There have been a large number of studies reporting the knee joint force during level walking, however, the data of during deep knee flexion are scarce, and especially the data about patellofemoral joint force are lacking. Deep knee flexion is a important motion in Japan and some regions of Asia and Arab, because there are the lifestyle of sitting down and lying on the floor directly. Such data is necessary for designing and evaluating the new type of knee prosthesis which can flex deeply. Therefore we estimated the patellofemoral and tibiofemoral forces in deep knee flexion by using the masculoskeltal model of the lower limb. The model for the calculation was constructed by open chain of three bar link mechanism, and each link stood for thigh, lower leg and foot. And six muscles, gluteus maximus, hamstrings, rectus, vastus, gastrocnemius and soleus were modeled as the lines connecting the both end of insertion, which apply tensile force at the insertion on the links. And the model also included the gravity forces, thigh-calf contact forces on the Inputting the data of floor reacting forces and joint angles, the model calculated the muscle forces by the moment equilibrium conditions around each joint, and some assumptions about the ratio of the biarticular muscles. And then, the joint forces were estimated from the muscle forces, using the force equilibrium conditions on patella and tibia. The position/orientation of each segments, femur, patella and tibia, were decided by referring the literature. The motion to be analyzed was standing up from kneeling posture. The joint angles during the motion are shown in Fig.1. This motion included the motion from kneeling to squatting, rising the knee from the floor by flexing hip joint, and the motion from squatting to standing. The test subject was a healthy male, age 23[years], height 1.7[m], weight 65[kgw]. Results were shown in Fig.2. The patellofemoral force was little at standing posture, the end of the motion, however, was as large as tibiofemoral force during the knee joint angle was over 130 degrees. The reason of this was that the patellofemoral joint force was heavily dependent on the quadriceps forces, and the quadriceps tensile force was large at deep knee flexion, at kneeling or squatting posture. The maximum tibiofemoral force was 3.5[BW] at the beginning of standing up from squatting posture. And the maximum patellofemoral force was 3.8[BW] at the motion from kneeling to squatting posture. The conclusion was that the patellofemoral joint force might not be ignored in deep knee flexion and the design of the knee prosthesis should be include the strength design of patellofemoral joint

Introduction. High-flexion knee implants have been developed to accommodate a large range of motion (ROM > 120°) after total knee arthroplasty (TKA). In a recent follow-up study, Han et al. [1] reported a disturbingly high incidence of femoral loosening for high-flexion TKA. The femoral component loosened particularly at the implant-cement interface. Highly flexed knee implants may be more sensitive to femoral loosening as the knee load is high during deep knee flexion [2], which may result in increased tensile and/or shear stresses at the femoral implant fixation. The objective of this study was to analyse the load-transfer mechanism at the femoral implant-cement interface during deep knee flexion (ROM = 155°). For this purpose, a three-dimensional finite element (FE) knee model was developed including high-flexion TKA components. Zero-thickness cohesive elements were used to model the femoral implant-cement interface. The research questions addressed in this study were whether high-flexion leads to an increased tensile and/or shear stress at the femoral implant-cement interface and whether this would lead to an increased risk of femoral loosening. Materials & methods. The FE knee model utilized in this study has been described previously [3] and consisted of a proximal tibia and fibula, TKA components, a quadriceps and patella tendon and a non-resurfaced patella. For use in this study, the distal femur was integrated in the FE model including cohesive interface elements and a 1 mm bone cement layer. High-flexion TKA components of the posterior-stabilised PFC Sigma RP-F (DePuy, J&J, USA) were incorporated in the FE knee model following the surgical procedure provided by the manufacturer. A full weight-bearing squatting cycle was simulated (ROM = 50°-155°). The interface stresses calculated by the FE knee model were decomposed into tension, compression and shear components. The strength of the femoral implant-cement interface was determined experimentally using interface specimens to predict whether a local interface stress-state calculated by the FE knee model would lead to interface debonding. Results. During deep knee flexion, tensile stress concentrations were found at the femoral implant-cement interface particularly beneath the anterior flange. Shear stress concentrations were observed at the interface beneath the anterior flange and the posterior femoral condyles. The peak tensile interface stress increased from 1.6 MPa at 120° of flexion to 5.5 MPa during deep knee flexion at the interface beneath the anterior flange. The peak shear stress was even higher at this interface location and increased from 4.1 MPa at 120° of flexion to 11.0 MPa at maximal flexion (155°). Based on the interface strength experiments, 5.8% of the interface beneath the anterior flange was predicted to debond at 120° of flexion, which increased to 10.8% during deep knee flexion. Discussion. Obviously, the FE knee model utilized in this study contains limitations which may have affected the interface stresses calculated. However, the results presented here clearly demonstrate increasing tensile and shear stresses in substantial parts of the femoral implant-cement beneath the anterior flange during deep knee flexion. Based on the interface strength experiments the anterior interfacial stress-state calculated by the FE knee model leads to local interface debonding during deep knee flexion, which increases the risk of femoral loosening. Proper anterior fixation of the femoral component is essential to reduce the risk of femoral loosening for high-flexion TKA

