Aims. The aim of this study was to compare a bicruciate-retaining (BCR) total knee arthroplasty (TKA) with a posterior cruciate-retaining (CR) TKA design in terms of kinematics, measured using fluoroscopy and stability as micromotion using radiostereometric analysis (RSA). Methods. A total of 40 patients with end-stage osteoarthritis were included in this randomized controlled trial. All patients performed a step-up and lunge task in front of a monoplane fluoroscope one year postoperatively. Femorotibial contact point (CP) locations were determined at every flexion angle and compared between the groups. RSA images were taken at baseline, six weeks, three, six, 12, and 24 months postoperatively. Clinical and functional outcomes were compared postoperatively for two years. Results. The BCR-TKA demonstrated a kinematic pattern comparable to the natural knee’s screw-home mechanism in the step-up task. In the lunge task, the medial CP of the BCR-TKA was more anterior in the early flexion phase, while laterally the CP was more posterior during the entire movement cycle. The BCR-TKA group showed higher tibial migration. No differences were found for the clinical and functional outcomes. Conclusion. The BCR-TKA shows a different kinematic pattern in early flexion/late extension compared to the CR-TKA. The difference between both implants is mostly visible in the flexion phase in which the anterior cruciate ligament is effective; however, both designs fail to fully replicate the motion of a natural knee. The higher migration of the BCR-TKA was concerning and highlights the importance of longer follow-up. Cite this article: Bone Joint J 2023;105-B(1):35–46

Aims. This study compared patient-reported outcomes of three total knee arthroplasty (TKA) designs from one manufacturer: one cruciate-retaining (CR) design, and two cruciate-sacrificing designs, anterior-stabilized (AS) and posterior-stabilized (PS). Methods. Patients scheduled for primary TKA were included in a single-centre, prospective, three-armed, blinded randomized trial (n = 216; 72 per group). After intraoperative confirmation of posterior cruciate ligament (PCL) integrity, patients were randomly allocated to receive a CR, AS, or PS design from the same TKA system. Insertion of an AS or PS design required PCL resection. The primary outcome was the mean score of all five subscales of the Knee injury and Osteoarthritis Outcome Score (KOOS) at two-year follow-up. Secondary outcomes included all KOOS subscales, Oxford Knee Score, EuroQol five-dimension health questionnaire, EuroQol visual analogue scale, range of motion (ROM), and willingness to undergo the operation again. Patient satisfaction was also assessed. Results. Patients reported similar levels of pain, function, satisfaction, and general health regardless of the prosthetic design they received. Mean maximal flexion (129° (95% confidence interval (CI) 127° to 131°) was greater in the PS group than in the CR (120° (95% CI 121° to 124°)) and AS groups (122° (95% CI 120° to 124°)). Conclusion. Despite differences in design and constraint, CR, AS, and PS designs from a single TKA system resulted in no differences in patient-reported outcomes at two-year follow-up. PS patients had statistically better ROM, but the clinical significance of this finding is unclear. Cite this article: Bone Joint J 2023;105-B(12):1271–1278

Purpose. To compare postoperative clinical outcomes between posterior cruciate ligament (PCL) retaining and resecting total knee arthroplasty (TKA) using same cruciate-substituting (CS) inserts, and to elucidate the clinical relevance of the residual PCL in cruciate-retaining TKA, considering intraoperative influence factors, such as the posterior tibial slope, posterior condylar offset, joint gap, joint balance, and joint laxity. Methods. A total of 64 consecutive knees (44 patients) were enrolled in this study and divided into following two groups: 39 knees underwent PCL-retaining TKA group (CR group), and 25 underwent PCL-resecting TKA group (CS group). Preoperative patients’ demographic data and one-year postoperative clinical outcomes including range of motion, the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Japanese Orthopaedic Association (JOA) score, and Forgotten Joint Score-12 (FJS-12) were compared between two groups. Results. Regarding range of motion, the average preoperative ROM was -14.3/120.0 degrees in the CR group and improved to -2.4/118.9 degrees postoperatively. In the CS group, the average preoperative ROM was -7.5/130 degrees and changed to -2.2/122.4 degrees postoperatively. There was no significant difference in the postoperative ROM between the groups (P=0.16). The KOOS (from 47.1 to 69.5 in CR group; from 41.1 to 70.8 in CS group) and JOA scores (from 59.2 to 76.9 in CR group; from 55.6 to 80.8 in CS group) were significantly improved postoperatively in both groups (P < 0.01). However, there was no significance in these postoperative scores between two groups (P = 0.09). There was also no significance in FJS-12 between two groups (70.3 in CR group and 66.9 in CS group; P=0.53). Conclusions. Residual PCL in TKA with a CS insert would not impact one-year postoperative clinical outcomes including KOOS, JOA, and FJS-12

