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.

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 an unicompartmental knee replacement (UKR) was also improved.

Minimal invasive techniques have been developed to decrease the surgical trauma related to the prosthesis implantation. The benefits of minimal-incision surgery might include less surgical dissection, less blood loss and pain, an earlier return to function, a smaller scar, and subsequently lower costs. However, there might be a concern about the potential of minimal invasive techniques for a loss of accuracy. Navigation might help to compensate for these difficulties.

Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear. The benefits might be a better survival and less bone loss during revisions. However, these prosthesis are technically more demanding, and involve the specific risk of bearing luxation. Again, navigation might help to compensate for these difficulties.

INTRODUCTION

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. Navigation system might address this issue.

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.

Navigation systems have proved to improve the accuracy of the bone resection during total knee replacement (TKR). They might also be helpful to assess intra-operatively the knee kinematics before and after prosthesis implantation.

We are using the OrthoPilot^® system (Aesculap, Tuttlingen, FRG) on a routine basis for TKR. The current standard version of the software helps the surgeon orienting the bone resections and allows measuring the ligamentous balancing. This version was modified to allow a continuous tracking of the 3D tibio-femoral movement during passive knee flexion and extension. The kinematics was assessed by measuring the tibial movement in these three planes with the femur as reference.

For the purpose of the study, following data were registered before and after implanting the prosthesis: flexion-extension angle, varus-valgus angle, rotational angle, antero-posterior translation. Additionally, the gap between the contact point of the femoral component and the corresponding point of the tibial resection was measured after prosthesis implantation. Two successive registrations were performed by each of the 100 patients of the study before and after prosthesis implantation. The pre-and post-implantation kinematic curves were respectively compared by each patient to assess reproducibility. The pre-and postimplantation kinematic curves were compared by each patient to assess the modification due to prosthesis implantation. The results were compared to the current available literature.

The kinematic curves were plotted from maximal extension to maximal flexion. The observed 3D kinematics seem to be in agreement with the current literature in both in-vitro and in-vivo studies. We could observe the tibial internal rotation and the femoral roll-back during flexion. Some patients experienced paradoxical movement, both before and after implantation. However the post-implantation kinematics was generally closer to the expected one than the pre-implantation kinematics.

The software has definitely the potential to assess the intra-operative knee kinematics during various surgical procedures. It might help to try several solutions (orientation of the resections, implant combination or design, ligamentous balancing… ) before final implantation, in order to choose the best individual compromise. The actual relevance of such a study remains to be defined. It might be interesting to compare these data with in-vivo kinematic studies by the same patients.

Purpose of the study: It has been demonstrated that navigation systems improve the quality of implantation of total knee arthroplasty (TKA). The definitions of the reference alignment for the femur are not however consensual. We wanted to define the different alignments of the femur on the lateral view, including the femoral head and comparing the alignments with those defined by the measured axes during navigated implantation.

Material and methods: We analysed 30 navigated TKA or unicompartmental prosthesis implantations. The following lines were drawn on the pre and postoperative lateral telemetric views: anatomic axis aligned on the anterior cortical of the femur, mechanical alignment n°1 (centre of the femoral head to the most distal point of the Blumensaat line), mechanical alignment n°2 (centre of the femoral head to the junction between the anterior two-thirds and the posterior third of the femoral condyles). The anatomic diaphyseal alignment was taken as the reference and the angles between this reference line and the other lines was measure. In addition, the sagittal orientation of the femoral component measured during the operation by the navigation system in relation to the n°2 mechanical alignment was noted; this orientation was also measured on the postoperative lateral telemetric views in relation to this same mechanical alignment.

Results: The mean difference between the anatomic cortical alignment and the reference was 0.3 (−1 to +). The mean difference between the n°1 mechanical alignment and the reference was −1.1 (−5 to +3). The mean difference between the mechanical alignment n°2 and the reference was 0.8 (−4 to 4). The mean intraoperative sagittal orientation of the femoral component was 0.0 (−2 to 2). The mean postoperative sagittal orientation of the femoral component was 1.1 (−4 to 6).

