The posterior tibial slope angle (PTS) in posterior cruciate retaining total knee arthroplasty influences the knee kinematics, knee stability, flexion gap, knee range of motion (ROM) and the tension of the posterior cruciate ligament (PCL). The current technique of using an arbitrary (often 3–5 degrees) PTS in all cases seldom will restore native slope in cruciate retaining TKA. Questions/Purposes: The primary objective was to determine if we could surgically reproduce the native PTS in cruciate-retaining total knee arthroplasty. The second objective was to determine if reproduction of native slope was significant – ie influenced clinical outcome. We evaluated the radiographic and clinical outcomes of a series of consecutive total knee arthroplasties using the PFC sigma cruciate-retaining total knee system in 215 knees. The tibial bone cut was planned to be parallel to the patient's native anatomical slope in the sagittal plane. An “Angel Wing” instrument was placed on the lateral tibial plateau and the slope of the cutting guide adjusted to make the cutting block parallel to the patient's native tibial slope. All true lateral radiographs of the knee were measured for PTS using a picture achieving and communication system (PACS). PTSs were measured with reference to the proximal tibial medullary canal (PTS-M) and the proximal tibial anterior cortex (PTS-C). The knee ROM, Knee Society Score, Western Ontario and McMaster University Osteoarthritis Index (WOMAC) and SF-12 at the last follow-up were evaluated as clinical outcomes. The mean preoperative PTS-M was 6.9±3.3 degrees and the mean postoperative PTS-M was 7±2.4 degrees. The mean preoperative PTS-C was 12.2±4.2 degrees and the mean postoperative PTS-M was 12.6±3.4 degrees. There was no significant difference form the preoperative and postoperative PTS measurement in both techniques (p>0.05). We used an arbitrary 3 degrees as an acceptable range for PTS-M reproduction. The PTS-M was reproduced within 3 degrees in 144 knees (67%); designated as Group A. The 71 knees with a difference more than 3 degrees in (33%) were designated as Group B. Group A showed significantly larger gain in ROM compared with group B (p=0.04). Group A also had significantly better improvement in Knee society score and WOMAC score and SF-12 physical score when compare with group B (p<0.01). Our modification of standard surgical technique reliably reproduced the native tibial slope in cruciate-retaining total knee arthroplasty. More importantly, reproduction of the patient's native PTS within 3 degrees resulted in better clinical outcomes manifested by gain in ROM and knee functional outcome scores

Introduction. Although total knee arthroplasty (TKA) is generally considered successful, 16–30% of patients are dissatisfied. There are multiple reasons for this, but some of the most frequent reasons for revision are instability and joint stiffness. A possible explanation for this is that the implant alignment is not optimized to ensure joint stability in the individual patient. In this work, we used an artificial neural network (ANN) to learn the relation between a given standard cruciate-retaining (CR) implant position and model-predicted post-operative knee kinematics. The final aim was to find a patient-specific implant alignment that will result in the estimated post-operative knee kinematics closest to the native knee. Methods. We developed subject-specific musculoskeletal models (MSM) based on magnetic resonance images (MRI) of four ex vivo left legs. The MSM allowed for the estimation of secondary knee kinematics (e.g. varus-valgus rotation) as a function of contact, ligament, and muscle forces in a native and post-TKA knee. We then used this model to train an ANN with 1800 simulations of knee flexion with random implant position variations in the ±3 mm and ±3° range from mechanical alignment. The trained ANN was used to find the implant alignment that resulted in the smallest mean-square-error (MSE) between native and post-TKA tibiofemoral kinematics, which we term the dynamic alignment. Results. Dynamic alignment average MSE kinematic differences to the native knees were 1.47 mm (± 0.89 mm) for translations and 2.89° (± 2.83°) for rotations. The implant variations required were in the range of ±3 mm and ±3° from the starting mechanical alignment. Discussion. In this study we showed that the developed tool has the potential to find an implant position that will restore native tibiofemoral kinematics in TKA. The proposed method might also be used with other alignment strategies, such as to optimize implant position towards native ligament strains. If native knee kinematics are restored, a more normal gait pattern can be achieved, which might result in improved patient satisfaction. The small changes required to achieve the dynamic alignment do not represent large modifications that might compromise implant survivorship. Conclusion. Patient-specific implant position predicted with MSM and ANN can restore native knee function in a post-TKA knee with a standard CR implant

Background. The constraint of total knee replacement (TKR) implants is not simply defined and many of the factors that influence it are not well understood. Variability in the constraint of different TKR implants designed for the same indication (e.g. cruciate-retaining, or posterior-stabilized) have been previously demonstrated, but these differences among implants have yet to be simply quantified. Furthermore, the relative importance of several variables on the implant constraint remains unknown. The purpose of this study was to quantify the differences in constraint that exist between different implant designs, and to examine the effects of axial load and flexion angle on the constraint of current cruciate-retaining (CR) TKR components. Methods. Four contemporary CR TKR designs underwent laxity testing using a multi-axis mechanical test machine. Implants were tested at flexion angles of 0°, 20°, 90° and maximum flexion and axial loads of 712 N (1 BW) and 1424 N (2 BW). Friction-free motion in all secondary degrees of freedom was allowed. Force-displacement curves were generated for each testing condition in both anterior-posterior (AP) and rotational tests. AP constraint (N/mm) and rotational constraint (Nm/deg) were then calculated. Results. Differences in the AP and rotational constraint of the various implants were identified. The rotating platform implant was the most AP constrained and least rotationally constrained of the implants studied. Among the fixed bearing implants, NexGen CR had less AP and rotational constraint than the Genesis II and PFC Sigma. Doubling the applied axial load during the laxity tests resulted in a significant increase in both AP (p<0.0001) and rotational (p<0.0001) constraint. AP and rotational constraint decreased with increasing flexion angles. Conclusion. The constraints of four contemporary CR TKR designs were quantitatively compared and ranked according to their calculated constraints. Differences in the constraint of these designs were identified. This quantitative analysis is an important step towards the creation of a clinically meaningful constraint index that would aid surgeons in choosing the optimal implants for their TKR patients. Additionally, the analysis of the effects of axial load and flexion angle on constraint has implications which may influence how in vitro testing of implants is conducted as well as clinical implications in terms of how the constraint envelope of a given implant may influence the feel and function that a TKR patient experiences