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

Whether it is best to retain the posterior cruciate ligament in the degenerated knee, i.e. using a cruciate-retaining (CR) total knee prosthesis (TKP), or to use a more constraint posterior-stabilized (PS) TKP is of debate. There are limited studies comparing the effect of both methods on implant fixation and clinical outcome, leaving it up to the surgeon to base this decision on anything but conclusive evidence. We assessed the effect of two different philosophies in knee arthroplasty on clinical outcome and tibial component migration measured with radiostereometric analysis (RSA), by directly comparing the CR and PS version of an otherwise similarly designed cemented TKP. Sixty patients were randomized and received a Triathlon TKP (Stryker, NJ, USA) of either CR (n=30) or PS (n=30) design. RSA measurements (primary outcome) and clinical scores including the Knee Society Score and Knee injury and Osteoarthritis Outcome Score were evaluated at baseline, at three months postoperatively and at one, two, five and seven years. A linear mixed-effects model was used to analyse the repeated measurements. Both groups showed a similar implant migration pattern, with a maximum total point motion at seven years follow-up of around 0.8 mm of migration (mean difference between groups 95% CI −0.11 to 0.15mm, p=0.842). Two components (one of each group) were considered to have an increased risk of aseptic loosening. Both groups improved equally after surgery on the KSS and KOOS scores and no differences were seen during the seven years of follow-up. No differences in implant migration nor clinical results were seen seven years after cruciate-retaining compared to posterior-stabilized total knee prostheses

Introduction. Maintaining posterior stability in total knee arthroplasty (TKA) may be achieved by using a posterior stabilized TKA, retaining and balancing the posterior cruciate ligament (PCL) using a traditional cruciate-retaining design (CR), or by increasing the sagittal plane conformity of the tibial insert. In the latter case, stability is achieved by the addition of an anterior buildup on the tibial polyethylene creating the so-called “anterior stabilized” (AS) design. We hypothesized that using an AS tibial insert would provide similar function and survivorship as compared to using a more traditional CR bearing when the PCL is either recessed or balanced. Methods. Between 2004 and 2016, 1,731 modular CR TKAs were implanted in 1,509 patients using the same CR TKA design. The diagnosis was osteoarthritis in 98%. 58% of patients were female. Average age of 64.9 years. Within this group, 868 TKAs (50.1%) had a standard CR tibial bearing (3-degree posterior slope and no posterior lip) implanted (CR-S). 480 TKAs (27.8%) had a lipped CR modular tibial bearing (2.5 mm elevated posterior lip) implanted (CR-L). Starting in 2013, 383 TKAs (22.1%) were implanted with an AS modular tibial bearing (9–11 mm anterior lip and a 5 mm posterior lip). If the PCL was considered non-functional or absent, an AS bearing was placed. If the PCL was considered functional, a standard bearing or lipped bearing was used. Clinical and radiographic analysis was performed according to the Knee Society (KS) grading system. The most recent clinical and radiographic evaluation was used for post-operative analysis. The average follow-up in the entire cohort of TKAs was 5.5 years (range 2 to 14.3 years). Kaplan-Meier analysis was used to determine prosthesis survivorship with failure defined as aseptic loosening of the prosthesis (with or without revision) or tibial insert exchange. Results. At final follow-up, there were no significant differences in knee flexion, pain, function, or stair scores. Walking scores were significantly lower in the AS group. Posterior instability was higher in the CR-S group, whereas the manipulation rate was highest in the CR-L group (1.7% versus 1.3% and 0% in the CR-S and AS groups, respectively). Kaplan-Meier survivorship at five years, excluding infection, demonstrated no significant difference between the three groups (CR-S, CR-L, and AS tibial insert groups, 99% 100% and 99% respectively). Conclusion. When the PCL is considered non-functional at operation, the AS insert provided similar final flexion, function, stair score, and five-year survivorship when compared to using the standard and lipped CR tibial insert when the PCL was balanced. Using an ultra-congruent AS dished tibial component appears to be a reasonable option when the PCL is completely released or found deficient at operation. For figures, tables, or references, please contact authors directly

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

Aims

Patient dissatisfaction is not uncommon following primary total knee arthroplasty. One proposed method to alleviate this is by improving knee kinematics. Therefore, we aimed to answer the following research question: are there significant differences in knee kinematics based on the design of the tibial insert (cruciate-retaining (CR), ultra-congruent (UC), or medial congruent (MC))?

