Aims

Total knee arthroplasty (TKA) may provoke ankle symptoms. The aim of this study was to validate the impact of the preoperative mechanical tibiofemoral angle (mTFA), the talar tilt (TT) on ankle symptoms after TKA, and assess changes in the range of motion (ROM) of the subtalar joint, foot posture, and ankle laxity.

Aims

This study compared the cobalt and chromium serum ion concentration of patients treated with two different metal-on-metal (MoM) hinged total knee arthroplasty (TKA) systems, as well as a titanium nitride (TiN)-coated variant.

Aims

The aim of this study was to determine the association between knee alignment and the vertical orientation of the femoral neck in relation to the floor. This could be clinically important because changes of femoral neck orientation might alter chondral joint contact zones and joint reaction forces, potentially inducing problems like pain in pre-existing chondral degeneration. Further, the femoral neck orientation influences the ischiofemoral space and a small ischiofemoral distance can lead to impingement. We hypothesized that a valgus knee alignment is associated with a more vertical orientation of the femoral neck in standing position, compared to a varus knee. We further hypothesized that realignment surgery around the knee alters the vertical orientation of the femoral neck.

Aims

Eight-plates are used to correct varus-valgus deformity (VVD) or limb-length discrepancy (LLD) in children and adolescents. It was reported that these implants might create a bony deformity within the knee joint by change of the roof angle (RA) after epiphysiodesis of the proximal tibia following a radiological assessment limited to anteroposterior (AP) radiographs. The aim of this study was to analyze the RA, complemented with lateral knee radiographs, with focus on the tibial slope (TS) and the degree of deformity correction.

Aims

Robotic-assisted unicompartmental knee arthroplasty (UKA) promises accurate implant placement with the potential of improved survival and functional outcomes. The aim of this study was to present the current evidence for robotic-assisted UKA and describe the outcome in terms of implant positioning, range of movement (ROM), function and survival, and the types of robot and implants that are currently used.

Objectives

Unicompartmental knee arthroplasty (UKA) is an alternative to total knee arthroplasty for patients who require treatment of single-compartment osteoarthritis, especially for young patients. To satisfy this requirement, new patient-specific prosthetic designs have been introduced. The patient-specific UKA is designed on the basis of data from preoperative medical images. In general, knee implant design with increased conformity has been developed to provide lower contact stress and reduced wear on the tibial insert compared with flat knee designs. The different tibiofemoral conformity may provide designers the opportunity to address both wear and kinematic design goals simultaneously. The aim of this study was to evaluate wear prediction with respect to tibiofemoral conformity design in patient-specific UKA under gait loading conditions by using a previously validated computational wear method.

Introduction. Recent studies have challenged the concept that a single ‘correct’ alignment to standardised anatomical references is the primary driver of TKA performance with regards to patient satisfaction outcomes. Patient specific variations in musculoskeletal anatomy are one explanation for this. Virtual simulated environments such as rigid body modelling allow for the impact of component alignment and variable patient specific musculoskeletal anatomy to be studied simultaneously. This study aims to determine if the output kinematics derived from consideration of both postoperative component alignment and patient specific musculoskeletal modelling has predictive potential of Patient Reported Outcomes. Method. Landmarking of key anatomical points and 3D registration of implants was performed on 96 segmented post-operative CT scans of TKAs. Both femoral and tibia implant components were registered. Acadaver rig validated platform for generating patient specific rigid body musculoskeletal models was used to assess the resultant motions and contact forces through a 0 to 140 degree deep knee bend cycle. Resultant kinematics were segmented and tested for differentiation with and correlation to a 12 month postoperative Knee injury and Osteoarthritis Outcome Score (KOOS). Results. Significant negative correlations (p<0.05) were found between the postoperative KOOS symptoms score and the rollback occurring in midflexion, quadriceps force in mid flexion, patella shear force and patella tilt at 90 degrees of flexion. A significant positive correlation was found between lateral shit of the patella through flexion and the symptoms score. (p<0.05) When segmenting those KOOS scores performing in the lowest 20% of patients, both rollback and the three patella measurements have statistically significantly different means (t test, p<0.05). There were other trends present that are discernible but do not have linear correlations, as they are cross-dependant on other kinematic factors or are not linear in nature. When segmenting the varus/valgus angular change into those with a varus angular change from extension to full flexion between 0 and 4 degrees (long leg axis, not implant to implant) and those with either further varus change or a valgus change, a statistically significant difference of 7 points (p<0.05) in the postoperative KOOS pain score is observed. Likewise, measured rollback of no more than 6mm without roll forward scored 10 points higher (p<0.05) in the postoperative KOOS score. These two parameters form a ‘kinematic safe zone' of outcomes in which the postoperative KOOS score is 12 points higher (p<0.05). Conclusions. The study showed statistically significant correlations between kinematic factors in a simulation of postoperative TKA and post-operative KOOS scores. The kinematic factors so captured are the result of both the variation in implant position and the subject specific, variable musculoskeletal anatomy. The presence of a ‘kinematic safe zone' in the data suggests a subject specific optimisation target for any given individual patient and the opportunity to preoperatively determine a subject specific implant position target

