Traditionally sequential medial soft tissue release is performed for balancing in total knee arthroplasty for varus knees. Its effects on kinematics have been described in extension and 90° flexion in coronal plane. This is the first study to describe its effects on kinematics throughout flexion. 12 cadaveric knees were studied using a computer navigation system to assess kinematics. Femoro-Tibial-Mechanical-Angle(FTMA) was studied in extension, 0°, 5°, 30°,45°,60°,90° and maximum flexion. Sequential medial release was performed in 7 steps, described by Luring et al(Ref). At each step FTMA was measured without and with stressing. A 10 Newton Meter moment arm was applied for varus and valgus stress. Most of the initial release steps had little effect on FTMA without force applied, especially in the initial 60° of flexion. Application of varus force demonstrated very small changes. Application of valgus force demonstrated little change in initial arc of flexion until step 5 was reached (Table 1). Our study concludes the present sequence of medial release may not be correct and should be further investigated to modify the sequence for soft tissue balancing in TKR surgery

Abstract. Background. Conventional TKR aims for neutral mechanical alignment which may result in a smaller lateral distal femoral condyle resection than the implant thickness. We aim to explore the mismatch between implant thickness and bone resection using 3D planning software used for Patient Specific Instrumentation (PSI) TKR. Methods. This is a retrospective anatomical study from pre-operative MRI 3D models for PSI TKR. Cartilage mapping allowed us to recreate the native anatomy, enabling us to quantify the mismatch between the distal lateral femoral condyle resection and the implant thickness. Results. We modelled 292 knees from PSI TKR performed between 2012 and 2015. There were 225 varus knees and 67 valgus knees, with mean supine hip-knee-angle of 5.6±3.1 degrees and 3.6±4.6 degrees, respectively. In varus knees, the mean cartilage loss from medial and lateral femoral condyle was 2.3±0.7mm and 1.1±0.8mm respectively; the mean overstuffing of the lateral condyle 1.9±2.2mm. In valgus knees, the mean cartilage loss from medial and lateral condyle was 1.4±0.8mm and 1.5±0.9mm respectively; the mean overstuffing of the lateral condyle was 4.1±1.9mm. Conclusions. Neutral alignment TKR often results in overstuffing of the lateral condyle. This may increase the patello-femoral pressure at the lateral facet in flexion. Anterior knee pain may be persistent even after patellar resurfacing due to tight lateral retinacular structures. An alternative method of alignment such as anatomic alignment may minimise this problem

Mechanical alignment (MA) techniques for total knee arthroplasty (TKA) may introduce significant anatomic modifications, as it is known that few patients have neutral femoral, tibial or overall lower limb mechanical axes. A total of 1000 knee CT-Scans were analyzed from a database of patients undergoing TKA. MA tibial and femoral bone resections were simulated. Femoral rotation was aligned with either the trans-epicondylar axis (TEA) or with 3° of external rotation to the posterior condyles (PC). Medial-lateral (DML) and flexion-extension (DFE) gap differences were calculated. Extension space ML imbalances (3mm) occurred in 25% of varus and 54% of valgus knees and significant imbalances (5mm) were present in up to 8% of varus and 19% of valgus knees. For the flexion space DML, higher imbalance rates were created by the TEA technique (p < 0 .001). In valgus knees, TEA resulted in a DML in flexion of 5 mm in 42%, compared to 7% for PC. In varus knees both techniques performed better. When all the differences between DML and DFE are considered together, using TEA there were 18% of valgus knees and 49% of varus knees with < 3 mm imbalances throughout, and using PC 32% of valgus knees and 64% of varus knees. Significant anatomic modifications with related ML or FE gap imbalances are created using MA for TKA. Using MA techniques, PC creates less imbalances than TEA. Some of these imbalances may not be correctable by the surgeon and may explain post-operative TKA instability. Current imaging technology could predict preoperatively these intrinsic imitations of MA. Other alignment techniques that better reproduce knee anatomies should be explored

Introduction. Robotics have been applied to total knee arthroplasty (TKA) to improve surgical precision in component placement and joint function restoration. The purpose of this study was to evaluate prosthetic component alignment in robotic arm-assisted (RA)-TKA performed with functional alignment and intraoperative fine-tuning, aiming for symmetric medial and lateral gaps in flexion/extension. It was hypothesized that functionally aligned RA-TKA the femoral and tibial cuts would be performed in line with the preoperative joint line orientation. Methods. Between September 2018 and January 2020, 81 RA cruciate retaining (CR) and posterior stabilized (PS) TKAs were performed at a single center. Preoperative radiographs were obtained, and measures were performed according to Paley's. Preoperatively, cuts were planned based on radiographic epiphyseal anatomies and respecting ±3° boundaries from neutral coronal alignment. Intraoperatively, the tibial and femoral cuts were modified based on the individual soft tissue-guided fine-tuning, aiming for symmetric medial and lateral gaps in flexion/extension. Robotic data were recorded. Results. A total of 56 RA-TKAs performed on varus knees were taken into account. On average, the tibial component was placed at 1.9° varus (SD 0.7) and 3.3° (SD 1.0) in the coronal and sagittal planes, respectively. The average femoral component alignment, based on the soft tissue tensioning with spoons, resulted as follows: 0.7° varus (SD 1.7) in the coronal plane and 1.8° (SD 2.1) of external rotation relative to surgical transepicondylar axis in the transverse plane. A statistically significant linear direct relationship was demonstrated between radiographic epiphyseal femoral and tibial coronal alignment and femoral (r=0.3, p<0.05) and tibial (r=0.3, p<0.01) coronal cuts, resepctively. Conclusion. Functionally aligned RA-TKA performed in varus knees, aiming for ligaments’ preservation and balanced flexion/extension gaps, provided joint line respecting femoral and tibial cuts on the coronal plane