Discussion: The differences between the orientations of the different sagittal alignments of the femur were minimal. The cortical axis has a smaller variance and could be considered as the most reliable reference, but this alignment does not include the femoral anteversion. The difference between the sagittal orientation of the femoral component as measured by the navigation system and as measured on the postoperative x-rays was also minimal, and probably of no significance clinically.

Conclusion: The choice of the sagittal alignment of the femur is of little importance. The intraoperative navigated measurement of the sagittal orientation of the femoral component is reliable.

Purpose of the study: Leg length discrepancy (LLD) can be a common reason for patient dissatisfaction after implantation of a total hip arthroplasty (THA). The failure rate is non negligible for conventional implantation techniques. Navigation systems might be able to improve precision.

Material and method: We used an imageless navigation system (Orthopilot™, Aesculap, FRG) for routine first-intention THA. LLD was determined on the AP view of the pelvis in the upright position to determine the desired correction. Captors were screwed onto the homolateral iliac crest and femur. The system analysed their respective positions at the beginning of the procedure thus defining the reference length. During implantation, the size and the height of the femoral implant and the length of the prosthetic neck were programmed virtually by the navigation system in order to obtain the desired correction which was then reproduced on the definitive implants. At the end of the operation, the final length of the limb was measured the same way as initially. The result of the correction was measured on the AP view of the pelvis in the upright position under the same conditions as initially. We compared 30 navigated THA with 30 THA implanted with the conventional technique. We analysed the residual length discrepancy and the percentage of the cases where the desired correction was achieved. Student’s t test and the chi-square test were used for the statistical analysis taking p< 0.05 as significant.

Results: Residual length discrepancy was 5 mm for the navigated THA and 9 mm for the conventional THA. The mean difference between the desired correction and the final correction was 2 mm for the navigated THA and 6 mm for the conventional THA. The desired length was obtained in 26 hips with navigated THA and in 17 with conventional THA. Residual LLD > 10mm was observed in 2 navigated THA and 9 conventional THA. All differences were significant.

Discussion: The navigation system used in this study enabled improved quality correction of lower limb length after implantation of a THA. Patient satisfaction should be globally improved.

Purpose of the study: Revision total knee arthroplasty (rTKA) is becoming a routine procedure. The technical problems are greater than with a first-intention implantation because of the potential malposition of the initial implants, loss of bone stock, and prior ligament injury. It could be hypothesised that as for implantation of a primary TKA, navigation might improve the quality of the implantation.

Material and methods: We used the Orthopilot™ (Aesculap, RFA) navigation system for first-intention TKA. The standard software was used for revisions. The acquisition of the anatomic and kinematic data was performed while the initial implants in situ. The implants were then removed. Any bone recuts required were done under navigation control. The size of the implants and their thickness were determined after digital simulation of residual laxity; ligament balance was adapted from this data. The system does not allow navigation for centromedullary stem extensions nor for filling potential bone defects. Sixty patients underwent the procedure. There was a comparative series of 30 patients who underwent manual conventional revision using an instrumentation guided by the centromedullary femoral and tibial stems. The quality of the implantation was determined by measuring the alignment of the limb and the orientation of the implants on the postoperative x-rays. Outcome was analysed with Student’s t test and the chi-square test with p< 0.05 taken as significant.

Results: There was a significant improvement in quality of the implantation for all radiographic criteria in the navigation group. Limb alignment was restored in 88% of the navigated cases and 73% of the conventional cases. Similar differences were observed for femoral and tibial implant position on the lateral and AP views.

Discussion: The objectives set for implant orientation and ligament balance can be met with the navigation system for the majority of knees, with a rate similar to that achieved with primary implantation. The navigation system is an appreciable aid for these often difficult procedures where visual information can be misleading.

Conclusion: The navigation system used here facilitated revision TKA.

Introduction: Navigation system might help improving the quality of implantation of a revision total knee replacement (TKR).

