Knee kinematics are not different between asymmetrical and symmetrical tibial baseplates in total knee arthroplasty: A fluoroscopic analysis of step-up and lunge motions.

PURPOSE: This clinical fluoroscopy study investigated knee kinematics of two different cemented fixed-bearing, posterior-stabilised (PS) total knee arthroplasty (TKA) designs: an asymmetric tibial component including an asymmetric insert designed to optimise personalised balance and fit and its precursor symmetrical design with symmetric insert. METHODS: A consecutive series of patients (16 TKAs from each treatment group) participating in a randomised controlled trial comparing TKA migration was included. The exclusion criterion was the use of walking aids. Flat-panel fluoroscopic recordings of step-up and lunge motions were acquired 1-year postoperatively. Medial and lateral contact points (CPs) were determined to calculate CP displacement, femoral axial rotation and pivot position. Using linear mixed-effects modelling techniques, kinematics between TKA designs were compared. RESULTS: During knee extension between 20° flexion and full extension, the CPs moved anteriorly combined with a small internal femoral rotation (a screw-home mechanism). Whereas CP movement was reversed: femoral rollback, external femoral rotation while flexing the knee between full extension and 20° knee flexion, At larger flexion angles, femoral axial rotation (FAR) occurred around a lateral pivot point both during step-up and lunge. The symmetric design had a 2.3° larger range of FAR compared to the asymmetric design during lunge (p = 0.02). All other kinematics were comparable. CONCLUSION: Despite the differences in design, this study showed that the asymmetric and symmetric PS TKA designs had mostly comparable knee kinematics during step-up and lunge motions. It is therefore expected that the functionality of the successor TKA design is similar to that of its precursor design. LEVEL OF EVIDENCE: Level II, prospective comparative study.

Total Knee Arthroplasty Kinematics.

Knee kinematics is an analysis of motion pattern that is utilized to assess a comparative, biomechanical performance of healthy nonimplanted knees, injured nonimplanted knees, and various prosthetic knee designs. Unfortunately, a consensus between implanted knee kinematics and outcomes has not been reached. One might hypothesize that the kinematic variances between the nonimplanted and implanted knee might play a role in patient dissatisfaction following TKA. There is a wide range of TKA designs available today. With such variety, it is important for surgeons and engineers to understand the various geometries and kinematic profiles of available prostheses. The purpose of this review is to provide readers with the pertinent information related to TKA kinematics.

Maximum flexion and lateral rollback revealed better patient satisfaction after total knee arthroplasty.

INTRODUCTION: Patient satisfaction is an important outcome of total knee arthroplasty (TKA). However, we cannot predict how and why patients are satisfied or dissatisfied with TKA. The hypothesis of this study was that patient-reported outcomes (PROs) correlate with in vivo kinematics after TKA. MATERIALS AND METHODS: One hundred knees were analyzed after TKA. The in vivo kinematics of deep knee bending motion were estimated from single-plane fluoroscopy using a two-to-three-dimensional registration technique. Active knee flexion, femoral rotation and rollback were evaluated. The PROs were obtained after surgery using the 2011 Knee Society Scoring System (KSS), and their relationship with in vivo kinematics was determined. RESULTS: The average minimum and maximum flexion were -2.4 ± 7.3° and 113.2 ± 13.6°, respectively. The average femoral rotation was 7.4 ± 3.4°, and the average medial and lateral rollback were 2.4 ± 4.8 mm and 7.2 ± 5.6 mm, respectively. The multiple regression analysis revealed that the maximum flexion angle significantly contributed to symptoms and satisfaction. In addition, lateral rollback was also a significant factor affecting patient satisfaction. Lateral rollback and lateral Anterior-Posterior (AP) position at maximum flexion were correlated with the maximum flexion angle, whereas femoral rotation did not correlate with flexion angles. CONCLUSIONS: Maximum flexion and lateral rollback are important for better patient satisfaction after TKA. To obtain the maximum flexion angle, it was necessary to perform the normal kinematic pattern with a large amount of lateral rollback.

Comparable in vivo joint kinematics between self-reported stable and unstable knees after TKA can be explained by muscular adaptation strategies: A retrospective observational study.