Aims. The aims of this prospective study were to determine the effect of osteophyte excision on deformity correction and soft- tissue gap balance in varus knees undergoing total knee arthroplasty (TKA). Patients and Methods. Limb deformity in coronal (varus) and sagittal (flexion) planes, medial and lateral gap distances in maximum knee extension and 90° knee flexion and maximum knee flexion were recorded before and after excision of medial femoral and tibial osteophytes using computer navigation in 164 patients who underwent 221 computer-assisted, cemented, cruciate- substituting TKAs. Results. Mean varus and flexion deformities of 4.5°±3° (0.5° to 30° varus) and 4.9°±5.9° (−15° hyperextension to 30° flexion) reduced significantly (p<0.0001) to mean varus deformity of 1°±2.3° and mean flexion deformity of 2.7°±4.2° after excision of medial femoral and tibial osteophytes. The mean medio-lateral (ML) soft-tissue gap difference in maximum knee extension and 90°knee flexion of 2.7±3.6mm and 0.7±2.6mm reduced significantly (p<0.0001) to mean ML soft-tissue gap difference of 0.7±2.5mm in maximum knee extension and 0.1±1.9mm in 90°knee flexion. The mean maximum knee flexion (122.8°±8.4°) increased significantly to mean maximum knee flexion of (125°±8°). Conclusion. Excision of medial femoral and tibial osteophytes during TKA in varus knees significantly improves varus and flexion deformities, mediolateral soft-tissue gap imbalance in maximum extension and in 90°knee flexion and maximum knee flexion. Clinical Relevance. Excision of medial femoral and tibial osteophytes can be a useful, initial step towards achieving deformity correction and gap balance without having to resort to soft-tissue release during TKA in varus knees

For many years, achieving a neutral coronal Hip-Knee-Ankle angle (HKA) measured on radiographs has been considered a factor of success for total knee arthroplasty (TKA). Lower limb HKA is influenced by the acquisition conditions, and static HKA (sHKA) may not be representative of the dynamic loading that occurs during gait. The primary aim of the study was to see if the sHKA is predictive of the dynamic HKA (dHKA). A secondary aim was to document to what degree the dHKA changes throughout gait. We analysed the 3-D knee kinematics during gait of a cohort of 90 healthy individuals (165 knees) with the KneeKG™ system. dHKA was calculated and compared with sHKA values. Knees were considered “Stable” if the dHKA remained positive or negative – i.e. in valgus or varus – for greater than 95% of the corresponding phase and “Changer” otherwise. Patient characteristics of the Stable and Changer knees were compared to find contributing factors. The dHKA absolute variation during gait was 10.9±5.3° [2 .4° – 28.3°] for the whole cohort. The variation was greater for the varus knees (10.3±4.8° [2.4° – 26.3°]), than for the valgus knees (12.8±6.1° [2.9° – 28.3°], p=0.008). We found a low to moderate correlation (r = 0.266 to 0.553, p < 0 .001) between sHKA and the dHKA values for varus knees and no correlation valgus knees. Twenty two percent (36/165) of the knees demonstrated a switch in the dHKA (Changer). Proportion of Changer knees was 15% for varus sHKA versus 39% for valgus sHKA (p < 0.001). Lower limb radiographic measures of coronal alignment have limited value for predicting dynamic measures of alignment during gait