Purpose. Use of theguide angle method using intramedullary guide angle for distal femoral cutting in total knee arthroplasty may cause error when rotation of the femur occurs or the insertion point of the intramedullary guide is incorrectly positioned in preoperative radiography. On the other hand, use of the measured cutting method, in which resection of distal femoral condyles is performed according to predicted measured thickness in a preoperative radiograph can allow for correction of these errors intraoperatively. Therefore, we compared these two distal femoral bone cutting methods for restoration of accurate coronal alignment. Methods. Between 2010 and 2012, 47 patients (70 knees) underwent total knee arthroplasty for treatment of osteoarthritis with varus deformity and flexion contracture less than 10 degrees. Bone resection depending on distal femur resection thickness measured before the operation was performed in 38 cases (Group I). Distal femoral cutting using the guide angle was performed in 32 cases (Group II). Radiographic evaluation, including mean value of lower leg mechanical axis angle and the frequency of errors of more than 3 degrees, was performed for comparison between the two groups. Results. In Group I, mechanical axis was corrected from 8.4 ± 4.9 degrees (−7.2 to 16.9) on average before the operation to 0.1 ± 2.4 degrees (−5.87 to 2.98) after the operation, and, in Group II, from 6.7 ± 3.6 degrees (0.4 to 14.7) on average before the operation to 0.5 ± 2.8 degrees (−5.4 to 6.9) after the operation. No statistically significant difference in mechanical axis (p = 0.554) was observed between the two groups after the operation, and no difference in errors of more than 3 degrees was observed between the two groups, with four of 38 cases (11 %) in Group I and six of 32 cases (19%) in Group II (p = 0.495). Conclusions. No significantly different results were observed between the measured resection technique and the existing guide angle technique. Therefore, predictive measurement of distal femoral cutting thickness is another useful method for restoration of accurate coronal alignment

The radiologic and clinical results of High Tibial Osteotomies (HTO) strongly rely on the accuracy of correction, and inadequate intraoperative measurements of the leg axis can lead to over or under- correction. Over the past few years, navigation systems have been proven that navigation systems provide reliable real-time intro-operative information, may increase accuracy, and improves the precision of orthopaedic surgeries. We assessed the radiological and clinical results of navigation- assisted open wedge HTO versus conventional HTO at 24 months after surgery. A total of sixty-five open wedge HTOs were performed using navigation system and compared with forty-six open HTOs that had been performed using the conventional cable technique in terms of intraoperative leg axis assess. The Orthopilot navigation system (HTO version 1.3, B. Braun Aesculap, Tuttligen, Germany) used throughout the procedure of navigated open wedge HTO. The aim of the correction was to achieve of 3°of valgus (2–4°) on both method. For the radiological evaluation, postoperative leg axes were examined using weight bearing full-leg radiography obtained at postoperative two years after surgery. To assess correction accuracies, we compared mechanical tibiofemoral angles and intersections of the mechanical axis of the tibial plateau (%) in both groups. Outliers were defined as under-corrections of < 2° of valgus and as over-corrections of > 5° of valgus. The posterior slope of the proximal tibia was measured using the proximal tibial anatomical axis (PTAA) method. HSS (Hospital for Special Surgery) scores and ROMs (ranges of motion) were evaluated and all complications were recorded and surgical and radiation times were measured. Navigated HTOs corrected mechanical axes to 2.8° valgus (range −3.1∼5.3) with few outliers (9.5%), and maintained posterior slopes (8.5±2.3° preoperatively and 11.0±2.8° postoperatively) (P>0.05). In the conventional group, the mean valgus correction was satisfactory (2.2° valgus), but only 67.4% were within the required range (2∼5° valgus), and 26.1% of cases were under-corrected and 6.5% of cases were over-corrected. Posterior slope increased from 8.0° to 10.6° on average without significant change after surgery. Total fluoroscopic radiation time during navigated HTO was 8.1 seconds (5∼12s) as compared with 46.2 seconds (28∼64 s) during conventional HTO (p<0.05). The surgery time for navigated HTO was 11.2 minutes longer than for conventional HTO (55.5 minutes). No specific complications related to the navigation were encountered. At clinical follow up, mean HSS scores of the navigated HTO and conventional groups improved to 91.8 and 92.5 from preoperative values of 55.3 and 55.9, respectively (p>0.05), and all patients achieved full ROM. Navigation for HTO significantly improved the accuracy of postoperative leg axis, and decreased the variability of correction with fewer outliers, and without any complications. Moreover, it allows multi-plane measurements to be made, in the sagittal and transverse planes as well as the frontal plane intra-operatively in real time, compensates to some extent for preoperative planning shortcomings based on radiography, and significantly reduces radiation time

