Aims. This study aimed to analyze kinematics and kinetics of the tibiofemoral joint in healthy subjects with valgus, neutral, and varus limb alignment throughout multiple gait activities using dynamic videofluoroscopy. Methods. Five subjects with valgus, 12 with neutral, and ten with varus limb alignment were assessed during multiple complete cycles of level walking, downhill walking, and stair descent using a combination of dynamic videofluoroscopy, ground reaction force plates, and optical motion capture. Following 2D/3D registration, tibiofemoral kinematics and kinetics were compared between the three limb alignment groups. Results. No significant differences for the rotational or translational patterns between the different limb alignment groups were found for level walking, downhill walking, or stair descent. Neutral and varus aligned subjects showed a mean centre of rotation located on the medial condyle for the loaded stance phase of all three gait activities. Valgus alignment, however, resulted in a centrally located centre of rotation for level and downhill walking, but a more medial centre of rotation during stair descent. Knee adduction/abduction moments were significantly influenced by limb alignment, with an increasing knee adduction moment from valgus through neutral to varus. Conclusion. Limb alignment was not reflected in the condylar kinematics, but did significantly affect the knee adduction moment. Variations in frontal plane limb alignment seem not to be a main modulator of condylar kinematics. The presented data provide insights into the influence of anatomical parameters on tibiofemoral kinematics and kinetics towards enhancing clinical decision-making and surgical restoration of natural knee joint motion and loading. Cite this article: Bone Joint Res 2024;13(9):485–496

Purpose and background. Identifying features in nonspecific low back pain (NSLBP) subjects that distinguish them from controls, or for elucidating subgroups, has proved elusive. Yet these would be helpful to monitor progress, improve management, and understand the nature of the condition. Previous work using quantitative videofluoroscopy (QF) has indicated that the distribution of motion between lumbar intervertebral joints is more uneven in those with a history of NSLBP. However, there maybe other features of these complex motion patterns yet to be revealed. A multivariate analysis was therefore carried out to explore other possible differences. Methods and results. Intervertebral motion data of L2/3 to L4/5, from a previously published study was used. This examined 40 patients with NSLBP and 40 healthy controls, matched for gender, age and body mass index, who underwent passive recumbent QF in the coronal and sagittal planes. For each motion direction, principal components analysis was carried out and salient dimensions selected. Using a lower dimensional principal components (PC) representation, groups were compared using Hoteling's T test. Linear and quadratic discriminant analysis (LDA and QDA) was carried out using PC representations to examine group differences. The features most clearly distinguishing groups from the LDA was examined graphically. An analysis of the sensitivity of the results to the number of PC dimensions was carried out. The performance of the LDA and QDA classifiers were examined using leave-one-out cross-validation. Conclusions. Hotelling tests revealed significant differences between groups for right and left side-bending. This was confirmed by LDA and QDA. There was no clear difference in the performance of these classifiers and performance did not improve by including more than 4 PC dimensions. Visualisation of the LDA indicated that patients had relatively lower amplitude motion at L4/5, compensated by higher amplitude at L2/3/4. These results point to additional features of lumbar motion that differentiates NSLBP. No conflicts of interest. No funding obtained (however, the original study was funded by NIHR - CATCDRF09)

