Introduction. Low dose technology of an EOS scanner allows mechanical axis radiographs to be produced using a continuously moving x-ray emitting a thin beam to form a single image which includes all three joints, without the need for stitching. The aim of this study was to identify necessary improvements to enable effective interpretation of the radiographs, and to assess whether the quality of the radiographs varied by production method compared to a previous audit of CR and DR radiographs. Materials and Methods. 8 domains were identified based on a previous audit using the acronym MECHANIC each defining the qualities required for a radiograph to meet the criteria. 100 mechanical axis radiographs produced using conventional and digital methods were analysed in the original study to assess how many radiographs met the described criteria. The same criteria were amended and used to assess 123 different mechanical axis radiographs in the follow up study following the introduction of the EOS scanner, in which 77 were produced using EOS and 46 were produced using conventional and digital methods. Results. The second study showed improvement in 2 of the 6 domains being assessed and the result remained the same in 1 domain, with a mean change of +2%. There was a large increase in the number of radiographs with impeccable stitching in the second study due to the use of the EOS scanner. When comparing the methods of production, there were a greater percentage of EOS radiographs meeting the criteria for each domain compared to conventional and digital radiographs. Those produced using the EOS scanner had a mean 0.83% more radiographs meeting the criteria per domain. Conclusions. The overall quality of mechanical axis radiographs being produced has increased, but varies largely between the 6 domains. The EOS produced radiographs overall were of a greater quality than those produced using conventional and digital methods, but still had areas which required significant improvement

This study evaluates the effect of lower limb post-operative mechanical axis on the long term risk of revision surgery following primary total knee arthroplasty (TKA). The study is relevant because many recent clinical trials have evaluated the optimal surgical technique for accurately aligning components in TKA, despite little evidence that alignment may effect the long-term clinical outcome. The data used in this study was collected prospectively as part of a randomized control trial comparing the long term survival of cemented versus uncemented TKA. The trial included 501 press-fit condylar posterior cruciate ligament-retaining prostheses performed by the senior author (PJG) or under his direct supervision. The post-operative mechanical axis alignment of the lower limb was measured following TKA using standard AP weight-bearing long leg alignment radiographs. A comparison was made between a well-aligned group with a mechanical axis alignment within 3° of neutral; and a poorly-aligned group whose mechanical axis alignment deviated greater than 3° from neutral. Survival analysis used revision surgery, with exchange of any of the three originally inserted components (femoral, tibial, polyethylene insert), as the endpoint. There was no loss to follow-up in this study. The minimum follow-up of TKAs in this study was 5.8 years. In the population of TKAs that were followed up at 10 years, 6% (17/270) required revision surgery. There was a significant difference in the rate of revision surgery between the well-aligned group 5% (11/227) and the poorly-aligned group 14% (6/43 p< 0.05). This study shows that post-operative lower limb mechanical axis alignment is an important determinant of the need for revision surgery at 10 years. Surgeons performing TKA should pay particular attention to the placement of the tibial and femoral components, so that a mechanical axis within 3° of neutral is achieved

The weight bearing axis of the limb goes from the pelvis to the ground and includes the hindfoot. However, the influence of hindfoot alignment on mechanical axis deviation and overall limb alignment after total knee arthroplasty (TKA) is unknown. This study aimed to assess the change in hindfoot alignment after TKA for knee osteoarthritis, the difference in mechanical axis deviation at the knee when calculated using the ground mechanical axis as compared to the conventional mechanical axis, and the effect of hindfoot alignment on the overall postoperative limb alignment after TKA. We evaluated the pre- and postoperative hip-knee-ankle (HKA) angle, conventional mechanical axis deviation (CMAD), ground mechanical axis deviation (GMAD), and tibiocalcaneal angle (TCA) in 125 patients who underwent 165 consecutive TKAs. Overall, the change in pre- and postoperative mean TCA was not significant (p=0.48) whereas it was significant (p=0.01) in knees with =15° deformity where the hindfoot valgus decreased by approximately 25%. Preoperatively, there was no significant difference between mean CMAD and mean GMAD whereas postoperatively the difference was significant (p=0.0001). Hindfoot valgus alignment of =10° was present in 22.5% of limbs and 29% limbs had a postoperative GMAD of =10 mm in spite of the limb alignment being restored to within 3° of neutral after TKA. Despite accurate restoration of limb alignment after TKA, as a result of persistent hindfoot valgus alignment the ground mechanical axis may pass lateral to the centre of the knee joint - with potential detrimental effects on bone, ligaments and implants

