INTRODUCTION. There is a growing interest in surgical variables that are controlled by the orthopaedic surgeon, including lower leg alignment and soft tissue balancing. Since more tight control over these factors is associated with improved outcomes of total knee arthroplasty (TKA), several computer navigation systems have been developed. Many meta-analyses showed that mechanical axis accuracy and component positioning are improved using computer navigation and one may therefore expect better outcomes with computer navigation but studies showing this are lacking. Therefore, a systematic review with meta-analysis was performed on studies comparing functional outcomes of computer-navigated and conventional TKA. Goals of this study were to (I) assess outcomes of computer-navigated versus conventional TKA and (II) to stratify these results by the surgical variables the systems aim to control. METHODS. A systematic search in PubMed, Embase and Cochrane Library was performed for comparative studies reporting functional outcomes of computer-navigated versus conventional TKA. Knee Society Scores (KSS) Total were most often reported and studies reporting this outcome score were included. Outcomes of computer-navigated and conventional TKA were compared (I) in all studies and (II) stratified by navigation systems that only controlled for lower leg alignment or systems that controlled for lower leg alignment and soft tissue balancing. Level of evidence was determined using the adjusted Oxford Centre for Evidence-Based Medicine tool and methodological quality was assessed using Grades of Recommendation, Assessment, Development, and Evaluation (GRADE) tool. Outcomes were reported in mean difference (MD) with 95% confidence intervals [Lower Bound 95%, Upper Bound 95%]. RESULTS. Twenty-eight studies reported KSS Total outcomes in 3,504 patients undergoing computer-navigated or conventional TKA. Fifteen studies were evidence level I, five studies level II and eight studies level III. Study quality varied between low and high with most studies having high methodological quality. Patients reported better outcomes following computer navigated TKA than conventional TKA (MD 2.86 [0.96, 4.76], p=0.003), which was both seen at short-term follow-up of six months and one year (MD 5.20 [3.41, 7.00] and MD 8.46 [0.65, 16.28], respectively) and at mid-term follow-up (≥4 years) (MD 2.65 [0.96, 4.76]) (Figure 1). In studies that used computer navigation for controlling lower leg alignment, no difference in functional outcomes was seen between computer-navigated and conventional TKA (MD 0.66 [−2.06, 3.38], p=0.63, Figure 2). However, in studies that used computer navigation for controlling lower leg alignment and soft tissue balancing, patients reported superior functional outcomes following computer-navigate over conventional TKA (MD 4.84 [1.61, 8.07], p=0.003, Figure 3). CONCLUSION. This is the first meta-analysis showing superior functional outcomes following computer-navigated over conventional TKA. Stratifying results by variables the systems control, superiority in functional outcomes following computer-navigated over conventional TKA were only seen in systems that controlled soft tissue balancing. This suggests that soft tissue balancing plays an important role in short-term outcomes of TKA. Manually controlling all these surgical variables can be difficult for the orthopaedic surgeon and findings in this study suggest that computer navigation may help managing these multiple variables and improve outcomes. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Aim. Computer-navigated total knee arthroplasty has been shown to improve the outcome in outliers with consistent results. The aim of this study is to evaluate the clinical and radiographic outcomes of computer-navigated knee arthroplasty with respect to deformity and body mass index (BMI). Materials and Methods. Data was prospectively collected for 117 consecutive patients undergoing primary computer-navigated total knee arthroplasty using Ci Brainlab system with J&J PFC PS implants by a single surgeon utilising a tibia cut first, gap-balancing technique. Pre-operative and post-operative long-leg films, weight-bearing, films were taken and the long-axis was measured by a single observer. Intra-operative computer navigation long-axis values were stored as screenshots intra-operatively after registration and after implant was cemented. BMI, range of motion (ROM), SF 36 and Oxford knee scores were recorded both before surgery and on follow-up. Minimum 2-year follow-up. Eight patients were lost to follow-up and 8 had incomplete 2 year data. Data was analysed using the Chi-squared test for categorical variables and the t-test for continuous variables. Results. Eighty-four (83.2%) female, 17 (16.8%) male patients age 65.3±6.9 years with a pre-operative BMI of 27.2±4.1 (18.6 to 40.0). Eighty-eight (87.1%) met the Singapore definition of overweight with BMI>23 kg/m2. Forty-two (41.6%) had a BMI>27.5 kg/m2 indicative of obesity in Singapore. Pre-operative radiographic axis was 9.3±10.6° varus. Thirty (29.7%) patients had a pre-operative coronal plane deformity of more than 15°. Meanoperative duration 96.0±10.7 mins. Post-operative radiographic axis was 0.05±3.0° valgus. Significant improvement was seen in knee extension, knee flexion, SF 36 and Oxford knee scores at 2 years. No significant improvement in extensor lag and straight leg-raising at 2 years. Pre-operative axis >15° was not significantly related to operative duration. BMI>23 kg/m2 was significantly related to longer operative time (88.8±10.8 vs. 97.1±10.3 min, p<0.021). BMI >27.5 kg/m2 not significantly related to operative duration, pre-operative SF36 or Oxford knee scores. Post-operative axis deviation of more than 3° not significantly related to BMI > 23 or 27.5 kg/m2, similar to post-implant navigation axis. BMI >23 kg/m2 not significantly related to 2 year SF36, Oxford knee score and range of motion at 2 years. BMI >27.5 kg/m2 not significantly related to 2 year SF36 or Oxford knee scores. Conclusion. Although restoration of coronal alignment even in deformity >15° is possible with computer navigation, post-operative extensor lag and weakness is still a problem determined by pre-operative extensor lag and weakness in straight leg raising. Computer navigation is useful when exposure and landmarks to assess alignment are difficult such as in obesity where the standard external tibia jig doesn't sit well with the thick subcutaneous layer and for determining the epicondylar axis of the femur in a deep wound. Despite the technical challenges of performing a total knee arthroplasty with obesity, BMI is not a determinant of functional scores when computer navigation is used

