Non-navigation Group Research Articles

Navigated versus conventional transfixation of AC joint injuries: Feasibility and accuracy

Objective: Transfixation of the acromioclavicular (AC) joint is a well-established technique for treating Rockwood IV to VI lesions. However, several complications, including pin breakage or pin migration due to incorrect placement, have been reported in the literature. A cadaveric study was performed to investigate whether the use of 3D navigation might improve the accuracy of AC joint transfixation.Methods: Seventeen transfixations of the AC joint (8 non-navigated, 9 navigated) were performed minimally invasively in cadaveric shoulders. For the navigated procedures, a 3D C-arm (Ziehm Vision FD Vario 3D) and a navigation system (BrainLab VectorVision) were used. Reference markers were attached to the spina scapulae, then a 3D scan was performed and the data transferred to the navigation system. Two Kirschner wires (K-wires) were placed either freehand under fluoroscopic control (in the non-navigated group) or with the use of a navigated drill guide. Radiological analysis was performed with OsiriX software, measuring the distance of the K-wires from the center of the AC joint. For statistical analysis, Student's t-test was performed, with the significance level being set to p < 0.05.Results: The maximum distance of the K-wires from the center of the AC joint was 5.4 ± 1.1 mm for the freehand non-navigated group and 3.1 ± 1.6 mm for the navigated group (p = 0.0054). The minimum distance of the K-wires from the AC joint center was 3.0 ± 0.6 mm for the freehand group and 1.6 ± 0.6 mm for the navigated group (p = 0.0002). The radiation time was significant lower for the freehand group (41.25 ± 20.4 seconds versus 79.5 ± 13.3 seconds for the navigated group, p = 0.004). There was no statistical difference between the groups with respect to the time required for surgery (11.25 ± 3.6 min for the freehand group and 12.6 ± 4.6 min for the navigated group; p = 0.475). In the freehand group, the AC joint was penetrated by both K-wires in 87.5% of the procedures, compared to 100% in the navigated group. Both K-wires were placed completely intraosseously in the clavicula in 50% of the procedures in the freehand group, compared to 88% in the navigated group.Conclusion: Three-dimensional navigation may improve the accuracy of AC joint transfixation techniques. However, the radiation time is increased when using the navigated procedure, while the overall operation time remains comparable. Nevertheless, a 3D C-arm with a variable isocentric design is recommended for the acquisition of the shoulder scans.

Computer-assisted navigation for the intraoperative assessment of lower limb alignment in high tibial osteotomy can avoid outliers compared with the conventional technique

Longterm outcomes after valgization high tibial osteotomy (HTO) to treat varus osteoarthritis seem to depend mainly on correction precision. Intraoperative assessment of leg alignment based on radiological visualization of the mechanical axis is difficult and its precision is limited. A promising approach to improving precision is to make use of navigation systems. The case-control study reported here involved the evaluation of patients whose varus osteoarthritis had been treated by open-wedge high tibial ostoetomy, and an analysis of the effect of computer-guided navigation on postoperative leg alignment. Forty patients with medial varus osteoarthritis managed by open-wedge high tibial osteotomy using a surgical navigation system were included in the present study (Group 1). They were compared with a retrospective control group (Group 2) of 40 patients with respect to postoperative leg alignment, correlation of planned and definitive correction, and postoperative deviation from the Fujisawa point. The mean values for planned and definitive correction showed no significant differences for identical demographic data. As a percentage of the width of the tibial plateau the postoperative weight-bearing radiographs showed a mechanical line that intersected with the knee base line at the desired value of 62% (Fujisawa point) in 58.8% (SD ± 6.1) in Group 1 and in 58.6% (SD ± 8.1) in Group 2. Despite similar mean values a significantly higher number of corrections were outside the reference area (n = 7) in the non-navigated group, whereby all corrections were within the desired range in the navigated group. There were no significant differences in operation time. This study showed that the use of a navigation system can not increase the precision of the open-wedge HTO procedure in patients with varus osteoarthritis but it can eliminate the outliers of a well defined range. Case-control study, Retrospective comparative study, Level III.