The alignment of prostheses components has a major impact on the longevity of total knee protheses as it significantly influences the biomechanics and thus also the load distribution in the knee joint. Knee joint loads depend on three factors: (1) geometrical conditions such as bone geometry and implant position/orientation, (2) passive structures such as ligaments and tendons as well as passive mechanical properties of muscles, and (3) active structures that are muscles. The complex correlation between implant position and clinical outcome of TKA and later in vivo joint loading after TKA has been investigated since 1977. These investigations predominantly focused on component alignment relative to the mechanical leg axis (Mikulicz-line) and more recently on rotational alignment perpendicular to the mechanical axis. In general four different approaches can be used to study the relationship between implant position and knee joint loads: In anatomical studies (1), the influence of the geometrical conditions and passive structures can be analyzed under the constraint that the properties of vital tissue are only approximated. This could be overcome with an intraoperative load measurement approach (2). Though, this set up does not consider the influence of active structures. Although post-operative in vivo load measurements (3) provide information about the actual loading condition including the influence of active structures, this method is not applicable to investigate the influence of different implant positions. Using mathematical approaches (4) including finite element analysis and multi-body-modeling, prostheses positions can be varied freely. However, there exists no systematical analysis of the influence of prosthesis alignment on knee loading conditions not only in axial alignment along and rotational alignment perpendicular to the mechanical axis but in all six degrees of freedom (DOF) with a validated mathematical model. Our goal was therefore to investigate the correlation between implant position and joint load in all six DOF using an adaptable biomechanical multi-body model. A model for the simulation of static single leg stance was implemented as an approximation of the phase with the highest load during walking cycle. This model is based on the AnyBody simulation software (AnyBody Technology A/S, Denmark). As an initial approach, with regard to the simulation of purely static loading the knee joint was implemented as hinge joint. The patella was realised as a deflection point, a so called “ViaNode,” for the quadriceps femoris muscle. All muscles were implemented based on Hill's muscle model. The knee model was indirectly validated by comparison of the simulation results for single and also double leg stance with in-vivo measurements from the Orthoload database (www.orthoload.de). For the investigation of the correlation between implant position and knee load, major boundary conditions were chosen as follows:. •. Flexion angle was set to 20° corresponding to the position with the highest muscle activity during gait cycle. •. Muscle lengths and thereby also muscle loads were adapted to the geometrical changes after each simulation step representing the situation after post-operative rehabilitation. As input parameters, the tibial and femoral components' positions were independently translated in a range of ±20mm in 10 equally distant steps for all three spatial directions. For the rotational alignment in adduction/abduction as well as flexion/extension the tibial and femoral components' positions were varied in the range of ±15° and for internal/external rotation within the range of ±20°, also in 10 equally angled steps. Changes in knee joint forces and torques as well as in patellar forces were recorded and compared to results of previous studies. Comparing the simulation results of single and double leg stance with the in-vivo measurements from the Orthoload database, changes in knee joint forces showed similar trends and the slope of changes in torques transmitted by the joint was equal. Against the background of unknown geometrical conditions in the Orthoload measurements and the simplification (hinge joint) of the initial multi-body-model compared to real knee joints, the developed model provides a reasonable basis for further investigations already – and will be refined in future works. As influencing parameters are very complex, a non-ambiguous interpretation of force/torque changes in the knee joint as a function of changes in component positions was in many cases hardly possible. Changes in patella force on the other hand could be traced back to geometrical and force changes in the quadriceps femoris muscle. Positional changes mostly were in good agreement with our hypotheses based on literature data when knee load and patellar forces respectively were primarily influenced by active structures, e.g. with regard to the danger of patella luxation in case of increased internal rotation of the tibial component. Whereas simulations also showed results contradicting our expectations for positional changes mainly affecting passive structures, e.g. cranial/caudal translation of the femoral component. This shows the major drawback of the implemented model: Intra-articular passive structures such as cruciate and collateral ligaments were not represented. Additionally kinematic influences on knee and patella loading were not taken into account as the simulations were made under static conditions. Implementation of relative movements of femoral, tibial and patella components and simulation under dynamic conditions might overcome this limitation. Furthermore, the boundary condition of complete muscle adaptations might be critical, as joint loads might be significantly higher shortly after operation. This could lead to a much longer and possibly ineffective rehabilitation process