Accurate placement of unicompartmental knee arthroplasty components is thought to be essential for the long-term survival and efficacy of the prosthesis. Computer navigation is being explored as a means of improving the accuracy of component position. There are few published studies comparing conventional and computer-navigated techniques using the same prosthesis. Twenty-two Allegretto [Zimmer] medial unicompartmental knee prostheses were placed in 18 patients using the AxiEM [Medtronic] computer-navigated system. The immediate post-operative AP and lateral radiographs were analysed and compared with an equivalent cohort of 30 prostheses in 29 patients with medial unicompartmental arthritis in whom the Allegretto was placed without the aid of computer navigation. All operations were performed by the senior author in a rural Queensland hospital. No cases were lost to follow-up. The data was not normally distributed. The mean, SD and variance of the data sets was calculated and significance tested with a 2-tailed Mann-Whitney U-test. Computer navigated tibial components were implanted with a mean of 2 degrees of varus compared with 1 degree of valgus with conventional navigation [p = 0.027]. Our target was 0–4 degrees of varus. Eighteen of the 20 computer-navigated cases, 90% fell within the recommended range [0–4 degrees of varus] compared with only 40%, 12 of the 30 conventionally-implanted cases. This is demonstrated by the greater range and variance of the conventional navigation data set. Posterior slope for the computer navigated components was 1 degree compared with 3 degrees for conventional navigation [0.010]; only 1 computed navigated component [5%] was implanted with anterior slope compared with 4 cases for conventional navigation [13%]. Measurements of femoral component flexion and position with respect to the tibial component were not significantly different but demonstrated greater variance for the conventionally navigated data set. Accurate component positioning improves efficacy and prosthesis survival for patients who meet the indications for unicompartmental surgery. However proponents acknowledge the weaknesses of conventional jigs for unicompartmental prostheses. In this study computer navigation has been shown to improve the accuracy of component placement

Robotic-guided arthroplasty procedures are becoming increasingly common. We introduced a new computer-navigated TKA system with a robotic cutting-guide into a community-based hospital and characterized the accuracy and efficiency of the technique. We retrospectively reviewed our first 100 cases following IRB approval. Tourniquet time, intraoperative bone-cut accuracy and final limb alignment as measured by the computer were collected and divided into consecutive quartiles: Groups I, II, III, and IV; 25 cases per group. All resections were planned neutral to the mechanical axis. Postoperative component alignment and overall mechanical axis limb alignment were also measured on standing long-leg radiographs by two independent observers at minimum six weeks follow-up. Radiographic alignment was available for 62 cases. Intraoperative Computer Data: Bone-cut accuracy was a mean 0.1° valgus, SD±0.8° for both the femur and tibia (range, femur: 2.0° valgus to 1.5° varus; range, tibia: 3.5° valgus to 1.5° varus). Final limb alignment was within 3° for 98% (97/99) of cases (range: 2.0° valgus to 3.5° varus). Radiographic Alignment: Pre-operative mechanical alignment ranged from −14.5° valgus to 21.5° varus. Radiographic femoral and tibial component alignment was within 3° of neutral in 98.4% of cases (61/62). Final limb alignment was within 3° for 87.1% (54/62) of cases (range: 4.5° varus to 4.5° valgus). Learning curve: Mean tourniquet time was 60minutes ±9.9SD (range 46–79) for Group I and 49.5minutes for Groups II, III, and IV (range 35–68), p = 0.0001. Mean tourniquet time for the first ten and second ten procedures was 65±10.6minutes and 55±8.3minutes, respectively, p = 0.034. There were no differences in accuracy among the four groups (p>0.05). Imageless computer-navigated TKA with a robotic cutting guide allowed one surgeon to make bone resections within 3° of neutral in 98% of cases. Radiographic limb alignment was less precise, which is consistent with the known limitations inherent to this measurement technique. Surgeons can expect this procedure to take 15 additional minutes during the first ten cases and five additional minutes during the second ten cases on average, without compromising accuracy