Methods: 30 cases of revision TKR were operated on with an image-free system, and matched to 30 cases of conventional revision TKR. Quality of implantation was analyzed in both groups on post-operative long-leg X-rays. Following items were recorded: coronal femoro-tibial angle, coronal and sagittal orientation of femoral and tibial implants. The rate of globally satisfactory implanted prostheses and the rate of prostheses implanted within the desired range for each criterion were recorded in both groups and compared with a Chi² test and an ANOVA test at a 5% level of significance.

Results: 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. Similar differences were observed for the coronal and sagital orientation of the femoral and tibial implants. Overall, 78% of the implants were oriented satisfactorily for the four criteria for navigated cases, and only 58% for conventional cases.

Discussion: 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.

Introduction: Data about sagittal orientation of the femoral component of a total knee replacement (TKR) are scarce, mainly because the definition of the femur axes on the lateral plane is not fully validated.

Methods: We analyzed 60 patients scheduled for TKR. Following axes were drawn on pre-operative long leg lateral X-rays: distal anterior cortex axis, anatomic diaphyseal axis, and three different mechanical axes from the center of the femoral head: #1 to the lowest point of the Blumensaat line, #2 to the midportion of the femoral condyles, #3 to the junction between the anterior two-third and the posterior third of the femoral condyles. The cortical axis was considered as the reference, and the angles between this reference and the other axes were recorded (more fiexion was considered positive).

Results: The mean orientation of the diaphyseal axis and the reference was +0.6°±3° (range, −1° to +3°). The mean orientation of the mechanical axis 1 was −0.8°±2.1° (range, −5° to +4°). The mean orientation of the mechanical axis 2 was −0.6°±2.1° (range, −5° to +4°). The mean orientation of the mechanical axis 3 was +0.8°±2.1° (range, −3° to +5°).

Discussion: There were few differences between the orientation of the different axes of the femur on the lateral view. The cortical axis has the lowest variance and may be the more reliable to document the femoral orientation on the lateral view. However this axis does not take into account the anteversion of the femoral neck.

We are using a non image based navigation system on a routine basis for unicompartmental knee replacement (UKR). We prospectively studied 60 patients who underwent navigated minimally invasive UKR for primary medial osteoarthritis at our hospital between October 2005 and October 2006. We established a navigated control group of 60 patients who underwent conventional implantation of a UKA at our hospital between April 2004 and September 2005. There were 42 male and 78 female patients with a mean age of 65 years (range, 44–87 years). There were no differences in all preoperative parameters between the two groups.

The accuracy of implant positioning was determined using predischarge standard anteroposterior and lateral radiographs. The following angles were measured: femorotibial angle, coronal and sagittal orientation of the femoral component, coronal and sagittal orientation of the tibial component. When the measured angle was in the expected range, one point was given. The accuracy was defined as the sum of the points given for each angle, with a maximum of five points (all items fulfilled) and a minimum of 0 point (no item fulfilled). Our primary criterion was the radiographic accuracy index on the postoperative radiograph evaluation. All other items were studied as secondary criteria.

The mean accuracy index was similar in the two groups: 4.1 ± 0.8 in the study group and 4.2 ± 1.2 in the control group. 36 patients (60%) in the control group and 37 patients (62%) in the study group had the maximum accuracy index of five points. All measured angles were similar in the two groups. There were no differences between the percentages of patients in the two groups achieving the desired implant positions. Mean operating time was similar in the two groups. There were no intraoperative complications in either group. The groups had similar major postoperative complication rates during hospital stay (3% for both).

The used navigation system is based on an anatomic and kinematic analysis of the knee joint during the implantation. The modification of the existing software for minimal invasive approach has been successful. It enhances the quality of implantation of the prosthetic components and avoids the inconvenient of a smaller incision with potential less optimal visualization of the intra-articular reference points. However, all centers observed a significant learning curve of the procedure, with a significant additional operative time during the first implantations. The postoperative rehabilitation was actually easier and faster, despite the additional percutaneous fixation of the navigation device. This system has the potential to allow the combination of the high accuracy of a navigation system and the low invasiveness of a small skin incision and joint opening.

