Aims. In Asia and the Middle-East, people often flex their knees deeply in order to perform activities of daily living. The purpose of this study was to investigate the 3D kinematics of normal knees during high-flexion activities. Our hypothesis was that the femorotibial rotation, varus-valgus angle, translations, and kinematic pathway of normal knees during high-flexion activities, varied according to activity. Materials and Methods. We investigated the in vivo kinematics of eight normal knees in four male volunteers (mean age 41.8 years; 37 to 53) using 2D and 3D registration technique, and modelled the knees with a computer aided design program. Each subject squatted, kneeled, and sat cross-legged. We evaluated the femoral rotation and varus-valgus angle relative to the tibia and anteroposterior translation of the medial and lateral side, using the transepicodylar axis as our femoral reference relative to the perpendicular projection on to the tibial plateau. This method evaluates the femur medially from what has elsewhere been described as the extension facet centre, and differs from the method classically applied. . Results. During squatting and kneeling, the knees displayed femoral external rotation. When sitting cross-legged, femurs displayed internal rotation from 10° to 100°. From 100°, femoral external rotation was observed. No significant difference in varus-valgus angle was seen between squatting and kneeling, whereas a varus position was observed from 140° when sitting cross-legged. The measure kinematic pathway using our methodology found during squatting a medial pivoting pattern from 0° to 40° and bicondylar rollback from 40° to 150°. During kneeling, a medial pivot pattern was evident. When sitting cross-legged, a lateral pivot pattern was seen from 0° to 100°, and a medial pivot pattern beyond 100°. Conclusion. The kinematics of normal knees during high flexion are variable according to activity. Nevertheless, our study was limited to a small number of male patients using a different technique to report the kinematics than previous publications. Accordingly, caution should be observed in generalizing our findings. Cite this article: Bone Joint J 2018;100-B:50–5

Aims. Mobile-bearing unicompartmental knee arthroplasty (UKA) with a flat tibial plateau has not performed well in the lateral compartment, leading to a high rate of dislocation. For this reason, the Domed Lateral UKA with a biconcave bearing was developed. However, medial and lateral tibial plateaus have asymmetric anatomical geometries, with a slightly dished medial and a convex lateral plateau. Therefore, the aim of this study was to evaluate the extent at which the normal knee kinematics were restored with different tibial insert designs using computational simulation. Methods. We developed three different tibial inserts having flat, conforming, and anatomy-mimetic superior surfaces, whereas the inferior surface in all was designed to be concave to prevent dislocation. Kinematics from four male subjects and one female subject were compared under deep knee bend activity. Results. The conforming design showed significantly different kinematics in femoral rollback and internal rotation compared to that of the intact knee. The flat design showed significantly different kinematics in femoral rotation during high flexion. The anatomy-mimetic design preserved normal knee kinematics in femoral rollback and internal rotation. Conclusion. The anatomy-mimetic design in lateral mobile UKA demonstrated restoration of normal knee kinematics. Such design may allow achievement of the long sought normal knee characteristics post-lateral mobile UKA. However, further in vivo and clinical studies are required to determine whether this design can truly achieve a more normal feeling of the knee and improved patient satisfaction. Cite this article: Bone Joint Res 2020;9(7):421–428

It is recommended in the TKA operation to balance the tension of soft tissues to make the rectangular gap in both flexion and extension because significant imbalance may result in eccentric stress on the polyethylene insert. However, no intensive research has been done on the medial and lateral laxity of the normal knee. X-ray of 50 normal knees were taken under the varus or valgus stress in both extension and flexion at 80 degrees. The angle of lines on the femoral condyles and tibia plateau was measured. The same methods were also done for the 20 osteoarthritis knees. In extension of the normal knees, the mean angle was 5.06 degrees in varus stress and was 2.46 degrees in valgus stress. In flexion of the normal knees, the mean angle was 5.04 degrees in varus stress and was 1.82 degrees in valgus stress. Therefore, the lateral laxity was significantly larger than the medial laxity in both extension and flexion (p< 0.0001). The lateral laxity was significantly larger also in osteoarthritis knees (p< 0.0001). There are some arguments about the priority to make the perfect rectangular gaps. The methods to measure the tension of soft tissues during the operation are not accurate and does not always reflect the post-operative tensions. Furthermore, the tension during the operation may be different from dynamic phase such as walking and standing. The present study showed that the mediolateral laxity was asymmetrical in the normal knees. This imbalance may be necessary for the medial pivot movement of the normal knee. These results suggest that a slight lateral laxity is acceptable during TKA operation and may be beneficial to achieve the normal kinematics especially for the cruciate retaining prosthesis