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

Purpose. This study was to investigate the effect of posterior tibial slope (PTS) on the kinematics in the cruciate-retaining total knee arthroplasty (CR-TKA) using 2- to 3- dimensional registration technique. Material & Methods. A total of 75 knees in 58 patients were recruited and categorized into the following two groups according to PTS. Group A was categorized PTS under 7degrees (n = 33) and group B was categorized PTS over 7 degrees (n = 42). The average age of group A and group B at the time of fluoroscopic surveillance date was 73.5 ± 7.4 years and 74.3 ± 4.5 years, respectively and the average follow-up period from operation date to fluoroscopic surveillance date was 13.8 ± 9.3 months and 16.7 ± 8.6 months, respectively. In vivo kinematics during sequential deep knee bending under weight-bearing condition were evaluated using fluoroscopic image analysis and 2- to 3- dimensional registration technique. Range of motion (ROM), axial rotation, anteroposterior (AP) translations of medial and lateral nearest points of the femoral component relative to the tibial component were measured and compared between the two groups. The nearest points were determined by calculating the closest distance between the surfaces of femoral component model and the axial plane of coordinate system of the tibial component. We defined external rotation and anterior translation as positive. P values under 0.05 was defined as statistically significant. Results. The mean PTS in group A and B were 5.5 ± 1.4°and 9.9 ± 1.9°, respectively. There was no statistically significant difference in the degrees of axial rotation from 0° to 110° of flexion between the two groups (4.9 ± 4.2° vs 5.2 ± 4.2°, p > 0.05), respectively. The hyperextension of group B were significantly larger than group A (−2.3 ± 6.6°vs −9.8 ± 8.7°, p <0.05). The ROM of group B were significantly larger than group A (118.7 ± 10.8°vs 128.7 ± 17.7°, p <0.05). However, there was no significant difference in the maximum flexion between the two groups (116.4 ±10.8°vs 118.9±14.5°, p >0.05), respectively. In terms of AP translation, medial nearest points were located significantly more posterior at 0°, 10°, 30°, 40° of flexion in group B compared to group A. There was no significant difference in the location of lateral nearest points between the two groups during all knee range of motion. Discussion/Conclusion. The results shown in this study demonstrated that the PTS influenced the kinematics and ROM under weight-bearing condition in CR-TKA. The large PTS induced great posterior displacement of medial nearest points during early flexion phase and increased hyperextension between the femoral and tibial components

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

The aim of the study was to compare clinical results after cruciate-retaining total knee arthroplasty (TKA) between the ceramic and the Co-Cr alloy condylar prostheses. In a prospective semi-randomised study, 218 patients underwent cruciate-retaining TKA with the Co-Cr alloy prosthesis (Kinemax®, Howmedica) or the LFA-I® prosthesis (Kyocera) composed of an alumina ceramic femoral component and a titaniumalloy tibial component with a UHMWPE insert. In each surgery, both components were fixed with PMMA cement. All the patients underwent the same postoperative management. Finally, 110 knees with the ceramic prosthesis and 84 knees with the Co-Cr prosthesis were followed up for 24 to 124 months (the average of 56 months). Two revisions were performed in each group (tibial tray breakage and infection in the ceramic group, and loosening and infection in the Co-Cr group). In the remaining patients, there were no significant differences in the HSS knee score (85 and 86 points, respectively) and the ROM (112 and 113 degrees) between the two groups. In radiological evaluation, a radiolucent line was more frequently observed with the significance (p< 0.05) in the Co-Cr alloy group (9.5 %) than in the ceramic group (2.7 %). In the mid-term follow-up evaluations, the clinical results of the ceramic TKA are equivalent to those of the Co-Cr alloy TKA. In addition, the ceramic prosthesis showed some statistical tendency of superiority to the Co-Cr prosthesis concerning the radiolucent line. These results encouraged us to conduct a long-term follow-up study on the ceramic total knee prosthesis

Purpose: A common difficulty with manually-performed total knee arthroplasties (TKAs) is obtaining accurate intra-operative soft tissue balancing, an aspect of this procedure that surgeons traditionally address through their “subjective feel” and experience with an unphysiological joint condition. We have therefore developed a new tensor for TKAs that enables us to assess for soft tissue balancing throughout the range of motion about the knee with a reduced patello-femoral (PF) joint and femoral component in place. This tensor permits us to intra-operatively reproduce the post-operative alignment of the PF and tibio-femoral joints. The main purpose of this study is to compare ligament balance in cruciate-retaining (CR) and posterior-stabilized (PS) TKAs. Methods: Using the tensor, we intra-operatively compared the ligament balance measurements of CR and PS TKAs performed at 0, 10, 45, 90 and 135° of flexion, with the patella both everted and reduced. From a group of 40 consecutive females (40 varus osteoarthritic knees) blinded to the type of implant received, we prospectively randomized 20 patients to receive a CR TKA (NexGen CR Flex) and the other 20 patients a PS TKA (NexGen LPS Flex). The CR TKA group had a mean age of 73.7 ± 1.3 years while the PS TKA group had a mean age of 73.8 ± 1.7 years. Results: The mean values of varus angle in CR TKA with the knee at 0, 10, 45, 90 and 135 degrees of flexion were 3.0, 3.2, 2.7, 4.2 and 5.1 ° with the patella everted, and 3.9, 4.2, 2.5, 2.0 and 2.0 ° with the patella reduced. The mean values of varus angle in PS TKA at these same degrees of flexion, respectively, were 3.0, 4.1, 6.0, 6.2 and 6.1 ° with the patella everted, and 3.8, 4.1, 6.3, 6.3 and 4.9 ° with the patella reduced. While the ligament balance measurements with a reduced patella of PS TKAs slightly increased in varus from extension to mid-range of flexion (p< 0.05), these values slightly decreased for CR TKA (p< 0.05). Additionally, the ligament balance at deep knee flexion was significantly smaller in varus for both types of prosthetic knees when the PF joint was reduced (p< 0.05). Conclusion: Accordingly, we conclude that the ligament balance kinematic patterns differ between everted and reduced patellae, as well as between PS and 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