Pedicle screw navigation: a systematic review and meta-analysis of perforation risk for computer-navigated versus freehand insertion

In this paper the authors' goal was to compare the accuracy of computer-navigated pedicle screw insertion with nonnavigated techniques in the published literature. The authors performed a systematic literature review using the National Center for Biotechnology Information Database (PubMed/MEDLINE) using the Medical Subject Headings (MeSH) terms "Neuronavigation," "Therapy, computer assisted," and "Stereotaxic techniques," and the text word "pedicle." Included in the meta-analysis were randomized control trials or patient cohort series, all of which compared computer-navigated spine surgery (CNSS) and nonassisted pedicle screw insertions. The primary end point was pedicle perforation, while the secondary end points were operative time, blood loss, and complications. Twenty studies were included for analysis; of which there were 18 cohort studies and 2 randomized controlled trials published between 2000 and 2011. Foreign-language papers were translated. The total number of screws included was 8539 (4814 navigated and 3725 nonnavigated). The most common indications for surgery were degenerative disease, spinal deformity, myelopathy, tumor, and trauma. Navigational methods were primarily based on CT imaging. All regions of the spine were represented. The relative risk for pedicle screw perforation was determined to be 0.39 (p < 0.001), favoring navigation. The overall pedicle screw perforation risk for navigation was 6%, while the overall pedicle screw perforation risk was 15% for conventional insertion. No related neurological complications were reported with navigated insertion (4814 screws total); there were 3 neurological complications in the nonnavigated group (3725 screws total). Furthermore, the meta-analysis did not reveal a significant difference in total operative time and estimated blood loss when comparing the 2 modalities. There is a significantly lower risk of pedicle perforation for navigated screw insertion compared with nonnavigated insertion for all spinal regions.

Editorial: Pedicle screw navigation

In their paper, Mr. Shin and colleagues present a metaanalysis comparing the accuracy of computer-navigated pedicle screw insertions versus nonnavigated techniques.1 The authors only included studies in which both techniques were performed. A total of 18 cohort studies and 2 randomized controlled trials, performed between 2000 and 2011, were evaluated. Approximately similar numbers of pedicle screws were placed in the 2 groups evaluated. The authors found that navigated screws violated the pedicle in 6% of instances, while nonnavigated screws had a 15% violation rate (p < 0.001). Despite this discrepancy, the revision surgery rates were not statistically different between the 2 groups. Additionally, the operative times and the blood loss were not significantly different between the groups. While the numbers appear to favor superior accuracy in the navigation group, the details of some of these studies lead to some problematic issues. Bias cannot be excluded in this meta-analysis. Articles that compared the 2 methods are very likely written by advocates of navigation. In fact, the authors of this meta-analysis state, “...the published literature is likely to exhibit a publication bias.” Issues that raise concern in these articles include the complication rates. With more than 8000 pedicle screws placed, the navigation group had a single wound infection, and the nonnavigation group had 3 wound infections in only 1 study in this group. These figures are at dramatic odds with the published wound infection rates for thoracic spinal surgery and cause the reader to be concerned that an underreporting of complications exists in these reports. The well-described in-out-in technique, used predominantly in the thoracic spine for placing larger screws into smaller pedicles, is ignored in this meta-analysis. No attempt was made to assess screw size. The clinical significance of placing a screw entirely within a pedicle is not clear from the wealth of published data on this topic. If a navigation advocate places smaller screws to remain intrapedicular, will maneuvers such as deformity correction be helped or hindered? This topic is not covered, and it bears much clinical import. While the authors of the meta-analysis state that radiographic evidence was required, it is not clear whether plain films or CT scans (much more accurate for this type of analysis) were assessed. The quoted survey of more than 3000 spine surgeons, with a 10% response rate, is not adequate to make scientific statements regarding this topic. Furthermore, it is likely that advocates of navigation were more likely to respond to a survey on its usage than spine surgeons who do not use, or possibly do not believe in, navigation. Additional information that would be useful for spine surgeons in determining the utility of navigation would be clinical outcomes, cost data, and radiation exposure. None of these was addressed in this meta-analysis. Some highly experienced spine surgeons who do not use navigation have reported better screw placement accuracy, using CT scanning data, than either of the groups in this meta-analysis. As such, it is possible that this meta-analysis has inadvertently skewed the argument in favor of surgeons who utilize navigation and may not be reflective of the spine surgical community at large. While this meta-analysis clearly shows that navigation is able to improve the accuracy of pedicle screw placement in the hands of surgeons who perform both navigation and nonnavigation techniques, this review is unable to determine whether there is a clinical advantage to the use of navigation for the reasons outlined above. (http://thejns.org/doi/abs/10.3171/2012.3.SPINE111098)