For a successful total knee arthroplasty (TKA) and long prosthesis lifespan, correct alignment of the implant components as well as proper soft tissue balancing are of major importance. In order to overcome weaknesses of existing imaging modalities for TKA planning such as radiation exposure and lack of soft tissue visualisation (X-ray and CT) and high cost, long acquisition times and geometric distortion (MRI), it is investigated if ultrasound (US) imaging is a suitable alternative. Currently, a reconstruction method of the bony knee morphology based on US imaging is developed at our research institute. For capturing the mechanical axis, being crucial for TKA planning, different approaches could be implemented. This work investigates whether a weight-bearing full leg X-ray registered with the local 3D-US knee dataset can be used for this purpose. Also, the impact of incorrect calibration data (i.e. uncalibrated X-rays) on the accuracy of the estimated mechanical axis is investigated. A 3D-2D projective, feature-based registration algorithm was used to spatially align the 3D US-based model to the 2D X-ray image before transferring the mechanical axis from the X-ray to the model. For validation, a CT-based local model and its projection were used and an initial error in translation and rotation was added. Also, calibration parameters such as the centre ray position and the source-to-image-detector distance were altered. The estimation error of the mechanical axis was less than 1°, the median error lower than 0.1° in the frontal plane. Even if the calibration data is not available, the accuracy remains sufficient for TKA planning. In this study, idealised 2D and 3D image information was used. In the future, this method should be tested using clinical X-ray images and 3D-US data

Background Computer navigation is increasingly being recognized as a valuable tool in restoring the mechanical axis post TKR. Its use is as yet not universal due to the costs involved, its availability and the fact that it can be cumbersome and time consuming to use. Additionally it requires the insertion of Schanz pins in the femur as well as the tibia which can be a matter of concern as regards stress fracture and infection. However, it is able to reliably locate the center of the femoral head which is an elusive landmark in the standard method. The center of the ankle involves registration for the medial and lateral malleoli which are subcutaneous and easily palpable. We decided to navigate only the distal femoral cut with a specialized navigation unit called Articular Surface Mounted navigation which does not require the insertion of additional pins through the femur or the tibia. We purposely did not use navigation for the rest of the bony cuts as all the other landmarks i.e. femoral epicondyles, tibial malleoli, and tuberosity etc are all easily palpable. This dramatically reduced the surgical time and increased its user friendliness. We are presenting our results. Aim. To analyse the radiographic results obtained with selective femoral navigation and compare with. standard navigational results from the literature. Non-navigated Knees form personal series. Materials and Methods. We have utilized the ASM navigation for distal femoral cut in 112 knees and obtained long X-rays (scanograms) and routine knee X-rays (AP, Lateral and skyline) to study the mechanical axis and component positioning. We measured the mechanical axis deviation, femoral and tibial angle on AP and lateral films and patellar tilt or subluxation on post-operative X-rays by a digital imaging programme called Image–J. (As suggested by the Knee Society roentgenographic Score). We have compared our results with other navigated series from literature and our own series of non-navigated knees. (113 knees) We also noted the surgical time to perform the operation and the occurrence of any complications. Results. Selective femoral navigation is able to restore the mechanical axis as reliably as other methods of navigation and more reliably than non-navigated knees. On an average, it adds less than 10 minutes to surgical time. Femoral angle, tibial angle patellar tilt and subluxation are similar in both navigated and non-navigated series. Navigation use was not associated with any increased complications and no complication could be ascribed to its use. Selective femoral navigation reduced the outliers in mechanical axis restoration when compared with standard femoral intrameduallry instrumentation. Discussion. Selective distal femoral navigation is a reliable tool in restoring mechanical axis post TKR. It is particularly valuable in knees that have pronounced femoral bowing

