conventional group, p=0.024). 91.3% of knees in the CASN group were within 3° of a neutral mechanical axis, versus 74% in the conventional group (p<0.001). The duration of surgery was significantly longer in the CASN group (84±22 vs 73±15min, p=0.001) and cost an additional USD 850 per operation. There were no significant differences in clinical outcomes or satisfaction rates at 6months post-operatively (p>0.05). CASN improved TKA mechanical alignment and component positioning, however, resulted in longer and costlier surgery with no benefits in short-term functional outcomes, despite providing familiarity to surgeons accustomed to conventional instrumentation. III.

Cervical screw placement using rapid prototyping drill templates for navigation: a literature review.

Due to the high screw malposition rate and the potential risk of neurovascular injury in cervical fixation surgeries, guided tools, mainly computer-assisted surgery navigation systems and rapid prototyping drill templates (RPDTs) have increasingly been developed to help surgeons improve screw placement accuracy. Although RPDTs have been used in cervical surgeries for almost 2 decades, no specific review has been performed detailing the state of this technique. Thus, in the current review, we fully discuss the status of applying RPDTs in cervical surgeries. Studies that tested the accuracy and reliability of RPDTs in guiding cervical screw placements were included in this review. The fabrication workflow and usage of RPDTs, the accuracy and reliability of using RPDTs for screw and plate placement, the advantages and disadvantages of RPDTs and their prospects for future applications as a part of cervical fixation instrumentation are discussed. As the design of RPDTs becomes more rational, the accuracy and reliability of these devices have significantly improved in cervical fixation surgeries. Moreover, RPDTs decrease the intraoperative radiation exposure for surgeons and patients relative to conventional methods. However, some disadvantages also exist. The fabrication of RPDTs is time-consuming, and the time required to learn the related software is long. We believe that because of their merits, the RPDT technique is worth promoting for use in cervical surgeries. However, the time-consuming fabrication workflow and the long period required to learn the related software might limit its widespread use. In the future, the workflow should be simplified to reduce the extra workload for surgeons. Moreover, more clinical studies with high-level evidence are still needed to further test its accuracy and feasibility.

Patient-specific and intra-operatively modifiable factors assessed by computer navigation predict maximal knee flexion one year after TKA

There are multiple factors affecting maximal knee flexion (MKF) after total knee arthroplasty (TKA). The aim of the study was to investigate whether patient-specific factors (PSF) and surgically modifiable factors (SMF), measured by means of a computer-assisted navigation system, can predict the MKF after TKA. Data from 99 patients collected during a randomized clinical trial were used for this secondary data analysis. The MKF of the patients was measured preoperatively and 1-year post-surgery. Multiple regression analyses were performed to investigate which combination of variables would be the best to predict the 1-year MKF. When considering SMF alone, the combination of three factors significantly predicted the 1-year MKF (p=0.001), explaining 22% of its variation. When considering only PSF, the combination of pre-op MKF and BMI significantly predicted the 1-year MKF (p<0.001), explaining 23% of its variation. When considering both groups of potential predictors simultaneously, the combination of five SMF with two PSF significantly predicted the 1-year MKF (p=0.001), explaining 32% of its variation. Computer navigation variables alone could explain 22% of the variance in the 1-year MKF. The larger proportion (32%) of the 1-year MKF variation could be explained with a combination of SMF and PSF. The results of studies in this area could be used to identify patients at risk of poor outcomes. Level II, Prognostic study.

Surgically modifiable factors measured by computer-navigation together with patient-specific factors predict knee society score after total knee arthroplasty.

BackgroundThe purpose was to investigate whether patient-specific factors (PSF) and surgically modifiable factors (SMF), measured by means of a computer-assisted navigation system, can predict the Knee Society Scores (KSS) after total knee arthroplasty (TKA).MethodsData from 99 patients collected during a randomized clinical trial were used for this secondary data analysis. The KSS scores of the patients were measured preoperatively and at 4-years follow-up. Multiple regression analyses were performed to investigate which combination of variables would be the best to predict the 4-years KSS scores.ResultsWhen considering SMF alone the combination of four of them significantly predicted the 4-years KSS-F score (p = 0.009), explaining 18 % of its variation. When considering only PSF the combination of age and body weight significantly predicted the 4-years KSS-F (p = 0.008), explaining 11 % of its variation. When considering both groups of predictors simultaneously the combination of three PSF and two SMF significantly predicted the 4-years KSS-F (p = 0.007), explaining 20 % of its variation.ConclusionsYounger age, better preoperative KSS-F scores and lower BMI before surgery, a positive tibial component slope and small changes in femoral offset were predictors of better KSS-F scores at 4-years.