Background

Stress fractures at tracker after computer navigated total knee replacement are rare. Periprosthetic fracture after Minimally Invasive Plate Osteosynthesis (MIPO) of stress fracture through femoral tracker is unique in orthopaedic literature. We are reporting this unique presentation of periprosthetic fractures after MIPO for stress fracture involving femoral pin site track in computer assisted total knee arthroplasty, treated by reconstruction nail (PFNA).

Correct alignment of tibial and femoral components is one of the most important factors that determine favorable long-term results of total knee arthroplasty (TKA). Computer-assisted TKA allows for more accurate component positioning and continuous intraoperative monitoring of the alignment. However, the pinholes created by the temporally anchored pins used as reference points may cause problems. Here we report a case of tibial stress fracture that occurred after a TKA was performed with the use of a computer navigation system.

INTRODUCTION

As computer navigated surgery continues to progress to the forefront of orthopedic care, the application of a navigated total shoulder arthroplasty has yet to appear. However, the accuracy of these systems is debated, as well as the dilemma of placing an accurate tool in an inaccurate hand. Often times a system's accuracy is claimed or validated based on postoperative imaging, but the true positioning is difficult to verify. In this study, a navigation system was used to preoperatively plan, guide, and implant surrogate shoulder glenoid implants and fiducials in nine cadaveric shoulders. A novel method to validate the position of these implants and accuracy of the system was performed using pre and post operative high resolution CT scans, in conjunction with barium sulfate impregnated PEEK surrogate implants.

Purpose

Computer navigation system has been reported as a useful tool to obtain the proper alignment of lower leg and precise implantation in TKA. This system alsoãζζhas shown the accurate gap balancing which was lead to implants longevity and optimal knee function. The aim of this study was determine that the postoperative acquired deep knee flexion would be influenced by intraoperative kinematics on navigated TKA even under anesthesia.

Introduction

Severe angular deformities in total knee arthroplasty require specific attention to bone resections and soft tissue balancing. This can add technical complexity and time, with some authors reporting an increase of approximately 20 minutes in mean surgery time when managing large deformities with conventional instrumentation [1].

We evaluate the utility of computer-navigation with imageless BoneMorphing® and Apex Robotic Technology, or A.R.T.® for managing large deformities in TKA. BoneMorphing® allows for real-time visualization of virtual bone resection contours, limb alignment and soft-tissue balance during TKA. A.R.T. permits accurate cutting and recutting of the distal femur in 1 mm increments. We asked what effects do severe pre-operative deformities have on post-operative alignment and surgery time in comparison to knees with only mild deformities when using this system.

Purpose. The purpose of this study was to compare joint line changes between posterior-stabilized (PS) and cruciate-retaining (CR) computer navigated total knee arthroplasties (TKA) and to evaluate the impact on functional outcome. Background. Restoration of the native joint line has been a common goal in all TKA designs. Computer-navigated TKA in increasingly being favoured by many surgeons, due to increased precision and lesser complications. Few studies have reported the effect of computer navigated TKA on joint line restoration. It remains to be seen if the greater precision offered by computer-navigated TKA in restoration of joint line translates to improvement in functional outcome. Methods. This study assessed joint line changes following computer-assisted navigated total knee arthroplasty (TKA). A total of 195 patients were followed up for a period of 2 years following primary surgery. The change in the joint line was calculated based on the verified bony resections and the final thickness of the insert. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t-test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups at 6 months and 2 years of follow-up. Results. A total of 112 CR knees and 83 PS knees were analyzed. PS knees had a significantly greater joint line change as compared to CR knees with a p-value of 0.04 (Figure 1). Although the knee, function and oxford knee questionnaire scores were significantly better in the CR group at the 6-month follow-up, this did not translate into any significant difference in functional scores at the 2-year follow-up. It was also found that the PS group had significantly better final range of motion. Conclusion. CR knees are associated with significantly less joint line changes than PS knees in computer navigated TKA. PS knees have a greater range of motion at 2 years of follow-up. No significant difference in outcome was noted at 2 years follow-up