In the anatomical studies for Caucasian, it has been reported that the center of plateau tends to be located central or lateral from the tibial canal axis. However, in the three dimensional analysis of author, the center of plateau was located on average 4.4 mm medial from the point of tibial canal axis passing through the plateau. The purpose of this study is to examine the placement of the tibial component in relation to the anatomical axis of the tibia in total knee arthroplasties for Korean patients and to identify this mismatch affecting the measurement of postoperative mechanical axis. Measurements were performed on the pre- and postoperative radiographs of 60 osteoarthritic knees with varus deformity replaced between October 2005 and May 2008 using PFC. The inclusion criteria was the cases with the accurate coronal alignment of component, in which α angle ranged from 94 to 96° and β angle ranged from 89 to 91°. The mean age was 66.6 years (range, 54 to 79), and the body mass index was 27.0 kg/m2 (range, 20.7 to 37.7). Radiological measurements were performed using an orthoreontgenogram. Preoperatively, 30 patients with varus deformity lesser than vaurs 10° were classified to group A and 30 patients greater than vaurs 10° were classified to group B. Post-operatively, the distance between the midline of the tibial stem and anatomical axis (medial offset) was measured at the level of tibial resection. These distances were compared between the group A and B. The postoperative mechanical axes were compared between the group A and B. The intra- and inter-observer reliabilities were assessed. In this study, intraclass correlation coefficient values of all measurements were greater than 0.8. The mean preoperative mechanical axes were varus 7.4±2.3° in group A and varus 16.9±4.0° in group B (p=0.000). The mean medial offsets were 2.5±1.9mm (range, −3.6 to 5.9) in group A and 3.9±2.7mm (range, −1.1 to 10.2) in group B (p=0.021). The tibial stems were located medial to anatomical axis in 22 knees (73.3%) of group A and 26 knees (86.7%) of group B. The mean postoperative mechanical axis were varus 1.3± 1.2° (range, varus 3.6 to valugs 1.6°) in group A and varus 2.5± 2.0° (range, varus 5.9 to valugs 2.1°) in group B (p=0.004). In this study of TKA, the tibial component in relation to anatomical axis tends to be located medial. The postoperative mechanical axis remained more varus in spite of the accurate coronal alignment of the component as the preoperative varus deformity was more severe. This study suggests that the radiographic measurement of postoperative mechanical axis using a line passing the component center has the limitation

In order to understand the actual weight-bearing condition of lower extremity, the three dimensional (3D) mechanical axis of lower limb was compared with the loading direction of ground reaction force (GRF) in standing posture. Three normal subjects (male, 23–39 yo) participated in the study. A bi-planar radiograph system with a rotation table was used to take frontal and oblique images of entire lower limb. Each subject’s lower limb was CT scanned to create 3D digital models of the femur and tibia. The contours of the femur and tibia in both radiographs and the projected outlines of the 3D digital femur and tibia models were matched to recover six-degree of freedom parameters of each bone. The 3D mechanical axis was a line drawn from the centre of the femoral head to the centre of the ankle. A surface proximity map was created between the distal femoral articular surface and the proximal tibial articular surface. A force plate was positioned on the rotation table to measure GRF during biplanar X-ray exposure. Each subject put one’s foot measured on the force plate and the other on the shield. Bi-planar radiographs were taken in double-limb standing, double-limb standing with toe up in the leg measured, and single-limb standing. The anterior and medical deviations of the loading direction of GRF from the 3D mechanical axis were determined at the proximal tibia and normalized by the joint width in anteroposterior direction and by the joint width in lateral direction. For all subjects the passing points of the 3D mechanical axis at the proximal tibia were almost in the middle of the joint width in lateral direction. Compared to the 3D mechanical axis, the loading direction of GRF passed through the anterior region in double-limb standing and single-limb standing, and anteromedial region in single-limb standing. The normalized medial deviation was significantly greater in singlelimb standing than in double-limb standing (p=0.023). The separation distance tended to decrease in the medial compartment in single-limb standing, and to increase in toe up in the entire region. Deviation of the loading direction of GRF from the 3D mechanical axis at the proximal tibia varied among standing postures, relating to the change in weightbearing condition as indicated in the separation distance map. These results provide the mechanical perspective related to the causes and progression of knee OA and may contribute to the improvement of surgical treatments such as arthroplasty and osteotomy

Tibial and femoral loosening are major causes for implant failure in total knee arthroplasty. Jefferey (1991) reported a significantly lower rate of loosening when varus or valgus was within 3 degrees of mechanical axis in an eight year follow up. Coulle (Dec1999) reported 48% unacceptable alignment in non-navigated knees and Reed (Aug 2002) reported 35% alignments deviating more than 3 degrees from mechanical axis when navigation was not used. We report our series of 286 navigated knee replacements using the Aesculap Search system (21 cases) and the Aesculap e-motion versions 4.2, 4.3 and 4.4 (265 cases) between April 2003 and December 2012 by the author (A.D) and analysed the correction achieved against the zero mechanical axis. Postoperative measurement of the angles on long length films was done in 23 cases. This matched with the intraoperative corrections achieved as studied using per-operative computer data stored for every case. We continued to use the data stored in the AESCULAP System to correlate the findings in the rest of the cases. The average mechanical axis achieved was 1.3 degrees. All cases had mechanical axes within 3 degrees. We were thus able to achieve a high level of correction of the mechanical axes predictable to achieve better clinical outcomes