Background: Postoperative knee instability is one of the major reasons accounting for unsatisfactory outcomes, as well as a major failure mechanism leading to total knee arthroplasty (TKA) revision. Nevertheless, subjective knee instability is not well defined clinically, plausibly because the relationships between instability and implant kinematics during functional activities of daily living remain unclear. Although muscles play a critical role in supporting the dynamic stability of the knee joint, the influence of joint instability on muscle synergy patterns is poorly understood. Therefore, this study aimed to understand the impact of self-reported joint instability on tibiofemoral kinematics and muscle synergy patterns after TKA during functional gait activities of daily living. Methods: Tibiofemoral kinematics and muscle synergy patterns were examined during level walking, downhill walking, and stair descent in eight self-reported unstable knees after TKA (3M:5F, 68.9 ± 8.3 years, body mass index [BMI] 26.1 ± 3.2 kg/m2, 31.9 ± 20.4 months postoperatively), and compared against 10 stable TKA knees (7M:3F, 62.6 ± 6.8 years, 33.9 ± 8.5 months postoperatively, BMI 29.4 ± 4.8 kg/m2). For each knee joint, clinical assessments of postoperative outcome were performed, while joint kinematics were evaluated using moving video-fluoroscopy, and muscle synergy patterns were recorded using electromyography. Results: Our results reveal that average condylar A-P translations, rotations, as well as their ranges of motion were comparable between stable and unstable groups. However, the unstable group exhibited more heterogeneous muscle synergy patterns and prolonged activation of knee flexors compared to the stable group. In addition, subjects who reported instability events during measurement showed distinct, subject-specific tibiofemoral kinematic patterns in the early/mid-swing phase of gait. Conclusions: Our findings suggest that accurate movement analysis is sensitive for detecting acute instability events, but might be less robust in identifying general joint instability. Conversely, muscle synergy patterns seem to be able to identify muscular adaptation associated with underlying chronic knee instability. Funding: This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.

Kinematically Aligned Total Knee Arthroplasty Using Medial Pivot Knee Prosthesis Enhances Medial Pivot Motion: A Comparative Kinematic Study With Mechanically Aligned Total Knee Arthroplasty.

BACKGROUND: Clinical outcomes of kinematically aligned total knee arthroplasty (KA-TKA) have been reported as comparable or superior to those of mechanically aligned TKA (MA-TKA). However, cruciate-retaining prostheses have mostly been used for KA-TKA. This study used medial pivot knee prostheses for KA-TKA, and knee kinematics after KA-TKA were assessed and compared with those after MA-TKA. METHODS: Thirteen knees in 9 patients undergoing primary TKA (8 KAs, 5 MAs) were subjected to two-dimensional (2D) to three-dimensional (3D) registration analysis at 1 year postoperatively. Each patient performed weight-bearing activities, and movements were recorded as intermittent digital radiographic images. Three-dimensional implant positions during activities were analyzed for anterior-posterior translation in the sagittal plane, condylar liftoff and mediolateral translation in the coronal plane, and femoral rotation in the axial plane. RESULTS: Posterior translation of the lateral femoral condyle from 0° to 100° was larger in KA-TKA than in MA-TKA (P = .006). The degrees of condylar liftoff and mediolateral translation were comparable between TKAs. Total external rotation of the femoral component relative to tibial component was significantly greater for KA-TKA (7.7 ± 5.2°) than for MA-TKA (1.3 ± 3.3°; P = .03). The kinematic path of the femoral component revealed greater medial pivoting motion in KA-TKA than in MA-TKA. CONCLUSIONS: KA-TKA using a medial pivot knee prosthesis successfully reproduced the medial pivot pattern and achieved larger femoral external rotation relative to the tibia than MA-TKA. KA-TKA was able to maximize the primary concept of the medial pivot knee prosthesis.

Variations in morphological characteristics of prostheses for total knee arthroplasty leading to kinematic differences.

BACKGROUND AND PURPOSE: The aim of this study is to compare kinematics during weight-bearing deep knee-bending motion in patients after bilateral total knee arthroplasty (TKA) of two types: 1) a conventional ScorpioFlex prosthesis and 2) a contemporary redesigned non-restrictive-geometry (NRG) prosthesis installed by the same surgeon. METHODS: We enrolled 15 patients who underwent conventional ScorpioFlex posterior-stabilised TKA in one knee and contemporary NRG TKA on the contralateral side (the same surgeon). During fluoroscopic examination, each patient performed weight-bearing deep knee bending. Motions among all components were analysed using a two- to three-dimensional registration technique. RESULTS: The mean maximum flexion was 108° (SD 8) and 120° (SD 9) after ScorpioFlex and NRG TKAs, respectively; there were statistically significant differences between the groups. From extension to maximal flexion, the medial condyle translated by 4.8mm (SD 1.2) and 5.4mm (SD 2.4) posteriorly after ScorpioFlex TKA and NRG TKA, respectively. The lateral femoral condyle moved 8.4mm (SD 1.5) and 12.2mm (SD 2.1) posteriorly after ScorpioFlex TKA and NRG TKA, respectively. There were no significant differences in medial condyle translation between the groups except for the lateral condyle. The total amount of tibial axial rotation during extension to flexion was 5.1° (SD 1.8) after ScorpioFlex and 13.2° (SD 3.4) after NRG TKAs; there were statistically significant differences between the groups. CONCLUSIONS: NRG resulted in much better maximum flexion, lateral condyle movement and tibial internal rotation than did ScorpioFlex TKAs. The observed kinematic differences are most likely caused by variations in the morphological characteristics of the two implants.