We previously compared component alignment in total knee replacement using a computer-navigated technique with a conventional jig based method. Improved alignment was seen in the computer-navigated group (Beaver et al. JBJS 2004 (86B); 3: 372–7.). We also reported two-year results showing no difference in clinical outcome between the two groups (Beaver et al. JBJS 2007 (89B); 4: 477–80). We now report our five-year functional results comparing navigated and conventional total knee replacement. To our knowlege this represents the first Level 1 study comparing function in navigated and conventional total knee replacement at five years. An original cohort of 71 patients undergoing Duracon (Stryker Orthopaedics, St. Leonards, Australia) total knee replacement without patellar resurfacing were prospectively randomised to undergo operation using computer navigation (Stryker Image Free Computer Navigation System (version 1.0; Stryker Orthopaedics))(n=35) or a jig-based method (n=36). The two groups were matched for age, gender, height, weight, BMI, ASA grade and pre-operative deformity. All operations were performed by a single surgeon. All patients underwent review in our Joint Replacement Assessment Clinic at 3, 6 and 12 months and at 2 and 5 years. Reviews were undertaken by senior physiotherapist blinded to participant status using validated outcome scoring tools (Knee Society Score, WOMAC Score and Short Form SF-36 Score). All patients underwent CT scanning of the implanted prosthesis as per Perth CT Knee Protocol to assess component alignment. After 5 years 24 patients in the navigated group and 22 patients in the conventional group were available for review. At 5 years no statistically significant difference was seen in any of the aforementioned outcome scores when comparing navigated and conventional groups. No statistically significant difference was seen between 2- and 5-year results for either group. Due to the relatively low numbers in each group these data were compared with retrospective cohorts of navigated (n=100) and conventional (n=70) Duracon total knee replacements performed outwith this study over the same 5-year period. WITHIN the retrospective cohorts no statistically significant differences were found when comparing any of the aforementioned outcome scores. In addition, when comparing parallel scores between prospective and retrospective groups again no statistically significant differences were identified. At 5-years post-operatively the functional outcome between computer navigated and conventional total knee replacement appears to be no different despite the better alignment achieved using navigation

Introduction: We previously compared component alignment in total knee replacement using a computer-navigated technique with a conventional jig based method. Improved alignment was seen in the computer-navigated group (Beaver et al. JBJS 2004 (86B); 3: 372–7.). We also reported two-year results showing no difference in clinical outcome between the two groups (Beaver et al. JBJS 2007 (89B); 4: 477–80). We now report our five-year functional results comparing navigated and conventional total knee replacement. To our knowlege this represents the first Level 1 study comparing function in navigated and conventional total knee replacement at five years. Methods: An original cohort of 71 patients undergoing Duracon (Stryker Orthopaedics, St. Leonards, Australia) total knee replacement without patellar resurfacing were prospectively randomised to undergo operation using computer navigation (Stryker Image Free Computer Navigation System (version 1.0; Stryker Orthopaedics))(n=35) or a jig-based method (n=36). The two groups were matched for age, gender, height, weight, BMI, ASA grade and pre-operative deformity. All operations were performed by a single surgeon. All patients underwent review in our Joint Replacement Assessment Clinic at 3, 6 and 12 months and at 2 and 5 years. Reviews were undertaken by senior physiotherpist blinded to participant status using validated outcome scoring tools (Knee Society Score, WOMAC Score and Short Form SF-36 Score). All patients underwent CT scanning of the implanted prosthesis as per Perth CT Knee Protocol to assess component alignment. Results: After 5 years 24 patients in the navigated group and 22 patients in the conventional group were available for review. At 5 years no statistically significant difference was seen in any of the aforementioned outcome scores when comparing navigated and conventional groups. No statistically significant difference was seen between 2- and 5-year results for either group. Due to the relatively low numbers in each group these data were compared with retrospective cohorts of navigated (n=100) and conventional (n=70) Duracon total knee replacements performed outwith this study over the same 5-year period. WITHIN the retrospective cohorts no statistically significant differences were found when comparing any of the aforementioned outcome scores. In addition, when comparing parallel scores between prospective and retrospective groups again no statistically significant differences were identified. Conclusion: At 5-years post-operatively the functional outcome between computer navigated and conventional total knee replacement appears to be no different despite the better alignment achieved using navigation