Introduction. Many fluoroscopic studies on total knee arthroplasty (TKA) have identified kinematic variabilities compared to the normal knee, with many subjects experiencing paradoxical motion patterns. The intent of this study was to investigate the results of a newly designed PCR TKA to determine kinematic variabilities and assess these kinematic patterns with those previously documented for the normal knee. Methods. The study involves determining the in vivo kinematics for 80 subjects compared to the normal knee. 10 subjects have a normal knee, 40 have a Journey II PCR TKA and 40 subjects with the Journey II XR TKA (BCR). Although all PCR subjects have been evaluated, we are continuing to evaluate subjects with a BCR TKA. All TKAs were performed by a single surgeon and deemed clinically successful. All subjects performed a deep knee bend from full extension to maximum flexion while under fluoroscopic surveillance. Kinematics were calculated via 3D-to-2D registration at 30° increments from full extension to maximum flexion. Anterior/posterior translation of the medial (MAP) and lateral (LAP) femoral condyles and femorotibial axial rotation were compared during ranges of motion in relation to the function of the cruciate ligaments. Results. Of the 40 PCR TKAs, the average overall flexion was 112.6°, while the average for normal subjects was 139.0°. Initial BCR subjects revealed a higher than expected 128.0°. From 0=30° knee flexion, PCR subjects demonstrated −4.74±4.94 mm of posterior LAP movement, −2.04±4.07 mm of MAP movement and 3.61±8.13° of external axial rotation. In the same range of motion, normal subjects exhibited −8.80±3.32 mm of LAP movement, −3.81±1.03 mm of MAP movement and an axial rotation of 11.34±3.78°. From 30=90° knee flexion, PCR subjects demonstrated 4.37±8.26 mm of LAP movement, 0.12±7.95 mm of MAP movement and 0.79±11.43° of axial rotation. In the same range of motion, normal subjects exhibited −4.28±3.13 mm of LAP movement, −1.11±2.76 mm of MAP movement and axial rotation of 6.54±4.33°. From 0°-maximum flexion, PCR subjects demonstrated −2.71±5.37 mm of LAP movement, 1.79±4.88 mm of MAP movement and 5.99±5.26° of axial rotation. In the same range of motion, normal subjects exhibited −17.83±6.04 mm of LAP movement, −9.11±4.93 mm of MAP movement and axial rotation of 23.66±7.81°. Overall, the BCR subject displayed kinematic patterns similar to those of a normal knee; more detailed numbers will be presented in the presentation. Discussion. Subjects having a PCR TKA experienced excellent weight-bearing flexion and kinematic patterns similar to the normal knee, but less in magnitude. These subjects experienced posterior femoral rollback in early and late flexion. During mid-flexion, subjects having a PCR TKA did experience some variable motion patterns, which may be due to the absence of the ACL. Subjects having a BCR TKA experienced more continuous rollback throughout flexion, more similar to the normal knee. Similar to the normal knee, subjects having a PCR TKA did experience progressive axial rotation throughout knee flexion (Figures). Significance. While they still experience normal-like rollback during early (0°–30°) and late flexion (90°-120°), subjects with a PCR TKA consistently demonstrated Anteriorization of the joint in mid-flexion

Background. The Bi-Cruciate Stabilized (BCS) total knee arthroplasty (TKA) incorporates two cam-post mechanisms in order to replicate the functionality and stability provided by the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) in the native knee. Recently (2012), a second generation BCS design has introduced femur and tibial bearing modifications that are intended to delay lateral femoral condyle rollback and encourage more stable positioning of the medial femoral condyle to more closely replicate normal knee kinematics. The purpose of this study was to compare the kinematics of this TKA to the normal knee during a weight bearing flexion activity. Methods. In vivo kinematics were derived for 10 normal non-implanted knees and 40 second generation BCS TKAs all implanted by a single surgeon. Computed tomography (CT) scans were obtained for each normal patient, and 3D reconstruction of the femur, tibia/fibula, and patella was performed. Fluoroscopic images were captured at 60 Hz using a mobile fluoroscopic unit that tracked the knee while patients performed a deep knee bend (DKB) from full extension to maximum flexion. A 3D-to-2D image registration technique was used at 30° increments to determine the transformations of the segmented bones or TKA components. The anterior-posterior motion of the lateral femoral condyle contact point (LAP) and the medial femoral condyle contact point (MAP), as well as tibio-femoral axial rotation, were measured at 30° increments from full extension to maximum flexion. Statistical analysis was conducted at the 95% confidence level. Results. From full extension to 120° of knee flexion the lateral condyle contact point translated posteriorly by 14.55 mm ± 5.11 mm and 10.47 mm ± 3.14 mm in the Normal and BCS groups respectively (p=0.1984). Over the same range of motion, the anterior-posterior motion of the medial condyle contact point in the Normal and BCS groups was −5.05 mm ± 2.91 mm and −10.66 mm ± 4.46 mm respectively (p=0.0433). Significant differences in LAP and/or MAP position existed at each flexion increment from 0–120° of flexion (Figure 1). The Normal group exhibited 19.85° ± 6.92° of axial rotation from full extension to 120° of flexion, while the BCS rotated 7.36° ± 4.31° (p=0.0085). Significant differences in femoral rotation with respect to the tibia existed at full extension as well as at 30° and 60° of knee flexion (Figure 2). Conclusions. Like the normal knee, the BCS experiences larger amounts of posterior motion in the first 30 degrees of knee flexion, compared to its mid-flexion phases (30°–90°). After 90 degrees the posterior motion in the BCS continues to increase, likely in part due to posterior cam-post engagement as intended. In this sample of normal knee subjects, very little posterior motion of either femoral condyle happens between 90 and 120 degrees of knee flexion although significant amounts of rollback are expected thereafter as reported in the literature. The axial rotation experienced by the BCS group is quite less than that experienced by the Normal group, however it is quite comparable to other TKAs, if not greater

