We investigated the characteristics of patients who achieved Japanese-style deep flexion (seiza-sitting) after total knee replacement (TKR) and measured three-dimensional positioning and the contact positions of the femoral and tibial components. Seiza-sitting was achieved after surgery by 23 patients (29 knees) of a series of 463 TKRs in 341 patients. Pre-operatively most of these patients were capable of seiza-sitting, had a lower body mass index and a favourable attitude towards the Japanese lifestyle (27 of 29 knees). According to two-/three-dimensional image registration analysis in the seiza-sitting position, flexion, varus and internal rotation angles of the tibial component relative to the femoral component had means of 148° (sd 8.0), 1.9° (sd 3.2) and 13.4° (sd 5.9), respectively. Femoral surface contact positions tended to be close to the posterior edge of the tibial polyethylene insert, particularly in the lateral compartment, but only 8.3% (two of 24) of knees showed femoral subluxation over the posterior edge. The mean contact positions of the femoral cam on the tibial post were located 7.8 mm (sd 1.5) proximal to the lowest point of the polyethylene surface and 5.5 mm (sd 0.9) medial to the centre of the post, indicating that the post-cam contact position translated medially during seiza-sitting, but not proximally. Collectively, the seiza-sitting position seems safe against component dislocation, but the risks of posterior edge loading and breakage of the tibial polyethylene post remain.

Cite this article: Bone Joint J 2013;95-B:782–7.

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

Flexion after total knee arthroplasty (TKA) has recently been improved by changing implant designs, surgical techniques and early postoperative rehabilitation protocols. Especially for Asian people, deep knee flexion is essential because of their life style. Small numbers of patients can achieve full flexion after TKA, however, most current prostheses are not designed to allow deep knee flexion safely. Furthermore, the kinematics involved in knee flexion greater than 90 degrees in cases of TKA is still unknown, even though fluoroscopic studies have shown the paradoxical anterior femoral translation in posterior cruciate retaining (CR) TKA with knee flexion up to 90 degrees. The purpose of this study was to determine the femoro-tibial contact pattern in deep knee flexion. The knee that had been operated upon was passively flexed from 90 degrees up to the maximum flexion under anesthesia soon after the surgery. Lateral roentgenograms of the knee were taken during flexion, and the three-dimensional kinematics was analyzed using image-matching techniques. Nine patients with CR type were included. The average maximum flexion angle was 131.8 °. The contact point moved posteriorly with deep knee flexion except for one patient. Five out of nine patients showed external rotation of the femoral condyle. Two patients showed internal rotation, and the other two exhibited no rotational movement. None of the patients showed dislocation or disengagement of the components. At the maximum flexion, the edge of the posterior flange of the femoral component contacted the polyethylene insert. This study was performed under non-weight-bearing conditions, but deep knee flexion is not usually performed in weight-bearing conditions. Most of the CR type showed posterior roll back during deep knee flexion. The design of the posterior flange of the femoral component should be changed to prevent damage to the polyethylene