Introduction. Computer-assisted hip navigation offers the potential for more accurate placement of hip components, which is important in avoiding dislocation, impingement, and edge-loading. The purpose of this study was to determine if the use of computer-assisted hip navigation reduced the rate of dislocation in patients undergoing revision THA. Methods and Materials. We retrospectively reviewed 72 patients who underwent computer-navigated revision THA [Fig. 1] between January 2015 and December 2016. Demographic variables, indication for revision, type of procedure, and postoperative complications were collected for all patients. Clinical follow-up was performed at 3 months, 1 year, and 2 years. Dislocations were defined as any episode that required closed or open reduction or a revision arthroplasty. Data are presented as percentages and was analyzed using appropriate comparative statistical tests (z-tests and independent samples t- tests). Results. All 72 patients (48% female; 52% male) were included in the final analysis [Fig. 2]. Mean age of patients undergoing revision THA was 70.4 ± 11.2 years. Mean BMI was 26.4 ± 5.2 kg/m. 2. The most common indications for revision THA were instability (31%), aseptic loosening (29%), osteolysis/eccentric wear (18%), infection (11%), and miscellaneous (11%). During revision procedure, polyethylene component was most commonly changed (46%), followed by femoral head (39%), and acetabular component (15%). At 3 months, 1 year, and final follow-up, there were no dislocations among all study patients (0%). Compared to preoperative dislocation values, there was a significant reduction in the rate of dislocation with the use of computer-assisted hip navigation (31% vs. 0%; p<0.05). Discussion. Our study demonstrates a significant reduction in the rate of dislocation following revision THA with the use of computer navigation. Although the cause of postoperative dislocation is often multifactorial, the use of computer-assisted surgery may help to curtail femoral and acetabular malalignment in revision THA

Introduction. Robotic-guided arthroplasty procedures are becoming increasingly common, though to our knowledge there are no published studies on robotic cutting guides in TKA. We introduced a new computer-navigated TKA system with a robotic cutting-guide into a community-based hospital and characterized the accuracy and efficiency of the technique with respect to bone cutting, component alignment and final limb alignment, and tourniquet time. Methods. The first 100 cases from a single-surgeon were retrospectively reviewed following IRB approval. Intra-operative bone-cut accuracy and overall limb alignment as measured by the computer were collected and divided into consecutive quartiles: Group I, cases 1–25; Group II, cases 26–50; Group III, cases 51–74; Group IV, cases 75–100. All resections were planned neutral to the mechanical axis. Postoperative component alignment and the overall mechanical axis limb alignment in the coronal plane were also measured on standing long-leg AP radiographs by two independent observers at a minimum six weeks post-op. This mechanical radiographic alignment was available for 62 cases. Tourniquet time (the time prior to incision until after cementation) and robotic cutting guide use time were also analyzed. Results. Intra-operative Computer Data: Bone-cut accuracy was a mean 0.1° valgus, SD±0.8° for both the femur and tibia (range, femur: 2.0° valgus to 1.5° varus; range, tibia: 3.5° valgus to 1.5° varus). Final limb alignment was within 3° of neutral for 98% (96/98) of cases (range: 2.0° valgus to 3.5° varus). Radiographic Alignment Data: Pre-operative mechanical alignment ranged from −14.5° valgus to 21.5° varus. Radiographic femoral and tibial component alignment was within 3° of neutral in 98.4% of cases (61/62). Final limb alignment was within 3° of neutral for 87.1% (54/62) of cases (range: 4.5° varus to 4.5° valgus). Learning curve: Mean tourniquet time was 10 minutes longer for Group I (60 minutes ± 9.9SD, range 46–79) than for groups II, III, and IV (average mean 49.5min, range 35–68), p=0.0001. Within Group I, mean tourniquet time for the first ten and second ten procedures was 65 ± 10.6 min and 55 ± 8.3 min, respectively, p=0.034. Robotic-guide use time was also longer for the first quartile (7.8 ± 1.9 minutes, range 4–12), than for Groups II, III, and IV (average 5.2 minutes, range, 3–8), p<0.001. There were no significant differences in any of the accuracy measures among the different groups (p>0.05). Conclusion. Imageless computer-navigated TKA with a robotic cutting guide allowed one surgeon to make bone resections within 3° of neutral in 98% of cases. Radiographic limb alignment was less precise, which is consistent with the known limitations inherent to this measurement technique. During the learning curve phase, surgeons can expect the procedure to take an average of 15 extra minutes during the first ten cases and 5 extra minutes during the second ten without compromising accuracy