Background. To prevent excessive tension on the posterior cruciate ligament (PCL) in cruciate-retaining total knee arthroplasty (CR-TKA), some knee prosthesis-systems offer the option of creating a posterior slope for the tibial polyethylene insert. Vanguard® Complete Knee System offers two different types of tibial bearing for CR. -TKA. CR Lipped Bearing (LB) has a slightly raised posterior lip, whereas CR Standard Bearing (SB) is recessed downward at the posterior margin and has 3° posterior slope. The objective of this study was to investigate the effect of the tibial bearing slope on PCL load using the original devise in vivo conditions. Material and Methods. Twenty osteoarthritic varus knees were included in this study. After implantation of the trial components, PCL stiffness was measured using the original tension analyzer intra-operatively. Elastic modulus of PCL was calculated at 90 and 120 degrees knee flexion on two types of bearing surface. Results. Elastic modulus of PCL was 7.2±0.9 N/mm (mean±SE) at 90 degrees knee flexion, and 9.5±1.1 N/mm (mean±SE) at 120 degrees knee flexion with the Lipped Bearing (no slope). With the Standard Bearing (3 degrees posterior slope), elastic modulus decreased to 6.0±0.5 N/mm (mean±SE) at 120 degrees knee flexion. Discussion and Conclusion. Higher PCL stiffness was observed at 120 degrees knee flexion than 90 degrees knee flexion with Lipped Bearing surface (no slope), but using the Standard Bearing (3 degrees posterior slope), PCL stiffness decreased significantly at 120 degrees knee flexion. Therefore a posterior tibial slope of bearing insert prevents an excessive load on PCL at high knee flexion angles

INTRODUCTION. The medial-stabilised (MS) knee implant, characterised by a spherical medial condyle on the femoral component and a medially congruent tibial bearing, was developed to improve knee kinematics and stability relative to performance obtained in posterior-stabilised (PS) and cruciate-retaining (CR) designs. We aimed to compare in vivo six-degree-of-freedom (6-DOF) kinematics during overground walking for these three knee designs. METHODS. Seventy-five patients (42 males, 33 females, age 68.4±6.6 years) listed for total knee arthroplasty (TKA) surgery were recruited to this study, which was approved by the relevant Human Research Ethics committees. Each patient was randomly- assigned a PS, CR or MS knee (Medacta International AB, Switzerland) resulting in three groups of 23, 26 and 26 patients, respectively. Patients visited the Biomotion Laboratory at the University of Melbourne 6±1.1 months after surgery, where they walked overground at their self-selected speed. A custom Mobile Biplane X-ray (MoBiX) imaging system tracked and imaged the implanted knee at 200 Hz. The MoBiX system measures 6-DOF tibiofemoral kinematics of TKA knees during overground gait with maximum RMS errors of 0.65° and 0.33 mm for rotations and translations, respectively. RESULTS AND DISCUSSION. Mean walking speeds for the three groups were not significantly different (PS, 0.86±0.14 m/s CR, 0.82±0.17 m/s and MS, 0.87±0.14 m/s, p>0.25). While most kinematic parameters were similar for the PS and CR groups, mean peak-to-peak anterior drawer was greater for PS (9.89 mm) than CR (7.75 mm, p=0.004), which in turn was greater than that for MS (4.43 mm, p<0.001). Mean tibial external rotation was greater for MS than PS (by 3.12°, p=0.033) and CR (by 3.34°, p=0.029). Anterior drawer and lateral shift were highly coupled to external rotation for MS but not so for PS and CR. The contact centres on the tibial bearing translated predominantly in the anterior-posterior direction for all three designs. Peak-to-peak anterior-posterior translation of the contact centres in the medial compartment was largest for PS (7.09 mm) followed by CR (5.45 mm, p=0.003) and MS (2.89 mm, p<0.001). The contact centre in the lateral compartment was located 2.5 mm more laterally for MS than PS and CR (p<0.001). The centre of rotation of the knee in the transverse plane was located in the medial compartment for MS and in the lateral compartment for both PS and CR. CONCLUSIONS. We quantitatively compared in vivo 6-DOF joint motion for PS, CR, and MS knees during locomotion. A higher degree of coupling between external rotation and anterior-posterior translation, greater constraint in the anterior-posterior direction, and a more medialised joint centre of rotation observed for the MS knees are explained by the highly congruent medial articulation characterising this design