Application of Intraoperative Computed Tomography With or Without Navigation System in Surgical Correction of Spinal Deformity

A retrospective analysis of patients undergoing spinal deformity correction surgery by the assistance of intraoperative computed tomography (iCT) with or without navigation system. To share our preliminary experience and analysis of the iCT navigation system applied to spinal deformity surgery. The iCT navigation system has been shown to improve accuracy and safety in posterior instrumentation. It not only decreased the operation time but also prevented excessive radiation exposure to the medical staff. To date, there are only few reports about the application of the iCT navigation system in spinal deformity surgery. From April 2009 to September 2010, 59 patients who had a diagnosis of scoliosis, kyphosis, or scoliokyphosis and underwent iCT-assisted surgical correction were included. Without randomization, 28 patients were operated with the iCT-navigation system, and the other 31 patients were operated with standard procedure under iCT assistance. The detailed procedures, preoperative and intraoperative images were illustrated. The accuracy of screw placement, time for screw insertion, postoperative correction rate, and iCT scanning data were analyzed. There were significant differences between 2 groups in (1) the preoperative Cobb angle (76.2° and 62.6° in the navigation and non-navigation groups), (2) the accuracy and the revision rate of thoracic pedicle screws and total pedicle screws, and (3) the average screw insertion time. The breach rate and the revision rate of thoracic pedicle screws and total pedicle screws were significantly lower and the average screw insertion time was significantly lesser in the navigation group than in the non-navigation group. There were no statistically significant difference in (1) the breach rate and the revision rate of lumbar pedicle screws, (2) the mean iCT scanning time and time-out, (3) the mean number of fusion segments, (4) the mean number of iCT scans, and (5) the postoperative correction rate. Complications were encountered in 2 patients in the non-navigation group but none in the navigation group. There was no reoperation due to implant malposition in both groups. The iCT navigation system provides desirable accuracy of posterior spinal instrumentation for patients during surgical correction of spinal deformity without radiation exposure to the medical staff, especially in thoracic spine instrumentation. Meanwhile, the iCT in itself is an effective means of assessing complex instrumentation of the spinal deformity.

Patient Navigation: The Promise to Reduce Health Disparities

Patient Navigation: The Promise to Reduce Health Disparities

Reply to the letter by J.-Y. Jenny regarding our article “Comparative study of the use of computer assisted navigation system for axial correction in medial unicompartmental knee arthroplasty”