INTRODUCTION. Computer-aided systems have been developed recently in order to improve the precision of implantation of a total knee replacement (TKR). Several authors demonstrated that the accuracy of implantation of TKR was higher with the help of a navigation system in comparison to the conventional, manual technique. Theoretically, the clinical results and the survival rates should be improved. Our team was one of the first all over the world which decided to use routinely a navigation system for TKR. Prostheses designed with a mobile bearing polyethylene component allow an increased congruence between femoral and tibial gliding surface, and should decrease the risk of long-term polyethylene wear. We designed a prosthetic system with one of the highest congruence on the current market. These prostheses might be technically more demanding than more conventional designs, and involve specific complications like bearing luxation. Navigation systems might be helpful in this was as well. In the present study, we wanted to test clinically the theoretic advantages of these three specific points of our system (navigated implantation, mobile bearing and increased congruence) with a five-year clinical and radiological follow-up. MATERIAL AND METHODS. 128 patients were operated on at our Department with this TKR system between 2000, and were contacted for a five-year clinical and radiological follow-up. The clinical and functional results were evaluated according to the Knee Society Scoring System (KSS). The subjective results were analyzed with the Oxford Knee Score. The accuracy of implantation was assessed on post-operative long leg antero-posterior and lateral X-rays. The survival rate after 5 years was calculated according to the Kaplan-Meier technique. RESULTS. The mean clinical score was 87 points (maximum of 100 points). The mean pain score was 43 points (maximum of 50 points). The mean flexion angle was 118°, and 33% oft he patients were able to reach 130° of knee flexion or more. The mean functional score was 70 points (maximum of 100). The mean Oxford Score was 23 points (best score = 12 points, worst score = 60 points). An optimal correction of the coronal leg axis (less than 3° off the neutral axis) was obtained in 87% of the cases. 67% of the cases had an optimal implantation of both tibial and femoral implants on both coronal and sagittal planes. The Kaplan-Meier survival rate was 97.4% after 5 years. DISCUSSION. The present study confirmed the efficiency of the navigation system used on the accuracy of implantation. The clinical and functional results after 5 years were at least as good as those published after conventional implantation of uncongruent prostheses. The survival rate was comparable as well to the already accepted gold standards. We observed no complication directly related to the new prosthetic system. The mean flexion angle was better that the results we observed with the previously used fixed bearing system. The question of the polyethylene wear could not be assessed because of the too short follow-up period. An additional follow-up study is planned after 5 more years