Total Knee Arthroplasty (TKA), has now become a reliable, successful, and widely used treatment for osteoarthritis. Numerous reports indicate that for the majority of patients, the TKA lasts a lifetime with pain relief and the ability to perform most everyday activities. However there are a number of ways in which the procedure can be further improved, the focus here being on function. One of the problems in evaluating function is that it depends upon the inherent ability, motivation, and expectation of the patients. There are several well-used questionnaire systems which capture functional ability objectively. In the effort to simplify evaluation, a ‘forgotten knee’ evaluation has been introduced, the concept being that ‘the ideal TKA design’ would feel and function like a normal knee. Such a measure would include factors such as surgical technique, alignment, and rehabilitation, as well as the TKA design itself. Another approach to evaluation is to measure biomechanical parameters, such as in gait analysis and fluoroscopy, which evaluate kinematic or kinematic parameters, using normal controls for comparison. Nevertheless, such evaluations still include factors other than the TKA design itself, and do not apply to new designs. The approach taken here for the evaluation of a new TKA design independent of other factors, is to measure the neutral path of motion and the laxity boundaries of the loaded knee on the application of shear and torque over a full range of flexion. The benchmark is the same kinematic data from the normal intact knee. The rationale has some analogy to the ‘forgotten knee’ in that if the laxity response of a design of TKA is the same as that of the anatomic knee itself, the behavior of that implanted knee in any functional condition will be indistinguishable from that of the anatomic knee itself. Such a testing concept has some similarities to the constraint test described in the ASTM standard. In this paper, a novel design algorithm is proposed for creating different design concepts. First, a general morphological form is formulated for each design concept, a Cam-Post PS, a Saddle-Ramp, and a Converging Condyle, all with overall anatomic-like surfaces. Each femoral component is then designed, which is then moved through the normal neutral path and laxity paths, which creates the tibial surface. The concepts are evaluated using a Desktop Knee Machine configured to move the knee dynamically through full flexion while applying combinations of compression, shear and torque; kinematic data being captured optically and plotted using custom software. The normal benchmark was obtained from 10 normal knee specimens, which showed the restraint of the medial femoral condyle to anterior displacement and the overall rollback and laxity laterally. Compared with standard CR and PS designs, the Guided Motion designs were seen to more closely resemble normal. It is proposed that this approach can result in designs which will more likely reproduce a ‘forgotten knee’ and achieve the optimal function for a given patient

Introduction. It is well known that total knee arthroplasty (TKA) does not preserve normal knee kinematics. This outcome has been attributed to alteration of soft-tissue balance and differences between the geometry of the implant design and the normal articular surfaces. Bicompartmental knee arthroplasty (BKA) has been developed to replace the medial and anterior compartments, while preserving the lateral compartment, the anterior cruciate ligament (ACL), and the posterior cruciate ligament (PCL). In a previous study, we reported that unicompartmental knee arthroplasty did not significantly change knee kinematics and attributed that finding to a combination of preservation of soft-tissue balance and minimal alteration of joint articular geometry (Patil, JBJS, 2007). In the present study, we analyzed the effect of replacing trochlear surface in addition to the medial compartment by implanting cadaver knees with a bicompartmental arthroplasty design. Our hypothesis was that kinematics after BCKA will more closely replicate normal kinematics than kinematics after TKA. Methods. Eight human cadaveric knees underwent kinematic analysis with a surgical navigation system. Each knee was evaluated in its normal intact state, then after BKA with the Deuce design (Smith & Nephew, Memphis, TN), then after ACL sacrifice, and finally after implanting a PCL-retaining TKA (Legion, Smith & Nephew). Knees were tested on the Oxford knee rig, which simulates a quadriceps-driven dynamic deep knee bend. Tibiofemoral rollback and rotation and patellofemoral shift and tilt were recorded for each condition and compared using repeated measures ANOVA for significance. Results. Statistically significant differences were noted in femoral rollback between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. Statistically significant differences were noted in tibiofemoral rotation between TKA and Intact conditions but not between Intact and BKA or between Intact and BKA without ACL. No significant differences in patellar lateral shift or lateral tilt were found among the four conditions tested. Discussion & Conclusion. BKA prostheses that preserve the ACL and PCL allow for more normal knee kinematics than does conventional TKA. Our results supported our primary hypothesis that a bicompartmental approach would not significantly alter knee kinematics. These results also imply that replacement of the medial compartment and trochlear surface are not major factors contributing to altered knee function. The results that we observed may not necessarily apply to other BKA designs and should therefore not be extrapolated beyond the prosthesis designs in this study. Additionally, the current study was designed to only evaluate kinematics, and we can not make conclusions regarding implant wear, fixation, durability, ideal patient selection, and reproducibility of successful clinical outcomes. Lastly, the current study was undertaken using relatively normal cadaveric knees whereas in vivo arthroplasty is typically reserved for arthritic knees that are often affected by contracture and/or deformity. We therefore believe that clinical studies with well-defined measures of success need to be conducted before far-reaching conclusions can be drawn regarding the utility of these implants in clinical practice