We thank Dr. J.-Y. Jenny for his interest in our article [5] and the points raised. Our hypothesis like his was that computer-assisted surgery (CAS) would improve alignment in unicompartmental knee arthroplasty (UKA). However, follow-up assessment did not support the hypothesis. With regard to his comments on power analysis, we acknowledge that the number of cases in our series was limited to make a definitive conclusion on the role of computer navigation in UKA. Our sample size was similar to his (60 cases) [2] and other published studies [1, 3] in examining the role of navigation in the UKA. Based on the results of coronal femorotibial mechanical angle measurement published by Jenny and Boeri [2], to detect a mean difference of 0.8 degrees with 2.0 degree standard deviation and a 95% confidence level, 246 cases would been required in each arm of the study (conventional and navigated) prospectively if power of 0.8 is assumed. This would require a multi-centre trial. The differences in the results between our desired mechanical axis range and Kennedy Protocol [4] were due to the difference in definition. Our ‘‘desired post-operative mechanical limb alignment’’ was strict—between 1 degree valgus and 1 degree varus (narrower than Dr Jenny’s 0–5 degrees varus). The computer system recorded this in every case after prosthesis insertion and yet based on the CT scanogram hip/knee/ankle assessment by an independent observer that was achieved in 4 out of 21 cases in the non-navigated group and 3 out of 30 cases in the CAS group. The Kennedy Protocol assessment of desired zones 2 & C is much more forgiving occupying 40% of the tibial width but it correlates with clinical outcome and so was included. This was achieved in more than 90% in both groups. Hence, there was no ‘‘huge discrepancy’’. The ‘‘Results’’ description of desired range may have been confusing to the reader and if so we apologise—it was elaborated in the ‘‘Discussion’’ section. Dr Jenny had asked us to explain why our results were different to his. With the CAS group, there was not much difference. He had similarly found no significant difference in the mean or range of the coronal femorotibial mechanical angle (i.e. mechanical axis) between the two groups, and we each had 9–10 degrees variance between the most varus and most valgus angles. The most obvious difference between us was in the conventional group. Our variance from most varus to most valgus angles was 9 degrees, whereas his was 20 degrees. Our group was prospective and randomized, whereas he retrospectively selected 30 conventional cases from 256 to match 30 navigated cases. Our resurfacing surgical technique allowed adequate exposure but was not ‘‘minimally invasive’’; the senior surgeon has more than three decades of experience with UKA; there was minimal bone resection; and alignment was based on restoring the joint line and soft tissue tension with no releases. One of our aims was to study the correlation between intra-operative limb alignment measurement and postoperative radiological measurement. Results indicated a low correlation rate for both conventional and computerassisted techniques (19%; 10%). The cause can be debated. We enthusiastically support research into computerassisted surgery but perhaps our study indicates the need for UKA-specific software and importantly a good foundation in conventional surgical techniques. M.-H. Lim (&) A. Tallay J. Bartlett Warringal Hospital, Melbourne, VIC, Australia e-mail: write2lim@hotmail.com

Alignment guided by computer navigation of the femoral component in hip resurfacing

Surgical navigation systems are offered to provide more precise implantation of the femoral component in hip resurfacing (HR), allowing to reduce the risk of malpositioning and of femoral neck fracture and notching. We conducted a retrospective analysis of 30 HR divided into two cohorts and compared the results of a nonnavigated group (15 hips) with those of a navigated group (15 hips). The BrainLAB Computer Navigation System was used in all cases. No notching occurred in either group. The femoral component did not show better positioning in the navigated group, but more outlier cases were observed in the nonnavigated group (7, versus 3 in the navigated group). Although there are no long-term studies showing that surgical navigation increases the survival of HR, the avoidance of outlier values justifies its use, especially during the surgical learning curve, which is a difficult and lengthy one.

Evaluation of a Computed Tomography–Based Navigation System Prototype for Hip Arthroscopy in the Treatment of Femoroacetabular Cam Impingement

The purpose of this study was to investigate the impact of a new computed tomography-based computer navigation system on the accuracy of arthroscopic offset correction in patients with cam type femoroacetabular impingement (FAI), and to evaluate if the accuracy of offset restoration compromises the early clinical outcome. We prospectively treated 50 patients (25 navigated and 25 non-navigated) by hip arthroscopy and arthroscopic offset restoration for cam FAI. The patients were a mean age 42.9 years, and the average follow-up was 26.7 months, with no patients lost to follow-up. Magnetic resonance imaging scans were performed preoperatively and 6 weeks postoperatively. A postoperative alpha angle of less than 50 degrees or a reduction of the alpha angle of more than 20 degrees was considered to be successful offset restoration. Outcomes were measured with a visual analogue scale for pain, range of motion, and the nonarthritic hip score. The mean alpha angle improved from 76.5 degrees (range, 57 degrees to 110 degrees) to 54.2 degrees (range, 40 degrees to 84 degrees). In both the navigated and the non-navigated groups, 6 patients (24%) showed insufficient offset correction. Range of motion, visual analogue scale for pain scores, and nonarthritic hip scores significantly improved in all subgroups. Statistical analysis showed no significant difference regarding the clinical outcome between patients with sufficient and insufficient correction of the alpha angle. In this series, a significant percentage of patients (24%) showed an insufficient correction of the alpha angle after hip arthroscopy for cam FAI. This study shows that the presented navigation system could not improve this rate and that the insufficient accuracy of reduction of the alpha angle does not appear to compromise the early clinical outcome. Level II, prospective comparative study.