Introduction. Most of the algorithm available today to balance varus knee is based on a surgeon's hands-on experience without full understanding of pathological anatomy of varus knee. The high-resolution MRI allows us to recognize the anatomical details of the posteromedial corner and the changes of the soft tissue associated with the osteoarthritis and varus deformity. We have in this study, reviewed 60 cases of severe varus knee scheduled for TKR and compared it to normal MRI and those MRI were evaluated and read by a musculoskeletal radiologist. We have documented clearly the changes that happens in soft tissue, leading to tight medial compartment. We will also show multiple short intra-operative video confirming that MRI findings. Material & method. We have retrospectively reviewed the MRI on 60 patients with advanced osteoarthritis varus knee. We also reviewed 20 MRI for a normal knee matched for age. We evaluated the posteromedial complex and MCL in sagittal PD-weighted VISTA to check the alignment of the MCL and posteromedial complex and the associate MCL bowing and deformity that could happen in osteoarthritis knee. We have measured the thickness of the posteromedial complex and the posterior medial bowing of the superficial MCL and the involvement of the posterior oblique ligament in those patients. To measure the posterior bowing of the MCL, a line was drawn through the posterior aspect of both menisci and we measured the distance between the posterior edge of MCL to that line in actual image. To measure the thickness of the posteromedial complex, we measured it at two areas in the posterior medial corner posteriorly at the level of the medial meniscus. Measuring the medial bowing of the MCL was done by a line drawn through the medial edge of the femoral condyle and the tibial condyle at the level of the medial meniscus to the inner aspect of the MCL. The normal distance between the posterior aspects of the MCL to the posterior meniscus line was approximately measured 2 cm. in average. Results. We were able to recognize and measure the medial deviation of MCL in all arthritic knees due to the deformity and the effect of the medial margin osteophyte and medial extrusion of the meniscus. Thickening of posteromedial complex was recognized in the majority of the cases with prominent thickening seen in 50/60 knees with average thickness measuring approximately 1.2 cm due to the synovial thickening, adhesions, granulation tissue, degenerated medial meniscus, and involvement of the posterior oblique ligament and the capsular branch of the semimembranosus tendon, as well as the oblique popliteal ligament. The involvement of posterior oblique ligament were seen in majority of the cases. In 55 cases we have showed a heterogeneous appearance of the ligament and loss of normal signal within the postero medial complex and we have documented that the oblique ligament will cause the posterior bowing of the MCL. The medial bowing of the MCL is also correlated to the severity of the varus deformity with an average distance to the normal medial line of the medial meniscus measuring approximately 1.1 cm. Discussion. Our study shows that the changes affecting the superficial MCL is likely to be secondary to the obvious changes involving the posteromedial complex and to the marginal osteophyte as well as the extrusion of the medial meniscus. Also, we have confirmed that there are deforming structures such as the oblique ligament with adhesion and thickening with all the posterior medial complex. Those changes clearly caused the posterior bowing to the superficial MCL without an actual shortening of the ligament. The scarring tissue in the posteromedial corner and the adhesion is acting as a soft phyte tensioning and deforming the ligament and the posterior capsule. The oblique ligament act as a deforming forces forcing the superficial MCL to bow posteriorly. The lengths of the superficial MCL stayed the same. Conclusion. The conventional wisdom of releasing the distal attachment of the superficial medial MCL to balance knee has to be a challenge based on our MRI finding. Releasing the superficial MCL can sometimes lead to a major instability of the knee requiring a more constrained implant. Our MRI assessment clearly showed that the Superficial MCL is deformed because of posterior bowing and medial bowing and considerable thickening of the posteromedial corner, as well as the accompanying osteophyte. We believe that clearing the superficial MCL and excising those thickened scar tissue in the posterior medial corner will enable us to balance the knee without creating instability Conclusion: The conventional wisdom of releasing the distal attachment of the superficial medial MCL to balance knee has to be a challenge based on our MRI finding. Releasing the superficial MCL can sometimes lead to a major instability of the knee requiring a more constrained implant. Our MRI assessment clearly showed that the Superficial MCL is deformed because of posterior bowing and medial bowing and considerable thickening of the posteromedial corner, as well as the accompanying osteophyte. We believe that clearing the superficial MCL and excising those thickened scar tissue in the posterior medial corner will enable us to balance the knee without creating instability

Background. Achieving a neutral static Hip-Knee-Ankle angle (sHKA) measured on radiographs has been considered a factor of success for total knee arthroplasty (TKA). However, recent studies have shown that sHKA seems to have no effect on TKA survivorship. sHKA is not representative of the dynamic loading occurring during gait, unlike the dynamic HKA (dHKA). Research question. The primary objective was to see if the sHKA is predictive of the dynamic HKA (dHKA). A secondary objective was to document to what degree the dHKA changes during gait. Methods. We analysed 3D knee kinematics during gait of a cohort of 90 healthy individuals with the KneeKG™ system. dHKA was calculated and compared with sHKA. Knees were considered “Stable” if the dHKA remained in valgus or varus for greater than 95% of the corresponding phase, and “Changer” otherwise. Patient characteristics of the Stable and Changer knees were compared to find associated factors. Results. dHKA absolute variation during gait was 10.9±5.3° for the whole cohort. The variation was less for the varus knees (10.3±4.8°), than for the valgus knees (12.8±6.1°, p=0.008). We found low to moderate correlations (r=0.266 to 0.553, p<0.001) between sHKA and dHKA values for varus knees and no significant correlation for valgus knees. Twenty two percent (36/165) of the knees were considered Changers. The proportion of knees that were Changers was 15% of the varus versus 39% of the valgus (p < 0.001). Significance. Lower limb radiographic measures of coronal alignment have limited value for predicting dynamic measures of alignment during gait