Introduction. Tibial slope was shown to majorly affect the outcomes of Total Knee Arthroplasty (TKA). More slope of the tibial component could help releasing a too tight flexion gap in cruciate-retaining (CR) TKA and is generally associated with a wider range of post-operative knee flexion. However, an excessive tibial slope could jeopardize the knee stability in flexion. The mechanism by which tibial slope affects the function of CR-TKA is not well understood. Moreover, it is not known whether the tibial bone resection should be performed by referencing the anterior cortex (AC) of the tibia or the center of the tibial plateau (CP) and whether the choice of either technique plays a role. The aim of this study was to investigate the effect of tibial slope on the position of tibiofemoral (TF) contact point, knee ligament forces, quadriceps muscle forces, and TF and patellofemoral (PF) joint contact forces during squat activity in CR-TKA. Methods. A previously validated musculoskeletal model of CR-TKA was used to simulate a squat activity performed by a 86-year-old male subject wearing an instrumented prosthesis [1,2]. Marker data over four consecutive repetitions of a squat motion were tracked using a motion optimization algorithm. Muscle and joint forces and moments were calculated from an inverse-dynamic analysis, coupled with Force-Dependent Kinematics (FDK) to solve knee kinematics, ligament and contact forces simultaneously. The tibial slope in the postoperative case was 0 degree and constituted the reference case for our simulations. In addition, eight additional cases were simulated with −3, +3, +6, +9 degrees of tibial slope, four of them simulating an AC referencing technique and four a CP technique. Results. Compared to the reference case with no added slope, the total excursion of the tibiofemoral contact point increased on both medial and lateral side when more slope was added using the AC referencing technique, and decreased with negative slope. The total excursion of the contact point remained about unchanged when using the CP technique but the contact point shifted of about 1 mm more posteriorly, on the lateral side, and 0.7 mm, on the medial side, on average. In both AC and CP techniques the quadriceps forces, TF and PF contact forces decreased with more slope, but the PF contact forces were more drastically reduced using CP, with 3.5% less force every 3 degrees of added slope in flexion, on average. Medial and lateral collateral ligament became slack in flexion already with +6 degrees of slope when AC technique was used, whereas they always maintained some residual tension using the CP technique even at the highest slope. Discussion and conclusion. Increasing the tibial slope affected substantially the knee function during squatting and the effects differed depending on the referencing technique. The CP referencing helps preserving the flexion gap and knee stability in flexion, by mantaining tension in both collateral ligaments. It also reduces the quadriceps forces and relieves the PF joint contact forces, which could potentially decrease pain in patients with a TKA and achieve a wider range of knee motion

INTRODUCTION:. A discrepancy exists between biomechanical and clinical outcome studies when comparing cruciate-retaining (CR) versus posterior stabilized (PS) component designs. The purpose of this study is to re-evaluate experimental model results using half-body specimens with intact extensor mechanisms and navigation to evaluate PS and CR component gaps though an entire range of motion. METHODS:. A custom-designed knee testing apparatus was used for secure anchoring of the lower half of cadaver pelvic, allowing full range of knee motion and the application of traction throughout that range. Eight sequential testing regimens: were conducted with knee intact, with CR TKA in place, with PS TKA with quadriceps tendon in place, with PS TKA with sectioned quadriceps tendon in place, with and without traction at each stage. At each stage, a navigated knee system with dedicated software was used to record component gapping through a full range of motion from 0° to 120°. The amount of traction used was 22N. Each knee (n = 10) was taken through 6 full ranges of motion at every stage. At each stage, corroboration of navigation findings was attempted using a modified gap balancer to take static gap measurements at 0° and 90° with 12 in. lbs of torque was applied. RESULTS:. The difference in component gapping between CR and PS knees resulted in a range from −0.85 mm to 0.62 mm. The range of component gapping was from −0.67 mm to 0.70 mm with both constructs under 22N traction load. There was no significant difference between loaded and unloaded component gaps, and there were no statistically significant differences in component gapping between CR and PS knees throughout a full range of motion. Static flexion-extension gap measurements, were significantly different from previously published data, notably at in 90° flexion gap measurement. The comparison of the sectioned unloaded and sectioned loaded quadriceps tendon constructs gave a range of distraction of tibio-femoral gaps from 1.85 to 5.22 mm and 1.46 to 4.60 mm, respectively. These measurements were significantly increased over previously reported findings. CONCLUSION:. There was no significant difference between the CR and PS TKA designs with respect to component gapping when measured through a complete range of motion with an intact extensor mechanism. This data contradicts earlier results, obtained from less complete specimens, and correlates with clinical studies which show no gap differences in CR and PS knees. We conclude that the sectioned quadriceps tendon influences knee flexion-extension gaps in a PS TKA construct model. This finding suggests that intact extensor mechanisms may be required to perform proper kinematic studies of TKA, and this may be a contributing factor in the discrepancies observed between previous biomechanical and clinical outcome studies. Clinical Relevance: The findings of this study may solve the controversy regarding differences of the CR and PS TKA designs observed using biomechanical models