Introduction. Navigation in total hip arthroplasty (THA) has the goal to improve accuracy of cup orientation. Measurement of cup orientation on conventional pelvic radiographs is susceptible to error due to pelvic malpositioning during acquisition. A recently developed and validated software using a postoperative radiograph in combination with statistical shape modelling allows calculation of exact 3-dimensional cup orientation independent of pelvic malpositioning. Objectives. We asked (1) what is the accuracy of computer-navigated cup orientation (inclination and anteversion) and (2) what is the percentage of outliers (>10° difference to aimed inclination and anteversion) using postoperative measurement of 3-dimensional cup orientation. Methods. We performed a retrospective comparative study including a single surgeon series with 114 THAs (109 patients). Surgery was performed through the anterolateral approach with the patient in supine position. An image-free navigation system (PiGalileo, Smith & Nephew) with a passive digital reference base for the pelvic wing and one for the distal femur was used. The anterior pelvic plane (APP) was registered manually using a pointer and used as anatomical reference. After implantation of the press-fit cup (EP-Fit plus, Smith & Nephew) the final cup orientation (inclination and anteversion) was registered with the navigation system. Postoperative orientation was calculated using validated software to calculate 3-dimensional cup orientation. The postoperative anteroposterior pelvic radiograph in combination with a statistical model of the pelvis allowed calculation of inclination and anteversion referenced to the APP. The software was previously validated using CT measurements and revealed a mean accuracy of 0.4° for inclination 0.6° for anteversion with a maximum error of 3.3° and 3.6°, respectively. The mean postoperative inclination in the current series was 46° ± 4° (range, 35° – 60°) and the mean anteversion was 23° ± 6° (range, 11° – 37°). Accuracy was calculated as the absolute difference of the intraoperative registered cup orientation and the postoperative calculated orientation. An outlier was defined if cup orientation was outside a range of ±10° of inclination and/or anteversion. Results. (1) The mean accuracy for inclination was 3 ± 3° (0 – 17°) and 6 ± 5° (0 – 22°) for anteversion. (2) Three out of 114 cups (3%) were outliers for inclination. An increased percentage of outliers was found for anteversion with 23 out of 114 cups (20%; p<0.001). In total, 25 cups (22%) were outliers (See Figure 1). Conclusions. Previous studies evaluating accuracy of cup orientation were limited in numbers of hips due to the use of CT or used measurements on conventional postoperative radiographs which are prone to error due to pelvic malpositioning. Novel and validated software allows accurate and anatomically referenced measurement of postoperative cup orientation. This study is the single largest case series with 3-dimensional measurement of cup orientation for validation of navigated THA. Computer-assisted image-free navigation of cup orientation showed a high accuracy of cup orientation with 78% within a narrow range of ±10° of inclination and anteversion. Accuracy of cup inclination was increased compared to cup anteversion. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Introduction. Hip and knee joint replacement is nowadays one of the most common surgeries in Germany. The frequency of peri- and post-operative complications varies depending on the study. Since 2001, every hospital in Germany is required to report any peri- and post-operative complication to an external institute for quality control. The purpose of this study was to evaluate the published data of these institutes and to differentiate between the rate of peri- and early postoperative complications of conventional and computer navigated surgical procedures. The hypothesis of the study was that there is no increase in the rate of peri- and early post-operative complications as a result of the navigated surgical procedure. Materials and Methods. A retrospective analysis of the data on primary total knee and hip replacements between 2004 and 2012 were conducted. The share of navigated procedures, additional operating time due to navigation, the peri- and early post-operative surgical and general rates of complications and the comparison of patient population (age, sex and ASA-classification) were subject of the analysis. Results. Overall, the number of implanted knee endoprostheses rose from 110.000 in 2004 to 133.000 in 2012, including a doubling in the share of the navigated knee endoprostheses from 6.8% to 11.2%. Additional operative time for the implantation of knee prostheses decreased from initially 20 min. to 11.3 min. The rate of patients with at least one surgical intra and post-operative surgical complication decreased nearly 50.0% both, conventional and computer-navigated total knee arthroplasty. Focusing solely on the rate of general post-operative complications, a decrease from 5.9 % (conventional) or 4.7% (navigated) to 2.9%, respectively, was observed. In the area of hip prostheses, the total number increased from 138.000 (2004) to 152.500 (2012), with a relatively stable share of navigated prostheses from 1.63% to 1.4%. Additional operative time in case of the navigation decreased from 14.8 min. to 5.3 min. The rate of patients with at least one surgical intra or post-operative complication showed a decrease from 5.0% to 3.0% for both. The rate of post-operative general complications with navigated prostheses showed a higher drop in percentage points from 4.5% to 1.85% than with non-navigated prostheses, which decreased from 5.0% to 3.0%. Discussion. Despite high expertise and having used navigation for years, still very few endoprostheses are navigated. However, through a regular application of the navigation, a significant reduction of the operational time was accomplished in knee and hip replacement. The analysis did not show an increase in either peri- or early post-operative appearance of complications