Comparative study of the use of computer assisted navigation system for axial correction in medial unicompartmental knee arthroplasty

The aim of our study was to compare the use of the Orthopilot Navigation system with conventional non-navigation technique for medial UKA with respect to the intraoperative mechanical limb alignment measurements and correlation with the postoperative radiological measurements. The postoperative mechanical limb alignment axes of 51 consecutive medial unicompartmental knee arthroplasty performed by a single surgeon over a 12-month period were measured. The cases were randomly assigned to two groups of which 21 cases were performed using conventional non-navigation based technique and 30 cases were performed using the Orthopilot Navigation System. Computed tomography (CT) scanogram was performed for all cases within the same hospitalization stay to assess the postoperative mechanical limb alignment. Our results showed that the non-navigated group had a more neutral mechanical axis with a narrower range compared to the navigation assisted group. The difference in the mean mechanical axis between the two groups was statistically not significant. There was poor correlation between the intraoperative navigation system measurements and the postoperative radiological measurements. In conclusion, the use of computer navigation in UKA is not as well validated as compared to TKA. We did not demonstrate any improvement in postoperative axial limb alignment measurement in using a computer navigation system compared to conventional non-navigation technique.

Navigation Did Not Improve the Precision of Minimally Invasive Knee Arthroplasty

Potential advantages of minimally invasive total knee arthroplasty (TKA) include decreased pain, faster recovery, and increased quadriceps muscle strength. Computer-assisted navigation has been associated with more accurate component alignment. We evaluated two groups of 50 patients who had minimally invasive TKAs performed with and without navigation by two surgeons. A comparison of 50 previous TKAs by each of the two surgeons showed similar results. The mean operative times for the navigation and nonnavigation groups were 112 minutes (range, 63-297 minutes) and 54 minutes (range, 35-86 minutes), respectively. The mean estimated blood losses, mean Knee Society pain as well as functional scores and mean component alignments were similar. The number of knees that deviated by more than 3 degrees from the normal anatomic axis was three and one in the navigated and nonnavigated groups, respectively. Complication rates were 6% and 4% in the navigated and nonnavigated groups, respectively. Our data demonstrate no distinct advantage of navigation when combined with a minimally invasive approach. Level II, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

Femoral Component Positioning in Hip Resurfacing With and Without Navigation

Early failures after hip resurfacing often are the result of technical errors in placing the femoral component. We asked whether image-free computer navigation decreased the number of outliers compared with the conventional nonnavigated technique. We retrospectively compared 51 consecutive hip resurfacings performed using image-free computer navigation with 88 consecutive hip resurfacings performed without navigation. Patient demographics were similar. There were no differences in the average native femoral neck-shaft angles, planned stem-shaft angles, or postoperative stem-shaft angles. However, when the postoperative stem-shaft angle was compared with the planned stem-shaft angle, there were 33 patients (38%) in the nonnavigated group with a deviation greater than 5 degrees in contrast to none in the navigated group. Notching was present in four patients in the nonnavigated group and none in the navigated group. The average operative time was 111 minutes for the navigated group and 105 minutes for the nonnavigated group. Image-free navigation decreased the number of patients with potentially undesirable implant placements. Level III, therapeutic study. See the Guidelines for Authors for a complete description of levels of evidence.