Purpose of the study: Congruence between the femoral component and the insert has been proposed to decrease wear in total knee arthroplasty (TKA). This congruence should favour unidirectional movement between the components because multidirectional movements carry a risk factor for wear up to 30-fold higher than unidirectional movements. This study explored in vivo displacements between the insert and the femoral component of a prosthesis in order to determine whether they meet the required kinematic criteria. Material and methods: Twelve patients (7 women, 5 men) aged 45 to 79 years with BMI from 23 to 35 underwent knee surgery for osteoarthritis and were included in this study. The prosthesis was a mobile plateau pros-thesis implanted by the same surgeon using a navigation system. During the procedure, four tantalum beads were implanted in the polyethylene under stereotaxic guidance. The postoperative evaluation was performed at six months with the clinical evaluation (KSS, WOMAC) a 3D fluoroscopic protocol (walking, stairs, get up and go) and a radiostereometric analysis (RSA). Results: Active flexion under weight bearing was 118 (range 102–125) and the mean KSS 165. The videofluoroscopy combined with RSA showed congruent axial rotation between the femoral component and the insert in the flexion arc 0/60 with a mean difference of 0.38 per degree of flexion (SD 1.85). Beyond 60° flexion, the posterior displacement of the condyle was greater than the insert rotation. Discussion: Compared with other 3D videofluoroscopic studies, this analysis adds greater accuracy due to the implantation of tantalum beads in the insert, enabling a study of insert displacement in relation to the metal components. This method demonstrates that for the implant studied here, rotation of the insert follows the displacement of the femoral component exactly from 0 to 60° flexion, this is a gliding displacement. Then beyond 60°, a gliding plus rolling movement occurs displacing the femoral component posteriorly. Conclusion: This in vivo study in patients with a mobile plateau knee prosthesis demonstrates that the insert has a rotation exactly like the femoral component and that complete congruency is maintained between the femoral component and the insert with a pure gliding contact from 0 to 60° flexion. The prerequisite criteria for this type of prosthesis designed to reduce the wear factor are thus confirmed

Introduction. The SAIPH™ (MatOrtho, UK) total knee replacement is a new fixed-bearing prosthesis design having attributes of a mobile bearing and the posterior stabilised categories for knee arthroplasties. The implant design goal is an articulation that provides definitive anteroposterior stability to beneficially control tibiofemoral translation, the ability for the tibia to axially rotate to accommodate various lifestyle activities, and to maintain a relatively posterior femoral position on the tibia to facilitate range of motion. This study aims to analyze knee kinematics of the SAIPH™ total knee arthroplasty (TKA) by videofluroscopy during four different weightbearing activities. Method. Fourteen consecutive patients operated on by a single surgeon, with a minimum follow up of 24 months were included in this IRB-approved study. A medially conforming knee was implanted in all cases. Participants in the study were asked to perform weightbearing kneeling, lunging, step-up/down and pivoting activities while their knee motions were recorded by videofluoroscopy. Three-dimensional (3D) joint kinematics were determined using model-image registration. The 3D orientation of each TKA component was expressed using standard joint angle conventions, and the anterior/posterior location of each condyle was expressed relative to the deepest part of the tibial sulcus. Results. Maximum knee flexion during the kneeling activity averaged 127 ° (100°–155°). Condylar contact was posterior on the tibia during kneeling (Figure 1). The medial femoral condyle (MFC) translated an average of 4 mm (SD 3 mm) posteriorly at 127 ° of kneeling flexion. The lateral femoral condyle (LFC) translated posteriorly 8 mm (SD 3 mm). None of these knees demonstrated paradoxical forward slide of the femur during this activity. The tibia rotated internally an average of 5° during flexion. During the lunge activity mean knee flexion was 121°. There was a similar asymmetric posterior translation of the femoral condyles, 5 mm for the MFC, and 8 mm for the LFC, and an average internal rotation of the tibia of 3°. During the step-up/down activity the MFC translated posteriorly 2 mm, and the LFC 3 mm (Figure 2). The tibia internally rotated 4° from extension to 85° flexion during stepping. During the pivot activity, the MFC remain stable in the tibial sulcus and the LFC translated posteriorly while the tibia rotated externally to internally (Figure 3). Conclusion. The SAIPH™ knee shows a medial pivot motion with tibial internal rotation of the tibia during active weightbearing flexion and deep knee flexion, as seen in previous studies. The kinematics are similar in pattern to normal knees showing an asymmetric posterior translation of the lateral femoral condyle and tibial internal rotation with knee flexion. A medially conforming implant design provides intrinsic anteroposterior stability to control femoral translation across the entire range of flexion, allows tibial rotation, and provides functional flexion comparable to specialized posterior-stabilised implant designs