Revision total knee replacement (TKR) is a challenging procedure, especially because most of the standard bony and ligamentous landmarks used during primary TKR are lost due to the index implantation. One might also assume that the conventional instruments, which rely on visual or anatomical alignments or intra-or extramedullary rods, are associated with significant higher variation of the leg axis correction, especially in cases with significant bone loss which prevents to control the exact location of the usual, relevant landmarks. Navigation system might address this issue. We are using an image-free system (ORTHOPILOT TM, AESCULAP, FRG) for routine implantation of primary TKR. The standard software was used for revision TKR. Registration of anatomic and cinematic data was performed with the index implant left in place. The components were then removed. New bone cuts as necessary were performed under the control of the navigation system. The size of the implants and their thickness was chosen after simulation of the residual laxities, and ligament balance was adapted to the simulation results. The system did not allow navigation for intramedullary stem extensions and any bone filling which may have been required. 60 navigated cases were compared with 30 conventional cases. We observed a significant improvement of all radiological items by navigated cases. Limb alignment was restored in 88% of the navigated cases and 73% of the conventional cases. The coronal orientation of the femoral component was acceptable in 92% of the navigated cases and 81% of the conventional cases. The coronal orientation of the tibial component was acceptable in 89% of the navigated cases and 73% of the conventional cases. The sagittal orientation of the tibial component was acceptable in 87% of the navigated cases and 71% of the conventional cases. Overall, 78% of the implants were oriented satisfactorily for the four criteria for navigated cases, and only 58% for conventional cases. The navigation system enables reaching the implantation goals for implant position in the large majority of cases, with a rate similar to that obtained for primary TKA. The rate of optimally implanted prosthesis was significantly higher with navigation than with conventional technique. The navigation system is a useful aid for these often difficult operations, where the visual information is often misleading

Correct positioning and alignment of components during primary total knee replacement (TKR) is widely accepted to be an important predictor of patient satisfaction and implant durability. This retrospective study reports the effect of the post-operative mechanical axis of the lower limb in the coronal plane on implant survival following primary TKR.

A total of 501 TKRs in 396 patients were divided into an aligned group with a neutral mechanical axis (± 3°) and a malaligned group where the mechanical axis deviated from neutral by > 3°. At 15 years’ follow-up, 33 of 458 (7.2%) TKRs were revised for aseptic loosening. Kaplan-Meier survival analysis showed a weak tendency towards improved survival with restoration of a neutral mechanical axis, but this did not reach statistical significance (p = 0.47).

We found that the relationship between survival of a primary TKR and mechanical axis alignment is weaker than that described in a number of previous reports.

Background: Navigation allows for determination of the mechanical axis of the lower extremity. We evaluated the intra- and inter-observer reliability with an image-free navigation system and determined the accuracy of the navigation system to monitor changes in lower limb alignment as compared to alignment measured with a novel 3D CT method.

Methods: A total of 13 cadaver legs were used to evaluate the intra- and inter-observer registration reliability by three observers. Navigated HTOs were then performed on all legs and pre/postoperative values of the varus-valgus angles were recorded. Data were compared to equivalent measures obtained by 3D CT using intra-class correlation coefficients (ICCs).

Results: The ICCs for intra-observer varus-valgus reliability ranged from 0.756 to 0.922, inter-observer reliability was 0.644. ICCs for navigation-CT comparison were 0.784 for varus-valgus angle (pre-op), 0.846 (postop) and 0.873 (delta). Maximum differences in navigation-CT measurements in varus-valgus angle (delta) were 4.5° for all trials. There was poor reliability and accuracy in the axial plane (tibial rotation) as well as fair reliability and accuracy in the sagittal plane (tibial slope).

Conclusion: Image-free navigation is reliable for dynamic monitoring of coronal leg alignment but shows relevant limitations in determination of sagittal and axial plane alignment.

We conducted a retrospective study to investigate the effect of femoral bowing on the placement of components in total knee replacement (TKR), with regard to its effect on reestablishing the correct mechanical axis, as we hypothesised that computer-assisted total knee replacement (CAS-TKR) would produce more accurate alignment than conventional TKR. Between January 2006 and December 2009, 212 patients (306 knees) underwent TKR. The conventional TKR was compared with CAS-TKR for accuracy of placement of the components and post-operative alignment, as determined by five radiological measurements. There were significant differences in the reconstructed mechanical axes between the bowed and the non-bowed group after conventional TKR (176.2° (sd 3.4) vs 179.3° (sd 2.1), p < 0.001).

For patients with significant femoral bowing, the reconstructed mechanical axes were significantly closer to normal in the CAS group than in the conventional group (179.2° (sd 1.9) vs 176.2° (sd 3.4), p < 0.001). Femoral bowing resulted in inaccuracy when a conventional technique was used. CAS-TKR provides an effective method of restoring the mechanical axis in the presence of significant femoral bowing.