Introduction. The convincible wisdom is that the release of MCL in severe varus knee should be progressive. This release is usually carried on after resecting the osteophyte and gradually carried on until the MCL is well balanced. However, sometimes, extensive release and releasing the superficial MCL can lead to instability in flexion. On a personal communication with many Asian surgeons they have been doing a careful release of the posteromedial corner in the varus knee and in majority of cases such release is adequate. And even in severe cases of varus knee superficial MCL doesn't need to be released. 20 total knee replacements were performed by the same surgeon using ZimmerPS implant. In the varus deformity ranges from 15–35 degrees. The first bony section was made carefully. All osteophytes were removed and resected. The posterior bone osteophytes were also resected and the intercondylar notches were made along with the posterior release. After doing the bony cut in 18 of those cases the medial compartment was still tight and both flexion and extension. A careful release was carried in the postal medial corner-First using an osteotome around the posteromedial corner to release the soft tissue. After that the thick fibrous tissue that formed like pseudo meniscus was also resected until we were able to reach the posterior capsule. In some cases those scar tissues even extended to the capsule requiring the resecting of the postal medial capsule. We meticulously resected all those scar tissues and in many of those cases were able to visualize the MCL ligament which was well preserved. A tensioning device was used before and after the release. In all of those cases we were able to document an opening ranging from two to seven millimeter after the proper release. In all cases the superficial MCL were still intact and can be operated carefully. Result. This study clearly shows that we did not have to release the superficial MCL and the careful posteromedial release was adequate to obtain a good balance gap immediately and the knee was quite stable. The superficial MCL was maintained and preserved and tensioning device clearly document opening after releasing the postural medial corner. Discussion. In varus knee there is an extensive scar tissue which can sometimes tension the mcl ligament and releasing the deep mcl along with posture medial corner without releasing the superficial will preserve the stability of the knee allowing us to ambulate the patient immediately and preventing instability. Conclusion. Although MCL release has been described in diff ways in multiple literatures, little attention has been paid to the posture medial corner. This paper clearly shows that the complex anatomy of the posture medial corner along with scarring can lead to a tight mcl Releasing such structures would balance MCL&LCL without compromising the superficial MCL which normally lead to obvious flexion instability and a mid-section instability. We strongly recommend surgeon to do the posteromedial release before doing any release to the superficial mcl. Doing so will prevent the incidence of instability after extensive release in varus deformity

Introduction:. Varus alignment of the knee is common in patients undergoing unicondylar knee replacement. To measure the geometry and morphology of these knees is to know whether a single unicondylar knee implant design is suitable for all patients, i.e. for patients with varus deformity and those without. The aim of this study was to identify any significant differences between normal and varus knees that may influence unicondylar implant design for the latter group. Methodology:. 56 patients (31 varus, 25 normal) were evaluated through CT imaging. Images were segmented to create 3D models and aligned to a tri-spherical plane (centres of spheres fitted to the femoral head and the medial and lateral flexion facets). 30 key co-ordinates were recorded per specimen to define the important axes, angles and shapes (e.g. spheres to define flexion and extension facet surfaces) that describe the femoral condylar geometry using in-house software. The points were then projected in sagittal, coronal and transverse planes. Standardised distance and angular measurements were then carried out between the points and the differences between the morphology of normal and varus knee summarised. For the varus knee group, trends were investigated that could be related to the magnitude of varus deformity. Results:. Several significant differences between normal and varus knees were found, but most of these were small differences unlikely to be clinically significant or have an influence on implant design. However, two strong trends were observed. Firstly, the version of the femoral neck was significantly less for patients with varus knees (mean difference 9°; p < 0.05). The second trend was a significant difference in the sagittal morphology of the medial condyle. The kink angle, the angle formed by the intersection of the circles fitted to the flexion and extension facet surfaces, and their centres (Figure 1) was either absent or small in normal knees (mean 1°). An absent kink angle occurs when the circle defining the flexion facet surface lies within or makes a tangent to the circle defining the extension facet. However, for varus knees, the mean kink angle was 9°, with positive correlation with the angle of varus deformity (Figure 2). Discussion:. Varus knees have a significantly larger kink angle than normal knees, influencing the relative positions of the flexion and extension facet spheres that define the medial condylar geometry, contributing to the commonly observed ‘flattening’ of the medial condyle in the sagittal plane. Varus knees are also associated with significantly less anteversion of the femoral neck. It has been shown that reduced femoral neck anteversion causes increased loading of the medial condyle [1], and our results support this finding. The data generated in this study will feed further biomechanical testing to investigate the influence of kink angle and femoral neck version on the kinematics and load distribution in the varus knee

Introduction. Studies have shown that dissatisfaction following TKA may stem from poor component placement and iatrogenic factors related to variability in surgical execution. A CT-based robotic assisted system (RA) allows surgeons to dynamically balance the joint prior to bone resection. This study aimed to determine if this system could improve TKA planning, reduce soft tissue releases, minimize bone resection, and accurately predict component size in varus knee. Method. Four hundred and seventy four cases with varus deformity undergoing primary RATKA were enrolled in this prospective, single center and surgeon study. Patient demographics and intraoperative surgical details were collected. Initial and final 3-dimensional alignment, component position, bone resection depths, use of soft tissue releases, knee balancing gaps, and component size were collected intraoperatively. WOMAC and KOOS Jr. scores were collected 6 months, and 1 year postoperatively. Descriptive statistics were applied to determine the changes in these parameters between initial and final values. Results. Native deformity ranged from 1 to 19 degrees of varus. 86% of patients in this study did not require a soft tissue release regardless of their level of coronal or sagittal deformity. Complex deformities who required a soft tissue release were corrected on average to 3 degrees varus while cases without releases were corrected to 2 degrees varus on average with the overall goal as traditional mechanical alignment. All surgeons achieved their planned sizes on the tibia and femur more than 98% of the time within one size, and 100% of the time within two sizes. Flexion and extension gaps during knee balancing were within 2mm (mean 1mm) for all knees. At latest follow-up, radiographic evidence suggested well-seated and well-fixed components. Radiographs also indicated the patella components were tracking well within the trochlear groove. No revision and re-operation were reported. Mean WOMAC total score was improved from 23.8±8.0 pre-op to 8.9±7.9 1-year post-op (p<0.01). Mean KOOS Jr. score was improved from 46.8±11.6 pre-op to 77.9±14.8 1-year post-op (p<0.01). Discussion and Conclusions. New tools may allow for enhanced execution and predictable balance for TKA, which may improve patient outcomes. In this study, preoperative planning via CT scan allowed surgeons to assess bony deformities and subtly adjust component position to reduce soft tissue trauma. While this study has several limitations, RATKA for varus knees should continue to be investigated. For any figures or tables, please contact authors directly