Introduction Although most surgeons agree that the functional results obtained with modern total knee arthroplasty are acceptable, it is clear that even with the most recent designs it is still impossible to duplicate the behaviour and functional performance of a normal knee. Methods I present a review of the literature and personal experience. Results Recent kinematic studies have shown that modern TKA designs consistently provoke aberrant kinematics compared to the normal knee, mainly due to the absence of the ACL and the inability to maintain a functional PCL. With regard to roll-back, PS cam-post designs appear to perform better than PCL retaining knees, but only in deeper degrees of flexion, usually only beyond 90°. Whether it is striclty necessary to try to obtain normal kinematics with our TKA designs, is still an open debate. Conclusions It is clear however that the aberrant kinematics we have noted with the current designs, are the direct cause of the flexion limit we see in many of our patients. Furthermore they probably also are the basis for many of the discomorts associated with modern TKA, such as difficulties in stair descent, chair rise, pivoting activities, thrust instabilities etc. With regard to these issues, I believe there are two potential directions to improve our current TKA designs; (1) by introducing the concept of guided-motion (intrinsic mechanism), or (2) by maintaining or restoring the (extrinsic) determinants of kinematics, i.e. the cruciate ligaments, the joint configuration and the extra-articular structures. In relation to the conduct of this study, one or more of the authors has received, or is likely to receive direct material benefits

Previous in vivo studies have not documented if ethnicity or gender influence knee kinematics for the healthy knee joint. Other measurements, such as hip-knee-ankle alignment have been previously shown to be significantly different between females and males, as well as Japanese and Caucasian populations in the young healthy knee [. 1. ]. Differences in knee kinematics in high flexion positions may relate to both etiology of osteoarthritis and success in knee replacement designs. Although differences in knee anatomy have been identified, their significance in knee function has not yet been clarified. Therefore, the objective of this study was to determine the 3D, in vivo normal knee kinematics for various subjects from different gender and ethnic backgrounds, and to identify significant differences, if any, between populations. The 3D, in vivo, weight bearing normal knee kinematics was determined for 79 healthy subjects, including 48 Caucasians, 24 Japanese, 42 males, and 37 females. Each participant performed deep knee bend activity from a standing (full extension) to squatting to a lunge motion, until maximum knee flexion was reached. The study was approved by the Institutional Review Board and informed consent form was obtained from all subjects. The 3D bone models, created by segmentation from MR images, were used to recreate the 3D knee kinematics using the previously described fluoroscopic and 3D-to-2D registration techniques (Fig. 1) [. 2. ,. 3. ]. Tibiofemoral rotations were described using the ISB recommended Grood and Suntay convention [. 4. ,. 5. ]. Anterior-posterior translations of the centers of the posterior femoral condyles were normalized due to significantly different anthropometry in the subjects. Anterior cruciate ligament (ACL) laxity was also measured using a KT-1000 device for 72 of these subjects. Statistical analysis was performed using the Student’s t-test, set at the 95% confidence interval. Most subjects achieved very high flexion, however substantial variability occurred in all groups. Range of motion (ROM) varied from 117° to 177°, while average external rotation was 31°± 9.9° for all subjects. Japanese and female subjects achieved greater ROM than Caucasian (p=0.048) and male (p=0.014) subjects. From full extension to 140° of flexion (which 87% of subjects achieved), few significant differences between any of the populations were observed. At deeper flexion, the external rotation was higher for female than for male subjects, however not statistically significant (p=0.0564 at 155°). Also at deep flexion, the adduction was significantly higher for female subjects. The translations of the lateral condyle were very similar between respective groups, but at deep flexion, the medial condyle remained significantly more anterior for females, leading to greater axial rotation and ROM. As ACL laxity increased, flexion/extension ROM significantly increased (r2=0.184, p< 0.001). In addition, ACL laxity was also higher for females (6.8 mm) compared to males (5.6 mm, p=0.011), as well as Japanese (7.5 mm) compared to Caucasian (5.6 mm, p=0.0002) subjects. High variability and ROM in knee kinematics were similar to those seen in previous studies of healthy subjects during a deep knee bending activity [. 6. ]. Subjects in this study achieved much greater axial rotation and ROM than previously analyzed TKA patients. A relationship was found between greater axial rotation and increased ROM, and may be related in part to increased ACL laxity in the knee. Significant differences in ROM and laxity were identified between genders and ethnic groups. Also the medial condyle remaining significantly more anterior for females than for males in deep flexion may explain higher external rotation and consequently higher flexion experienced by women. However, understanding the causes for variability within each group may be the key to improved implant design