Performance of local optimization in single-plane fluoroscopic analysis for total knee arthroplasty.

Fluoroscopy-derived joint kinematics plays an important role in the evaluation of knee prostheses. Fluoroscopic analysis requires estimation of the 3D prosthesis pose from its 2D silhouette in the fluoroscopic image, by optimizing a dissimilarity measure. Currently, extensive user-interaction is needed, which makes analysis labor-intensive and operator-dependent. The aim of this study was to review five optimization methods for 3D pose estimation and to assess their performance in finding the correct solution. Two derivative-free optimizers (DHSAnn and IIPM) and three gradient-based optimizers (LevMar, DoNLP2 and IpOpt) were evaluated. For the latter three optimizers two different implementations were evaluated: one with a numerically approximated gradient and one with an analytically derived gradient for computational efficiency. On phantom data, all methods were able to find the 3D pose within 1mm and 1° in more than 85% of cases. IpOpt had the highest success-rate: 97%. On clinical data, the success rates were higher than 85% for the in-plane positions, but not for the rotations. IpOpt was the most expensive method and the application of an analytically derived gradients accelerated the gradient-based methods by a factor 3-4 without any differences in success rate. In conclusion, 85% of the frames can be analyzed automatically in clinical data and only 15% of the frames require manual supervision. The optimal success-rate on phantom data (97% with IpOpt) on phantom data indicates that even less supervision may become feasible.

Plantar-flexion of the ankle joint complex in terminal stance is initiated by subtalar plantar-flexion: A bi-planar fluoroscopy study.

Gross motion of the ankle joint complex (AJC) is a summation of the ankle and subtalar joints. Although AJC kinematics have been widely used to evaluate the function of the AJC, the coordinated movements of the ankle and subtalar joints are not well understood. The purpose of this study was to accurately quantify the individual kinematics of the ankle and subtalar joints in the intact foot during ground walking by using a bi-planar fluoroscopic system. Bi-planar fluoroscopic images of the foot and ankle during walking and standing were acquired from 10 healthy subjects. The three-dimensional movements of the tibia, talus, and calcaneus were calculated with a three-dimensional/two-dimensional registration method. The skeletal kinematics were quantified from 9% to 86% of the full stance phase because of the limited camera speed of the X-ray system. At the beginning of terminal stance, plantar-flexion of the AJC was initiated in the subtalar joint on average at 75% ranging from 62% to 76% of the stance phase, and plantar-flexion of the ankle joint did not start until 86% of the stance phase. The earlier change to plantar-flexion in the AJC than the ankle joint due to the early plantar-flexion in the subtalar joint was observed in 8 of the 10 subjects. This phenomenon could be explained by the absence of direct muscle insertion on the talus. Preceding subtalar plantar-flexion could contribute to efficient and stable ankle plantar-flexion by locking the midtarsal joint, but this explanation needs further investigation.

Detecting condylar contact loss using single-plane fluoroscopy: a comparison with in vivo force data and in vitro bi-plane data.

Knee contact mechanics play an important role in knee implant failure and wear mechanics. Femoral condylar contact loss in total knee arthroplasty has been reported in some studies and it is considered to potentially induce excessive wear of the polyethylene insert.Measuring in vivo forces applied to the tibial plateau with an instrumented prosthesis is a possible approach to assess contact loss in vivo, but this approach is not very practical. Alternatively, single-plane fluoroscopy and pose estimation can be used to derive the relative pose of the femoral component with respect to the tibial plateau and estimate the distance from the medial and lateral parts of the femoral component towards the insert. Two measures are reported in the literature: lift-off is commonly defined as the difference in distance between the medial and lateral condyles of the femoral component with respect to the tibial plateau; separation is determined by the closest distance of each condyle towards the polyethylene insert instead of the tibia plateau.In this validation study, lift-off and separation as measured with single-plane fluoroscopy are compared to in vivo contact forces measured with an instrumented knee implant. In a phantom study, lift-off and separation were compared to measurements with a high quality bi-plane measurement.The results of the in vivo contact-force experiment demonstrate a large discrepancy between single-plane fluoroscopy and the in vivo force data: single-plane fluoroscopy measured up to 5.1mm of lift-off or separation, whereas the force data never showed actual loss of contact. The phantom study demonstrated that the single-plane setup could introduce an overestimation of 0.22mm±±0.36mm. Correcting the out-of-plane position resulted in an underestimation of medial separation by -0.20mm±±0.29mm.In conclusion, there is a discrepancy between the in vivo force data and single-plane fluoroscopic measurements. Therefore contact loss may not always be determined reliably by single plane fluoroscopy analysis.

Is greater than 145{degrees} of deep knee flexion under weight-bearing conditions safe after total knee arthroplasty?: a fluoroscopic analysis of Japanese-style deep knee flexion.

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