A Program to Enhance Completion of Screening Colonoscopy Among Urban Minorities

Although colonoscopy is becoming the preferred screening test for colorectal cancer, screening rates, particularly among minorities, are low. Little is known about the uptake of screening colonoscopy or the factors that predict colonoscopy completion among minorities. This study investigated the use of patient navigation within an open-access referral system and its effects on colonoscopy completion rates among urban minorities. This was a cohort study that took place at a teaching hospital in New York. Participants were mostly African Americans and Hispanics directly referred for screening colonoscopy by primary care clinics from November 2003 to May 2006. Once referred, a bilingual Hispanic female patient navigator facilitated the colonoscopy completion. Completion rates, demographic factors associated with completing colonoscopy, endoscopic findings, and patient satisfaction were analyzed. Of 1169 referrals, 688 patients qualified for and 532 underwent navigation. Two thirds (66%) of navigated patients completed screening colonoscopies, 16% had adenomas, and only 5% had inadequate bowel preps. Women were 1.31 times more likely to complete the colonoscopy than men (P = .014). Hispanics were 1.67 times more likely to complete the colonoscopy than African Americans (P = .013). Hispanic women were 1.50 times more likely to complete the colonoscopy than Hispanic men (P = .009). Patient satisfaction was 98% overall, with 66% reporting that they definitely or probably would not have completed their colonoscopy without navigation. By using a patient navigator, the majority of urban minorities successfully completed their colonoscopies, clinically significant pathology was detected, and patient satisfaction was enhanced. This approach may help increase adherence with screening colonoscopy efforts in other clinical settings.

Comparison of the acetabular orientation after minimally-invasive total hip arthroplasty with and without computer-navigation: a clinical report of 106 hip in 87 patients

To evaluate the acetabular angle after minimally-invasive total hip arthroplasty (MIS-THA) with or without computer-navigation. 87 consecutive orthopedic patients (106 hips) underwent MIS-THA with computer-navigation (40 cases with 53 hips) or without computer-navigation (47 cases with 53 hips). The full leg length and pelvis were measured with radiography preoperatively and post-operatively. The average length of incision of the navigation group was 8.9 cm (7.8 - 10.5 cm), and the average length of incision of the non-navigation group was 9.1 cm (7.5 - 11 cm) The average cup inclination on the plain post-operative radiography of the navigation group was 40.58 degrees +/- 5.09 degrees (30 degrees - 54 degrees ), only the cup abduction being 54 degrees , significantly less steep than that of the control group [44.17 degrees +/- 8.71 degrees (28 degrees - 70 degrees , t' = 2.56. P = 0.012). Among the 47 control cases 40 cases showed the cup abduction of 30 degrees - 50 degrees , 3 showed the cup abduction of < 30 degrees , and 10 showed the cup abduction of > 50 degrees . The computer-navigation MIS-THA was significantly more accurate than the conventional MIS-THA. Pearson chi-square test showed that there was not significant difference in the percentage of cases with acetabular abduction < 30 degrees , between these two groups (chi(2) = 1.37, P = 0.24), and there was a significant difference in the percentage of cases with acetabular abduction > 50 degrees , between these two groups (chi(2) = 8.22, P = 0.0042). There was a significant difference in the percentage of cases with the acetabular abduction < 30 degrees and > 50 degrees calculated together between these 2 groups (chi(2) = 11.85, P = 0.0006), MIS-THA with computer-navigation allows accurate orientation of the cup implant components without direct visualization of the bony landmarks.

Randomized Clinical Study to Compare the Accuracy of Navigated and Non-Navigated Thoracic Pedicle Screws in Deformity Correction Surgeries