Introduction:. One of the important factors for success in TKA is to achieve proper stability of the knee joint. It is currently unknown that how much joint laxity exists in mid-range to deep knee flexion, postoperatively. We hypothesized that retaining the PCL or not during TKA has an influence on the postoperative joint laxity from mid-range to deep knee flexion. The purpose of this study was to investigate the postoperative coronal joint laxity throughout the full range of motion by the 3-dimensional in vivo analysis, both in PS and CR TKA. Methods:. We implanted 5 knees with a PS TKA using a NexGen LPS-flex and 5 knees with a CR TKA using a NexGen CR-flex. All of them were the osteoarthritis patients. We performed all operations with a measured resection technique. Four weeks after TKA, the valgus- and varus-stress radiographic assessments were performed at the five flexion angles from full extension to maximum flexion. The patients sat on the radiolucent chair with their lower legs hanging down. The examiner held their thigh, and a force of 50N was applied 30 cm distal to the tibiofemoral joint. The series of static fluoroscopic images via a flat panel detector were stored digitally. A 3-dimentional to 2-dimentional techniqueusing an automated shape-matching algorithm was employed to determine the relative 3-dimentional positions of the femoral component and tibial component in each fluoroscopic image (KneeMotion; LEXI, Tokyo). On the coronal plane of the tibial component, the angle between the tangent line of the condyles of the femoral component and the tibial plateau was measured as the joint laxity for valgus (α valgus) or varus (α varus). The flexion angle between the femoral component and tibial component was also measured. Results:. The total laxity (α valgus + α varus) tended to increase until deep knee flexion in PS TKA. While in CR TKA, the total laxity tended to increase until mid-range of knee flexion and then decreased until maximum flexion (Fig. 1). PS TKA: In varus stress, the mean tilting angles were 2.4, 3.6, 3.6, 4.1, 5.4 degrees at −2.3, 25.3, 42.2, 72.1, 97.1 degrees of knee flexion, respectively. The tilting angle measured at maximum flexion was significantly larger than that measured at full extension (p < 0.05) (Fig. 2). CR TKA: In valgus stress, the mean tilting angles were 0.8, 2.8, 2.8, 2.0, 0.6 degrees at −6.4, 24.1, 35.8, 67.7, 87.8 degrees of knee flexion, respectively. The tilting angles measured at full extension and maximum flexion were significantly smaller than that measured at 24.1 and 35.8 degrees of knee flexion (p < 0.05) (Fig. 3). Discussion:. In PS TKA, joint laxity for varus at maximum flexion was significantly larger than that at full extension. While in CR TKA, joint laxity for varus indicated no significant differences among at each flexion angle. Moreover, joint laxity for valgus at full extension and maximum flexion were significantly smaller than that at mid-range flexion in CR TKA. Retaining the PCL during TKA has a strong influence on the postoperative coronal joint laxity especially in deep knee flexion

The objective of this study is to introduce the forces acting on the knee joint while ascending from kneeling. Our research group has developed a new type of knee prosthesis which is capable of attaining complete deep knee flexion such as a Japanese style sitting, seiza. Yet we could not set up various kinds of simulation or experiment to assess the performance of our prosthesis because the data about joints' forces during the ascent from deep knee flexion are lacking. Considering this circumstance, we created a 2D mathematical model of lower limb and determined knee joint force during ascent from kneeling to apply them for the assessment of our prosthesis. Ten male and five female healthy subjects participated in the measurement experiment. Although the measurement of subjects' physical parameters was non-invasive and direct, some parameters had to be determined by referring to the literature. The data of ground reaction force and each joint's angle during the motion were collected using a force plate and video recording system respectively. Then the muscle forces and the joints' forces were calculated through our mathematical model. In order to verify the validity of our model approach, we first introduced the data during the activities with small/middle knee flexion such as level walking and rising from a chair; these kinds of data are available in the literature. Then we found our results were in good agreement with the literature data. Next, we introduced the data during the activities with deep knee flexion; double leg ascent [Fig.1 (a)] and single leg ascent [Fig.1 (b)] from kneeling without using the upper limbs. The statistics of the maximum values on the single knee joint for all the subjects were; during double leg ascent, Fmax = 4.6±0.6 (4.3-5.2) [BW: (force on the knee joint)/(body weight)] at knee flexion angle of b =140±8 (134-147)°, during double leg ascent, Fmax = 4.9±0.5 (4.0-5.6) [BW] at b = 62±33 (28-110)° for the dominant leg, and Fmax = 3.0±0.5 (22.2-3.8) [BW] at b = 138±6 (130-150)° for the supporting leg respectively. We found that the moment arm length, i.e., the location of muscle insertion significantly affected the results, while ascending speeds did not affect the results much. We may conclude that the single leg ascent should be recommended since Fmaxdid not become large while deep knee flexion. The values could be used for assessing the strength of our knee prosthesis from the risk analysis view point

Many recent knee prostheses are designed aiming to the physiological knee kinematics on tibiofemoral joint, which means the femoral rollback and medial pivot motion. However, there have been few studies how to design a patellar component. Since patella and tibia are connected by a patellar tendon, tibiofemoral and patellofemoral motion or contact forces might affect each other. In this study, we aimed to discuss the optimal design of patellar component and simulated the knee flexion using four types of patellar shape during deep knee flexion. Our simulation model calculates the position/orientation, contact points and contact forces by inputting knee flexion angle, muscle forces and external forces. It can be separated into patellofemoral and tibiofemoral joints. On each joint, calculations are performed using the condition of point contact and force/moment equilibrium. First, patellofemoral was calculated and output patellar tendon force, and tibiofemoral was calculated with patellar tendon force as external force. Then patellofemoral was calculated again, and the calculation was repeated until the position/orientation of tibia converged. We tried four types of patellar shape, circular dome, cylinder, plate and anatomical. Femoral and tibial surfaces are created from Scorpio NRG PS (Stryker Co.). Condition of knee flexion was passive, with constant muscle forces and varying external force acting on tibia. Knee flexion angle was from 80 to 150 degrees. As a result, the internal rotation of tibia varied much by using anatomical or plate patella than dome or cylinder shape. Although patellar contact force did not change much, tibial contact balances were better on dome and cylinder patella and the medial contact forces were larger than lateral on anatomical and plate patella. Thus, the results could be divided into two types, dome/cylinder and plate/anatomical. It might be caused by the variations of patellar rotation angle were large on anatomical and plate patella, though patellar tilt angles were similar in all the cases. We have already reported that the anatomical shape of patella would contact in good medial-lateral balance when tibia moved physiologically, therefore we have predicted the anatomical patella might facilitate the physiological tibiofemoral motion. However, the results were not as we predicted. Actually our previous and this study are not in the same condition; we used a posterior-stabilized type of prosthesis, and the post and cam mechanism could not make the femur roll back during deep knee flexion. It might be better to choose dome or cylinder patella to obtain the stability of tibiofemoral joint, and to choose anatomical or plate to the mobility