Computer based navigation system improved the accuracy of limb and component alignment and decreased the incidence of outliers. The majority of previous studies were based on the infrared navigation system. We evaluate the availability and accuracy of the electromagnectic(EM) navigation system in total knee arthroplasty. From July 2006 to January 2007, 40 patients (50 TKAs) with osteoarthritis were participated in this study. AxiEM(Medtronics) was used and Nexgen CR(26 cases), and Nexgen CR flex(24 cases) were used. We analyzed the failure mode of navigation (7 cases), operation time and radiologic results (limb and component alignment). Total registration time was 4 minutes 45 seconds in average (Range: 3 minutes 45 seconds – 6 minutes 55 seconds). Failures in clinical applications resulted from non-recognition of EM tracker or paddle by metallic interference in 4 cases and from informational changes during surgery by fixation loss or loosening of the tracker in 3 cases. Radiologically, the mechanical axis changed from −11.2±7.21 (Range: −25.8~3.1) to 1.0±1.25(Range: −2.1~4.0) and 1 case of outlier occurred (valgus 4°). Component alignment is measured as followed: 89.3±1.6° of Theta angle, 89.9±1.5° of Beta angle, 1.8±2.5° of Gamma angle, 86.1±2.9 of Delta angle°. There were no complications related to the EM navigation. The EM navigation system helped to achieve accurate alignment of component and lower leg axis without any complications. It had several advantages such as relatively less invasiveness in fitting small instruments, not disturbing operation field, no interrupted line of sight, portable use, and applicability to any implant. However, metallic interference may be still problematic. The EM navigation had advantages; less invasiveness, no disturbing operation field, no interrupted line of sight, portable use and applicability to any implants. But metallic interference may be still problematic

Revision total knee replacement (TKR) is a challenging procedure, especially because most of the standard bony and ligamentous landmarks used during primary TKR are lost due to the index implantation. However, as for primary TKR, restoration of the joint line, adequate limb axis correction and ligamentous stability are considered critical for the short- and long- term outcome of revision TKR. There is no available data about the range of tolerable leg alignment after revision TKR. However, it is logical to assume that the same range than after primary TKR might be accepted, that is ± 3° off the neutral alignment. One might also assume that the conventional instruments, which rely on visual or anatomical alignments or intra- or extra-medullary rods, are associated with significant higher variation of the leg axis correction, especially in cases with significant bone loss which prevents to control the exact location of the usual, relevant landmarks. Navigation system might address this issue. We used an image-free system (ORTHOPILOT TM, AESCULAP, FRG) for routine implantation of primary TKR. The standard software was used for revision TKR. Registration of anatomic and cinematic data was performed with the index implant left in place. The components were then removed. New bone cuts as necessary were performed under the control of the navigation system. The size of the implants and their thickness was chosen after simulation of the residual laxities, and ligament balance was adapted to the simulation results. The system did not allow navigation for intra-medullary stem extensions and any bone filling which may have been required. This technique was used for 54 patients. The accuracy of implantation was assessed by measuring following angles on the post-operative long-leg radiographs: mechanical femoro-tibial angle (normal = 0°, varus deformation was described with a positive angle); coronal orientation of the femoral component in comparison to the mechanical femoral axis (normal = 90°, varus deformation was described with an angle < 90°); coronal orientation of the tibial component in comparison to the mechanical tibial axis (normal = 90°, varus deformation was described with an angle < 90°); sagittal orientation of the tibial component in comparison to the proximal posterior tibial cortex (normal = 90°, flexion deformation was described with angle < 90°). Individual analysis was performed as follows: one point was given for each fulfilled item, giving a maximal accuracy note of 4 points. Prosthesis implantation was considered as satisfactory when the accuracy note was 4 (all fulfilled items). The rate of globally satisfactory implanted prostheses and the rate of prostheses implanted within the desired range for each criterion were recorded. Limb alignment was restored in 88%. The coronal orientation of the femoral component was acceptable in 92% of the cases. The coronal orientation of the tibial component was acceptable in 89% of the cases. The sagittal orientation of the tibial component was acceptable in 87% of the cases. Overall, 78% of the implants were oriented satisfactorily for the four criteria. The navigation system enables reaching the implantation objectives for implant position and ligament balance in the large majority of cases, with a rate similar to that obtained for primary TKA. The navigation system is a useful aid for these often difficult operations, where the visual information is often misleading