Introduction. Our unit has extensive experience with the use of Ilizarov circular frames for acute fracture and nonunion surgery. We have observed and analysed fracture healing patterns which question the role of relative stability in fracture healing and we offer limb mechanical axis restoration as a more important determinant. Aim. To assess for the presence of external callus, when only relative stability has been achieved but with anatomical restoration of the mechanical axis (ARMA). Methods. We retrospectively reviewed diametaphyseal proximal and distal tibial fractures treated with Ilizarov frame fixation in our unit between 2009 and 2017. We also reviewed cases where the Ilizarov frame technique had been used for complex femoral and humeral non-unions. Radiographs in 4 views were reviewed to assess bone healing, the presence of external callus and correction of lower limb mechanical axis. Results. 45 tibial plateau fractures, 42 distal tibial fractures and 20 humeral and 3 femoral non-unions were reviewed. Where ARMA was achieved, bone healing was observed to occur without external callus. ARMA proved more challenging in the distal tibia and where ARMA was not achieved external callus was visible during fracture healing. Conclusion. ARMA bone healing is reliable and occurs without formation of external callus, despite relative stability. This would suggest that external callus is produced not in response to just the magnitude of strain but also the direction of strain. Restoration of the mechanical axis is an important step in achieving union and needs to be considered when fixing fractures or treating non-unions

INTRODUCTION. Recent studies indicated that the knee has a single flexion/extension axis but debated the location of this axis. The relationship of the flexion/extension axis in the coronal plane to the mechanical axis has received little attention. The purpose of this study was to investigate the relationship of the various axes and references with respect to the mechanical axis in the coronal plane. MATERIALS AND METHODS. Subjects were prospectively scanned into a Virtual Bone Database (Stryker Orthopaedics, Mahwah, NJ). Database is a collection of body CT scans from subjects collected globally. Only CT Scans that met the following qualifications were accepted: ≤1 mm voxels and had slice thickness that was equal to the spacing between the slices (≤ 1.0mm). For each CT Scan, a frontal plane was created through the 2 most posterior points of the medial/lateral condyles and the most posterior point of the trochanter. Then, a transverse plane was created perpendicular to the frontal plane and bisects the 2 most distal points on the medial/lateral condyles. Finally, a saggital plane was created that was perpendicular to the frontal and transversal planes. The following axes were identified: Mechanical Axis of the Femur (MAF) (line between the center of the femoral head and the center of the knee sulcus); Transepicondylar Axis Posterior Cylindrical Axis (PCA) (line between the Medial/Lateral Condylar Circle – best fit circle to three points identified on surface). Measurements made: Angle of MAF and the Joint-Line (Femoral Joint Angle), Angle of the MAF and the Transepicondylar Axis (Femoral TE Angle), and Angle of the MAF and the Posterior Cylindrical Axis (Femoral PC angle). Angles measuring 90° were neutral or perpendicular to the MAF. Angles measured <90° were valgus and >90° were varus. RESULTS. CT Scans from 519 knees were studied. The mean femoral joint angle was 86.1°±2.0°(Range:80.2°-92.2°). The mean TE angle was 88.8°±2.5°(Range:81.7°-98.4°). The mean Femoral PC angle was 87.9°±2.2°(Range:81.8°-94.0°). The average deviations from a neutral resection were 3.8°, 1.2° and 2.1° for the Femoral Joint Angle, Femoral TE Angle respectively. The mean Femoral Joint angle had the lowest variability, while the mean Femoral TE angle showed the largest. CONCLUSION. On average, the transepicondylar axis and the posterior cylindrical axis were approximately perpendicular to the mechanical axis in the coronal plane. Although surgeons do not align components in the coronal plane specifically to either axis, this data suggests that the average value is within the accepted ±3° range reported. The PCA values are closer to the values of the femoral joint line when compared to the TEA. The PCA may be a more reproducible landmark as it may be determined by either preoperative imaging or intraoperatively from instrumentation that references the distal/posterior surfaces. Further research is warranted