Introduction. 11%–19% of patients are unsatisfied with outcomes from Total Knee Arthroplasty (TKA). This may be due to problems of alignment or soft-tissue balancing. In TKA, often a neutral mechanical axis is established followed by soft tissue releases to balance and match the flexion/extension gaps with the distal femoral and proximal tibial resections at right angles to the mechanical axis. Potential issues with establishment of soft tissue balance are due to associated structures such as bone tissue of the knee, the static (or passive) stabilizers of the joint (medial and lateral collateral ligaments, capsule, and anterior and posterior cruciate ligaments), and the dynamic (or active) stabilizers around the knee. An optimized balance among these systems is crucial to the successful outcome of a TKA. Additionally, the importance of correct femoral rotation has been well documented due to its effect on patella alignment and flexion instability, range of motion, and polyethylene wear. There are several methods used in TKA procedures to establish femoral component rotation. The more prominent ones are a conventional method of referencing to the posterior condylar axis with a standard external rotation of 3° (PCR), anterior-posterior line or “Whiteside's line” (AP axis), transepicondylar axis (TEA) (Figure 1), and the gap balancing technique, however, it is not yet clear, which method is superior for femoral rotational component alignment. In the current study, we sought to investigate an alternative method based on soft-tissue, dynamic knee balancing (DKB) while using an alternative analysis approach. DKB dictates femoral component rotation on the basis of ligament balance and force measures. DKB has become more prominent in TKA surgeries. While retaining ligament balance in TKA, it is possible that this technique also leads to higher precision of rotational alignment to the anatomical axis. The primary objective of this study was to compare efficiency of DKB versus other methods for rotational implant alignment based on post-surgery computed tomography (CT). Methods. 31 patients underwent computer-navigated total knee arthroplasty for osteoarthritis with femoral rotation established via a flexion gap balance device (Synvasive eLibra). Alternative, hypothetical alignments were assessed based on anatomical landmarks during the surgery. Postoperative computed tomography (CT) scans were analyzed to investigate post-surgery rotational alignment. Repeated measures ANOVA and Cochran's Q test were utilized to test differences between the DKB method and the other techniques. Results. Significant differences were observed between the DKB method and TEA method (p=0.02), between DKB and AP method (p=0.04), and DKB and PCR method (p=0.02): The DKB method showed the lowest rotational deviation from CT-determined true anatomical TEA (aTEA)(Figure 2). The DKB method established femoral rotation within ±3 more often than the other techniques (Figure 3), further analysis revealed a significant proportional difference between DKB and PCR method (p=0.01), between DKB and TEA (p=0.02) and DKB and AP (p=0.04). Conclusions. DKB showed promising results in our study regarding femoral rotation accuracy in comparison to other methods. DKB may be a valuable tool due to its ability to establish soft-tissue balance in addition to high accuracy of femoral rotation

Introduction. High tibial osteotomy (HTO) is a commonly used surgical technique for treating moderate osteoarthritis (OA) of the medial compartment of the knee by shifting the center of force towards the lateral compartment. The amount of alignment correction to be performed is usually calculated prior to surgery and it's based on the patient's lower limb alignment using long-leg radiographs. While the procedure is generally effective at relieving symptoms, an accurate estimation of change in intraarticular contact pressures and contact surface area has not been developed. Using electromyography (EMG), Meyer et al. attempted to predict intraarticular contact pressures during gait patterns in a patient who had received a cruciate retaining force-measuring tibial prosthesis. Lundberg et al. used data from the Third Grand Challenge Competition to improve contact force predictions in total knee replacement. Mina et al. performed high tibial osteotomy on eight human cadaveric knees with osteochondral defects in the medial compartment. They determined that complete unloading of the medial compartment occurred at between 6° and 10° of valgus, and that contact pressure was similarly distributed between the medial and lateral compartments at alignments of 0° to 4° of valgus. In the current study, we hypothesised that it would be possible to predict the change in intra-articular pressures based on extra-articular data acquisition. Methods. Seven cadavers underwent an HTO procedure with sequential 5º valgus realignment of the leg up to 15º of correction. A previously developed stainless-steel device with integrated load cell was used to axially load the leg. Pressure-sensitive sensors were used to measure intra-articular contact pressures. Intraoperative changes in alignment were monitored in real time using computer navigation. An axial loading force was applied to the leg in the caudal-craneal direction and gradually ramped up from 0 to 550 N. Intra-articular contact pressure (kg) and contact area (mm2) data were collected. Generalised linear models were constructed to estimate the change in contact pressure based on extra-articular force and alignment data. Results. The application of an axial load results in axial angle changes and load distribution changes inside the knee joint. Preliminary analysis has shown that it is possible to predict lateral and medial compartment pressures using externally acquired data. For lateral compartment pressure estimation, the following equation had an R of 0.86: Lateral compartment pressure = −1.26*axial_force + 37.08*horizontal_force − 2.40*vertical_force − 271.66*axial_torque − 32.64*horizontal_torque + 18.98*vertical_torque − 24.97*varusvalgus_angle_change + 86.68*anterecurvature_angle_change − 17.33*axial_angle_change − 26.14. For medial compartment pressure estimation, the following equation had an R2 of 0.86: Medial compartment pressure = −2.95*axial_force −22.93*horizontal_force − 9.48*vertical_force − 34.53*axial_torque + 6.18*horizontal_torque − 127.00*vertical_torque − 110.10*varusvalgus_angle_change − 15.10*anterecurvature_angle_change + 55.00*axial_angle_change + 193.91. Discussion. The most important finding of this study was that intra-articular pressure changes in the knee could be accurately estimated given a set of extra-articular parameters. The results from this study could be helpful in developing more accurate lower limb realignment procedures. This work complements and expands on previous research by other groups aimed at predicting intra-articular pressures and identifying optimal alignment for unloading arthritic defects. A possible clinical application of these findings may involve the application of a predetermined axial force to the leg intra-operatively. Given the estimated output from the predictive equation, one could then perform the opening wedge until the desired estimated intra-articular pressure is achieved. With this method, an arthrotomy and placement of intra-articular pressure sensors would not be needed. This work is not without its limitations. This experiment was performed on cadaveric specimens. Therefore, we cannot directly predict what the pressures would be in a de-ambulating patient. However, these sort of experiments do help us understand the complex biomechanics of the knee in response to alterations in multi-planar alignment. Further in vivo research would be warranted to validate these results. Additionally, given our current experimental setup, only axial loading could be performed for testing. Further experiments involving dynamic motion of the lower limb under load would further help us understand the changes in pressure at difference flexion angles. Continued experiments would help us gather additional data to better understand the relationship between these variables and to construct a more accurate predictive model. In summary, we have established a framework for estimating the change in intra-articular contact pressures based on extra-articular, computer-navigated measurements. Quantifying the resulting changes in load distribution, alignment changes, torque generation and deflection will be essential for generating appropriate algorithms able to estimate joint alignment changes based on applied loads