Revision TKR is a challenging procedure, especially because most of the standard bony and ligamentous landmarks are lost due to the primary implantation. However, as for primary TKR, restoration of the joint line, adequate limb axis correction and ligamentous stability are considered critical for the short- and long-term outcome of revision TKR. There is no available data about the range of tolerable leg alignment after revision TKR. However, it is logical to assume that the same range than after primary TKR might be accepted, that is ± 3° off the neutral alignment. One might also assume that the conventional instruments, which rely on visual or anatomical alignments or intra- or extramedullary rods, are associated with significant higher variation of the leg axis correction. We used an image-free system (ORTHOPILOT TM, AESCULAP, FRG) for routine implantation of primary TKA. The standard software was used for revision TKA. Registration of anatomic and kinematic data was performed with the index implant left in place. The components were then removed. New bone cuts as necessary were performed under the control of the navigation system. The size of the implants and their thickness was chosen after simulation of the residual laxities, and ligament balance was adapted to the simulation results. The system did not allow navigation for centromedullary stem extension and any bone filling which may have been required. This technique was used for 54 patients. The accuracy of implantation was assessed by measuring the limb alignment and orientation of the implants on the post-operative radiographs. Limb alignment was restored in 88%. The coronal orientation of the femoral component was acceptable in 92% of the cases. The coronal orientation of the tibial component was acceptable in 89% of the cases. The sagittal orientation of the tibial component was acceptable in 87% of the cases. Overall, 78% of the implants were oriented satisfactorily for the five criteria. The navigation system enables reaching the implantation objectives for implant position and ligament balance in the large majority of cases, with a rate similar to that obtained for primary TKA. The navigation system is a useful aid for these often difficult operations, where the visual information is often misleading. The navigation system used enables facilitated revision TKA

Long term successful results of high tibial osteotomy (HTO) strongly depend on the degree of correction, and inadequate intraoperative measurements of the leg axis can lead to under or over correction, and surgeons have to solve these problems based on personal experience. This study was undertaken to investigate and compare the clinical and radiological results of navigation assisted open wedge high tibial osteotomy (HTO) versus conventional HTO at 12 months after surgery, for unicompartmental gonarthrosis. Forty navigated open HTOs with an anterior opening gap of approximately 70% of the posterior gap were included and compared with forty open HTOs performed using the conventional cable technique in terms of intraoperative leg axis assess. Navigated HTOs corrected mechanical axes to 2.9° valgus (range 0.5–6.2) with few outliers (12.5%), and maintained posterior slopes (7.9±2.3° preoperatively and 8.3±2.8° postoperatively) (P> 0.05). However, in the conventional group, only 63% of cases were within the satisfactory range (valgus 2–5°), and tendencies toward undercorrection and an increase in posterior slope were observed. Clinically both groups showed satisfactory results. Navigated HTO significantly improved the accuracy of postoperative mechanical axis and decreased correction variabilities with fewer outliers

Computer based navigation system improved the accuracy of limb and component alignment and decreased the incidence of outliers. The majority of previous studies were based on the infrared navigation system. We evaluate the availability and accuracy of the electromagnectic(EM) navigation system in total knee arthroplasty. From July 2006 to January 2007, 40 patients (50 TKAs) with osteoarthritis were participated in this study. AxiEM(Medtronics) was used and Nexgen CR(26 cases), and Nexgen CR flex(24 cases) were used. We analyzed the failure mode of navigation (7 cases), operation time and radiologic results (limb and component alignment). Total registration time was 4 minutes 45 seconds in average (Range : 3 minutes 45 seconds ~ 6 minutes 55 seconds). Failures in clinical applications resulted from non-recognition of EM tracker or paddle by metallic interference in 4 cases and from informational changes during surgery by fixation loss or loosening of the tracker in 3 cases. Radiologically, the mechanical axis changed from −11.2±7.21 (Range : −25.8~3.1) to 1.0±1.25(Range : −2.1~4.0) and 1 case of outlier occurred (valgus 4°). Component alignment is measured as followed: 89.3±1.6° of Theta angle, 89.9±1.5° of Beta angle, 1.8±2.5° of Gamma angle, 86.1±2.9 of Delta angle°. There were no complications related to the EM navigation. The EM navigation system helped to achieve accurate alignment of component and lower leg axis without any complications. It had several advantages such as relatively less invasiveness in fitting small instruments, not disturbing operation field, no interrupted line of sight, portable use, and applicability to any implant. However, metallic interference may be still problematic. The EM navigation had advantages; less invasiveness, no disturbing operation field, no interrupted line of sight, portable use and applicability to any implants. But metallic interference may be still problematic