Background. In recent literatures, medial instability after TKA was reported to deteriorate early postoperative pain relief and have negative effects on functional outcome. Furthermore, lateral laxity of the knee is physiological, necessary for medial pivot knee kinematics, and important for postoperative knee flexion angle after cruciate-retaining total knee arthroplasty (CR-TKA). However, the influences of knee stability and laxity on postoperative patient satisfaction after CR-TKA are not clearly described. We hypothesized that postoperative knee stability and ligament balance affected patient satisfaction after CR-TKA. In this study, we investigated the effect of early postoperative ligament balance at extension on one-year postoperative patient satisfaction and ambulatory function in CR-TKAs. Materials & Methods. Sixty patients with varus osteoarthritis (OA) of the knee underwent CR-TKAs were included in this study. The mean age was 73.6 years old. Preoperative average varus deformity (HKA angle) was 12.5 degrees with long leg standing radiographs. The knee stability and laxity at extension were assessed by stress radiographies; varus-valgus stress X-ray at one-month after operation. We measured joint separation distance (mm) at medial compartment with valgus stress as medial joint opening (MJO), and distance at lateral compartment with varus stress as lateral joint opening (LJO) at knee extension position. To analyze ligament balance; relative lateral laxity comparing to the medial, varus angle was calculated. New Knee Society Score (NKSS) was used to evaluate the patient satisfaction at one-year after TKA. We measured basic ambulatory functions using 3m timed up and go test (TUG) at one-year after surgery. The influences of stability and laxity parameters (MJO, LJO and varus angle at extension) on one-year patient satisfaction and ambulatory function (TUG) was analyzed using single linear regression analysis (p<0.01). Results. MJOs at knee extension one-month after TKA negatively correlated to patient satisfaction (r=−0.37, p<0.01) and positively correlated to TUG time (r=0.38, p<0.01). LJOs at knee extension had no statistically significant correlations to patient satisfaction and TUG. The extension varus angle had significant positive correlation with patient satisfaction (r=0.40, p<0.01). Discussions. In our study, we have found significant correlations of the early postoperative MJOs at extension to postoperative patient satisfaction and TUG one-year after CR-TKA. Our results suggested that early postoperative medial knee stabilities at extension were important for one-year postoperative patient satisfaction and ambulatory function in CR-TKA. Other interest finding was that postoperative patient satisfaction was positively correlated with extension varus angle. This finding suggested that varus ligament balance; relative lateral laxity to medial stability, was beneficial for postoperative patient satisfaction after CR-TKA. Intra-operative soft tissue balance had been reported to significantly affect postoperative knee stabilities. Therefore, with our findings, surgeons might be better to manage intra-operative soft tissue balance to preserve medial stability at extension with permitting lateral laxity, which would enhance patient satisfaction and ambulatory function after CR-TKA for varus type OA knee. Conclusion. Early postoperative medial knee stability and relative lateral laxity would be beneficial for patient satisfaction and function after CR-TKA

Introduction. Controversy still exists as to whether total knee arthroplasty (TKA) provides reproducible knee kinematics during activities. In this study, we evaluated the in vivokinematics of stair-climbing after TKA using a 3D-to-2D model-to-image registration technique. Patients and Methods. A total of twenty four knees in nineteen patients following cruciate-retaining (CR) or posterior-stabilized (PS) TKA were randomly included in the study. The twenty-four knees included 22 female knees and 2 male knees in patients aged 73 years. The pre-operative diagnosis was osteoarthritis in 22 knees and rheumatoid arthritis in 2 knees. The average follow-up period after surgery was 29 months, and average post-operative knee extension/flexion angle was 2°/121°. The average knee score was 93 and the average functional score was 77. Continuous sagittal radiological images were obtained during stair-climbing for each patient using a large flat panel detector. Anteroposterior (AP) tibiofemoral position, implant flexion, and axial rotation angles were determined in three dimensions using a 3D-to-2D model-to-image registration technique. In CR TKA, the minimum distances between the femoral trochlea and the intercondylar eminence of the tibial insert were measured using a CAD software program. In PS TKA, the minimum distances between the femoral cam and the posterior aspect of the tibial post and between the femoral trochlea and the anterior aspect of the tibial post were measured. Results. The average implant flexion angle at foot strike/toe off during stair-climbing was 65.6°/−5.9° after CR TKA and 72.3°/−0.5° after PS TKA. The average AP tibiofemoral position from the center of the tibial insert at foot strike/toe off was 9.2mm posterior/1.0mm posterior after CR TKA and 8.6mm posterior/1.0mm posterior after PS TKA. The average tibiofemoral rotation angle at foot strike/toe off was −6.0°/−2.1° after CR TKA and −8.6°/2.7° after PS TKA. In CR TKA, the average of the minimum distance between the intercondylar notch of the femoral trochlea and the intercondylar eminence of the tibial insert at foot strike/toe off was 26.9mm/4.6mm. No knees demonstrated impingement of the femoral trochlea on the tibial insert (Fig. 1). In PS TKA, the average of the minimum post-cam and femoral trochlea-anterior post distances at foot strike/toe off were 4.0 ± 1.9 mm/18.2 ± 4.1 mm and 19.3mm/1.6mm. No knees demonstrated post-cam engagement, but four knees demonstrated anterior tibial post impingement from −0.5° of implant flexion (Fig. 2). Discussion. This study characterized knee kinematics during stair-climbing after two different types of total knee prostheses. Mid-flexion AP stability was demonstrated in all knees after CR TKA during stair-climbing. It could be assumed that the retained posterior cruciate ligament was functioning. However, paradoxical femoral translation and/or reverse axial rotation due to deficiency of the anterior cruciate ligament were shown in 75% of knees at low flexion. The post-cam mechanism did not function during stair-climbing after PS TKA and 33% of knees demonstrated forward sliding of the femur at mid-flexion. The post-cam mechanism should be configured to function at mid-flexion. Unintended anterior tibial post impingement, which was observed in 33% of knees at knee extension, provided anterior femoral position