Introduction: Total knee arthroplasty in obese patients remains a challenge to most surgeons. Surgical complication rates as well as perioperative morbidity are higher than total knee arthroplasty in the nonobese. The purpose of this paper is to review our experience with total knee arthroplasty in superobese patients (BMI> 50).

Methods: From 1998–2005, 84 patients underwent 148 knee arthroplasties. Sixty-four patients underwent simultaneous bilateral total knee arthroplasties and 20 patients underwent unilateral knee arthroplasties. They were compared with similar group of nonobese patients who underwent knee arthroplasties during the same time period. All patients received combined regional and general anesthesia.

Results: Mean follow-up was 3.8 years (2–7). Knee society scores improved by 36 points in the superobese (pre-op 47 to 83 post-op) and by 45 points in the non-obese (pre-op 47 to 93 post-op) (p< .05). There was a greater incidence of complications in the superobese group, namely superficial wound infections and deep vein thrombosis. There was late loosening in three tibial components and instability in two patients that required revision in the superobese group. No reoperations in the nonobese group.

Conclusion: Although total knee arthroplasty may be safely performed in the superobese, it may be complicated by infection, loosening, instability, and lower knee scores.

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.

Navigation systems are able to measure very accurately the movement of bones, and consequently the knee laxity, which is a movement of the tibia under the femur. These systems might help measuring the knee laxity during the implantation of a total (TKR) or a unicompartmental (UKR) knee replacement.

20 patients operated on for TKR (13 cases) or UKR (7 cases) because of primary varus osteoarthritis have been analyzed. Pre-operative examination involved varus and valgus stress X-rays at 0 and 90° of knee flexion. The intra-operative medial and lateral laxity was measured with the navigation system at the beginning of the procedure and after prosthetic implantation. Varus and valgus stress X-rays were repeated after 6 weeks. X-ray and navigated measurements before and after knee replacement were compared with a paired Wilcoxon test at a 0.05 level of significance.

The mean pre-operative medial laxity in extension was 2.3° (SD 2.3°). The mean pre-operative lateral laxity in extension was 5.6° (SD 5.1°). The mean pre-operative medial laxity in flexion was 2.2° (SD 1.9°). The mean pre-operative lateral laxity in flexion was 6.7° (SD 6.0°). The mean intra-operative medial laxity in extension at the beginning of the procedure was 3.6° (SD 1.7°). The mean intra-operative lateral laxity in extension at the beginning of the procedure was 3.0° (SD 1.3°). The mean intra-operative medial laxity in flexion at the beginning of the procedure was 1.9° (SD 2.6°). The mean intra-operative lateral laxity in flexion at the beginning of the procedure was 3.5° (SD 2.7°). The mean intra-operative medial laxity in extension after implantation was 2.1° (SD 0.9°). The mean intra-operative lateral laxity in extension after implantation was 1.9° (SD 1.1°). The mean intra-operative medial laxity in flexion after implantation was 1.9° (SD 2.5°). The mean intra-operative lateral laxity in flexion after implantation was 3.0° (SD 2.8°). The mean post-operative medial laxity in extension was 2.4° (SD 1.1°). The mean post-operative lateral laxity in extension was 2.0° (SD 1.7°). The mean post-operative medial laxity in flexion was 4.4° (SD 3.3°). The mean post-operative lateral laxity in flexion was 4.7° (SD 3.2°).