When compared with traditional techniques, computer-assisted total knee arthroplasty (TKA) has been shown to allow more accurate coronal alignment of the implants with fewer “outliers.” Most navigation systems in computer-assisted TKA utilize rigidly-fixed trackers placed on both the femur and tibia, a computer workstation, and navigation software to determine the mechanical axis of the extremity intraoperatively, in real time. The purpose of this study was to report the initial experience of a single surgeon with a novel navigation system. This system utilizes a “pinless” technique using trackers that are mounted at the articular surface of the knee instead of being fixed to the femur and tibia. Sixty-Six consecutive TKAs were performed using a novel “pinless” navigation system by a single surgeon. At 4 weeks post-operatively, coronal alignment was assessed with long-standing AP radiographs. The alignment measurements were then compared to historical controls. The average alignment in the coronal plane was 1.73° +/−1.50° deviation from neutral alignment. Variance was 2.26°. The c onfidence interval constructed with an alpha value of.05 was (1.50°, 2.40°). Five knees had a coronal alignment greater than 3° from neutral. Of these five, three had an ipsilateral total hip replacement, and 2 were morbidly obese. There were no pin site infections nor pin site fractures. There was 1 late hematogenous infection. This study reports an initial single-surgeon experience of a novel “pinless” navigation technique for TKA. The technique in this study is a novel and safe method to reconstruct a neutral mechanical axis, as it avoids the morbidity of the application of navigation tracking pins and therefore enhances patient safety

Introduction. The success of knee replacement surgery depends, in part, on restoration of the correct alignment of the leg with respect to the load-bearing vector passing from the hip to the ankle (the mechanical axis). Conventional thinking is that the correct angle of resection of the distal femur (Valgus Cut Angle, VCA) depends on femoral length or femoral offset, though femoral bowing, in addition to length and medial offset, may also have a significant influence on the VCA. We hypothesized that femoral bowing has a strong effect on the VCA necessary to restore physiologic alignment after arthroplasty or osteotomy. Methods. A total of 102 long-leg radiographs were obtained from patients scheduled for primary total knee arthroplasty. The patients on average were 41% male 59% female, 67.9 ± 11.1 years, 67.0 ± 4.7 in, 192 ± 43 lbs, and had a BMI of 29.7 ± 4.8. All radiographs were prepared with the feet placed in identical rotation and the patellae pointing forward, and were excluded if there was evidence of malrotation, as defined by (i) a difference in the medial head offsets of the right and left femur of >3mm, (ii) a difference in the width of the tibiofibular syndesmoses, or (iii) a difference in the rotation of one foot compared to the other. The following anatomic variables were measured on each radiograph: (i) the neck shaft angle (NSA) of the femur, (ii) the length of the femur, (iii) the length of the femoral shaft, (iv) the medial head offset, (v) the medial-lateral bow of the distal femur, (vi) the hip- knee axis angle, (vii) the mechanical axis deviation of the extremity at the knee, (viii) the medio-lateral bow of the tibia, and (ix) the valgus cut angle required to restore the mechanical axis to the center of the knee during surgery (VCA). Bivariate plots were constructed using the measurements thought to influence the VCA: femoral bowing, femoral offset, and length of femur. Multivariate regression was then used to find the variable that had the strongest effect on the VCA. Results. The bivariate plot of offset and VCA yielded an R2 of 0.02544 (p = 0.11) was not statistically significant. However, the bivariate plot of femoral length and VCA yielded an R2 of 0.1294 (p = 0.0002) showing significant correlation. Lastly, the bivariate plot of femoral bowing and VCA yielded an R2 of 0.59136 (p < 0.00001) demonstrating significant correlation (Figure 3). Multivariate analysis revealed that femoral bowing was the best predictor of VCA: VCA = 5.46–0.363 femoral bowing (°) + 0.106 Femoral offset (mm) − 0.010 femoral length (mm). Discussion. While clinicians performing knee replacements typically do not consider femoral bowing when selecting the valgus angle appropriate for each patient, our findings demonstrate that femoral bowing has a potent effect on VCA. The multivariate regression indicated that femoral bowing had the highest effect on VCA followed by offset and femoral length. These findings suggest that surgeons should consider measuring long alignment radiographs before performing a total knee arthroplasty