Introduction / Purpose. Many factors can influence postoperative knee flexion angle after total knee arthroplasty (TKA), and range of flexion is one of the most important clinical outcomes. Although many studies have reported that postoperative knee flexion is influenced by preoperative clinical conditions, the factors which affect postoperative knee flexion angle have not been fully elucidated. As appropriate soft-tissue balancing as well as accurate bony cuts and implantation has traditionally been the focus of TKA success, in this study, we tried to investigate the influence of intraoperative soft-tissue balance on postoperative knee flexion angle after cruciate-retaining (CR) TKA using a navigation system and offset-type tensor. Methods. We retrospectively analyzed 55 patients (43 women, 12 men) with osteoarthritis who underwent TKA using the same mobile-bearing CR-type implant (e.motion; B. Braun Aesculap, Germany). The mean age at the time of surgery was 74.2 (SD 7.3) years. The exclusion criteria for this study included valgus deformity, severe bony defect requiring bone graft or augmentation, revision TKA, active knee joint infection, and bilateral TKA. Intraoperative soft-tissue balance parameters such as varus ligament balance and joint component gap were measured in the navigation system (Orthopilot 4.2; B. Braun Aesculap) while applying 40-lb joint distraction force at 0°, 10°, 30°, 60°, 90°, and 120° of knee flexion using an offset-type tensor with the patella reduced. Varus ligament balance was defined as the angle (degree, positive value in varus imbalance) between the seesaw and platform plates of the tensor that was obtained from the values displayed by the navigation system. To determine clinical outcome, we measured knee flexion angle using a goniometer with the patient in the supine position before and 2 years after surgery. Correlations between the soft-tissue parameters and postoperative knee flexion angle were analyzed using simple linear regression models. Pre- and postoperative knee flexion angle were also analyzed in the same manner. Results. Mean pre- and postoperative flexion angle were 120.5 ± 1.9° and 121.9 ± 1.3°, which did not show significant improvement after surgery. Varus ligament balance at 90° of flexion was positively correlated with postoperative knee flexion angle (R = 0.56, P < 0.001) and calculated joint gap of the lateral compartment at 90° of flexion showed positive correlation with postoperative knee flexion angle (R = 0.51, P < 0.001), while no correlation was found between joint gap of the medial compartment at 90° of flexion and postoperative knee flexion angle. Also, as with some past studies, joint component gap at 90° of flexion was slightly correlated with postoperative knee flexion angle (R = 0.30, P < 0.05) and pre- and postoperative knee flexion angle showed a significant positive correlation (R = 0.63, P < 0.001). Conclusions. Varus ligament balance at mid to deep flexion was a factor that predicted postoperative knee flexion angle after CR-TKA. In addition to preoperative knee flexion angle and joint component gap at 90° of flexion, lateral laxity at 90° of flexion is one of the most important factors affecting postoperative knee flexion angle

Purpose. The purpose of this study was to compare joint line changes between posterior-stabilized (PS) and cruciate-retaining (CR) computer navigated total knee arthroplasties (TKA) and to evaluate the impact on functional outcome. Background. Restoration of the native joint line has been a common goal in all TKA designs. Computer-navigated TKA in increasingly being favoured by many surgeons, due to increased precision and lesser complications. Few studies have reported the effect of computer navigated TKA on joint line restoration. It remains to be seen if the greater precision offered by computer-navigated TKA in restoration of joint line translates to improvement in functional outcome. Methods. This study assessed joint line changes following computer-assisted navigated total knee arthroplasty (TKA). A total of 195 patients were followed up for a period of 2 years following primary surgery. The change in the joint line was calculated based on the verified bony resections and the final thickness of the insert. The patients were stratified into two groups: the CR group and the PS group. The joint line changes of both groups were then compared using the Student t-test. Multivariate analysis and regression modelling were then utilized to analyze the functional outcomes of both groups at 6 months and 2 years of follow-up. Results. A total of 112 CR knees and 83 PS knees were analyzed. PS knees had a significantly greater joint line change as compared to CR knees with a p-value of 0.04 (Figure 1). Although the knee, function and oxford knee questionnaire scores were significantly better in the CR group at the 6-month follow-up, this did not translate into any significant difference in functional scores at the 2-year follow-up. It was also found that the PS group had significantly better final range of motion. Conclusion. CR knees are associated with significantly less joint line changes than PS knees in computer navigated TKA. PS knees have a greater range of motion at 2 years of follow-up. No significant difference in outcome was noted at 2 years follow-up

It is a well-known fact that total knee arthroplasty is a soft tissue operation. Soft tissue balancing is the key to success in total knee arthroplasty. It is paramount importance to preserve the maximal amount of bone on both the femur and tibial side. In Indian scenario, majority of the patients present relatively late with varus or valgus deformity. Adding to this problem is poor bone quality due to osteoporosis. Our technique of Posterior cruciate ligament (PCL) retaining TKA with tibial end plate resection facilitates soft tissue balancing, preserves PCL and maximizes bone preservation on both tibial and femoral side achieving good results in minimum seven year follow up. We retrospectively analyzed seven year outcomes of 120 knees (110 patients), mean age was 65 years (range 55 to 75 years), who received contemporary cruciate-retaining prostheses with tibial end plate resection technique. The diagnosis was osteoarthritis in 96%, Rheumatoid arthritis in 2% and posttraumatic arthritis in 2% cases. There were more number of flexible varus knees as compared to flexible valgus knees. All the patients were followed up for minimum of 84 months with average follow up of 96 months. They were followed up at 3mths, 6mths, 1,3,5,7,9 and 10 years. The functional assessment was done using knee society knee and function scores. Radiographic analysis was done to rule out subsidence and aseptic loosening. The statistical significance was assessed using chi square test. Survival analysis was done using the Kaplan Meier analysis with revision taken as the endpoint. The average ROM was 100 degrees preoperatively and 120 degrees at last follow-up. The average knee society knee score improved from 45 points preoperatively to 90 points at last follow-up. The average knee society functional score improved from 48 points preoperatively to 84 points at last follow-up (p<0.05). Radiolucency was observed in 20 knees but all except four were non-progressive lesions smaller than 2 mm. None of the implants were revised for subsidence or aseptic loosening of tibial component. The technique of PCL retaining total knee arthroplasty with tibial end plate resection in arthritic knees with flexible varus or valgus deformity yields good functional outcome in medium term follow up with relatively low incidence of subsidence of the tibial implant. This technique appears promising for total knee arthroplasty in osteoporotic bones where retaining the strong subchondral bone increases the longevity of the implant