There was a significant difference between navigated and radiographic measurements for the pre-operative medial laxity in extension (mean = 1.4° – p = 0.005), the pre-operative lateral laxity in extension (mean = 2.6° – p = 0.01), the pre-operative lateral laxity in flexion (mean = 3.3° – p = 0.005). There was no significant difference between navigated and radiographic measurements for the pre-operative medial laxity in flexion (mean = 0.3° – p = 0.63). There was a significant difference between navigated and radiographic measurements for the postoperative medial laxity in flexion (mean = 2.5° – p = 0.004). There was no significant difference between navigated and radiographic measurements for the postoperative medial laxity in extension (mean = 0.3° – p = 0.30), the post-operative lateral laxity in extension (mean = 0.2° – p = 0.76), the post-operative lateral laxity in flexion (mean = 1.7° – p = 0.06). These differences were less than 2 degrees in most of the cases, and then considered as clinically irrelevant.

The navigation system used allowed measuring the medial and lateral laxity before and after TKR. This measurement was significantly different from the radiographic measurement by stress X-rays for pre-operative laxity, but not statistically different from the radiographic measurement by stress X-rays for post-operative laxity. The differences were mostly considered as clinically irrelevant. The navigated measurement of the knee laxity can be considered as accurate. The navigated measurement is valuable information for balancing the knee during TKR. The reproducibility of this balancing might be improved due to a more objective assessment.

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.

Anterior cruciate ligament (ACL) reconstruction allows overall good results, but there is still a significant rate of failure. It is well accepted that the main reason for ACL reconstruction failure is a misplacement of tibial or femoral tunnels. Conventional techniques rely mainly on surgical skill for intra-operative tunnel placement. It has been demonstrated that, even by experienced surgeons, there was a significant variation in the accuracy of tunnel placement with conventional techniques. Navigation systems might enhance the accuracy of ACL replacement.

10 cadaver knees with intact soft-tissue and without any intra-articular abnormalities were studied. We used a non image based navigation system (OrthoPilot ®, Aesculap, Tuttlingen, FRG). Localizers were fixed on bicortical screws on the distal femur and on the proximal tibia. Both kinematic and anatomic registration of the knee joint were performed by moving the knee joint in flexion-extension and palpating relevant intra- and extra-articular landmarks with a navigated stylus. The most anterior, posterior, medial and lateral point of both tibial and femoral attachment of the ACL were marked with metallic pins. The navigated stylus was positioned on these points, and the system recorded its position in comparison to the bone contours. Subsequently, we performed conventional plain AP and lateral X-rays and a CT-scan, and measured the position of the pins in comparison to the bone contours. Finally, all measurements were made again with a caliper after disarticulating the knee joint. We calculated the center of the footprint as the mid-point between the four pins of both tibial and femoral attachment for each measurement technique. All measurements were expressed as percentages of the bone size to compensate for the different sizes.

There were no significant difference in the paired measurements of the location of the ACL footprints on both femur and tibia between anatomic, radiographic, CT-scan and navigated measurements. There was a significant correlation between the paired measurements of the location of the ACL footprints on both femur and tibia with either measurement techniques.

Anatomic measurement is the gold standard experimental technique for the positioning of the ACL foot-print, and CT-scan measurement is currently the gold standard technique in clinical situation. According to this reference, the position of ACL attachments on the tibia and on the femur can be accurately defined by the navigation system. Intra-operative measurement of the location of the bone tunnels during ACL replacement with this navigation system should be accurate as well.

Unicompartmental knee replacement (UKR) is accepted as a valuable treatment for isolated medial knee osteoarthritis. Minimal invasive implantation might be associated with an earlier hospital discharge and a faster rehabilitation. However these techniques might decrease the accuracy of implantation, and it seems logical to combine minimal invasive techniques with navigation systems to address this issue.

The authors are using a non image based navigation system (ORTHOPILOT ^™, AESCULAP, FRG) on a routine basis for UKR. We prospectively studied 60 patients who underwent navigated minimally invasive UKR for primary medial osteoarthritis at our hospital between October 2005 and October 2006. We established a navigated control group of 60 patients who underwent conventional implantation of a UKA at our hospital between April 2004 and September 2005. There were 42 male and 78 female patients with a mean age of 65 years (range, 44–87 years). There were no differences in all preoperative parameters between the two groups.