Introduction. Total knee arthroplasty (TKA) is a well-established procedure associated with excellent clinical results. We have previously reported that intraoperative knee kinematics correlate with the clinical outcome in mobile bearing TKA. In addition, the intraoperative knee kinematics pattern does not correlate with the degree of preoperative knee deformity in mobile bearing TKA. However, the relationship among preoperative knee deformity, intraoperative kinematics and clinical outcome in fixed bearing TKA has been unknown. The purpose of this study is to compare the relationship among preoperative knee deformity, knee kinematics after fixed bearing TKA and the clinical outcome including the subjective outcomes evaluated by the new knee society score (KSS). Materials and Methods. A cross-sectional survey of thirty-five consecutive medial osteoarthritis patients who had a primary TKA using a CT-based navigation system was conducted. All knees had a Kellgren-Lawrence grade of 4 in the medial compartment and underwent a primary posterior stabilized TKA (Genesis II, Smith&Nephew) between May 2010 and October 2012. In all cases, a computed tomography-guided navigation system (Brain LAB, Heimstetten, Germany) was used. All surgery was performed by the subvastus approach and modified gap technique. Intraoperative knee kinematics was measured using the navigation system after implantation and closure of the retinaculum and soft tissue except for the skin. Subjects were divided into two groups based on intraoperative kinematic patterns: a medial pivot group (M group, n=19)(Figure 1) and a non-medial pivot group (N group, n=16)(Figure 2). Subjective outcomes with the new KSS and clinical outcomes were evaluated. Statistical analysis to compare the two groups was made using unpaired a Student t test. Result. Regarding the postoperative clinical result (knee flexion angle, knee extension angle, mechanical FTA,% mechanical axis), there were no significant differences between the two groups. Although there were also no significant differences in KSS evaluation between the two groups, there was a tendency for M group to be superior to N group in current knee symptom (M group: 17.3±5.6, N group: 12.9±8.2, p = 0.07) and functional activities (M group: 55.1±21.5, N group: 42.7±22.6, p = 0.10). Regarding preoperative examination, varus knee deformity (mechanical FTA and% mechanical axis) in N group was significantly more severe than that of M group (p=0.04, p=0.04, respectively). Discussion. Over half of patients (54%) could achieve medial pivot kinematics in fixed bearing TKA with the possibility to improve a subjective clinical result. Although we previously could not detect any relationship between preoperative varus knee deformity and intraoperative kinematics in mobile bearing TKA, the preoperative varus knee deformity in the non-medial pivot group was significantly severer than that of the medial pivot group in fixed type TKA. Our results indicate that if a TKA is done to a severe varus knee deformity the postoperative knee kinematics tend to result in a non-medial pivot pattern. In conclusion, because it tends to result in a non-medial pivot pattern, extra care needs to be taken to avoid postoperative abnormal knee kinematics in the performance of a fixed type TKA to a severe varus knee deformity

Introduction. The prevalence of reversing of extension coronal deformity during flexion and how that may change the routine algorithm of soft tissue balancing in total knee arthroplasty (TKA) has not been published. We name this phenomenon, the reversing coronal deformity (RCD). We observed 12% (45 patients) of coronal deformities consistently reverse in flexion in the osteoarthritic knees before surgery. We conclude that RCD phenomena need to be addressed in every TKA and collateral ligament release need to be modified or avoided; otherwise postoperative flexion instability may be inevitable. Femoral rotation adjustment with posterior capsule release has to be attempted first in RCD patients. Method. We define RCD as the reversing of a coronal extension deformity of more than 2° while the knee reaches 90°of flexion. That is to say a 2° or more varus knee in extension becomes a 2° or more valgus at 90° of flexion or vice versa. We retrospectively analyzed, in a multicenter study the alignment patterns of 387 (US = 270, UK = 117) consecutive computer navigated TKA subjects (June 2004–May 2008). 364/387 (US = 252, UK = 112) subjects were eligible for analysis (23 subjects had incomplete data: US = 18, UK = 5). The coronal deformity kinematics was observed during the range of motion and the range of medial /lateral deflections were analyzed. Result:. 260/364 subjects had varus knees and 104/364 subjects had valgus knees. 18 subjects (7%) of the varus knees reversed to valgus and 27 subjects (26%) of valgus knees reversed to varus by 90°pre-operatively. Therefore, the total number of arthritic knees that reversed their coronal deformity from extension to 90° flexion was 45 (12.4%). Knee alignment in extension was 0° ± 2° in 99% of patients. 1% (4 subjects) had more than 2°of varus or valgus in extension. Collateral ligament was released in 4/45 RCD patients in which all had flexion instability of more than 10° (medial/lateral at 90°). The other 40 patients had posterior capsule release with or without femoral rotation adjustment to balance the flexion gap. None of them had flexion instability (medial /later gaping was 4° or less). The preoperative mean femoral rotation was 3.05° of external rotation (ER) in varus knees and 1.9° ER in valgus knee. While in RCD varus knees, the mean femoral rotation was 1.5 ° ER and RCD valgus knees 2.5°ER. Discussion and Conclusion. Our observation has shed the light on a new concept in the kinematics of the knee, namely the reversing of the coronal deformity (RCD) during flexion which occurs in 12% of patients undergoing TKA. Basically, a varus knee in extension behaves like a valgus knee in flexion and vice versa. It is crucial to be aware of this phenomenon when attempting to do soft tissue release to balance the gaps in TKA. Otherwise, widening one gap in extension to correct a fixed deformity may result in an unacceptable overcorrection of the same gap in flexion in those knees that manifest the reverse coronal deformity phenomena. Soft tissue balance algorithm was noted to be different in such cases in which early collateral ligament release resulted in flexion instability