Currently available knee prostheses can provide 100 to 110° of knee flexion and this is generally good enough to ascend and descend stairs, arise from a chair, and perform most of the daily life activity. However, in certain situations like gardening, sitting on the flat floor and activities that require a squatting position, deep knee bends are required. In some countries, such as Japan, deep knee flexion is very important for the activity of daily life such as leading a life on a Tatami mattress and using a Japanese style toilet. There are several crucial factors, which influence postoperative knee flexion. Those are 1.) preoperative range of motion, 2.) surgical technique, 3.) prosthesis design, and 4.) postoperative rehabilitation. If a patient has longstanding, poor, preoperative range of motion, then the extensor mechanism itself became stiff in addition to the periarticular fibrotic change of the soft tissue and severe destruction of the bony structure. In this circumstance, it is awfully difficult to obtain deep knee flexion with currently available prostheses and surgical techniques. This indicates that we cannot wait for the last minute to perform TKR if a patient desires to gain deep knee flexion after the surgery. Surgical technique influences postoperative range of motion significantly. Anatomically the structures that get tight in knee flexion are the extensor mechanism and PCL. Thus, to obtain more flexion you should recess tight PCLs if you choose PCR type prostheses. Since the appropriate amount of PCL recession is not always easy, PCS type prostheses generally yield better flexion. To reduce tension of the extensor mechanism you should resect more patella than usual but this may cause postoperative patellar fracture. Or you can deepen the patellar groove by prosthesis modification but we should remember that both of these techniques will cause loss of the extensor lever arm and power. All posterior overhanging bone should be knocked out after trial reduction of a femoral prosthesis. Slightly flexed positioning of the femoral component and posteriorly tilted positioning of the tibial component can provide better flexion although too much of this positioning causes postoperative extension block. Regarding the prosthesis design, PCS type prostheses can provide more predictable postoperative knee flexion. Other alternatives are a femoral component with a smaller AP dimension and deep patello-femoral groove. However, both of these will cause weaker extensor power. Posterior lip of the tibial polyethylene decreases the contact pressure in knee flexion but will prevent posterior roll back of the femur and can cause impingement in deep knee flexion. In the normal knee, extreme internal rotation of the tibia occurs in deep knee flexion and this rotation cannot be achieved by a currently available knee design. Mobile bearing prostheses may be needed to achieve better kinematics. Aggressive postoperative rehabilitation is advised to prevent postoperative contracture of the soft tissue. Finally, although getting deep knee flexion is needed it should be remembered that ensuring postoperative stability and long-term survivorship should always be the most important goal for successful TKR

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. Despite decades of clinical research in artificial joints and underlying failure mechanisms, systematical and reproducible identification of reasons for complications in total knee replacements (TKR) remains difficult. Due to the complex dynamic interaction of implant system and biological situs, malfunction eventually leading to failure is multifactorial and remains not fully understood. The aim of present study was to evaluate different TKR designs and positions with regard to joint kinematics and stability under dynamic conditions by using a robot-based hardware-in-the-loop (HiL) setup. Material & methods. An industrial 6-axis robot with 6-axis force-torque sensor mounted into its end-effector moved and loaded real, commercially available TKR (bicondylar, cruciate-retaining) that were in virtual interaction with a subject-specific computational multibody model representing the anatomical situs of the knee joint while performing passive seated deep knee flexion. The subject-specific musculoskeletal multibody model (MMB) included rigid bones of the lower right extremity. Bone and cartilage geometries were reconstructed from MRT/ CT data sets preserving anatomical landmarks and allowing for the calculation of inertial properties. M. quadriceps femoris was modeled as single passive tensile force elements. Knee ligaments were modelled as elastic spring elements with a nonlinear force-displacement characteristic. Providing the flexion angle, the robot moved and loaded the mounted femoral implant component with respect to the tibial component while being in continuous interaction with the MMB. Several influencing parameters like implant position (internal/external rotation, varus/valgus alignment) and design (fixed vs. mobile bearing, tibia-insert height) as well as ligament insufficiency and joint loading on joint kinematics and stability was systematically analysed. Results. Improper implant positioning caused joint instability, which was demonstrated in higher magnitudes of the relative kinematics. Negative effects by incorrect implant positioning could be partially compensated by a mobile bearing design. However, this was accompanied with an increase in tibiofemoral contact forces. High correlation of tibia-insert height on ligament and contact force was found. After releasing ligament structures, lower tibiofemoral contact forces and joint opening during deep knee flexion were observed. Conclusion. By means of HiL simulation different clinical and technical parameters of TKR were evaluated in a systematical and reproducible fashion under physiological-like boundary conditions with regard to joint kinematics and stability. The proposed HiL test setup combining robot-based testing with MMBs can contribute to deeper understanding of knee joint function and improvement of total knee implant systems. Acknowledgement. The authors would like to thank the Deutsche Forschungsgemeinschaft (grant numbers: WO WO 452/8-1, BA 3347/3-1 and KL 2327/4-1) for supporting the project

