Does the condylar lift-off method or the separation method better detect loss of contact between tibial and femoral implants based on analysis of single-plane radiographs following total knee arthroplasty?

BackgroundLoss of contact between the femoral and tibial implants following total knee arthroplasty (TKA) has been related to accelerated polyethylene wear and other complications. Two methods have been used to detect loss of contact in single-plane fluoroscopy, the condylar lift-off method and the separation method. The objectives were to assess the ability of each method to detect loss of contact.MethodsTKA was performed on ten cadaveric knee specimens. Tibial force was measured in each compartment as specimens were flexed from 0° to 90° while internal-external and varus-valgus moments were applied. Single-plane radiographs taken simultaneously with tibial force were analyzed for loss of contact using the two methods. Receiver operating characteristic (ROC) and optimum threshold distances were determined.ResultsFor the lift-off method and the separation method, the areas under the ROC curves were 0.89 vs 0.60 for the lateral compartment only and 0.81 vs 0.70 for the medial compartment only, respectively. For the lift-off method, the optimum threshold distances were 0.7 mm in the lateral compartment only and 0.1 mm in the medial compartment only but the false positive rate for the medial compartment only almost doubled. For both compartments jointly, the areas under the ROC curves decreased to 0.70 and 0.59 for the lift-off and separation methods, respectively.ConclusionWhen detecting loss of contact using single-plane fluoroscopy, the lift-off method is useful for the lateral compartment only but not for the medial compartment only and not for both compartments jointly. The separation method is not useful.     

A novel cross-shear metric for application in computer simulation of ultra-high molecular weight polyethylene wear

Wear testing of polyethylene in total joint replacements is common and required for any new device. Computational wear modelling has obvious utility in this context as it can be conducted with much greater economy than physical testing. Archard's law has become the accepted standard for wear simulation in total joints but it does not account for cross-shear, which is known to increase wear significantly relative to unidirectional sliding. The purpose of this study was to develop a robust cross-shear model applicable to any interface geometry under any kinematic conditions. The proposed metric, x ^*, is distinguished from existing cross-shear models by the fact that it measures cross-path motion incrementally throughout a motion cycle and quantifies cross-shear based on incremental changes in sliding direction. Validation showed strong support for the predictive capability of x ^* when applied to pin-on-disc test data.     

Foot structure and knee joint kinetics during walking with and without wedged footwear insoles

The relationship between static foot structure characteristics and knee joint biomechanics during walking, or the biomechanical response to wedged insoles are currently unknown. In this study, 3D foot scanning, dual X-ray absorptiometry and gait analysis methods were used to determine structural parameters of the foot and assess their relation to knee joint loading and biomechanical response to wedged insoles in 30 patients with knee osteoarthritis. In multiple linear regression models, foot fat content, height of the medial longitudinal arch and static hind foot angle were not associated with the magnitude of the knee adduction moment (R² = 0.24, p = 0.060), knee adduction angular impulse (R² = 0.21, p = 0.099) or 3D resultant knee moment (R² = 0.23, p = 0.073) during gait. Furthermore, these foot structure parameters were not associated with the patients’ biomechanical response to medial or lateral wedge footwear insoles (all p < 0.01). These findings suggest that static foot structure is not associated with gait mechanics at the knee, and that static foot structure alone cannot be utilized to predict an individual’s biomechanical response to wedged footwear insoles in patients with knee osteoarthritis.     

Enhanced computational prediction of polyethylene wear in hip joints by incorporating cross-shear and contact pressure in additional to load and sliding distance: Effect of head diameter

A new definition of the experimental wear factor was established and reported as a function of cross-shear motion and contact pressure using a multi-directional pin-on-plate wear testing machine for conventional polyethylene in the present study. An independent computational wear model was developed by incorporating the cross-shear motion and contact pressure-dependent wear factor into the Archard's law, in additional to load and sliding distance. The computational prediction of wear volume was directly compared with a simulator testing of a polyethylene hip joint with a 28 mm diameter. The effect of increasing the femoral head size was subsequently considered and was shown to increase wear, as a result of increased sliding distance and reduced contact pressure.     