Aims. The aim of this retrospective study was to measure and determine variation in VCA between the two limbs in a patient with windswept deformity on preoperative full-length, standing, hip-to-ankle radiographs. We hypothesised that there will be significant difference in VCA between the two limbs of a patient with arthritic windswept deformity and therefore it is necessary to individualise VCA for each limb preoperatively on full-length radiographs during TKA. Patients and Methods. In this retrospective study, femoral valgus correction angle (VCA) measured on full-length, hip-to-ankle, standing radiographs was compared between the varus and the valgus limbs in 63 patients with windswept deformities who underwent TKA. Results. The mean VCA in varus knees was significantly higher compared to mean VCA in valgus knees (p=0.002). The VCA was <5° in 40% of valgus knees compared to 6% in varus knees (p=0.0001) whereas VCA was 5°–7° in 73% of varus knees compared to 47% in valgus knees (p=0.0003). There was no difference in the percentage of varus or valgus knees with VCA >7° (p=0.18). A difference in VCA of <3° between the two limbs was seen in 63% of patients, a difference of ≥3° between the two limbs was seen in 18% of patients and 19% of patients had no difference in VCA between the two limbs. Conclusion. Significant difference in VCA is present between the varus and the valgus limbs in most patients withwindswept deformity undergoing TKA. Clinical Relevance. It may be necessary to individualise VCA for each limb preoperatively on full-length radiographs in patients with windswept deformities in order to minimize error while performing the distal femoral cut during TKA

Background. In order to restore the neutral limb alignment in total knee arthroplasty (TKA), surgical procedure usually starts with removing osteophytes in varus osteoarthritic knees. However, there are no reports in the literature regarding the exact influence of osteophyte removal on alignment correction. The purpose of this study was to define the influence of osteophyte removal alone on limb alignment correction in the coronal plane in TKA for varus knee. Methods. Twenty-eight medial osteoarthritic knees with varus malalignment scheduled for TKA were included in this study. After registration of a navigation system, each knee was tested at maximum extension, and at 30, 40 and 60 degrees of flexion before and after osteophyte removal. External loads of 10 N-m valgus torque at each angle and in both states were applied. Subsequently, the widths of the resected osteophytes were measured. Results. The average pre-operative hip-knee-ankle angle was −12.6 degrees. The average width of osteophytes was 7.1 mm in femur and 4.8 mm in tibia, respectively. Angle corrections after osteophyte removal were 2.5 degrees at maximum extension, 2.8 degrees at 30 degrees flexion and 2.5 degrees at 60 degrees flexion; and at all angles, the difference was significant. There was positive correlation between the widths of osteophytes and the degree of angle correction at 30 degrees. Conclusion. Correlation was found at 30 degrees of knee flexion between the widths of osteophytes and the degree of angle correction in the coronal plane in TKA. We found the degree of angle correction per 1mm width of osteophyte removal to be 0.4 degrees

Background. Differences of dynamic (extension vs. flexion) coronal alignment in osteoarthritic (OA) knees undergoing primary total knee arthroplasty (TKA) remain poorly studied. Methods. Prospectively collected measurements of dynamic coronal alignment using an imageless computer-navigation system (Stryker©) during primary TKA were analysed. Coronal alignment was represented by the hip-knee-ankle angle and determined at maximal extension and 90° flexion before making any bony cuts or ligamentous releases. Measurements were subgrouped according to coronal alignment in extension as varus (≤-3°), neutral (>−3°, <+3°) or valgus (≥+3°). Results. Of 545 knees (347 females), coronal alignment in extension was 261 (48%) varus, 197 (36%) neutral and 87 (16%) valgus. Varus extension alignment was more common in male vs. female OA knees (64% vs. 39%; p< .0001). Valgus extension alignment was more common in female vs male OA knees (19.5% vs 9.5%; p= .002). In flexion, 174 (66%) of varus OA knees remained varus and 6 (3.3%) evolved to valgus. Extension varus exceeding 10° in 29/261 (11%) varus knees remained flexion varus in 28 (96.5%). Mean (±SD) difference between extension and flexion in varus knees was 1.98° (±4.0°) valgus. Of 87 valgus knees, 44 (50.5%) remained valgus and 4 (4.5%) evolved into varus during flexion. Mean (±SD) difference between extension and flexion in valgus knees was 2.3° (±4.2°) varus. Dynamic coronal alignment was unchanged in 27/545 (4.9%) and alternated between varus and valgus in 10/348 (2.9%) varus or valgus AO knees. Conclusion. Different coronal alignment was observed in >95% of OA knees of which almost 3% alternated between varus and valgus. This insight of a dynamic coronal deformity might contribute to improving ligamentous release during TKA. Further studies including prognostic value and functional outcome are warranted. Level of evidence: Level II