High-flexion knee replacements have been developed to accommodate a large range of motion (ROM > 120°) after total knee arthroplasty (TKA). Femoral rollback or posterior translation of the femoral condyles during knee flexion is essential to maximise ROM and to avoid bone-implant impingement during deep knee flexion. The posterior cruciate ligament (PCL) has been described as the main contributor to femoral rollback. In posterior-stabilised TKA designs the PCL is substituted by a post-cam mechanism. The main objective of this study was to analyse the mechanical interaction between the PCL and a highflexion cruciate-retaining knee replacement during deep knee flexion. For this purpose, the mechanical performance of the high-flexion cruciate-retaining TKA design was evaluated and compared with two control designs including a highflexion posterior-stabilised design. Materials & Methods: Prosthetic knee kinematics and kinetics were computed using a three-dimensional dynamic finite element (FE) model of the knee joint. The FE knee model consisted of a distal femur, a proximal tibia and fibula, a quadriceps and patella tendon, a non-resurfaced patella, TKA components and a posterior cruciate ligament in case cruciate-retaining designs were evaluated. Tibio-femoral and patello-femoral contact were defined in the FE knee model and the polyethylene insert was modelled as a non-linear elastic-plastic material. Three different rotating platform TKA systems were analysed in this study: the high-flexion cruciate-retaining PFC Sigma CR150, the high-flexion posterior-stabilised PFC Sigma RP-F and the conventional cruciate-retaining PFC Sigma RP (Depuy, J& J, UK). Both the polyethylene stress characteristics and the tibio-femoral contact locations were evaluated during a squatting movement (ROM = 50° – 150°). Results: During deep knee flexion (ROM > 120°), the high-flexion cruciate-retaining TKA design showed a lower peak contact stress (74.7 MPa) than the conventional cruciate-retaining design (96.5 MPa). The posterior-stabilized high-flexion TKA design demonstrated the lowest peak contact stress at the condylar contact interface (54.2 MPa), although the post was loaded higher (77.4 MPa). All three TKA designs produced femoral rollback in the normal flexion range (ROM ≤ 120°), whereas the cruciate-retaining designs showed a paradoxical anterior movement of the femoral condyles during high-flexion. Discussion: PCL retention is a challenging surgical aim and affects the prosthetic knee load and kinematics as shown in this study. In addition, for adequate functioning the PCL should not be too tight or too lax after surgery. Hence, we investigated the effect of PCL laxity on the prosthetic performance and the best-balanced PCL was used in our simulations. Although PCL balancing is not an issue for posterior-stabilized TKA, we found the tibial post to be loaded relatively high for this implant type

Achieving deep flexion of knee after total knee arthroplasty (TKA) is particularly desirable in some Asian and Middle Eastern who have daily or religious customs typically use full knee flexion. After TKA, some patients complained about anterior knee pain during deep knee flexion. We evaluated the efficacy of arthroscopic fat pad resection in a series of patients suffering from anterior knee pain associated with high flexion achievement after TKA. The efficacy of fat pad resection via arthroscopy for treating anterior knee pain associated with high flexion angle (average = 133.1°) was evaluated in eight knees of eight patients among 207 knees performed between 1996 and 1999. The mean age of patients was 71.1 years when the primary TKA was performed. All implatants were posterior stabilized type (IB-II, Nexgen PS and LPS). The symptom of anterior knee pain during deep knee flexion developed within one year after TKA in all cases. In addition to pain in eight knees, two patients have crepitation as the knee was flexed and extended and three patients had hydrarthrosis. Impingement and fibrosis of fat pad were confirmed, and fibrous structures were removed by arthroscopy. Before arthroscopy, the symptom obviously subsided after injection of local anesthesia into infrapatellar fat pad. Patellar clunk syndrome is also soft tissue impingement and suprapatellar fibrous nodule becomes entrapped intercondylar notch on the femoral component during knee flexion. On this point, these cases does not cause by patellar clunk syndrome. After fat pad resection, the symptom disappeared, and keeps symptom-free after a mean follow-up of six years five months in all cases. Any complications following fat pad resection, such as patella baja and necrosis, were not experienced. Those cases achieving higher flexion angle tended to experience severe pain and shorter time interval between TKA and arthroscopic surgery, suggesting impingement of the infrapatellar fat pad is closely related to deep flexion after TKA. These results demonstrate that the anterior knee pain due to repetitive infrapatellar fat pad impingement is one of the complications during deep knee flexion after TKA, and the arthroscopic fat pad resection is useful to relief the anterior knee pain. Because of our experience with patients encountering anterior knee pain, we have begun to remove 70 to 80% of the fat pad during the primary TKA procedure since 1999, and until today, none developed anterior knee pain thought to be associated with fat pad impingement, patellar baja nor patellar necrosis. We suggest that fat pad resection is necessary to prevent the anterior knee pain due to fat pad impingement during deep flexion in TKA