Correlation of compartment pressure data from an intraoperative sensing device with postoperative fluoroscopic kinematic results in TKA patients

Fluoroscopy has recently been used to analyze postoperative kinematics in total knee arthroplasty (TKA). These analyses have reported varying results even in patients with similar implant design. In addition, patterns of wear in retrieved tibial polyethylene inserts of similar design have been found to vary substantially. These findings suggest that surgical technique, especially soft tissue balancing, may play a role in postoperative kinematics and implant failure. Accurate soft-tissue balancing is hypothesized to result in similar pressures within the medial and lateral compartments of the knee. However, a method of easily measuring these pressures at TKA has not been developed. In the present study, 32 patients were implanted with a mobile-bearing LCS TKA utilizing the balanced gap technique. An electronic pressure sensor, developed specifically to record pressure magnitude and distribution in the medial and lateral compartments, was incorporated into the implant trials. The knee was then passively taken through a range of motion while pressure data was recorded via computer. Postoperatively, 16 patients underwent active fluoroscopic kinematic analysis to assess for condylar liftoff and femorotibial translation. We found that abnormal compartment pressures and distributions as recorded by the intraoperative pressure sensor were correlated with inappropriate or paradoxical postoperative kinematics. In addition, subjects having similar pressures in both compartments throughout a range of motion did not experience condylar liftoff values greater than 1.0 mm. These data suggest that surgical technique influences the magnitude and distribution of forces at the articulation, postoperative kinematics, and likely, implant longevity.     

Internal kinetic changes in the knee due to high tibial osteotomy are well-correlated with change in external adduction moment: An osteoarthritic knee model

In-vivo quantification of loads in the constitutive structures of the osteoarthritic knee can provide clinical insight, particularly when planning a surgery like the opening-wedge high tibial osteotomy (HTO). A computational knee model was created to estimate internal kinetics during walking gait. An optimization approach partitioned loads between the muscles, ligaments, medial and lateral contact surfaces of the tibial–femoral joint. Three kinetic measures were examined in 30 HTO patients: external knee adduction moment (EKAM), medial compartment load (ML) and the medial-to-lateral compartment loads ratio (MLR). Three time points were compared: immediately pre-HTO, 6 and 12 months post-HTO. Three hypotheses were tested: (1) HTO reduces an EKAM, an ML and an MLR, (2) these measures are not significantly different at 6 and 12 months post-HTO, and (3) the change in the impulse of EKAM due to a HTO is well-correlated with the impulse of an MLR.The three hypotheses were confirmed. First peak of an EKAM during stance phase was reduced significantly by 1.70% BW-ht. ML and MLR at the same instance were reduced significantly by 0.56%BW and 1.0, respectively. These measures were not significantly different between 6 and 12 months post-HTO. Changes in impulse of an EKAM and an MLR were moderately well-correlated between the pre-HTO and 6 months post-HTO time points (R²=0.5485). Therefore, the external measure EKAM-impulse is a good proxy of the internal kinetic measure of an MLR-impulse, explaining about 55% of the variance in the change due to a HTO intervention.     

Modeling gait score of broiler chicken via production and behavioral data

Lameness in broilers may be associated with pain and is considered a major broiler production and welfare concern. Manual gait score assessment in commercial broiler houses is discrete, time-consuming, and laborious. As such, automatic methods for broiler gait score assessment are urgently needed. The objective of this study was to identify the relation of broiler gait score with several productions and behavioral metrics (bird BW, age, activity, and distribution), and establish three gait score prediction models for automatic gait score estimations in broiler farms with automatic weighing systems, camera systems, or both. Sixteen pens were used to rear Cobb 500 and Ross 708 broilers for eight and nine weeks, respectively (eight pens/strain, 12 birds/pen). The gait scores of all birds were assessed weekly by trained assessors following a six-point (0–5) scoring protocol from the third week. The pen’s average BW was measured weekly. Top-view cameras were installed to continuously record videos of broilers in all 16 pens. Images were extracted from video clips (10 min/hour) during a 16-hour light period to determine the activity index and distribution index through image processing. The gait score was positively correlated with BW (R² = 0.97 for Cobb and R² = 0.96 for Ross), while negatively correlated with activity (R² = 0.78 for Cobb and R² = 0.73 for Ross). The three models showed high accuracies in predicting broiler gait score based on variables of BW, age, activity index, and distribution index (R² = 0.90–0.91, RMSE = 0.38–0.41). The findings of this study demonstrated the potential of estimating broiler gait score using bird BW, age, activity index, and distribution index. This information will assist in the development of automated gait score assessment systems in broiler production.     