The natural knee allows multi-planar freedoms of rotation and translation, while retaining stability in the antero-posterior direction. It allows flexion with roll back, and medial, lateral and central rotation movements. The natural femoral condyles of the knee are spiral, therefore inducing a side to side translatory movement during flexion and extension. Incorporating all these features is vital in successful knee replacement design. The different knee designs currently in use demonstrate different deficiencies in knee function. A study of 150 Posterior Cruciate (PCL) Retaining Total Knee Replacements [1] has shown that in 72% of knees direct impingement of the tibial insert posteriorly against the back of the femur was responsible for blocking further flexion. The mean pre-operative range of flexion was 105° and post-operative was 105.9°. For every 2mm decrease in posterior condylar offset, the maximum flexion was reduced by 12.2°. The major disadvantage of the Posterior Stabilised (PS) Total Knee Replacement is gross anterior to posterior mid-flexion instability [2]. The Medial Rotation Total Knee Replacement is good in mid-flexion but not in high flexion where the femur slides forward on the tibia leading to impingement. The Birmingham Knee Replacement (BKR) is a rotating platform knee design which is stable throughout the range of flexion. In high flexion, the BKR brings the femur to the back of the tibia. The BKR also has spiral femoral condyles, matching the natural kinematics of the knee. The combined static and dynamic effect is 10mm lateral translation of the femur in flexion and vice versa in extension. Results for seventy nine BKRs (in seventy two patients) show the best Oxford Knee Score of 12 at follow up – excluding ten patients whose inferior scores were due to other pathologies. Knee flexion results show a 21° post-operative improvement in range of flexion. On objective independent testing, maximum walking speed is slower for patients with a standard knee replacement (6.5km/h) and the loading through the replaced side does not match the normal side. Comparatively, patients with a BKR have a faster maximum walking speed of 11km/h and the loading closely matches that of the normal knee. Studies based on the National Joint Register PROMs data [2] show that nearly thirty percent of Total Knee Replacement patients are not much better since their operation. A lot of improvement is needed in the design of knee replacements in order to achieve better function for knee replacement patients

Introduction: Understanding the in vivo motions of human joints has become increasingly important. Researchers have used in vitro (cadavers), non-invasive (gait labs), and in vivo (RSA, fluoroscopy) approaches to assess human knee motion. The objective of this study was to use fluoroscopy and computer tomography (CT) to accurately determine the 3D, in vivo, weight-bearing kinematics of normal knees. Methods: Five normal knees clinically assessed as having no pain or ligamentous laxity were analyzed. Using CT scanning, slices were obtained six inches proximal to the joint line on the femur and six inches of the proximal tibia. Three-dimensional CAD models of each subject’s femur, tibia and patella were recreated from the 3D bone density data. Each subject was then asked to perform five weight-bearing activities while under fluoroscopic surveillance: (1) deep knee bend, (2) normal gait, (3) chair rise, (4) chair sit, and (5) stair descent. The computer-generated 3D models of each subject’s femur and tibiaon (> 1