Purpose. Surgeons sometimes encounter moderate or severe varus deformed osteoarthritic cases in which medial substantial release including semimembranosus is compelled to appropriately balance soft tissues in total knee arthroplasty (TKA). However, medial stability after TKA is important for acquisition of proper knee kinematics to lead to medial pivot motion during knee flexion. The purpose of the present study is to prove the hypothesis that step by step medial release, especially semimembranosus release, reduces medial stability in cruciate-retaining (CR) total knee arthroplasty (TKA). Methods. Twenty CR TKAs were performed in patients with moderate varus-type osteoarthritis (10° < varus deformity <20°) using the tibia first technique guided by a navigation system (Orthopilot). During the process of medial release, knee kinematics including tibial internal rotation and anterior translation during knee flexion were assessed using the navigation system at 3 points; (1) after anterior cruciate ligament resection (pre-release), (2) medial tibial and femoral osteophyte removal and release of minimum deep layer of medial collateral ligament (minimum release) and (3) release of semimembranosus (semimembranosus release). In addition, the kinematics after all prostheses implantation (semimembranosus release group) were assessed and compared with those assessed in another 20 patients in which only minimum release was performed (minimum release group). Results. Kinematic pattern in step by step medial release exhibited external tibial rotation during mid-range of flexion and then shifted to internal tibial rotation toward to 120 degrees of knee flexion (Fig. A). During 60 to 120 degrees of flexion, semimembranosus release significantly reduced the amount of internal tibial rotation compared with pre-release (Fig. 1B). Tibial anterior translation showed no significant differences among each procedure. After all prostheses implanted, the amount of tibial internal rotation during 60 to 120 degrees of knee flexion was significantly maintained in minimum release compared with semimembranosus release group (Fig. 2). Conclusions. Semimembranosus release reduces tibial internal rotation in CR TKA, suggesting that semimembranosus release should be avoided in case of moderate varus-type osteoarthritis for considering medial stability

Purpose. The purpose of this study was to analyze rotational kinematic patterns in knees treated with either cruciate-retaining (CR) or posterior-stabilized (PS) total knee arthroplasty (TKA), using an intra-operative navigation technique, and to clarify the factors that affect of the rotational kinematics and the difference rotational kinematics patterns between CR- and PS- TKA. Methods. A total of 35 knees (35 patients) were included in this study, deformed valgus, sever flexion contractures, and highly unstable knees were excluded. These knees were allocated to CR (NexGen CR-Flex) or PS (NexGen PS-Flex) implants and underwent TKA with a computer navigation technique (precision N Knee Navigation Software v4.0; Stryker). There was no significant difference in pre-operative parameters between CR- and PS-TKA group: age, femorotibial angle (FTA), and chondylar twist angle (CTA). We measured two points during surgery. First, the skin incision was made and subcutaneous tissue was exposed. The joint capsule was temporality closed by three or four strand suture. Second, after the surgery was completed with satisfactory alignment and soft tissue balance, immediately following wound closure the measurement procedure was repeated. The surgeon gently applied a manual range of motion from full extension to flexion. The angle of internal rotation in tibia to the functional plane of tibia and femur was measured automatically at max extension, 0, 30, 45, 60, 90 degrees, and max flexion throughout the passive knee motion. Result. We categorized the post-operative rotational kinematics patterns to five types. Type A was increasing with the internal rotation angle in tibia with knee flexion. Type B was decreasing the internal rotation with knee flexion. Type C was decreasing the internal rotation from 0 to 45 or 60 degrees, Then graduated increasing until full flexion. Type D was the opposite type of type C. Type E was not able to categorize any pattern. (Figure 1) The individual kinematic pattern was variable in pre- and post-operative knee motion. Both CR- and PS-TKA had a tendency to remain the preoperative kinematic pattern (CR-TKA 66% and PS-TKA 59%) by comparing the pre- and post-operative kinematic pattern. But, type A was increased in post-operative PS-TKA. (Figure 2) We analyzed factors (age, pre-operative FTA, CTA, pre-operative knee extension, and post-operative FTA) that affect the change of rotational kinematics patterns before and after TKA. In CR-TKR, there were not any factors that influence with the changes of kinematic pattern. In PS-TKR, pre-operative knee extension angle affected accompanied by significant difference in the change of rotational kinematics patterns. Discussion & Conclusion. We analyzed the rotational kinematics patterns in knees treated with either CR- or PS-TKR, using an intra-operative navigation. Pre- and post-operative knee kinematics of TKA patients had a variety of rotational kinematics patterns. Both CR- and PS-TKA had a tendency to remain the preoperative kinematic pattern by comparing the pre- and post-operative kinematic pattern Pre-operative knee extension affected to the change of rotational kinematics pattern in PS-TKR