不同手术方式治疗老年膝内侧间室骨关节炎的疗效对比分析

摘要 目的：比较单踝关节置换术（UKA）和全膝关节置换术（TKA）治疗老年膝内侧间室骨关节炎的疗效。方法：选取2020年1月~2022年6月本院收治的100例老年膝内侧间室骨关节炎患者为研究对象,随机（随机数字表法）分为UKA组（n=50）和TKA组（n=50）,采取相应手术方法治疗。比较两组手术相关指标、美国特种外科医院（HSS）膝关节功能评分、膝关节屈伸活动度（ROM）、疼痛视觉模拟评分法（VAS）、健康调查12条简表（SF-12）评分及假体情况。结果：与TKA组相比,UKA组切口长度更短,术中出血量及术后引流量更少,手术时间、下地行走时间及住院时间更短,组间比较差异均有统计学意义（P<0.05）。UKA组术后2周、3个月及6个月时HSS评分均明显高于TKA组（P<0.05）。UKA组术后2周、3个月ROM均明显高于TKA组（P<0.05）。UKA组术后3个月VAS评分明显低于TKA组（P<0.05）。两组SF-12评分中生理及心理维度评分在术后6个月后均明显提高（P<0.05）;但组间比较差异均无统计学意义（P>0.05）。两组均无假体翻修病例。结论：UKA相比于TKA具有创伤更小、患者术后恢复更快、膝关节功能恢复更好的优势。     

Comparative diagnostic accuracy of knee adduction moments in knee osteoarthritis: a case for not normalizing to body size

Previous authors have questioned the practice of normalizing the external knee adduction moment during gait to body size when investigating dynamic joint loading in knee osteoarthritis (OA). The purpose of this study was to compare the abilities of non-normalized and normalized external knee adduction moments during gait in discriminating between patients with least and greatest severity of radiographic medial compartment knee OA. Subjects with mild (n=118) and severe (n=115) medial compartment knee OA underwent three-dimensional gait analysis. The peak external knee adduction moment was calculated and kept in its original units (Nm), normalized to body mass (Nm/kg) and normalized to body weight and height (%BW × Ht). Receiver Operating Characteristic (ROC) curve analysis indicated that non-normalized values better discriminated between patients with mild and severe knee OA. The area under the ROC curve for non-normalized peak knee adduction moments (0.63) was significantly (p<0.05) greater than when normalized to body mass (0.58), or to body weight times height (0.57). Post-hoc analysis of covariance indicated the mean difference in peak knee adduction moment between OA severity groups (7.23 Nm, p=0.003) was reduced by approximately 50% (3.60 Nm, p=0.09) when adjusted for mass. These findings are consistent with the suggestion that non-normalized values are more sensitive to radiographic disease progression. We suggest including knee adduction moment values that are not normalized to body size when investigating knee OA.     

In vivo contact kinematics and contact forces of the knee after total knee arthroplasty during dynamic weight-bearing activities

Analysis of polyethylene component wear and implant loosening in total knee arthroplasty (TKA) requires precise knowledge of in vivo articular motion and loading conditions. This study presents a simultaneous in vivo measurement of tibiofemoral articular contact forces and contact kinematics in three TKA patients. These measurements were accomplished via a dual fluoroscopic imaging system and instrumented tibial implants, during dynamic single leg lunge and chair rising-sitting. The measured forces and contact locations were also used to determine mediolateral distribution of axial contact forces. Contact kinematics data showed a medial pivot during flexion of the knee, for all patients in the study. Average axial forces were higher for lunge compared to chair rising-sitting (224% vs. 187% body weight). In this study, we measured peak anteroposterior and mediolateral forces averaging 13.3% BW during lunge and 18.5% BW during chair rising-sitting. Mediolateral distributions of axial contact force were both patient and activity specific. All patients showed equitable medial-lateral loading during lunge but greater loads at the lateral compartment during chair rising-sitting. The results of this study may enable more accurate reproduction of in vivo loads and articular motion patterns in wear simulators and finite element models. This in turn may help advance our understanding of factors limiting longevity of TKA implants, such as aseptic loosening and polyethylene component wear, and enable improved TKA designs.     