Objectives. Preservation of both anterior and posterior cruciate ligaments in total knee arthroplasty (TKA) can lead to near-normal post-operative joint mechanics and improved knee function. We hypothesised that a patient-specific bicruciate-retaining prosthesis preserves near-normal kinematics better than standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining prostheses in TKA. Methods. We developed the validated models to evaluate the post-operative kinematics in patient-specific bicruciate-retaining, standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under gait and deep knee bend loading conditions using numerical simulation. Results. Tibial posterior translation and internal rotation in patient-specific bicruciate-retaining prostheses preserved near-normal kinematics better than other standard off-the-shelf prostheses under gait loading conditions. Differences from normal kinematics were minimised for femoral rollback and internal-external rotation in patient-specific bicruciate-retaining, followed by standard off-the-shelf bicruciate-retaining and posterior cruciate-retaining TKA under deep knee bend loading conditions. Moreover, the standard off-the-shelf posterior cruciate-retaining TKA in this study showed the most abnormal performance in kinematics under gait and deep knee bend loading conditions, whereas patient-specific bicruciate-retaining TKA led to near-normal kinematics. Conclusion. This study showed that restoration of the normal geometry of the knee joint in patient-specific bicruciate-retaining TKA and preservation of the anterior cruciate ligament can lead to improvement in kinematics compared with the standard off-the-shelf posterior cruciate-retaining and bicruciate-retaining TKA. Cite this article: Y-G. Koh, J. Son, S-K. Kwon, H-J. Kim, O-R. Kwon, K-T. Kang. Preservation of kinematics with posterior cruciate-, bicruciate- and patient-specific bicruciate-retaining prostheses in total knee arthroplasty by using computational simulation with normal knee model. Bone Joint Res 2017;6:557–565. DOI: 10.1302/2046-3758.69.BJR-2016-0250.R1

Background. The overall goal of total knee arthroplasty (TKA) is to facilitate the restoration of native function following late stage osteoarthritis and for this reason it is important to develop a thorough understanding of the mechanics of a normal healthy knee. While there are several methods for assessing TKA mechanics, these methods have limitations that make them prohibitive to both replicating physiological systems and evaluating non-implanted knees. These limitations can be circumvented through the development of mathematical models that use anatomical and physiological inputs to computationally simulate joint mechanics. This can be done in an inverse or forward manner to solve for either joint forces or motions respectively. The purpose of this study is to evaluate one such forward model and determine the accuracy of the predicted motions using fluoroscopy. Methods. In vivo kinematics were determined during flexion from full extension to 120 degrees for ten normal, healthy, subjects using fluoroscopy and a 3D-to-2D registration method. All ten subjects had previously undergone CT scans allowing for the digital reconstruction of native femur and tibia geometries. These geometries were then input into a ridged body forward model based on Kane's system of dynamics. The resulting kinematics determined through fluoroscopy and the mathematical model were compared for all of the ten subjects. Results. The three kinematic parameters evaluated for this study were the initial positioning and translation of the medial and lateral condylar contact point in addition to the axial position and rotation of the femur with respect to the tibia. The model simulations demonstrated an average of −2.16mm of medial condyle translation, −14.03mm of lateral condyle translation, and 20.09°of axial rotation. Through fluoroscopy, subjects demonstrated an average of −3.63mm of medial condyle translation, −16.02mm of lateral condyle translation, and 15.65°of axial rotation. Comparing these two methods the model predicted on average an additional 1.47mm of medial condyle translation, 1.98mm of lateral condyle translation, and 4.44° less axial rotation compared to the fluoroscopic analysis of the same ten subjects. Conclusion. In comparing the simulation kinematics to the that of the fluoroscopic assessment, the results are comparably similar demonstrating a forward model can be a viable assessment of knee kinematics in the future. By validating mathematical simulation as a feasible means of mechanical assessment, it becomes possible to evaluate mechanics using inputs to reflect extraordinary and theoretical instances such as trauma patients and congenital deformities unable to be assessed by other methods. The nature of the model also allows for a seamless transition to assess TKA mechanics, creating a more efficient means of evaluating both device design and surgical technique

Aims

Commonly performed unicompartmental knee arthroplasty (UKA) is not designed for the lateral compartment. Additionally, the anatomical medial and lateral tibial plateaus have asymmetrical geometries, with a slightly dished medial plateau and a convex lateral plateau. Therefore, this study aims to investigate the native knee kinematics with respect to the tibial insert design corresponding to the lateral femoral component.

The objective was to develop a simple, rapid, and low-cost method for evaluating proposed new Total Knee (TKA) designs, and then to use the method to evaluate three different TKA models with different kinematic characteristics. In a previous study, we reported on the use of an Up-and-Down Crouching Machine, where the neutral path of motion for knee specimens were measured, and then TKR models were implanted and the tests repeated. These experiments showed that standard CR and PS designs behaved more like an ACL deficient knee, whereas Guided Motion knees produced motion similar to that of the intact specimens. However the method was time consuming, technically demanding, and expensive, and hence is suitable for designs which had already passed through a screening method. The latter was the subject of this present study, called the Desktop TKR Test Machine. The principle of the testing protocol on the machine, called Holistic Testing, was that a spectrum of compressive, shear and torque forces were applied to a knee, to represent a complete spectrum of daily and sporting activities. The resulting femoraltibial positions were measured, both the Neutral Path of Motion and the Laxity about the neutral path. The motions were displayed as both the motion of the transverse femoral axis on the tibial surface, and by the centers of the lateral and medial contact patches. Eight knee specimens were tested first, to act as a reference target for evaluating TKR models. Knee models were designed in the computer and made in a hard low-friction plastic using SLA and stereolithography. A typical Posterior-Stabilized (PS) TKA did not display the normal external femoral rotation with flexion, and also showed abnormal anterior sliding on the medial side prior to cam-post engagement. Guided Motion designs included a Medial Pivot type, and a Medial Pivot with a cam-post. Both of these had a dished medial side and a shallow lateral side, to more accurately reproduce anatomic motion characteristics. The guidedmotion design with the cam-post produced a neutral path and laxity more similar to that of normal. It was concluded that the test method satisfied the objective in terms of being a useful test method for rapid evaluation of new proposed TKR designs. The method was able to identify designs which showed motion and stability characteristics closer to the normal anatomic knee