Total knee arthroplasty has been the main treatment method among advanced osteoarthritis (OA) patients. The main post-operative evaluation considers the level of pain, stability and range of motion (ROM). The knee flexion level is one of the most important categories in the total knee arthroplasty patient's satisfaction in Asian countries due to consistent habits of floor-sitting, squating, kneeling and cross legged sitting. In this study, we discovered that the posterior capsular release enabled the further flexion angles by 14 degrees compared to the average ROM without posterior release group. Our objective was to increase the ROM using the conventional total knee arthroplasty by the posterior capsular release. Posterior capsular release is being used in order to manage the flexion contraction. Although the high flexion method extends the contact area during flexion by extending the posterior condyle by 2mm, the main problem has been the early femoral loosening. We searched for the method to get the deep knee flexion with the conventional knee prosthesis. 122 OA patients with less than preoperative 130 flexion that underwent conventional TKAs using Nexgen from January, 2014 to September, 2016 were reviewed. Posterior femoral osteophytes were removed as much as possible, but 74 cases were performed posterior capsular release, while 48 cases were not performed. After checking postoperative ROM after 6 months of operation, we compared 74 knees with a posterior capsular release and 48 knees without posterior capsular release. As a result, the average ROM in the posterior capsular release group was 132 degrees, but the average ROM without posterior release group is 118 degrees. No postoperative hyperextension was found when the adequate size of polyethylene (PE) thickness was utilized. Hence, the conventional TKA with a posterior capsular release showed satisfactory clinical outcomes in the deep knee flexion of Asians

Introduction. MERA Quest Knee System (Quest Knee) is a posterior cruciate ligament–retaining prosthesis considering the anatomical features and lifestyles of the Japanese. As for the anatomical features, we reduced the size of prosthesis and set a smaller interval of sizes because Japanese knees are smaller and flatter than those of Caucasians. As for the lifestyles, we evaluated in vivo patellar tracking during deep knee flexion and the condylar geometry in the axial plane of magnetic resonance imaging. It was found that the patella sank deeply into the intercondylar notch and that the articular surface of the lateral condyle began to curve steeply. We adopted this shape and engraved the lateral condyle deep to reduce the pressure of the patellofemoral joint and to get better range of motion (ROM). For the contact pressure rise in the femorotibial joint by engraving the lateral condyle, the insert was suited to the shape of the femoral component. Furthermore, we increased the thickness of the posterior flange of the femoral component and changed the posterior radius of curvature gradually, and this shape allowed the flexion of 155°. We have used Quest Knee for clinical applications from October 2009. We studied the short-term results of Quest Knee. Methods. Between June 2010 and July 2013, the same senior surgeon performed 59 consecutive primary operations with Quest Knee. Forty patients (44 knees) were women, and 14 patients (15 knees) were men. The mean patient age was 72.5 years (range, 59–89 years). All were osteoarthritis knees. Coronal deformity was varus in 58 knees and valgus in one knee. All operations were performed with a measured resection technique, and all patellae were resurfaced. Clinical evaluations were assessed using the Japanese Orthopaedic Association knee rating score (JOA score), and clinical ROM and standing femorotibial angle (FTA) were measured. Additionally, three-dimensional motion analysis of the patellar component during squatting was performed by the image matching method with image correlations. Results. The mean follow-up period was 17.4 months (range, 6–43 months). The JOA score at preoperative and follow-up were 57.5 ± 10.1 and 87.5 ± 5.6 points, respectively (P < 0.0001) (Fig. 1). The ROM at preoperative and follow-up were 127.4 ± 11.1 and 126.2 ± 9.0° (P = 0.47) (Fig. 2). The mean FTA at preoperative and follow-up were 184.2 and 172.3°. With regard to the three-dimensional motion analysis, the patella showed lateral shift during squatting (Fig. 3). Discussion. As for the patellofemoral contact pressure at flexion in total knee arthroplasty, a biomechanical study has reported that the pressures of posterior cruciate ligament–retaining and posterior-stabilized knees were 3.2 and 2.8 times as much as the body weight. This report suggests that the reduction of the pressure of the patellofemoral joint during deep knee flexion results in better ROM. We suppose that Quest Knee reduced the pressure, led the patella to the lateral side, and achieved better ROM. Conclusions. Short-term results of Quest Knee were good. More detailed studies are needed to get better function and long-term durability