Observations of knee arthroplasty kinematics generally show differences in anteroposterior translation when comparing posterior cruciate retaining (CR) and posterior stabilised (PS) designs. However, the PS cam/post mechanism is not engaged in extension. We hypothe-sised that there would be little difference between CR and PS knee kinematics during stance in gait. Videofluoroscopy and shape matching techniques were used to quantify motions of 47 fixed-bearing knee arthroplasties (24 CR, 23 PS) during gait and stair-climbing in consenting patients with excellent clinical/ functional performance at least one year post-surgery. The average centre of rotation (COR) was computed for each knee during the two activities; a lateral COR (−50% to 0%) indicates anterior femoral translation with flexion, a medial COR (0% to +50%) indicates posterior femoral translation with flexion. There was a significant difference between the average COR in the PS (+9%) and CR (−15%) knees for the stair climbing activity (p< 0.001), but not the stance phase of gait (−5% vs. −14%, respectively, p=0.664). The COR was more lateral for the stance phase of gait than for stair climbing in the PS knees (p=0.008), but not the CR knees (p=0.948). All knees showed more axial rotation during the stair activity (8°) than the stance phase of gait (5°, p< 0.001). During stance in gait, there were small but not significant differences in the centre of rotation between the CR and PS knees. For stair climbing, there were significant differences between CR and PS knee kinematics. These observations are consistent with the hypothesis that CR and PS kinematics ought to be similar near extension, where the articular constraints are similar, but might differ in deeper flexion activities where the intrinsic constraints of the arthroplasty are different. An improved understanding of arthroplasty function should facilitate further evolution of design, surgical techniques, and numerical analyses to optimise patient performance

Purpose: Cinematic studies after total knee arthroplasty without an anterior cruciate ligament demonstrate abnormal behaviour compared with the normal knee. The purpose of this cinematic analysis was to examine the knee behaviour after implantation of single-compartment prostheses with an intact anterior cruciate ligament. Material and methods: The femorotibial contact points were analysed by videofluoroscopy in 20 patients executing a complete weight-bearing extension to flexion movement. These patients had medial (n=16) or lateral (n=4) single-compartment implants. The clinical result in all patients was considered to be very good with a mean HSS score of 97.9 points at a mean 56 months postoperatively. The femorotibial contact points were determined using an automatic computerised adaptation-modelling system. An anterior contact on the medial tibial line in the sagittal plane was positive and a posterior contact was negative. The rotation axis in the craniopodal direction was measured between the anteroposterior longitudinal axis of the femoral component and the fixed axis of the tibial component. Results: The mean position of the contact point for medial single-compartment prostheses was −90.8 mm in complete extension, −1.4 mm at 30° flexion, −2.4 mm at 60°, and −1.7 mm at 90°. Mean position of the contact point for lateral single-compartment prostheses was −4.0 mm at complete extension, −7.9 mm at 30° flexion, −5.7 mm at 60° and −5/7 mm at 90°. Seven patients with a medial implant and two patients with a lateral implant exhibited paradoxical anterior translation of the femur during flexion. On the average, patients with a medial implant had normal 3.3° axial rotation at 90°; axial rotation was 11.2° for patients with a lateral implant. Discussion and conclusion: Cinematic analysis of the normal knee has demonstrated anterior femorotibial contact in extension and 14.2 mm posterior rolling of the femoral component during flexion. After total knee arthroplasty without preservation of the anterior cruciate ligament, the rolling movement is limited or absent and a paradoxical anterior translation can be observed. In the present study, the first reported on single-compartment implants, demonstrates that movement is similar to that in the normal knee but with major interindividual variability. A posterior contact at extension and a paradoxical anterior translation can also be observed. This suggests progressive development of anterior cruciate ligament laxity over time, which can at least in part explain the premature polyethylene wear observed after implantation of single-compartment knee implants