Introduction and Aims: The chronic ACL deficient knee has a natural history of degeneration and deterioration in function. It is unclear whether reconstruction will prevent this sequela. Reconstruction using hamstrings graft techniques have not been yet been evaluated over the long term. This prospective study used MRI to measure tibio-femoral contact patterns pre-and post-reconstruction.

Method: There were 20 subjects with an ACL injury of three years standing. The diagnosis was clinical and confirmed at surgery. They performed a closed chain leg-press, relaxed and against a 150N load. MRI recorded the tibio-femoral contact position at 15-degree intervals from zero to 90 degrees of knee flexion. Passive laxity was measured with a KT1000, and knee outcomes recorded using a Cincinnati score. Testing was performed pre-operatively, at 12 weeks and two years post-operatively.

Results: KT1000 showed a side-to-side difference of 5.1 ± 2.6mm pre-operatively, 2.5 ± 2.2mm at 12 weeks and 2.1 ± 2.3 at two years. Using Cincinnati ratings five rated ‘fair’, five rated ‘good’, and eight rated ‘excellent’. Tibio-femoral contact patterns loaded were not different loaded or unloaded, but medial and lateral compartments of the knee were significantly different (p< 0.001), demonstrating the longitudinal rotation of the knee during flexion, for healthy and injured knees. Pre-operatively the tibio-femoral contact patterns for the ACL injured knee were different to the healthy knee (p=0.014). At 12 weeks post-operatively the tibio-femoral contact patterns were not significantly different (p=0.117), and at two years the contact patterns were restored to those of the healthy knee (p=0.909). However, there were changes to the lateral compartment contact pattern that affected both the ACL injured, reconstructed and healthy knees over the two-year time period. In the healthy knees and also the reconstructed knees the lateral compartment showed less tibio-femoral rollback at two years.

Conclusion: The knee reconstruction restored the tibio-femoral contact pattern to that of the healthy contralateral knee, but both the healthy and reconstructed knees showed changes over time independent of surgery. One or more of the listed authors are receiving or have received benefits or support from a recognised academic body for the pursuance of the study.

Aims. An algorithm to determine the constitutional alignment of the lower limb once arthritic deformity has occurred would be of value when undertaking kinematically aligned total knee arthroplasty (TKA). The purpose of this study was to determine if the arithmetic hip-knee-ankle angle (aHKA) algorithm could estimate the constitutional alignment of the lower limb following development of significant arthritis. Methods. A matched-pairs radiological study was undertaken comparing the aHKA of an osteoarthritic knee (aHKA-OA) with the mechanical HKA of the contralateral normal knee (mHKA-N). Patients with Grade 3 or 4 Kellgren-Lawrence tibiofemoral osteoarthritis in an arthritic knee undergoing TKA and Grade 0 or 1 osteoarthritis in the contralateral normal knee were included. The aHKA algorithm subtracts the lateral distal femoral angle (LDFA) from the medial proximal tibial angle (MPTA) measured on standing long leg radiographs. The primary outcome was the mean of the paired differences in the aHKA-OA and mHKA-N. Secondary outcomes included comparison of sex-based differences and capacity of the aHKA to determine the constitutional alignment based on degree of deformity. Results. A total of 51 radiographs met the inclusion criteria. There was no significant difference between aHKA-OA and mHKA-N, with a mean angular difference of −0.4° (95% SE −0.8° to 0.1°; p = 0.16). There was no significant sex-based difference when comparing aHKA-OA and mHKA-N (mean difference 0.8°; p = 0.11). Knees with deformities of more than 8° had a greater mean difference between aHKA-OA and mHKA-N (1.3°) than those with lesser deformities (-0.1°; p = 0.009). Conclusion. This study supports the arithmetic HKA algorithm for prediction of the constitutional alignment once arthritis has developed. The algorithm has similar accuracy between sexes and greater accuracy with lesser degrees of deformity. Cite this article: Bone Joint Open 2020;1-7:339–345

To clarify the normal range of articular cartilage volumes of the patella and femur in the human knee joints of healthy adults using three-dimensional magnetic resonance imaging and to analyze the correlation of the articular volumes with the background characteristics.