Background. Various postoperative evaluations using fluoroscopy have reported in vivo knee flexion kinematics under weight bearing conditions. This method has been used to investigate which design features are more important for restoring normal knee function. The objective of this study is to evaluate the kinematics of a Posterior-Stabilized TKA in weight bearing deep knee flexion using 2D/3D registration technique. Patients and methods. We investigated the in vivo knee kinematics of 9 knees (9 patients) implanted with a Posterior Stabilized TKA (Triathlon PS, Stlyker Orthopedics, Mahwah, NJ). Under fluoroscopic surveillance, each patient did a deep knee flexion under weight-bearing condition. Femorotibial motion including tibial polyethylene insert were analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the knee flexion angle, femoral axial rotation, antero-posterior translation of contact points, and post-cam engagement were evaluated. Results. The mean maximum flexion angle was 121.0±9.5°. The amount of femoral axial rotation was 7.5±1.5°. The femorotibial contact point moved posterior㣣4.9±4.5mm on medial compartment, 10.0±3.3mm on lateral compartment with knee flexion. The mean knee flexion angle at initial post-cam engagement was 47.5±17.2°. The kinematic pattern was medial pivot. Discussion. The contact point constantly moved backward especially on the lateral side. At early flexion, both the medial and lateral contact point moved posteriorly, which might be caused by a change in sagittal radius at 10° flexion. The post-cam engagement occurred at midflexion, that might prevent the paradoxical anterior translation of the femur with respect to tibia during knee flexion

Background. The anatomy of the human knee is very different than the tibiofemoral surface geometry of most modern total knee replacements (TKRs). Many TKRs are designed with simplified articulating surfaces that are mediolaterally symmetrical, resulting in non-natural patterns of motion of the knee joint [1]. Recent orthopaedic trends portray a shift away from basic tibiofemoral geometry towards designs which better replicate natural knee kinematics by adding constraint to the medial condyle and decreasing constraint on the lateral condyle [2]. A recent design concept has paired this theory with the concept of guided kinematic motion throughout the flexion range [3]. The purpose of this study was to validate the kinematic pattern of motion of the surface-guided knee concept through in vitro, mechanical testing. Methods. Prototypes of the surface-guided knee implant were manufactured using cobalt chromium alloy (femoral component) and ultra-high molecular weight polyethylene (tibial component). The prototypes were installed in a force-controlled knee wear simulator (AMTI, Watertown, MA) to assess kinematic behavior of the tibiofemoral articulation (Figure 1). Axial joint load and knee flexion experienced during lunging and squatting exercises were extracted from literature and used as the primary inputs for the test. Anteroposterior and internal-external rotation of the implant components were left unconstrained so as to be passively driven by the tibiofemoral surface geometry. One hundred cycles of each exercise were performed on the simulator at 0.33 Hz using diluted bovine calf serum as the articular surface lubricant. Component motion and reaction force outputs were collected from the knee simulator and compared against the kinematic targets of the design in order to validate the surface-guided knee concept. Results. Under deep flexion conditions of up to 140° of squatting the surface-guided knee implants were found to undergo a maximum of 22.2° of tibial internal rotation and 20.4 mm of posterior rollback on the lateral condyle. Pivoting of the knee joint was centered about the highly congruent medial condyle which experienced only 1.6 mm of posterior rollback. Experimental results were within 2° (internal-external rotation) and 1 mm (anteroposterior translation) agreement with the design target throughout the applied exercises (Figure 2). Conclusion. The results of this test confirm that by combining a constrained medial condyle with guiding geometry on the lateral condyle, deep knee flexion activities of up to 140° can be performed while maintaining near-natural kinematics of the knee joint. The authors believe that the tested surface-guided implant concept is a significant step toward the development of novel TKR which allows a greater range of motion and could improve the quality of life for active patients undergoing knee replacement. For any figures or tables, please contact the authors directly

Background. The decision to choose CR (cruciate retaining) insert or CS (condylar stabilized) insert during TKA remains a controversial issue. Triathlon CS type has a condylar stabilized insert with an increased anterior lip that can be used in cases where the PCL is sacrificed but a PS insert is not used. The difference of the knee kinematics remains unclear. This study measured knee kinematics of deep knee flexion under load in two insert designs using 2D/3D registration technique. Materials and methods. Five fresh-frozen cadaver lower extremity specimens were surgically implanted with Triathlon CR components (Stryker Orthopedics, Mahwah, NJ). CR insert with retaining posterior cruciate ligament were measured firstly, and then CS insert after sacrificing posterior cruciate ligament were measured. Under fluoroscopic surveillance, the knees were mounted in a dynamic quadriceps-driven closed-kinetic chain knee simulator based on the Oxford knee rig design. The data of every 10° knee flexion between 0° and 140° were corrected. Femorotibial motion including tibial polyethylene insert were analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the knee flexion angle, femoral axial rotation, and anteroposterior translation of contact points. Results. The amount of femoral axial rotation from 0° flexion to 140° flexion was 11.0±3.6° in CR insert, and 9.4±4.3° in CS insert, respectively. In CR insert, the medial contact point moved 6.3±3.8 mm anteriorly from 30° to 100° flexion, and then moved 7.6±6.4 mm posteriorly from 100° to maximum flexion. The lateral contact point moved 4.0±4.1 mm anteriorly from 30° to 90° flexion, and then moved 8.2±9.7 mm posteriorly from 90° to maximum flexion. In CS insert, the medial contact point moved 5.2±3.5 mm anteriorly from 30°to 120° flexion, and then moved 3.3±1.1 mm posteriorly from 120° to maximum flexion. The lateral contact point moved 2.7±2.2 mm anteriorly from 30° to 110° flexion, and then moved 6.4±2.0 mm posteriorly from 110° to maximum flexion. No significant differences were observed in the amount of posterior translation between the two insert. Discussion. Triathlon CR and CS insert had a similar kinematics pattern. However, there are some limitations in this study. The deep knee flexion motion was studied in a quasi-static fashion. Additionally, the component positions and rotations were not known relative to the femoral and tibial bones