Randomized clinical trial (level I evidence). To compare the accuracy of non-navigation and Iso-C based navigation in pedicle screw fixation in thoracic spine deformities. Thoracic pedicle screw insertion for spinal deformity correction can be associated with increased pedicle breaches. Iso-C based navigation has been reported to improve the accuracy of pedicle screw placement, but its use in the presence of deformity has not been reported. Twenty-seven patients with scoliosis and 6 patients with kyphosis had a total of 478 thoracic pedicle screws. The average Cobb angle was 58.4 degrees +/- 8 degrees (range 50 degrees -80 degrees), and the mean kyphotic angle was 54.6 degrees +/- 4 degrees (range 51 degrees -76 degrees). By random allocation, 17 patients had screw insertion under navigation (242 screws) and 16 under fluoroscopic control (236 screws). The 2 groups were compared for accuracy of screw placement, time for screw insertion, and the number of times the C-arm had to be brought into the field. Two independent blinded observers determined accuracy using postoperative computed tomography assessments. There were 54 (23%) pedicle breaches in the non-navigation group as compared to only 5 (2%) in the navigation group (P < 0.001). Thirty-eight screws (16%) in the non-navigation group had penetrated the anterior or lateral cortex compared to 2 screws (0.8%) in the navigation group. Average screw insertion time in the non-navigation group was 4.61 +/- 1.05 minutes (range 1.8-6.5) compared to 2.37 +/- 0.72 minutes (range 1.16-4.5) in navigation group (P < 0.01). The C-arm had to be moved into the operation field on an average of 1.5 +/- 0.25 times (range 1-3) per screw. With single screening data, an average of 11.4 pedicles (range 9-14) could be visualized without necessity to bring the C-arm into operating field again. Iso-C navigation increases accuracy, and reduces surgical time and radiation in thoracic deformity correction surgeries.

Are systemic emboli reduced in computer-assisted knee surgery?

We undertook a prospective, randomised study using a non-invasive transcranial Doppler device to evaluate cranial embolisation in computer-assisted navigated total knee arthroplasty (n = 14) and compared this with a standard conventional surgical technique using intramedullary alignment guides (n = 10). All patients were selected randomly without the knowledge of the patient, anaesthetists (before the onset of the procedure) and ward staff. The operations were performed by a single surgeon at one hospital using a uniform surgical approach, instrumentation, technique and release sequence. The only variable in the two groups of patients was the use of single tracker pins of the imageless navigation system in the tibia and femur of the navigated group and intramedullary femoral and tibial alignment jigs in the non-navigated group. Acetabular Doppler signals were obtained in 14 patients in the computer-assisted group and nine (90%) in the conventional group, in whom high-intensity signals were detected in seven computer-assisted patients (50%) and in all of the non-navigated patients. In the computer-assisted group no patient had more than two detectable emboli, with a mean of 0.64 (SD 0.74). In the non-navigated group the number of emboli ranged from one to 43 and six patients had more than two detectable emboli, with a mean of 10.7 (sd 13.5). The difference between the two groups was highly significant using the Wilcoxon non-parametric test (p = 0.0003).Our findings show that computer-assisted total knee arthroplasty, when compared with conventional jig-based surgery, significantly reduces systemic emboli as detected by transcranial Doppler ultrasonography.

Limb alignment in computer-assisted minimally-invasive unicompartmental knee replacement

Twenty patients underwent simultaneous bilateral medial unicompartmental knee arthroplasty. Pre-operative hip-knee-ankle alignment and valgus stress radiographs were used to plan the desired post-operative alignment of the limb in accordance with established principles for unicompartmental arthroplasty. In each patient the planned alignment was the same for both knees. Overall, the mean planned post-operative alignment was to 2.3 degrees of varus (0 degrees to 5 degrees ). The side and starting order of surgery were randomised, using conventional instrumentation for one knee and computer-assisted surgery for the opposite side. The mean variation between the pre-operative plan and the achieved correction in the navigated and the non-navigated limb was 0.9 degrees (sd 1.1; 0 degrees to 4 degrees ) and 2.8 degrees (sd 1.4; 1 degrees to 7 degrees ), respectively. Using the Wilcoxon signed rank test, we found the difference in variation statistically significant (p < 0.001). Assessment of lower limb alignment in the non-navigated group revealed that 12 (60%) were within +/- 2 degrees of the pre-operative plan, compared to 17 (87%) of the navigated cases.Computer-assisted surgery significantly improves the post-operative alignment of medial unicompartmental knee arthroplasty compared to conventional techniques in patients undergoing bilateral simultaneous arthroplasty. Improved alignment after arthroplasty is associated with better function and increased longevity.