Reliability of surface electromyographic recordings during walking in individuals with knee osteoarthritis

To determine test–retest reliability of a surface electromyographic protocol designed to measure knee joint muscle activation during walking in individuals with knee osteoarthritis (OA). Twenty-one individuals with moderate medial compartment knee OA completed two gait data collections separated by approximately 1 month. Using a standardized protocol, surface electromyograms from rectus femoris plus lateral and medial sites for the gastrocnemii, vastii and hamstring muscles were recorded during walking. After full-wave rectification and low pass filtering, time and amplitude normalized (percent of maximum) waveforms were calculated. Principal component analysis (PP-scores) and co-contraction indices (CCI) were calculated from the waveforms. Intraclass correlation coefficients (ICC_2,k) were calculated for PP-scores and CCI’s. No differences in walking speed, knee muscle strength and symptoms were found between visits (p > 0.05). The majority of PP-scores (17 of 21) and two of four CCIs demonstrated ICC_2,k values greater than 0.81. Remaining PP-scores and CCIs had ICC_2,k values between 0.61 and 0.80. The results support that reliable EMG characteristics can be captured from a moderate knee OA patient population using a standardized protocol.     

Control of center of mass motion state through cuing and decoupling of spontaneous gait parameters in level walking

Can the center of mass (COM) motion state, i.e., its position and velocity relative to the base of support (BOS), which dictate gait stability, be predictably controlled by the global gait parameters of step length and gait speed, or by extension, cadence? The precise relationships among step length and gait speed, and the COM motion state are unknown, partially due to the interdependence between step length and gait speed and the difficulty in independent control of both parameters during spontaneous level walking. The purposes of this study were to utilize simultaneous audio-visual cuing to independently manipulate step length and gait speed, and to determine the extent to which the COM position and velocity can be subsequently controlled. Fifty-six young adults were trained at one of the three gait patterns in which both the step length and gait speed were targeted simultaneously. The results showed that the cuing could successfully “decouple” gait speed from step length. Although this approach did yield reliable control of the COM velocity through manipulation of gait speed (R²=0.97), the manipulation of step length yielded less precise control of COM position (R²=0.60). This latter control appears to require manipulation of an additional degree-of-freedom at the local segment level, such that the inclusion of trunk inclination with step length improved the prediction of COM position (R²=0.80).     

UKA与TKA治疗膝关节内侧单间室骨性关节炎的临床对比

目的:探究膝关节单髁置换术(UKA)与全膝关节置换术(TKA)治疗膝关节内侧单间室骨性关节炎的临床治疗效果。方法:将2011年4月-2015年7月期间因膝关节单间室骨性关节炎入院接受治疗的89例患者纳入本研究,随机分为研究组和对照组,研究组44例,行UKA手术,对照组45例,采用TKA手术方式治疗。对两组患者进行术后随访,对比临床治疗效果。结果:两组术前均有明显膝关节疼痛,术后膝关节疼痛均明显改善,组间差别无显著统计学意义(X2=1.323,P=0.2500.05);术后膝关节屈曲角度、HSS评分相对于术前均显著改善,研究组术后膝关节屈曲角度(111.2±18.8)度高于对照组的(98.6±14.7)度,差异有统计学意义(P0.05);HSS评分(87.6±13.7)分高于对照组的(73.2±16.8)分,差异有统计学意义(P0.05);研究组膝关节屈曲至90度时间比对照组短,数据差异有统计学差异(t=-2.303,P=0.0240.05)。结论:膝关节内侧单间室骨性关节炎采用UKA与TKA均能取得一定临床效果,减轻患者痛苦,改善膝关节功能,但UKA临床疗效较好,手术创伤较小,术后恢复较快。     

Knee Adduction Moment and Medial Contact Force – Facts about Their Correlation during Gait