Background. Various postoperative evaluations using fluoroscopy have reported in vivo knee flexion kinematics under weight bearing conditions. This method has been used to investigate which design features are more important for restoring normal knee function. The objective of this study is to evaluate the kinematics of a Low Contact Stress total knee arthroplasty (LCS TKA) in weight bearing deep knee flexion using 2D/3D registration technique. Patients and methods. We investigated the in vivo knee kinematics of 6 knees (4 patients) implanted with the LCS meniscal bearing TKA (LCS Mobile-Bearing Knee System, Depuy, Warsaw, IN). Mean period between operation and surveillance was 170.7±14.2 months. Under fluoroscopic surveillance, each patient did a deep knee flexion under weight-bearing condition. Femorotibial motion was analyzed using 2D/3D registration technique, which uses computer-assisted design (CAD) models to reproduce the spatial position of the femoral, tibial components from single-view fluoroscopic images. We evaluated the knee flexion angle, femoral axial rotation, and antero-posterior translation of contact positions. Results. The mean maximum knee flexion angle was 109.3±9.1°. The mean axial rotation of the femoral component exhibited gradual external rotation from full extension to maximum flexion reaching 9.4±5.9°. At full extension, the medial contact position was −3.7±2.9 mm, and the lateral contact position was −4.4±4.7 mm. The medial contact position moved 2.1 mm anteriorly from full extension to 80° of knee flexion, and then moved 0.4 mm posteriorly until maximum flexion. On the other hand, the lateral contact position stayed constant from full extension to 80° of knee flexion, and then moved 2.3 mm posteriorly until maximum flexion. At maximum flexion, the medial contact position moved anteriorly to a final position of 1.3±4.0 mm and the lateral contact position moved posteriorly to a final position of −6.8±3.8 mm. From the results of bilateral contact positions at each flexion angle, patterns of kinematic pathways were determined. From full extension to 80° of knee flexion, the kinematic pattern was a lateral pivot pattern, where the medial contact position kept moving forward while the lateral contact position remained constant. With more than 80° of knee flexion, kinematics changed into a medial pivot pattern. Discussion. This study has investigated the kinematics of a LCS meniscal bearing TKA. The typical subjects exhibited a lateral pivot pattern from full extension to 80° of knee flexion, that are not usually observed in normal knees. It might be caused by the geometry of replaced articular surfaces and the mobility of the meniscal-bearing insert. Further investigation should be necessary in more number of cases not only in this implant but also in other types of LCS

Introduction. There are over ½ million total knee replacement (TKR) procedures performed each year in the United States and is projected to increase to over 3.48 million by 2030. Concurrent with the increase in TKR procedures is a trend of younger patients receiving knee implants (under the age of 65). These younger patients are known to have a 5% lower implant survival rate at 8 years post-op compared to older patients (65+ years), and they are also known to live more active lifestyles that place higher demands on the durability and functional performance of the TKR device. Conventional TKR designs increase articular conformity to increase stability, but these articular constraints decrease patient range of knee motion, often limiting key measures of femoral rollback, A/P motion, and deep knee flexion. Without this articular constraint however, many patients report TKR “instability” during activities such as walking and stair descent, which can significantly impede confidence of movement. Therefore, there is a need for a TKR system that can offer enhanced stability while also maintaining active ranges of motion. Materials and Methods. A novel knee arthroplasty system has been designed that uses synthetic ligament systems that can be surgically replaced, to provide ligamentous stability and natural motion to increase the functional performance of the implant. A computational anatomical model (AnyBody) was developed that incorporated ligaments into an existing Journey II TKR. Ligaments were modeled and given biomechanical properties from literature. Simulated A/P drawer tests and knee flexion were analyzed for 2,916 possible cruciate ligament location and length combinations to determine the effects on the A/P stability of the TKR. A physical model was then constructed, and the design was verified by performing 110 N A/P drawer tests under 710 N of simulated body weight. Results and Discussion. As ACL insertion location moved posteriorly on the femur, it was found to decrease ACL ligament strain, enabling a higher range of flexion. In general, as ACL and PCL length increased, the A/P laxity of the TKR system increased linearly. Range of motion was found to be more dependent on ligament attachment location, and laxity was more dependent on ligament length. In this work, TKR stability was clearly affected by changes in synthetic ligament length and location. When comparing the laxity between a TKR with and without ligaments, the TKR with synthetic ligaments experienced significantly less displacement than a TKR without synthetic ligaments. Conclusions. The stability of a TKR can be increased while maintaining range of motion by incorporating synthetic ligaments into its design. The effectiveness of the ligaments was clearly dependent on two factors: length and location. It is imperative to the success of the implant to obtain the correct lengths and locations because improper placement or length can impact the outcome significantly. These results emphasize the need for a knee replacement that incorporates synthetic ligaments, with calibrated location and lengths, to significantly influence stability and possible kinematic performance of the TKR system, and potentially influencing long-term functional outcomes