There remains controversy as to whether computer-navigated TKA improves the overall alignment of the knee prosthesis. The aim of this study was to determine whether computer-assisted total knee arthroplasty provides superior prosthesis positioning when compared to a conventional jig-assisted total knee replacement. A prospective controlled study comparing computer navigated and conventional jig-assisted total knee replacement in 23 patients who underwent bilateral TKA was undertaken to determine if there was any significant difference in component position. The 23 patients (46 knees) were randomised to receive one conventional jig-assisted total knee replacement, and a contra lateral computer-assisted total knee replacement. A single experienced knee surgeon performed all procedures. A quantitative assessment of the spatial positioning of the implant in the 46 total knee replacements was determined using a low-dose dual-beam CT scanning technique. This resulted in six parameters of alignment that were compared. A blinded, independent observer recorded all radiological measurements. Median external rotation of the femoral component relative to the trans-epicondylar axis was −2 degrees in the computer-assisted group and −3 degrees in the jig-assisted group. Median femoral component flexion was identical in both groups at 0 degrees. Median valgus angulation of the femoral and tibial components was +1 degree and 0 degree respectively for the computer-assisted group and 0 degree and −1 degree for the jig-assisted group. Median posterior tibial prosthesis slope was +5 degree in both the computer-assisted group and the jig-assisted group. Computer-assisted implantation of total knee replacements does not offer a significant advantage in prosthesis alignment. Low dose dual-beam CT scanning provides a three dimensional model of the lower limb, allowing accurate measurement of prosthesis alignment

This multicenter study compared computer-navigated TKA using either MIS or conventional surgical technique, using a CR fixed bearing knee, Stryker Navigation system and dedicated MIS instrumentation. It was hypothesized that patients would benefit from the MIS technique by shorter recovery periods, less blood loss, faster wound healing and improved mobility during early rehabilitation. A prospective multicentre double-blind controlled trial included 69 patients matched for age, gender, BMI (MIS n=36, CONV n=33). Assessments at pre-op, 1 week, 3 and 6 months post-op included surgery time, bloodloss, range of motion, Knee Society Score (KSS) and WOMAC, Chair rise test and quadriceps strength. Radiographic analysis included radiographs for lucencies and CAT scans for alignment,. Four patients were lost to follow-up. The MIS group had significantly more prolonged surgery time and blood loss at 24 hours p<0.05. At 6 months mean flexion values for MIS (106,7°±12,91) and CONV 105,92 ±11,58) with no significant differences in flexion ROM between both groups at any time point. KSS scores showed a significant improvement (p<0,01) over time in both groups but no statistical significance between groups. WOMAC score also improved significantly (p<0,01) over time in both groups without reaching statistical significance. A significant decrease of anterior knee pain score was observed over time with no significant difference between both groups. Quadriceps strength recovery was not significant between groups but trended toward faster recovery in the MIS group. X-rays showed stable implants with no progressive radiolucent lines in all patients. The hypothesis that patients benefit from the MIS technique in the short term was not confirmed by the results of this study. The MIS surgery technique resulted in more blood loss intra-op and in the first 24hours post op as well as an elongated surgery time. The MIS surgery technique also failed to generate clear advantages in clinical or functional outcome that persisted over time