Purpose: To determine if use of CAS in TKA improves postoperative mechanical axis alignment and component position as compared to use of standard surgical instrumentation. Method: 200 patients were prospectively randomized to TKA utilizing CAS navigation vs. standard surgical technique. Two surgeons performed all procedures utilizing a subvastus approach, the BrainLab navigation system and posterior cruciate substituting implants. Postoperative mechanical axis alignment was measured on full length standing radiographs and component placement on CT (Perth protocol). Two independent raters measured radiographic angles. The variation in mechanical axis measures were compared between the two treatment groups using a two-sided permutation test. Results: Surgery has been completed on all 200 patients with patient demographics similar among the two treatment groups. Median tourniquet time was increased in the navigation group (82 mins versus 57 mins, p < 0.001). Radiographic analysis of the first 100 patients showed the standard deviation of the post-operative mechanical axis measurements to be 22% lower in the navigation group than the standard surgical instrumentation group (2.4 vs. 3.0), marginally significant (p = 0.055). Optimal mechanical axis alignment (to within 3 degrees or less) was achieved in 75% of patients with navigation and in 68% of patients with standard surgical instrumentation. Analysis of all 200 pts will be completed shortly as well as results of component placement based on postoperative CT. Conclusion: Based on analysis of the first 100 patients, use of CAS in TKA marginally statistically improved mechanical axis alignment precision compared to standard surgical technique

Purpose of the study: Computer assisted surgery for total knee arthroplasty is widely used in Europe. The reliability of these systems appears to be very good with bone cuts within 3° of the planned mechanical axis. Nevertheless, the relationship between intraoperative measurements provided by the navigation system and the postoperative gonometry can be used to assess the quality of realignment. The purpose of this work was to determine this relationship. Material and methods: Thirty-three knees operated on with the Navitrack® system were assessed. Two senior operaters performed all procedures. An Omnia® cemented prosthesis with an ultracongruent fixed plateau was used in all cases. Intraoperative measurements wer made with the definitive prosthesis after cement solidification without stress on the knee. Postoperative gonometry was undertaken when the intraoperative flexion had disappeared six weeks to six months after the operation. Gonometric measurements were made by an independent operator using a computerized system operating on digitalized x-rays. The gonometric protocol had been standardized previously and only the gonometric measurements in compliance with this protocol were retained for analysis. The difference between measurements was analyzed with the t test for paired variables. Search for correlations was also performed. Results: On average the intraoperative deviation was 0.8±0.8° (3° valgus to 2.4° varus). The postoperative gonometry showed 1.7±1.1° (3.4° valgus to 4.3° varus). The mean difference between the intraoperative axis and the measured postoperative axis was significant (p< 0.0001). There was no significant correlation between intraoperative and postoperative measurements. Discussion: Computer-assisted navigation systems have their limitations which should be measured. The present findings would demonstrate a significant difference of minimal amplitude between the intraoperative measurement and the postoperative gonometry. Although the clinical pertinence of this difference remains to be demonstrated, it must be kept in mind for safe use of these navigation systems

Introduction. The assumption that symmetric extension-flexion gaps improve the femoral condyle lift-off phenomenon and the patellofemoral joint congruity in total knee arthroplasty (TKA) is now widely accepted. Conventional understanding of knee kinematics suggests that the femoral component should be rotationally aligned parallel to the surgical epicondylar axis (SEA). On the other hand, the theory of the balanced gap technique suggests the knee be balanced in extension and flexion to achieve proper kinematics and stability of the knee without reference to fixed bony landmarks. The purpose of our study was to evaluate the relationship between rotation alignment of the femoral component and postoperative flexion gap balance, and the femoral rotational alignment in relation to the tibial mechanical axis in patients when implanted using a balanced gap technique. Materials and Methods. The subjects presented 53 consecutive osteoarthritic (OA) varus knees underwent primary Posterior-Stabilised (PS) -TKA (NexGen LPS-flex, Zimmer). All subjects completed written informed consent. The patient population was composed of 7 men and 35 women with a mean age of 72.5 ± 8.3 years. The average height, weight, BMI, weight-bearing FTA, and the patella height (Insall-Salvati ratio: T/P ratio) were 151.7 ± 7.7 cm, 62.6 ± 11.8 kg, 27.2 ± 4.5, 184.9 ± 5.9° and 0.93 ± 0.14 respectively. All procedures were performed through a medial parapatellar approach and a balanced gap technique used a newly developed versatile tensor device which can measure the medial and lateral gaps individually and make use of the balanced gap technique guide with patellofemoral joint reduction, which had been introduced in 56. th. ORS 2010. Pre- and post-operatively, a condylar twist angle (CTA) was evaluated using computed tomography (CT). To assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was evaluated using the epicondylar view radiographs by adding a 1.5 kg weight at the ankle. Coronal alignment of the tibial component in reference to the tibial mechanical axis (angle θ) was evaluated using plain AP radiography. Data were expressed as mean ± SD and analysed with Stat View version 5.0. Results. Extension gap was well balanced within 3 mm in all cases. The average of the preoperative CTA, the postoperative CTA, the LOA and the angle θ. were 6.0 ± 1.5°, 1.2 ± 2.4°, 0.8 ± 1.4° and 89.7 ± 1.2° respectively. No significant correlation was observed in between the postoperative CTA, the LOA and the angle θ. The degree of the clinical epicondylar axis (CEA) to the tibial machanical axis was 90.1 ± 2.9°. Only one knee needed lateral retinaculum release, because of poor patella tracking evaluated by no thumb test or one stitch method. Discussion. This study demonstrated that our balanced gap technique, using a newly developed tensor device, achieved good patellofemoral joint congruity and balanced flexion gaps postoperatively. Rotation alignment of the femoral component was slight internal rotation in reference to the CEA but not parallel to the SEA. Conclusion. The CEA was perpendicular to the tibial mechanical axis in PS-TKA with well balanced extension-flexion gap achieved by a balanced gap technique