The accuracy of implant positioning was determined using predischarge standard anteroposterior and lateral radiographs. The following angles were measured: femorotibial angle, coronal and sagittal orientation of the femoral component, coronal and sagittal orientation of the tibial component. When the measured angle was in the expected range, one point was given. The accuracy was defined as the sum of the points given for each angle, with a maximum of five points (all items fulfilled) and a minimum of 0 point (no item fulfilled). Our primary criterion was the radiographic accuracy index on the postoperative radiograph evaluation. All other items were studied as secondary criteria.

The mean accuracy index was similar in the two groups: 4.1 ± 0.8 in the study group and 4.2 ± 1.2 in the control group. 36 patients (60%) in the control group and 37 patients (62%) in the study group had the maximum accuracy index of five points. All measured angles were similar in the two groups. There were no differences between the percentages of patients in the two groups achieving the desired implant positions. Mean operating time was similar in the two groups. There were no intraoperative complications in either group. The groups had similar major postoperative complication rates during hospital stay (3% for both).

The used navigation system is based on an anatomic and kinematic analysis of the knee joint during the implantation. The modification of the existing software for minimal invasive approach has been successful. It enhances the quality of implantation of the prosthetic components and avoids the inconvenient of a smaller incision with potential less optimal visualization of the intra-articular reference points. However, all centers observed a significant learning curve of the procedure, with a significant additional operative time during the first implantations. The postoperative rehabilitation was actually easier and faster, despite the additional percutaneous fixation of the navigation device. This system has the potential to allow the combination of the high accuracy of a navigation system and the low invasiveness of a small skin incision and joint opening.

Accuracy of implantation is an accepted prognostic factor for the long term survival of total knee replacement (TKR). The use of navigation demonstrated a significant higher accuracy of implant orientation in comparison to conventional methods. However, these systems are often thought to be technically demanding, to increase operating time and to involve a long learning curve. We performed a prospective, multicenter study to compare the accuracy of implantation of a TKR measured on post-operative X-rays in experienced and less experienced centers.

All centers used the same navigation system (Ortho-Pilot ®, Asculap, Tuttlingen, FRG): 4 had already a significant experience with it (group A – 182 cases), 9 centers were considered as beginners with less than 10 cases performed prior to the study (group B – 221 cases). Accuracy of implantation was measured on post-operative antero-posterior and lateral long leg X-rays with five items: mechanical femoro-tibial angle, coronal orientation of the femoral component, sagittal orientation of the femoral component, coronal orientation of the tibial component, sagittal orientation of the tibial component.

When the measured angle was in the expected range, one point was given. The accuracy note was defined as the sum of all points given for each patient, with a maximum of 5 points (all items fulfilled) and a minimum of 0 point (no item fulfilled). The mean accuracy note was compared in the two groups by a Student t-test at a 0.05 level of significance. Power of the study was 0.80.

There were no significant differences in pre-operative parameters between the two groups, except for the clinical KSS. The mean operative time was significantly longer in group B than in group A (110 minutes vs 90 minutes, p=0.01). However this difference occurred mainly during the first twenty cases in the beginner centres where we observed a clear tendency to achieve the same operative time as the experienced centres at the end of the study. The mean accuracy note was 4.3 ± 0.8 (range, 1 to 5) in the control group and 4.3 ± 0.9 (range, 1 to 5) in the study group (p > 0.05). The power of the study to detect a 0.25 point difference in the post-operative accuracy note was retrospectively calculated to be 0.80. There were no significant differences between the two groups for all individual radiographic items.

This study is, to our knowledge, the first one which investigates the learning curve of navigated TKR The used navigation system allowed a very accurate implantation of a TKR in both experienced and less experienced centers. There was no detectable learning curve with respect to accuracy of TKR implantation, clinical outcome and complication rate. The duration of the learning curve when considering the operating time was 30 cases.

Purpose of the study: Navigation systems have proven efficacy for the implantation of unicompartmental knee prostheses. Minimally invasive methods, which limit access to non-operated compartments, might compromise system accuracy.