Although the pre- or intraoperative flexion angle in TKA has been commonly considered as a predictor of the postoperative flexion angle, patients with well flexion intraoperatively cannot necessarily obtain deep flexion angle postoperatively. The reason why inconsistencies remains has been unsolved. The intraoperative compressive force between femoral and tibial components has the advantage of the sequential changes during knee motion. However, the relationship between the compressive force and the postoperative ROM has not yet been clarified. We aimed to evaluate the intraoperative femorotibial compressive force during passive knee motion, and determine the relationship between the compressive force and the postoperative flexion angle. A total of 11 knees in 10 patients who underwent primary cruciate-retaining (CR) TKA (The FINE Total Knee System; Teijin Nakashima Medical Co., Ltd., Okayama, Japan) for osteoarthritis were studied retrospectively, with a mean age of 76 years via a measured resection technique. We developed a customized measurement device mimicking the tibial component with this platform of six load sensors arranged in two rows (medial and lateral) by three tandem sets (anterior, center and posterior): anteromedial (AM), anterolateral (AL); centromedial (CM), centrolateral (CL); and posteromedial (PM), posterolateral compartment (PL) (Fig. 1). At the step of the implant trial, this device was placed on the tibia with compressive force recorded three times, while the knee was subsequently taken from 0° to full flexion manually in 15 seconds with the flexion angle of the knee recorded simultaneously by using an electric goniometer (Fig. 2). Eligibility were evaluated for ROM using a long-armed goniometer preoperatively and at 6 months postoperatively. A p value of < 0.05 was considered significant. The mean compressive force at AM, AL, CM, CL, PM and PL was 0.7, 0.5, 1.3, 1.2, 3.4 and 2.6 kgf, with the peak force of 4.2, 2.5, 4.1, 2.5, 7.3 and 4.7 kgf, respectively. The mean pre- and postoperative extension and flexion angles were −11° and −6°; and 115° and 113°, respectively. There were no significant correlations between the mean force in any region of interest (AM to PL) and the postoperative flexion angle. The peak force in PM showed little correlation with the postoperative flexion angle (r = −0.17, p = 0.54), however, that in PL was strongly negatively correlated with the postoperative flexion (r = −0.86, p < 0.01). The current results suggest the presence of less force on the lateral side in flexion. We speculate that lower compressive force at the lateral side is essential for deep flexion as it has been reported that the lateral structure has more laxity than the medial side during flexion in healthy knees. Measurement between the femoral and tibial compressive force can contribute an achievement of more flexion angle following CR-TKA

Introduction. Appropriate intraoperative soft tissue balancing is recognized to be essential in total knee arthroplasty (TKA). However, it has been rarely reported whether intraoperative soft tissue balance reflects postoperative outcomes. In this study, we therefore assessed the relationship between the intra-operative soft tissue balance measurements and the post-operative stress radiographs at a minimum 1-year follow-up in cruciate-retaining (CR) TKA, and further analyzed the postoperative clinical outcome. Methods. The subjects were 25 patients diagnosed with osteoarthritis with varus deformity and underwent primary TKA. The mean age at surgery was 72.0 ± 7.5 years (range, 47–84 years). The Surgeries were performed with the tibia first gap technique using CR-TKA (e motion, B. Braun Aesculap) and the image-free navigation system (Orthopilot). We intraoperatively measured varus ligament balance (°, varus angle; VA) and joint component gap (mm, center gap; CG) at 10° and 90° knee flexion guided by the navigation system, with the patella reduced. At a minimum 1-year follow-up, post-operative coronal laxity at extension was assessed by varus and valgus stress radiographs of the knees with 1.5 kgf using a Telos SE arthrometer (Fa Telos) and that at flexion was assessed by epicondylar view radiographs of the knees with a 1.5-kg weight at the ankle. After calculating postoperative VA and CG from measurements of radiographs, measurements and preoperative and postoperative clinical outcome, such as Knee Society Clinical Rating System (Knee score; KSS, Functional score; KSFS) and postoperative knee flexion, were analyzed statistically using linear regression models and Pearson's correlation coefficient. Results. The mean follow-up duration was 22.0 months (range, 12–36 months). The average pre-operative KSS and KSFS was 57.0 points and 62.8, respectively, and the average post-operative scores were 98.4 points and 91.5, respectively. The both scores were significantly improved. The mean preoperative knee flexion angle was 121.8°, and postoperative knee flexion angle was 124.8°.ã��The mean pre- and post-operative joint component gaps at extension and flexion were 14.4 and 14.4 mm, and 15.6 and 16.5 mm, respectively. The mean pre- and post-operative values of varus ligament balance at extension and flexion were 2.5° and 2.7°, and 1.7° and 4.4°, respectively. Regression analysis revealed that the intraoperative CG was positively correlated with the postoperative CG at both extension and flexion (R = 0.45, P < 0.05; R = 0.52, P < 0.05, respectively) and intraoperative VA was positively correlated with the postoperative VA at extension (R = 0.52, P < 0.05) (Figure 1). Furthermore, postoperative flexion angle was positively correlated with the postoperative CG and VA at flexion (R=0.43, p<0.05, R=0.44, p<0.05, respectively) (Figure 2). Conclusion. We revealed that intraoperative soft tissue balance reflect postoperative soft tissue balance in CR-TKA. Furthermore, postoperative lateral laxity at flexion may permit the improvement of postoperative flexion angle

Introduction

A bicruciate retaining (BCR) TKA is thought to maintain a closer resemblance to the native knee kinematics compared to a posterior cruciate retaining (CR) TKA. With BCR TKAs retainment of the anterior cruciate ligament (ACL) facilitates proprioception and balance which is thought to lead to more natural knee kinematics and increased functional outcome. The aim of this study was to quantify and compare the kinematics of a BCR and CR TKA during functional tests.