Introduction:. Conventional understanding of knee kinematics suggests that the femoral component should be rotationally aligned parallel to the surgical epicondylar axis (SEA). In contrast, the balanced gap technique suggests the knee be balanced in extension and flexion to achieve proper kinematics and stability of the knee without reference to fixed bony landmarks. To investigate the functional flexion-extension axis (FFEA) when a balanced gap technique was used in the posterior-stabilized total knee arthroplasty (PS-TKA), the relationships between rotational alignment of the femoral component to the postoperative flexion gap balance and to the tibial mechanical axis were evaluated radiographically. Materials and Methods:. In this prospective study, 63 consecutive knees in 50 patients were included with medial osteoarthritis undergoing a primary PS-TKA (NexGen LPS-Flex, fixed surface, Zimmer; Warsaw, USA). All subjects completed written informed consent. The patient population was composed of 8 men and 42 women with a mean age of 73.0 ± 7.7 years. The average height, weight, BMI, weight-bearing femorotibial mechanical angle (FTMA), condylar twist angle (CTA), and the patella height (T/P ratio) were 150.9 ± 7.2 cm, 62.3 ± 10.1 kg, 27.3 ± 4.0 kg/m. 2. , 167.8 ± 5.5°, 5.9 ± 1.6° and 0.94 ± 0.15, respectively. All procedures were performed through a medial parapatellar approach and a balanced gap technique used a newly developed versatile tensor device. Pre- and post-operatively, the CTA was evaluated using computed tomography (CT). To assess the postoperative flexion gap balance, a condylar lift-off angle (LOA) was evaluated using the epicondylar view radiographs. The FTMA and coronal alignment of the tibial component in reference to the tibial mechanical axis (angle β) were evaluated using plain AP radiography. The FFEA (angle θ) of the knee was calculated as the following; (angle β) + (post-operative CTA) – (LOA). Correlations were analyzed with Pearson's correlation coefficient. Predictive variables were analyzed utilizing Stepwise regression. A value of p < 0.05 was considered significant. Results:. Only two knees (3.2%) needed a lateral retinaculum release due to poor patella tracking. The average post-operative FTMA, angle β, LOA, and CTA were 178.7 ± 3.0°, 89.6 ± 1.3°, 0.7 ± 1.5°, and 1.3 ± 2.3°, respectively. The average angle θ was 90.2 ± 2.8°, significantly correlating with the post-operative CTA (r = 0.77), angle β (r = 0.42) and the LOA (r=–0.37). Moreover, the predictive variables of the angle θ was the following, 68.41 + 1.04 × (post-operative CTA) + 0.12 × (post-operative FTMA) – 0.93 × (LOA). (R. 2. = 0.805). Discussion:. This study demonstrated that the clinical epicondylar axis (CEA) was closely perpendicular to the tibial mechanical axis in PS-TKA with well balanced extension-flexion gap achieved by the balanced gap technique. This result also suggests the possibility of that the femoral component which is rotationally aligned parallel to the CEA would make the flexion balance better when an anatomical measured resection technique is used in a PS-TKA. Conclusion:. The functional flexion-extension axis in a PS-TKA with well balanced extension-flexion gap closely approximates the clinical epicondylar axis