Introduction. Current techniques in total knee arthroplasty aim to restore the coronal mechanical axis to neutral. Preoperative planning has historically been based on long-leg standing films (LLSF) which allow surgeons to plan bony resection and soft tissue releases. However, LSSF can be prone to error if malrotated. Recently, patient-specific guides (PSG) utilizing supine magnetic resonance imaging (sMRI) have become an accepted technique for preoperative planning. In this study we sought to compare the degree of coronal deformity using LLSF and sMRI. Methods. Two hundred thirty knees underwent planning for total knee arthroplasty with sMRI and LLSF. Coronal plane deformity was determined based on the femoral-tibial angle (FTA) as defined by the angle formed between a line from the center of the femoral head to the intercondylar notch and a line from the middle of the tibial spines to the middle of the ankle joint. Mechanical axis values from the sMRI were compared with values obtained from LLSF. Results. There were 172 varus knees and 58 valgus knees. There was significant correlation (r=0.9215) between LLSF and sMRI for the measurement of coronal plane deformity for all knees. sMRI underestimated the severity of deformity by 2.19 degrees of varus (p<0.001). Additionally, as the severity of the deformity increased, there was also an increase in the discrepancy between sMRI and LLSF. There was a smaller discrepancy for valgus knees (−0.66 degrees) than varus knees (3.15 degrees, p<0.001). The discrepancy between the two modalities was not affected by gender (p=0.386). Conclusion. sMRI based imaging can help approximate coronal plane deformity in the preoperative planning of TKA but it has limitations. This MRI-based technique tended to underestimate deformity in varus knees and patients with extreme deformity. Surgeons may use sMRI for pre-operative planning but must understand that they tend to underestimate the severity of deformity

Introduction. A correct balancing of the knee following TKA surgery is believed to minimize instability and improve patient satisfaction. In that respect, trial components containing force sensors can be used. These force sensors provide insight in the medial/lateral force ratio as well as absolute contact forces. Although this method finds clinical application already, the target values for both the force magnitude and ratio under surgical conditions remain uncertain. Methods. A total of eight non-arthritic cadaveric knees have been tested mimicking surgical conditions. Therefore, the specimens are mounted in a custom knee simulator (Verstraete et al., 2015). This simulator allows to test full lower limb specimens, providing kinematic freedom throughout the range of motion. Knee flexion is obtained by lifting the femur (thigh pull). Knee kinematics are simultaneously recorded by means of a navigation system and based on the mechanical axis of the femur and tibia. In addition, the load transferred through the medial and lateral compartment of the knee is monitored. Therefore, a 2.4 mm thick sawing blade is used to machine a slot in the tibia perpendicular to the mechanical axis, at the location of the tibial cut in TKA surgery. A complete disconnection was thereby assured between the tibial plateau and the distal tibia. To fill the created gap, custom 3D printed shims were inserted (Fig. 1). Through their specific geometry, these shims create a load deviation between two pressure pads (Tekscan type 4011 sensor) seated on the medial and lateral side. Following the insertion of the shims, the knee was closed before performing the kinematic and kinetic tests. Results. Seven specimens showed a limited varus throughout the range of motion (ranging from 1° to 7° varus). The other knee was in valgus (4° valgus). Amongst varus knees, the results were very consistent, indicating high loads in full extension that rapidly decrease. Subsequently, the loads on the lateral side vanish. This leads to consistently high compartmental load ratios (medial load / total load) in flexion (Fig. 3). Discussion. In full extension the screw-home mechanism results in increased loads, both medially and laterally. Upon flexion, the lateral loads disappear. This is attributed to slackening of the lateral collateral ligament, in turn linked to the femoral rollback and slope of the lateral compartment. The isometry of the medial collateral ligament contributes on the other hand to the near-constant load in the medial compartment. The above particularly applies for varus knees. The single valgus knee tested indicated a higher load transmission by the lateral compartment, potentially attributed to a contracture of the lateral structures. With respect to TKA surgery, these findings are particularly relevant when considering anatomically designed implants. For those implants, this study concludes that a tighter medial compartment reflects that of healthy varus knees. Be aware however that in full extension, higher and up to equal loads can be acceptable for the medial and lateral compartment. For any figures or tables, please contact authors directly (see Info & Metrics tab above).