The Magna ROM 21 knee prosthesis was designed in 1994 to match the anatomical characteristics of the Japanese knee and achieve deep knee flexion to suit Japanese lifestyles. The prosthesis has a smaller anteroposterior mediolateral diameter ratio for the femur and tibia than do knees designed in the United States. The purpose of this study was to review the clinical results of the first 159 arthroplasties performed with this prosthesis in order to asses whether this cementless implant had achieved its design objectives. 159 knees were followed for 12.6 to 14.0 years (mean, 13.4 years). Preoperatively the mean The Knee Society knee score and function score were 24.9 and 27.5 points; postoperatively they were 94.6 and 83.8 points. The mean preoperative and postoperative ranges were 106 and 118 degrees, respectively. Total knee arthroplasty with the Magna ROM 21 resulted in an excellent range of motion and a high level of satisfaction wth the operation

Introduction. There are over one-half million total knee replacement (TKR) procedures performed each year in the United States and is projected to increase to over 3.48 million by 2030. Concurrent with the increase in TKR procedures is a trend of younger patients receiving knee implants (under the age of 65). These younger patients are known to have a 5% lower implant survival rate at 8 years post-op compared to older patients (65+ years), and they are also known to live more active lifestyles that place higher demands on the durability and functional performance of the TKR device. Conventional TKR designs increase articular conformity to increase stability, but these articular constraints decrease patient range of knee motion, often limiting key measures of femoral rollback, A/P motion, and deep knee flexion. Without this articular constraint however, many patients report TKR “instability” during activities such as walking and stair descent, which can significantly impede confidence of movement. Therefore there is a need for a TKR system that can offer enhanced stability while also maintaining active ranges of motion. Materials and Methods. A novel knee arthroplasty system was designed that uses synthetic ligament systems that can be surgically replaced, to provide ligamentous stability and natural motion to increase the functional performance of the implant. Using an anatomical knee model from the AnyBody software, a computational model that incorporated ligaments into an existing Journey II TKR was developed. Using the software ligaments were modeled and given biomechanical properties developed from equations from literature. Simulated A/P drawer tests and knee flexion test were analyzed for 2,916 possible cruciate ligament location and length combinations to determine the effects on the A/P stability of the TKR. A physical model was constructed, and the design was verified by performing 110 N A/P drawer tests under 710 N of simulated body weight. Results and Discussion. As ACL insertion location moved posteriorly on the femur, it was found to decrease ACL ligament strain, enabling a higher range of flexion. In general, as ACL and PCL length increased, the A/P laxity of the TKR system increased linearly. Range of motion was found to be more dependent on ligament attachment location, and laxity was more dependent on ligament length. In this work, TKR stability was clearly affected by changes in synthetic ligament length and location. When comparing the laxity between a TKR with and without ligaments, the TKR with synthetic ligaments experienced significantly less displacement than a TKR without synthetic ligaments as seen in Figure 1. Conclusions. This study shows that the stability of a TKR can be increased while maintaining range of motion by incorporating synthetic ligaments into this design. The effectiveness of the ligaments was clearly dependent on two factors: length and location, with incorrect lengths and locations significantly impairing ranges of motion. These results verify that a knee replacement can incorporate synthetic ligaments, and that with calibrated location and lengths, they can significantly influence stability and possible kinematic performance of the TKR system, and potentially influencing long-term functional outcomes. For any figures or tables, please contact the authors directly

Thigh-calf contact force is the force acting on posterior side of the thigh and calf during deep knee flexion. It has been reported the force is important to analyze the kinetics of a lower limb and a knee joint. Some previous researches reported the measured thigh-calf contact force, however, the values varied among the reports. Furthermore, the reports indicated that there were large variations even in a single report. One of the reports tried to find the relationship between the magnitude of thigh-calf contact force and anthropometric measurement as height, weight or perimeter of the lower limb, however, there could not found clear correlations. We considered that the cause of the variations might be the difference of the posture. At heel-rise squatting posture, we can bend or stand upright the upper body. Therefore we tried to create the equation to estimate the thigh-calf contact force by multiple regression analysis, using the anthropometric and posture parameters as explanatory variables. We performed the experiment to measure thigh-calf contact force, joint angles and anthropometric information. Test subjects were 10 healthy male. First we measured their height, weight, perimeter of the thigh and muscle mass of the legs and whole body. Muscle mass was measured by body composition meter (BC-118E, Tanita Co., Japan). Then, test subjects were asked to squat with their heels lifted and with putting the pressure distribution sensor between thigh and calf. And they bent their upper body forward and backward. The pressure sensor to be used was ConfroMat System (Nitta Co., Japan). After that, we measured the joint angles of the hip, knee and ankle, and the angle between the floor and upper body using the videos taken during the experiment. Then, we created the equation to estimate the thigh-calf contact force by linear combination of the anthropometric values and joint angles. The coefficients were settled as to minimize the average error between measured and estimated values. Results are shown in Fig.1. Forces were normalized by the body weight of the test subjects. Because the horizontal axes show the measured and vertical axis show the estimated values, the estimation is accurate when the plots are near the 45-degree line. Average error was 0.11BW by using only physical values, 0.15BW by angles and 0.06BW using both values. And the maximum error was 0.69BW, 0.43BW and 0.32BW respectively. Thus we could estimate the thigh-calf contact force by multiple regressions, using both physical parameters and angles to indicate the posture. Using the equation, we would be able to analyze the kinetics of a lower limb by physical and motion measurement. Our future work might be increasing the number of subjects to consider the appropriateness, because the test subjects of this study were very limited