Material and methods: A standard navigation software was used for kinematic acquisition of the lower limb and to acquire anatomic landmarks for both femorotibial compartments. A modified version of the navigation software designed for minimally invasive surgery replaed palpation of the anatomic landmarks of the non-operated compartment by a computation method based on other data. Three groups of patients were analyzed. Group 1 included 64 patients who underwent minimally invasive surgery for implantation of a medial unicompartmental prosthesis. Group B included 60 patients selected randomly among 140 cases of medial unicompartmental prosthesis patients treated with the standard navigation technique. Group C included 30 patients selected randomly among 180 patients who underwent total knee arthroplasty with the standard navigation system. The quality of the implantation was assessed on the postoperative ap and lateral views by comparing five criteria describing the desired prosthetic alignment. The number of criteria describing correct alignment was noted for each patient, thus yielding a quality score from 0 to 5. ANOVA was used to compare the mean scores of the three groups using Boneffini-Dunn correction at the 5% risk level.

Results: The mean quality score was 3.5±1.2 for group A, 4.5±0.8 for group B and 4.2±1.0 for grup C (p< 0.001). Ther was no significant difference between groups B and C (p=0.24). The quality score was significantly lower in group A (A versus B: p=0.015; A versus C: p< 0.001).

Discussion: The minimally invasive approach is proposed to enable more rapid functional recovery after implantation of a unicompartmental knee prosthesis. The long-term outcome however depends on the quality of the implantation. The quality of the implantation with a minimally invasive method should thus be equivalent to that achieved with the standard method. Conventional minimally invasive methods are more difficult. Navigation could be expected to overcome this difficulty without sacrificing implantation quality. However, the version used here did no enable an implantation equal to the quality achieved with the standard navigation system.

Conclusion: The standard navigation system for the conventional access remains the gold standard for implantation quality. Changes resulting from a less invasive approach should be validated before routine use.

Purpose of the study: Navigation systems have proven their capacity to improve the quuality of total knee arthroplasty (TKA) implantation. The navigation system coud also be used to record knee kinematics intraoperatively.

Material and methods: Twenty TKA implantations were studied. The series included six males and 14 females, mean age 71 years (range 63–78 years). All underwent surgery for overall osteoarthritis. A TKA with a mobile plateau was implanted with preservation of the posterior cruciate ligament. The OrthoPilot® imageless navigation system (Aesculap, Tuttlingen, German) was used. The software was modified to enable recording the relative movement of the femur in relation to the tibia during flexion-extension movements. Infrared locators were fixed on the lower part of the femur and the proximal part of the tibia. After kinematic and anatomic acquisition of conventional navigation data, the kinematic recordings were made during passive flexion-extension before performing any procedures on the bones. The system recorded femur rotation in relation to the tibia in the frontal plane (varus-valgus), in the sagittal plane (flexion-extension), and in the horizontal plane (internal-external rotation) as well as anteroposterior translation of the femur on the tibia. The prosthesis was implanted using the conventional navigation technique. After implantation, the same kinematic recordings were repeated. Each measurement was taken in duplicate to study reproducibility in the same patient. Pre- and postoperative kinematic recordings in the same patient were compared to obtain objective evidence of changes induced by prosthesis implantation. The pre- and postoperative results were compared with those reported to date in the literature.

Results: The recorded kinematic curves, both before and after TKA implantation, were coherent with generally accepted values, particularly for rotation and antero-posterior translation. Paradoxical kinematic recordings were noted after implantation. There was no significant difference between the two recordings in the same patient.

Discussion: The software enables a reliable study of knee kinematics before and after TKA implantation. This could be useful to test new prosthetic solutions, but also to choose for a given patient, the best kinematic compromise. It would be interesting to compare these results with data on in vivo kinematic recordings made in the same patients.

Conclusion: Intraoperative kinematic analysis is a research tool at the present time, but could be useful to improve the quality of TKA implantations.