Background. Constitutional knee varus increases the risk of medial OA disease due to increase in the knee adduction moment and shifting of the mechanical axis medially. Hueter-Volkmann's law states that the amount of load experienced by the growth plate during development influences the bone morphology. For this reason, heightened sports activity during growth is associated with constitutional varus due to added knee adduction moment. In early OA, X-rays often show a flattened medial femoral condyle extension facet (EF). However, it is unknown whether this is a result of osteoarthritic wear, creep deformation over decades of use, or an outcome of Hueter-Volkmann's law during development. A larger and flattened medial EF can bear more weight, due to increased load distribution. However, a flattened EF may also extrude the meniscus, leading meniscus degeneration and joint failure. Therefore, this study aimed to investigate whether varus knees have flattened medial EFs of both femur and tibia in a cohort of patients with no signs yet of bony attrition. Methods. Segmentation and morphology analysis was conducted using Materialise software (version 8.0, Materialise Inc., Belgium). This study excluded knees with bony attrition of the EFs based on Ahlbäck criteria, intraoperative findings, and operation notes history. Standard reference frames were used for both the femur and tibia to ensure reliable and repeatable measurements. The hip-knee-angle (HKA) angle defined varus or valgus knee alignment. Femur: The femoral EFs and flexion facets (FFs) had best-fit spheres fitted with 6 repetitions. (Fig1). Tibia: The slopes of the antero-medial medial tibial plateau were approximated using lines. (fig2). Results. 72 knees met the inclusion and exclusion criteria. The average age was 59 ± 11 years. The youngest was 31 and the oldest 84 years. Thirty-three were male and 39 were female. There was good intra- and inter-observer reliability for EF sphere fitting. Femur: The results demonstrated that the medial femoral condyle EF is flattened in knees with constitutional varus, as measured by the Sphere Ratios between the medial and lateral EF (varus versus straight: p = 0.006), and in the scaled values for the medial EF sphere radius (varus versus straight: p = 0.005). There was a statistically significant, moderate and positive correlation between the medial femoral EF radius, and the medial femoral EF-FF AP offset. (fig3). Tibia: There was a statistically significant difference between the steepness of the slopes of the medial tibial plateau EF in varus and valgus knees, suggesting varus knees have a less concave (flatter) medial EF. (fig3). Conclusions. In comparison to straight knees, varus knees have flattened medial EFs in both femur and tibia. As this was the case in knees with no evidence of bony attrition, this could mean flattened medial EFs may be a result of medial physis inhibition during development, due to Hueter-Volkmann's law. Flattened medial EFs may increase load distribution in the medial compartment, but could also be a potential aetiology in primary knee OA due to over extrusion of the medial meniscus and edge loading

Introduction. Surgical planning for Patient Specific Instrumentation (PSI) in total knee arthroplasty (TKA) is based on static non-functional imaging (CT or MRI). Component alignment is determined prior to any assessment of clinical soft tissue laxity. This leads to surgical planning where assumptions of correctability of preoperative deformity are false and a need for intraoperative variation or abandonment of the PSI blocks occurs. The aim of this study is to determine whether functional radiology complements pre-surgical planning by identifying non-predictable patient variation in laxity. Method. Pre-operative CT's, standing radiographs and functional radiographs assessing coronal laxity at 20° flexion were collected for 20 patients. Varus/valgus laxity was assessed using the TELOS stress device (TELOS GmbH, Marburg, Germany, see Figure 1). The varus/valgus load was incrementally increased to either a maximum load of 150N or until the patient could not tolerate the discomfort. Radiographs were taken whilst the knee was held in the stressed position. CT scans were segmented and anatomical points landmarked. 2D–3D pose estimations were performed using the femur and tibia against the radiographs to determine knee alignment with each functional radiograph and so characterise the varus/valgus laxity. Results. The mean coronal alignment on CT and standing radiographs were 3.8° varus (SD, 5.6°) and 4.3° varus (SD, 6.7°) respectively. Of these, 5 of the knees were valgus aligned and 15 varus aligned in both standing and CT positions. The varus group had a mean of 5.9° in CT and 6.9° varus standing, while the valgus group had means of 4.4° valgus and 5.4° valgus in standing, indicating a collapse into further coronal malalignment while weightbearing. Each knee in the group had a laxity envelope calculated from the varus and valgus stressed radiographs. In the varus knees, the envelope ranged from 11.0° to 1.0° degree, with a mean of 5.1° (SD, 2.4°). In the valgus knees, the envelope ranged from 10.0° to 5.0° degrees, with a mean of 6.6° (SD, 2.3°), though this difference did not reach statistical significance. Using ±3° of neutral alignment as an indicator of correctable deformity, 7 of the 15 varus knees did not have a correctable deformity, while all of the valgus did. As determined by laxity limits, the CT and standing alignments were not well centered within their functional radiology groups. Specifically, for the valgus knees, 2 were near the valgus limit (lower quartile) of their laxity envelope, while for the varus knees, 9 were near their varus limit (upper quartile) and 2 at the valgus limit. In total, 65% of the knees did not have their standing alignment well centered on their functional laxity imits. Conclusions. Varus/valgus laxity in TKA appears to be subject specific and divorced from static radiological parameters. Surgical planning without reproducible clinical assessments of coronal laxity may not be sufficient to obtain a balanced TKA while avoiding ligament releases. Functional radiographs may be a viable method to individualise and refine the surgical plan in TKA on a per patient basis, incorporating objective information normally only available during the surgery itself. For any figures or tables, please contact authors directly (see Info & Metrics tab above).