Background. The patterns and magnitudes of axial femorotibial rotation are variable due to the prosthesis design, ligamentous balancing, and surgical procedures. LCS mobile-bearing TKA has been reported the good clinical results, however, knee kinematics has not been fully understood. Therefore, we aimed to investigate the effects of the weight-bearing (WB) condition on the kinematics of mobile-bearing total knee arthroplasty (TKA). Methods. We examined 12 patients (19 knees) implanted with a low contact stress (LCS) mobile-bearing TKA system using a two- to three-dimensional registration technique as previously reported [1]. All 12 patients were diagnosed with medial knee osteoarthritis. The in vivo kinematics of dynamic deep knee flexion under WB and non-WB (NWB) conditions were compared. We evaluated the knee range of motion, femoral axial rotation relative to the tibial component, anteroposterior translation, and kinematic pathway of the femorotibial contact point for both the medial and lateral sides. Results. Under the WB condition, the mean range of motion was 117.8° ± 16.7°. Under the NWB condition, the mean range of motion was 111.0° ± 4.4°. No significant difference in this value was apparent between the 2 conditions. The mean range of axial rotation from full extension to maximum flexion was 3.0° ± 1.5° under the WB condition and 2.2° ± 1.0° under the NWB condition. No significant difference in this value was apparent between the 2 conditions. With regard to the anteroposterior translation, the LCS mobile-bearing TKA system showed the same kinematic patterns under both conditions, except for axial rotation at 0°, 10°, and 110°. From hyperextension to maximum flexion, the kinematic pattern reflected a central pivot under both conditions (Figure 1). Conclusions. In conclusion, this study demonstrated that, in an LCS mobile-bearing TKA system, knee kinematics showed the same patterns under NWB and WB conditions, except for axial rotation at the early phase. Further understanding of knee kinematics could provide us with useful information for future design concepts of TKA implants

Introduction. Malrotation of the tibial component would lead to various complications after total knee arthroplasty (TKA) such as improper joint kinematics, patellofemoral instability, or excessive wear of polyethylene. However, despite reports of internal rotation of the tibial component being associated with more severe pain or stiffness than external rotation, the biomechanical reasons remain largely unknown. In this study, we used a musculoskeletal computer model to simulate a squat (0°–130°–0° flexion) and analyzed the effects of malrotated tibial component on lateral and medial collateral ligament (LCL and MCL) tensions, tibiofemoral and patellofemoral contact stresses, during the weight-bearing deep knee flexion. Materials and Methods. A musculoskeletal model, replicating the dynamic quadriceps-driven weight-bearing knee flexion in previous cadaver studies, was simulated with a posterior cruciate-retaining TKA. The model included tibiofemoral and patellofemoral contact, passive soft tissue and active muscle elements. The soft tissues were modeled as nonlinear springs using previously reported stiffness parameters, and the bony attachments were also scaled to some cadaver reports. The neutral rotational alignment of the femoral and tibial components was aligned according to the femoral epicondylar axis and the tibial anteroposterior axis, respectively. Knee kinematics and ligament tensions were computed during a squat for malrotated conditions of the tibial component. The tibial rotational alignments were changed from 15° external rotation to 15° internal rotation in 5° increments. The MCL and LCL tensions, the tibiofemoral and patellofemoral contact stresses were compared among the knees with different rotational alignment. Results. For the MCL, the neutral rotated tibial components caused a maximum tension of 67.3 N. However, the 15° internally rotated tibial components increased tensions to 285.2N as a maximum tension [Fig.1]. By contrast, with external rotation of the tibial component, the MCL tensions increased only a small amount. The LCL tension also increased but up to less than half of the MCL value [Fig.2]. The tibiofemoral and patellofemoral contact stresses increased because of a decreased contact area [Fig.3]. Discussion and Conclusion: In this computer simulation, excessive internal rotation in the tibial component increased MCL tensions and patellofemoral and tibiofemoral contact stresses. The current study suggests that increased MCL tensions and patellofemoral and tibiofemoral contact stresses caused by a malrotated tibial component could be one cause of patient complaints and polyethylene problems after TKA

Previously more femoral rollback has been reported in posterior-stabilized implants, but so far the kinematic change after post-cam engagement has been still unknown. The tri-condylar implants were developed to fit a life style requiring frequent deep flexion activities, which have the ball and socket third condyle as post-cam mechanism. The purpose of the current study was to examine the kinematic effects of the ball and socket third condyle during deep knee flexion. The tri-condylar implant analyzed in the current study is the Bi-Surface Knee System developed by Kyocera Medical (Osaka, Japan). Seventeen knees implanted with a tri-condylar implant were analyzed using 3D to 2D registration approach. Each patient was asked to perform a weight-bearing deep knee bend from full extension to maximum flexion under fluoroscopic surveillance. During this activity, individual fluoroscopic video frames were digitized at 10°increments of knee flexion. A distance of less than 1 mm initially was considered to signify the ball and socket contact. The translation rate as well as the amount of translation of medial and lateral AP contact points and the axial rotation was compared before and after the ball and socket joint contact. The average angle of ball and socket joint contact were 64.7° (SD = 8.7), in which no separation was observed after initial contact. The medial contact position stayed from full extension to ball and socket joint contact and then moved posteriorly with knee flexion. The lateral contact position showed posterior translation from full extension to ball and socket joint contact, and then greater posterior translation after contact (Figure 1). Translation and translation rate of contact positions were significantly greater at both condyles after ball and socket joint contact. The femoral component rotated externally from full extension to ball and socket joint contact, and then remained after ball and socket joint contact (Figure 2). There was no statistical significance in the angular rotation between ball and socket joint contact and maximum flexion. Translation of angular rotation was significantly greater before ball and socket joint contact, however, there was no significance in translation rate before and after ball and socket joint contact. The ball and socket joint was proved to induce posterior rollback intensively. In terms of axial rotation, the ball and socket joint did not induce reverse rotation, but had slightly negative effects after contact. The ball and socket provided enough functions as a posterior stabilizing post-cam mechanism and did not prevent axial rotation