Fifty seven knees of 57 healthy volunteers aged from twenties to forties (30 males and 27 females), who had no past history of joint disease or trauma in the legs, were imaged by a fat-suppressed three-dimensional sequence (SPGR; 1.5T GE; Horizon LX 8.2.5) The obtained data were analyzed by 4 examiners independently with a computer workstation, and a average of the four was adopted as the articular volume. Analyzed characteristics factors of the volunteers were: age, body weight, height, leg length, foot size, circumference of the thigh and lower leg, quadriceps angle, foot angle, body-mass index, and general laxity.

The mean articular cartilage volume was 7.2 +- 1.6 ml. It was significantly larger in males than in females. Concerning the relationship between the volume and the characteristic factors, there was a significant correlation of the cartilage volume with the foot size in males (r=0.47), and with height, leg length and foot size in females (r=0.53, 0.60, 0.60, respectively), but no significant correlation with the other factors.

Conclusion. The articular cartilage volumes of the patella and femur was 7.2+- 1.6 ml. The size of skeletal structure, especially the skeletal size of the lower extremity, were assumed to be important factors in estimating cartilage volume.

Background:. The literature is unclear about the optimal rotation of the femoral component during TKR. Measured resection techniques rely on the use of bony landmarks, while the balanced gap technique relies on soft tissue tensioning to guide the surgeon in rotating the femoral component. All these techniques still result in a wide range of component rotation. We compared the functional flexion axis (FFA) of 20 replaced knees to that of the contralateral normal knee to determine whether a balanced gap technique allowed us to recreate this normal anatomy. Methods:. We reviewed the records of our TKR's from Jan 2008 to Dec 2010 and included all patients who had a normally functioning contralateral knee, tibial cut <3° from perpendicular to the mechanical axis performed by/under supervision of a single surgeon. These patients were contacted for follow up and axial flexed knee x-rays to measure femoral rotation and FFA (angle between clinical transepicondylar line and mechanical axis of tibia). These values were compared between replaced and normal knees using Students T-test. Results:. 20 patients were eligible for the study. Femoral component rotation ranged from 4° internal to 5° external rotation (mean of 0.6° external). Mean difference in functional flexion axis was 3.7°, ranging from 0 to 6° (p<0.05). Conclusion:. The balanced gap technique is effective to restore the functional flexion axis of the replaced knee to that of the normal contralateral side

Background. While posterior cruciate retaining (PCR) implants are a more common total knee arthroplasty (TKA) design, newer bi-cruciate retaining (BCR) TKAs are now being considered as an option for many patients, especially those that are younger. While PCR TKAs remove the ACL, the BCR TKA designs keep both cruciate ligaments intact, as it is believed that the resection of the ACL greatly affects the overall kinematic patterns of TKA designs. Various fluoroscopic studies have focused on determination of kinematics but haven't defined differentiators that affect motion patterns. This research study assesses the importance of the cruciate ligaments and femoral geometry for Bi-Cruciate Retaining (BCR) and Posterior Cruciate Retaining (PCR) TKAs having the same femoral component, compared to the normal knee. Methods. The in vivo 3D kinematics were determined for 40 subjects having a PCR TKA, 10 having a BCR TKA, and 10 having a normal knee, in a retrospective study. All TKA subjects had the same femoral component. All subjects performed a deep knee bend under fluoroscopic surveillance. The kinematics were determined during early flexion (ACL dominant), mid flexion (ACL/PCL transition) and deep flexion (PCL dominant). Results. During the first 30 degrees of flexion, the ACL played an important role, as subjects having a BCR TKA experienced kinematic patterns more similar to the normal knee. During mid flexion, both TKAs experienced random kinematic patterns, which could be due to the ACL and PCL being less active or resected in PCR TKA. In deeper flexion, both TKAs experienced kinematic patterns similar to the normal knee, thus supporting the assumption that the PCL played a dominant role [Fig. 1, Fig. 2]. All three groups generally experienced progressive axial rotation throughout flexion [Fig. 3]. On average, subjects having a PCR TKA experienced 112.3° of flexion, which was greater than the BCR subjects. Conclusions. Both the BCR TKA and normal groups experienced similar kinematic patterns, but the femoral geometrical differences from the anatomical condition may have influenced decreased motion compared to the normal knee. Both TKAs experienced similar kinematic patterns in deeper flexion, with the PCR TKA experiencing excellent weight-bearing flexion. Results from this study suggest that the cruciate ligaments can play a role in kinematics, but femoral geometry working with the ligaments may be an option to consider