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

Recently, high-flexion knee implants have been developed to provide for a large range of motion after total knee arthroplasty. Since knee forces increase with larger flexion angles, it is commonly assumed that high-flex-ion implants are subjected to large loads in the highflexion range (flexion > 120°). However, high-flexion studies often do not consider thigh-calf contact which occurs during high-flexion activities such as squatting and kneeling. We hypothesized that thigh-calf contact is substantial and has a reducing effect on the prosthetic knee loading during deep knee flexion. The effect of thigh-calf contact on the loading of a knee implant was evaluated using a three-dimensional dynamic finite element knee model. The knee model consisted of a distal femur, a proximal tibia and fibula, a patella, high-flexion components of the PFC Sigma RP-F (Depuy, Warsaw, USA) and a quadriceps and patella tendon. Using this knee model, a squatting movement was simulated including thigh-calf contact characteristics of a typical subject which have been described in an earlier study. Thigh-calf contact considerably reduced the implant loading during deep knee flexion. At maximal flexion (155°), the compressive knee force decreased from 4.9 to 2.9 times bodyweight. The maximal joint forces shifted from occurring at maximal flexion angle to the flexion angle at which thigh-calf contact initiated (±130°). The maximal polyethylene contact stress at the tibial post decreased from 49.3 to 28.1 MPa at maximal flexion. This study confirms that thigh-calf contact reduces the knee loading during high-flexion. Both the joint forces and the polyethylene stresses reduced considerably when thigh-calf contact was included

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

We have developed a new tensor for total knee replacements which is designed to assist with soft-tissue balancing throughout the full range of movement with a reduced patellofemoral joint. Using this tensor in 40 patients with osteoarthritis we compared the intra-operative joint gap in cruciate-retaining and posterior-stabilised total knee replacements at 0°, 10°, 45°, 90° and 135° of flexion, with the patella both everted and reduced. While the measurement of the joint gap with a reduced patella in posterior-stabilised knees increased from extension to flexion, it remained constant for cruciate-retaining joints throughout a full range of movement. The joint gaps at deep knee flexion were significantly smaller for both types of prosthetic knee when the patellofemoral joint was reduced (p < 0.05)

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

A new type of knee prosthesis capable of making deep knee flexion has been long awaited for Asian and Muslim people. Our research group has developed such a prosthesis and designated it as CFK (Complete Flexion Knee). In order to assess the performance of CFK, we have set up various kinds of simulation/experimental projects, such as a cadaveric study, a mathematical model analysis, a photoelastic analysis and FEM analysis. For carrying out the above-mentioned projects, we faced the most fundamental problem; the information about the muscles’ forces and the forces acting on the joints is limited to that for ambulatory activities but not for squatting or sedentary sitting. The objective of this study is to introduce the force acting on the knee joint and the lower limbs’ muscle forces at deep knee flexion. A 2D mathematical model was used. The model was composed with three segments: upper leg, lower leg, and foot. The muscle groups incorporated into our model were gluteal muscles, quadriceps including rectus femoris and the vasti, hamstrings, and calf muscles including gastrocnemius and soleus. And thigh-calf contact was assumed to take place at 130° of knee flexion. Three equations were introduced from the moment equilibrium condition about each joint. Since the number of unknowns was six, being surplus to the number of equations, several muscles were grouped into one basing upon the EMG data. Double leg ascending motions from deep squatting with heel rising were studied for 10 healthy male subjects age of 24±2 years, height of 172±5.8 cm, weight of 66.5±8.7 Kg. The data of ground reaction force and angle of each joint during the motion were collected using a force plate and video recording system respectively. The length of each segment for each subject was directly measured. The mass of each segment and center of gravity was determined by referring to the literature. The results demonstrated that both the normal force acting on the knee joint and the quadriceps force became maximum when knee flexion angle became 130°(the angle at which the thigh-calf contact diminished), then decreased according as the knees extended. Both of their maximum value were proportional to the subject’s body weight and about seven times larger than that. Therefore it was justified that the joint force and quadriceps force were normalized by dividing them by the body weight. Ascending speeds did not affect the values of joint and quadriceps forces unless the motion was jumping