Constrained Statistical Modelling of Knee Flexion From Multi-Pose Magnetic Resonance Imaging.

Reconstruction of the anterior cruciate ligament (ACL) through arthroscopy is one of the most common procedures in orthopaedics. It requires accurate alignment and drilling of the tibial and femoral tunnels through which the ligament graft is attached. Although commercial computer-assisted navigation systems exist to guide the placement of these tunnels, most of them are limited to a fixed pose without due consideration of dynamic factors involved in different knee flexion angles. This paper presents a new model for intraoperative guidance of arthroscopic ACL reconstruction with reduced error particularly in the ligament attachment area. The method uses 3D preoperative data at different flexion angles to build a subject-specific statistical model of knee pose. To circumvent the problem of limited training samples and ensure physically meaningful pose instantiation, homogeneous transformations between different poses and local-deformation finite element modelling are used to enlarge the training set. Subsequently, an anatomical geodesic flexion analysis is performed to extract the subject-specific flexion characteristics. The advantages of the method were also tested by detailed comparison to standard Principal Component Analysis (PCA), nonlinear PCA without training set enlargement, and other state-of-the-art articulated joint modelling methods. The method yielded sub-millimetre accuracy, demonstrating its potential clinical value.

ENDOSCOPIC SURGERY OF THE PARANASAL SINUSES AND SKULL BASE NEOPLASMS WITH THE USE OF THE COMPUTER-ASSISTED NAVIGATION SYSTEM (CANS) IN PEDIATRIC PRACTICE

Backgroun d: In the last 10 years, the use of computer-assisted navigation systems (CANS) in endo-nasal endoscopic surgery of the paranasal sinuses and skull base in adults has been well studied. In pediatric practice, isolated cases of the use of this method have been described, with most of patients suffering from various types of sinusitis. Aim: To improve efficacy of the transnasal surgery for sinonasal, nasopharyngeal and skull base neoplasms in pediatric patients. Materials and methods: 77 patients aged from 22 days to 18 years with various nasal, nasopharyngeal, paranasal and skull base neoplasms were divided into two groups depending on the surgical technique. The main group included 40 patients in whom CANS guided surgery was used and the control group comprised 37 patients operated without CANS. Each group was divided into two subgroups based upon the complexity of the intervention (in subgroup 1, it was a biopsy and in subgroup 2, tumor excision). Results: There were no significant differences between 1st subgroups of both groups in the intervention duration, intra-operative blood loss, number of post-operative days in the hospital. Compared to the patients from the subgroup 2 of the control group, in those from the subgroup 2 of the main group the duration of intervention decreased by 60 minutes (p = 0.038, Mann-Whitney U-test), intra-operative blood loss decreased by half (p = 0.044, Mann-Whitney U-test), duration of hospital stay, by 2 days (p = 0.02, Student's t-test). The rates of radical excision was higher in the main group (p = 0.02, Fischer's exact test). Conclusion: The use of CANS in endonasal surgery allows for reduction of the intervention time and anesthesia duration, minimizes blood loss, is associated with earlier post-operative rehabilitation of children.

Inferior gluteal artery detection at the greater sciatic notch with a computer-assisted navigation system during pelvic and sacral tumor resection

Background: During pelvic and sacral tumor resection, important vessels, such as the inferior gluteal artery underneath the sciatic notch, are easily injured because of their invisibility. We employed a computer-assisted navigation system to preserve the inferior gluteal artery at the sciatic notch with visualization of the inferior gluteal artery at the sciatic notch, thus maintaining blood flow to the gluteus maximus.Methods: We present the results of seven patients (five men and two women) with a mean age of 64.8 years (58.4–78.8) in whom computer-assisted navigation surgery had been carried out for pelvic and sacral tumor resections.Results: Postoperative enhanced computed tomography (CT) confirmed the preservation of the inferior gluteal artery in all cases. At a mean follow-up of 21.3 months (3–39), the total postoperative complication rate was 25% (n = 2), including hematoma (n = 1) and wound necrosis (n = 1). There were no cases of deep infection.Conclusion: This new application of computer-assisted navigation to pelvic and sacral tumor resection can contribute to reducing postoperative complications related to insufficient flap perfusion.