Introduction. Recent advances in 3D printing enable the use of custom patient-specific instruments to place drill guides and cutting slots for knee replacement surgery. However, such techniques limit the ability to intra-operatively adjust an implant plan based on soft-tissue tension and/or joint pathology observed in the operating room, e.g. cruciate ligament integrity. It is hypothesized that given the opportunity, a skilled surgeon will make intra-operative adjustments based on intra-operative information not captured by the hard tissue anatomy reconstructed from a pre-operative CT scan or standing x-ray. For example, tibiofemoral implant gaps measured intra-operatively are an indication of soft-tissue tension in the patient's knee, and may influence a surgeon to adjust implant position, orientation or size. This study investigates the frequency and magnitude of intra-operative adjustments from a single orthopedic surgeon during 38 unicondylar knee arthroplasty (UKA) cases. Methods. For each patient, a pre-operative plan was created based on the bony anatomy reconstructed from the pre-operative CT. This plan is analogous to a plan created with patient-specific cutting blocks or customized implants. With robotic technology that utilizes pre-operative imaging, intra-operative navigation and robotic execution, this “anatomic” plan can be fine-tuned and adjusted based on the soft tissue envelop measured intra-operatively. The relative positions of the femur and the tibia are measured intra-operatively under a valgus load (for medial UKA, varus load for lateral UKA) for each patient from extension to deep knee flexion and used to compute the predicted space between the implants (gaps) throughout flexion. The planned position, orientation and size of the components can then be adjusted to achieve an optimal dynamic ligament balance prior to any bony cuts. This is the plan that is then executed under robotic guidance. Intra-operative adjustments are defined as any size, position or orientation changes occurring intra-operatively to the pre-operative anatomic plan. Results. The surgeon adjusted the pre-operative implant plan in 86.8% of cases, leading to combined RMS changes of 2.0 mm and 2.1 degrees to the femoral implant, and 0.9 mm and 1.4 degrees to the tibial implant. The RMS femoral implant translations and rotations were 1.0, 1.5, 0.9 mm and 1.0, 1.0, 1.7 degrees in the medial, anterior, and superior directions, respectively. The RMS tibial implant translations and rotations were 0.2, 0.4, 0.8 mm and 1.3, 0.4, 0.6 degrees in the medial, anterior, and superior directions, respectively. Implant sizes were adjusted in 36.8% of cases, with all changes occuring to the femoral implant, and 13 out of those 14 cases showing a reduction in the femoral implant size. Conclusions. These data support the hypothesis that surgical planning of UKA components based on accurate 3D dimensional reconstructions of anatomy alone is not adequate to create optimal implant gap spacing throughout flexion. Measurement and knowledge of the patient's soft tissue envelope allows for signficiant changes to the implant plan prior to any bony cuts

1. Introduction. Such a Total Knee Arthroplasty (TKA) that is capable of making high knee flexion has been long awaited for the Asian and Muslim people. Our research group has developed the TKA possible to attain complete deep knee flexion such as seiza sitting. Yet as seiza is peculiar to the Japanese, other strategies will be necessary for our TKA to be on the overseas market. Still it is impractical to prepare many kinds of modifications of our TKA to meet various demands from every country/region. To this end, we contrived a way to modularize the post-cum alignment of our TKA in order to facilitate the following three activities containing high knee flexion: praying for the Muslim, gardening or golfing for the Westerner, sedentary siting on a floor for the Asian. We performed simulation and experiment, such as a mathematical model analysis, FEM analysis and a cadaveric study, thereby determining the optimal combination of moduli for the above activities respectively. 2. Methods. We modularized the post-cum alignment by three parameters in three levels respectively (Fig.1). The shape of the post's sagittal section and the total shape of cum were unchanged. The three parameters for modularization were the post location which was shifted anterior and posterior by 5 mm from the neutral position, the post inclination which was inclined forward and backward by 5° from the vertical, and the radius of curvature of the post's horizontal section which was increased and decreased by 2 mm from the original value. It is crucial to decrease contact stress between the post and cum during praying for the Muslim and during gardening or golfing for the Westerner, which would be realized by choosing the optimal location and inclination of post when kneeling for the Muslim and when squatting for the Westerner respectively (Fig.2). As for the Asian, it is desirable for them to perform various kinds of sedentary sittings on a floor without difficulties, which would be facilitated by choosing the optimal radius of curvature value to increase range of rotation when the knee is in high-flexion (Fig.2). First we performed a mathematical model analysis to introduce the kinetic data during sit-to-stand activities. Then by using the above kinetic data we performed the FEM analysis to determine the contact stress between the post and cum during praying, gardening or golfing. Finally we carried out the cadaveric study to determine the range of rotation at high flexion of the knee. 3. Results and Discussion. The results of FEM analysis demonstrated that the best modular set for the activities for Muslim and Westerners were so that the post location should be shifted by 5 mm and the post inclination should not be applied (Fig.3). The results of cadaveric study demonstrated that the radius of horizontal curvature should be increased by 2mm so as to increase the range of rotation especially when the knee is in high flexion. The subjects for our future study are to verify the validities of the above results through our simulator tests