Introduction. An equal knee joint height during flexion and extension is of critical importance in optimizing soft-tissue balancing following total knee arthroplasty (TKA). However, there is a paucity of data regarding the in-vivo knee joint height behavior. This study evaluated in-vivo heights and anterior-posterior (AP) translations of the medial and lateral femoral condyles before and after a cruciate-retaining (CR)-TKA using two flexion axes: surgical transepicondylar axis (sTEA) and geometric center axis (GCA). Methods. Eleven patient with advanced medial knee osteoarthritis (age: 51–73 years) who scheduled for a CR TKA and 9 knees from 8 healthy subjects (age: 23–49 years) were recruited. 3D models of the tibia and femur were created from their MR images. Dual fluoroscopic images of each knee were acquired during a weight-bearing single leg lunge. The OA knee was imaged again one year after surgery using the fluoroscopy during the same weight-bearing single leg lunge. The in vivo positions of the knee along the flexion path were determined using a 2D/3D matching technique. The GCA and sTEA were determined based on existing methods. Besides the anterior-posterior translation, the femoral condyle heights were determined using the distances from the medial and lateral epicondyle centers on the sTEA and GCA to the tibial plateau surface in coronal plane (Fig. 1). The paired t-test was applied to compare the medial and lateral condyle motion within each group (Healthy, OA, and CR-TKA). Two-way ANOVA followed post hoc Newman–Keuls test was adopted to detect significant differences among the groups. p<0.05 was considered significant. Results. The results demonstrated that following TKA, the medial and lateral femoral condyle heights were not equal at mid-flexion (15° to 45°, medial condyle lower then lateral by 2.4mm at least, p<0.01), although the knees were well-balanced at 0° and 90° (Fig. 2). While the femoral condyle heights increased from the pre-operative values (>2mm increase on average, p<0.05), they were similar to the intact knees except that the medial sTEA was lower than the intact medial condyle between 0 and 90°. At deep flexion (>90°), both condyles were significantly higher (>2mm, p <0.01) than the healthy knees. Anterior femoral translation of the TKA knee was more pronounce at mid-flexion (Fig. 3), whereas limited posterior translation was found at deep flexion. Conclusion. Femoral condyle heights and AP translations of the CR TKA knees were significantly different from the healthy knees during the weight bearing flexion activity when measured using both the sTEA and GCA, especially at mid-flexion (15° to 45°) and deep flexion (>90°). These results suggest that a well-balanced knee intra-operatively might not necessarily result in mid-flexion and deep flexion balance during functional weight-bearing motion, implying mid-flexion instability and deep flexion tightness of the knee. The data could be useful for improvement of future prostheses designs and surgical techniques in treatment of patients with end-stage medial knee OA

Introduction. Total knee arthroplasty (TKA) with a computer-assisted navigation system has been developed to improve the accuracy of the alignment of osteotomies and implantations. One of the most important goals of TKA is to improve the flexion angle. Although accurate soft tissue balancing has been recognized as an essential surgical intervention influencing flexion angle, the direct relationship between post-operative flexion angle and intra-operative soft tissue balance during TKA, has little been clarified. In the present study, therefore, we focused on the relationship between them in cruciate-retaining (CR) TKA with a navigation system. Materials and methods. The subjects were 30 consecutive patients (2 men, 28 women), who underwent primary CR TKA (B. Braun Aesculap, e-motion) between May 2006 and December 2009. TKAs were performed using a image-free navigation system (OrthoPilot; B. Braun Aesculap, Tuttlingen, Germany). All cases were osteoarthritis with varus deformity. Average patient age at the time of surgery was 74.0 years (range, 62-86 years). After all bony resections and soft tissue releases were completed appropriately using a navigation system with tibia-first gap technique, a tensor was fixed to the proximal tibia and the femoral trial was fitted. Using the tensor that is designed to facilitate soft tissue balance measurements throughout the range of motion with a reduced patello-femoral (PF) joint and femoral component in place, the joint component gap and ligament balance (varus angle) were measured after the PF joint reduced and femoral component in place (Fig.1). Assessments of joint component gap and ligament balance were carried out at 0°, 30°, 60°, 90°, 120° flexion angle, which were monitored by the navigation system. Joint component gap change values during 30°- 0°, 60°- 0°, 90°- 0°, 120°- 0° flexion angle were calculated. The correlation between post operative flexion angles and pre-operative flexion angle, intra-operative joint component gaps, joint component gap change values and ligament balances were assessed using linear regression analysis. Results. Pre- and post-operative knee flexion angle averaged 120.5 ± 15.4° and 121.2 ± 8.3°. Pre-operative flexion angle was positively correlated with post-operative flexion angle (R = 0.408, P = 0.025). Average joint component gaps were 13.7, 17.1, 17.5, 16.0 and 15.3 mm at 0, 30, 60, 90 and 120° of flexion, respectively. Average ligament balances were 1.8, 1.3, -0.3, -4.2 and -4.9° in varus at 0, 30, 60, 90 and 120° of flexion, respectively. Average joint component gap changes were 3.4, 3.8, 2.4 and 1.6 mm at each range of motion between 30–0, 60-0, 90–0 and 120–0° of flexion, respectively. Joint component gap at 90° flexion (R = 0.473, P =0.008) and joint component gap change value 90–0° (R = 0.495, P =0.005) showed positive correlations with post-operative knee flexion angle (Fig.2). The other factors assessed in this study showed no correlation with post-operative knee flexion angle. Discussion. We performed an intra-operative assessment of soft tissue balance using the tensor in CR TKA with a navigation system. As previously reported, pre-operative flexion angle showed a positive correlation with post-operative flexion angle. Of note, the results showed smaller joint component gap at 90° flexion and joint gap change value 90–0° led to less flexion angle in CR TKA. Compared to posterior-stabilized TKA, CR TKA often results in tightened flexion gap. In such a situation, the results suggest that creation of relative larger flexion gap is important for acquisition of better flexion angle

Introduction

Initial stability of cementless total knee arthroplasty (TKA) tibial trays is necessary to facilitate biological fixation. Previous experimental and computational studies describe a dynamic loading micromotion test used to evaluate the initial stability of a design. Experimental tests were focused on cruciate retaining (CR) designs and walking gait loading. A FEA computational study of various constraints and activities found CR designs during walking gait experienced the greatest micromotion. This experimental study is a continuation of testing performed on CR and walking gait to include a PS design and stair descent activity.