The external knee adduction moment is considered a surrogate measure for the medial tibiofemoral contact force and is commonly used to quantify the load reducing effect of orthopedic interventions. However, only limited and controversial data exist about the correlation between adduction moment and medial force. The objective of this study was to examine whether the adduction moment is indeed a strong predictor for the medial force by determining their correlation during gait. Instrumented knee implants with telemetric data transmission were used to measure tibiofemoral contact forces in nine subjects. Gait analyses were performed simultaneously to the joint load measurements. Skeletal kinematics, as well as the ground reaction forces and inertial parameters, were used as inputs in an inverse dynamics approach to calculate the external knee adduction moment. Linear regression analysis was used to analyze the correlation between adduction moment and medial force for the whole stance phase and separately for the early and late stance phase. Whereas only moderate correlations between adduction moment and medial force were observed throughout the whole stance phase (R² = 0.56) and during the late stance phase (R² = 0.51), a high correlation was observed at the early stance phase (R² = 0.76). Furthermore, the adduction moment was highly correlated to the medial force ratio throughout the whole stance phase (R² = 0.75). These results suggest that the adduction moment is a surrogate measure, well-suited to predicting the medial force ratio throughout the whole stance phase or medial force during the early stance phase. However, particularly during the late stance phase, moderate correlations and high inter-individual variations revealed that the predictive value of the adduction moment is limited. Further analyses are necessary to examine whether a combination of other kinematic, kinetic or neuromuscular factors may lead to a more reliable prediction of the force magnitude.     

Accounting for spatial variation of trabecular anisotropy with subject-specific finite element modeling moderately improves predictions of local subchondral bone stiffness at the proximal tibia

IntroductionPreviously, a finite element (FE) model of the proximal tibia was developed and validated against experimentally measured local subchondral stiffness. This model indicated modest predictions of stiffness (R² = 0.77, normalized root mean squared error (RMSE%) = 16.6%). Trabecular bone though was modeled with isotropic material properties despite its orthotropic anisotropy. The objective of this study was to identify the anisotropic FE modeling approach which best predicted (with largest explained variance and least amount of error) local subchondral bone stiffness at the proximal tibia.MethodsLocal stiffness was measured at the subchondral surface of 13 medial/lateral tibial compartments using in situ macro indentation testing. An FE model of each specimen was generated assuming uniform anisotropy with 14 different combinations of cortical- and tibial-specific density-modulus relationships taken from the literature. Two FE models of each specimen were also generated which accounted for the spatial variation of trabecular bone anisotropy directly from clinical CT images using grey-level structure tensor and Cowin’s fabric-elasticity equations. Stiffness was calculated using FE and compared to measured stiffness in terms of R² and RMSE%.ResultsThe uniform anisotropic FE model explained 53–74% of the measured stiffness variance, with RMSE% ranging from 12.4 to 245.3%. The models which accounted for spatial variation of trabecular bone anisotropy predicted 76–79% of the variance in stiffness with RMSE% being 11.2–11.5%.ConclusionsOf the 16 evaluated finite element models in this study, the combination of Synder and Schneider (for cortical bone) and Cowin’s fabric-elasticity equations (for trabecular bone) best predicted local subchondral bone stiffness.     

In vivo tibiofemoral cartilage deformation during the stance phase of gait

The knowledge of articular cartilage contact biomechanics in the knee joint is important for understanding the joint function and cartilage pathology. However, the in vivo tibiofemoral articular cartilage contact biomechanics during gait remains unknown. The objective of this study was to determine the in vivo tibiofemoral cartilage contact biomechanics during the stance phase of treadmill gait. Eight healthy knees were magnetic resonance (MR) scanned and imaged with a dual fluoroscopic system during gait on a treadmill. The tibia, femur and associated cartilage were constructed from the MR images and combined with the dual fluoroscopic images to determine in vivo cartilage contact deformation during the stance phase of gait. Throughout the stance phase of gait, the magnitude of peak compartmental contact deformation ranged between 7% and 23% of the resting cartilage thickness and occurred at regions with thicker cartilage. Its excursions in the anteroposterior direction were greater in the medial tibiofemoral compartment as compared to those in the lateral compartment. The contact areas throughout the stance phase were greater in the medial compartment than in the lateral compartment. The information on in vivo tibiofemoral cartilage contact biomechanics during gait could be used to provide physiological boundaries for in vitro testing of cartilage. Also, the data on location and magnitude of deformation among non-diseased knees during gait could identify where loading and later injury might occur in diseased knees.     