Introduction: Computer assisted-surgery (CAS) brings in a great precision to the alignment of the components and the axis of the extremity in total knee arthroplasty (TKA). On the other hand, even though the MIS technique exerts a lesser aesthetic impact, favours the faster recovery of the patient and preserves the soft parts better, it can also lead to mistakes in the alignment of the implant due to the deficient visualization. Adding CAS to MIS may solve this potential complication. Objective: To compare the alignment of the components with regard to the mechanical axis in four TKA groups (standard surgery, MIS surgery, standard surgery with CAS, and MIS with CAS). Materials and Methods: Prospective and randomized study. 100 patients with Alhbäck degree III primary degenerative osteoarthritis of the knee and less than 10° of varus-valgus were included. The patients were randomly distributed in 4 groups of 25 patients each, and the same surgeons performed the surgery. Two CT surviews were performed on every patient, one preoperatively and one during the immediate postoperative period, including hip and ankle, where the femoral, tibial and femoro-tibial axis measurements were carried out. Results: Mean age was 71.63 years (SD 6.68); 81 % of patients were women. Preoperative mean varus was of 7.57° (SD 1.10). No significant differences were found in the femoro-tibial alignment nor in the components with regard to the mechanical femoral axis between the four groups (Table 1). Nevertheless, significant differences in favour of the MIS-CAS technique group for the alignment of the tibial component with regard to the mechanical tibial axis were found. Conclusions: The MIS technique allows for a well-aligned TKA implantation. Nevertheless, when CAS is coupled with this technique, the alignment of the tibial component is improved. It is possible for the association of MIS and CAS to become a true advance in TKA implantation

Introduction: Proper correction of proximal tibial deformities includes correction of the mechanical axis and parallelism of the knee to the ankle and ground. Optimally placed osteotomies are away from the very proximal deformity requiring controlled diaphyseal translation. The Metaphyseal Arc Correction System, a major simplification over the Ilizarov or Spatial Frame systems, is assessed in this study, as are methods to identify the plane of deformity. Method: Thirty-one consecutive cases of proximal tibial deformity in 18 patients were treated using the Metaphyseal Arc Correction Sysytem. There were six valgus deformities (three pts), one Morquio, two metaphyseal dwarfs ages six and eight years. The rest were varus deformities, 12 achondroplasia (six pts), eight infantile Blount’s (four pts) and five adolescent Blount’s (five pts). Comparison of two methods of identifying the plane of deformity was done in six cases: Herzenberg’s graphic method and the image method (rotating the limb until the maximum deformity is in the plane of the intensifier). Results: All but eight tibiae (five pts) were properly corrected. Four tibiae (two pts) were over corrected, two tibiae (one pt) were corrected but the knee and ankle were not parallel. Analysis of these six limbs revealed unrecognised deformity of the distal femur. Thus to get the joints parallel in four limbs the axis was overcorrected and in two limbs the axis was proper but the joints were not parallel. One failure occurred because the device was not placed in the plane of deformity, another because of premature fibula consolidation (or incomplete osteotomy). All other cases achieved deformity and axis correction with joint parallelism. Both methods of identifying the plane of deformity yielded similar results as long as the proximal tibia was centered to avoid image parallax. The graphic method gives accurate angles but could only be approximated clinically. There was one failure from inaccurate device placement using the image method. Ideally both methods should be used. Conclusion: The Metaphyseal Arc Correction System is convenient method of correcting proximal tibial deformities. It is easily applied and when properly positioned automatically corrects deformity, axis and joint parallelism, allowing optimum osteotomy placement. Positioning should use both the graphic and image methods. Failures were iatrogenic due to poor analysis, not the device

INTRODUCTION

Navigation systems have proved allowing performing measurement of the lower limb axis with a good accuracy, but the mandatory use of reference pins or screws limit their use to the operating room. The use of non-invasive navigation systems has been suggested to overcome this limitation. We conducted a prospective study to assess the validity of such a measurement system with non-invasive fixation of the reference arrays. The main goal was to compare this method with a standard, invasive navigation system requiring bony fixation of the arrays. The following hypothesis was tested: there will be a significant difference between the simultaneous measurement of the mechanical femoro-tibial angle by a standard navigation system and by the non-invasive navigation system.

Aims: The aim of our work was to measure, the necessary correction angle in unicompartmental knee prosthesis in order to make the patientñs functional result the best following the procedure.

Method: We included all the medial and all the lateral unicompartmental arthroplasties in our department in 1999. For the analysis of the functional results, we have reviewed the patients and recorded the clinical data with the help of the New Jersey Knee Score. We have had the postoperative weight bearing AP knee X-rays also at the same time.

Conclusion: This type of implant can be used with conþdence in medial unicompartmental knee arthroplasties up to 15 degrees of varus deformation preoperatively, according to the early postoperative results. We did not þnd any signiþcant difference in the early functional results between the 10 degrees or less and the more than 10 degrees corrected groups.