The role of computer assisted navigation in revision surgery for failed anterior cruciate ligament reconstruction of the knee: A continuous series of 52 cases

IntroductionThe causes of failure of anterior cruciate ligament (ACL) reconstruction mainly involve incorrect tunnel positioning. There is no intraoperative tool allowing the surgeon to test graft biomechanics and to confirm that the new graft is in an optimal position. HypothesisControl is improved with computer assisted navigation. Material and methodsIn this retrospective study, revision ACL reconstruction was performed with a new autologous graft in a continuous series of 52 failed ACL reconstructions. A computer assisted navigation system was used intraoperatively in all knees. Evaluation with this system confirmed the position of old and new tunnels as well as intraoperative laxity. ResultsEvaluation of tunnel position based on traditional radiological criteria found in the literature significantly underestimated graft biomechanics: 69% of the cases presented with unfavorable graft ansiometry (mean: 13±2.2mm) while the correct position of the tibial tunnel was identified in 64% of cases on radiography and the femoral tunnel in 48%. All new grafts were optimally positioned by the computer assisted navigation system with a mean isometery of 3.2 (±0.7) mm. Comparative pre- and postoperative evaluation of laxity showed a statistically significant improvement (P<0.001): preoperative and postoperative Lachman test: 10.5±2mm and 3±0.5, respectively; global rotational laxity: 24±5° and 37±7° respectively. ConclusionThe use of a computer assisted navigation system allows optimal positioning of the graft as well as a predictive assessment of laxity. Type of studyLevel IV, retrospective cohort study.

Intraoperative Cone Beam CT (O-Arm) and Stereotactic Navigation (StealthStation) System in Complex Adult Spine Surgery: Early Experience and Learning Curve

Introduction Computer-assisted navigation and intraoperative imaging systems have been shown to improve pedicle screw accuracy in a variety of instrumented spine surgeries. There is limited data evaluating the clinical learning curve for surgeons and its relationship to patient outcomes when using intraoperative navigation and imaging systems. We examined the clinical learning curve and patient outcomes of using O-Arm and StealthStation for six fellowship-trained spine surgeons at our institution, a single quaternary referral center, from 2009 to 2013. Materials and Methods This ambispective study examined 231 surgical cases where O-arm and StealthStation were used to facilitate pedicle instrumentation. The learning curve was determined by examining the year-by-year total operative time and blood loss, operative time and blood loss per surgical level, and the incidence of surgery-related adverse events. Adverse events were prospectively collected using the spine adverse events severity system (SAVES). Results O-arm and StealthStation were acquired at our institution in late 2008 and all spine surgeons were using this navigation system by the beginning of 2009. A total of 231 patients had screws placed using the O-arm and StealthStation between January 1, 2009 and December 31, 2012. There were 430 screws placed in 27 cases in 2009, 556 screws in 54 cases in 2010, 674 screws in 59 cases in 2011, and 758 screws in 75 cases in 2012, p &lt; 0.05. The average estimated blood loss (EBL) decreased from 1,229 mL in 2009 to 907 mL in 2012, p &lt; 0.05. The EBL per case per number of levels instrumented decreased from 5.72 mL in 2008 to 2.39 mL in 2012, p &lt; 0.05. Mean operating time decreased from 407 minutes to 378 minutes from 2009 to 2012, p &lt; 0.05. The number of misplaced screws per case decreased from 0.78 to 0.54 from 2009 to 2012, p &lt; 0.05. There were no significant differences in incidences of dural tear, surgical site infection, or other surgical adverse events during the study period. Conclusion Our results demonstrate that there is a learning curve to the use of intraoperative CT-based navigation, as measured by OR time, intraoperative blood loss, and screw malposition. There were no significant differences in surgical adverse events during this learning period.