Joint contact stresses calculated for acetabular dysplasia patients using discrete element analysis are significantly influenced by the applied gait pattern

Gait modifications in acetabular dysplasia patients may influence cartilage contact stress patterns within the hip joint, with serious implications for clinical outcomes and the risk of developing osteoarthritis. The objective of this study was to understand how the gait pattern used to load computational models of dysplastic hips influences computed joint mechanics. Three-dimensional pre- and post-operative hip models of thirty patients previously treated for hip dysplasia with periacetabular osteotomy (PAO) were developed for performing discrete element analysis (DEA). Using DEA, contact stress patterns were calculated for each pre- and post-operative hip model when loaded with an instrumented total hip, a dysplastic, a matched control, and a normal gait pattern. DEA models loaded with the dysplastic and matched control gait patterns had significantly higher (p = 0.012 and p < 0.001) average pre-operative maximum contact stress than models loaded with the normal gait. Models loaded with the dysplastic and matched control gait patterns had nearly significantly higher (p = 0.051) and significantly higher (p = 0.008) average pre-operative contact stress, respectively, than models loaded with the instrumented hip gait. Following PAO, the average maximum contact stress for DEA models loaded with the dysplastic and matched control patterns decreased, which was significantly different (p < 0.001) from observed increases in maximum contact stress calculated when utilizing the instrumented hip and normal gait patterns. The correlation between change in DEA-computed maximum contact stress and the change in radiographic measurements of lateral center-edge angle were greatest (R² = 0.330) when utilizing the dysplastic gait pattern. These results indicate that utilizing a dysplastic gait pattern to load DEA models may be a crucial element to capturing contact stress patterns most representative of this patient population.     

Material properties of articular cartilage in the rabbit tibial plateau

The material properties of articular cartilage in the rabbit tibial plateau were determined using biphasic indentation creep tests. Cartilage specimens from matched-pair hind limbs of rabbits approximately 4 months of age and greater than 12 months of age were tested on two locations within each compartment using a custom built materials testing apparatus. A three-way ANOVA was used to determine the effect of leg, compartment, and test location on the material properties (aggregate modulus, permeability, and Poisson's ratio) and thickness of the cartilage for each set of specimens. While no differences were observed in cartilage properties between the left and right legs, differences between compartments were found in each set of specimens. For cartilage from the adolescent group, values for aggregate modulus were 40% less in the medial compartment compared to the lateral compartment, while values for permeability and thickness were greater in the medial compartment compared to the lateral compartment (57% and 30%, respectively). Values for Poisson's ratio were 19% less in the medial compartment compared to the lateral compartment. There was also a strong trend for thickness to differ between test locations. Similar findings were observed for cartilage from the mature group with values for permeability and thickness being greater in the medial compartment compared to the lateral compartment (66% and 34%, respectively). Values for Poisson's ratio were 22% less in the medial compartment compared to the lateral compartment.     

Combined effects of speed and directional change on postural adjustments during gait initiation

The study of gait initiation (GI) has primarily focused on gait initiated in a forward direction, however, in everyday life, GI is often combined with a directional change. Ten young adults initiated gait with their right foot in four directions (to the left: −15°, straight ahead: 0°, to the right: 15° and 30°) at self-selected and fast gait speeds. The relationship between starting direction of GI and the lateral center of foot pressure displacement for normal (r² = 0.57) and fast gait speed (r² = 0.75) indicated that the lateral component plays an important role with regards to controlling the desired direction of gait. At the first step of the swing limb, the progression velocity of the center of mass (CM) remained slower for the 30° condition only, whereas no difference was found between directions for CM velocity perpendicular to the intended direction. These results suggest that postural adjustments are scaled to initiate gait in a predetermined direction. By the first step, the orientation of CM is toward the intended direction of gait, however, when gait is initiated in combination with a large change in direction, additional adjustments may be required to reach the intended progression velocity.