Comparison of three formal methods used to estimate the functional axis of rotation: an extensive in-vivo analysis performed on the knee joint

Estimating the main axis of rotation (AoR) of a human joint represents an important issue in biomechanics. This study compared three formal methods used to estimate functional AoR, namely a cylindrical fitting method, a mean helical axis transformation, and a symmetrical axis approach. These methods were tested on 106 subjects undergoing navigated total knee arthroplasty. AoR orientation in 3D and in the frontal and coronal planes provided by each method was compared to the transepicondylar axis direction. Although all the methods resulted effective, significant differences were identified among them, relatively to the orientation in 3D and in the frontal plane projection. This was probably due to the presence of secondary rotations during the first degrees of knee flexion.     

Effects of radiograph projection parameter uncertainty on TKA kinematics from model-image registration

Model-image registration techniques have been used extensively for the measurement of joint kinematics in vivo. These techniques typically utilize an explicit measurement of X-ray projection parameters (principal distance, principal point), which is easily done for prospective studies. However, there is vast opportunity to derive useful information from previously collected clinical radiographic films where the projection parameters are unknown. The purpose of this study was to determine variation in measured knee arthroplasty kinematics when the X-ray projection parameters were unknown, but bounded. Based on the clinical radiographic protocol, a nominal principal point was chosen and eight additional points ±2 and ±5 cm in the horizontal and vertical directions were defined. Tibiofemoral kinematics were determined for all nine projection parameter sets for a series of 10 lateral radiographs. In addition, the principal distance was varied ±15 cm and tibiofemoral kinematics were determined for these two projection sets. Measured joint kinematics varied less than 0.6° and 0.4 mm for ±2 cm variations in principal point location, and 0.7° and 0.6 mm for ±5 cm variations in principal point location. Measured joint kinematics varied less than 0.6° and 0.7 mm for ±15 cm variations in principal distance. Variation in X-ray principal point and principal distance over clinically bounded ranges has a small effect on knee arthroplasty kinematics computed from model-image registration with high-quality clinical radiographs.     

骨水泥凝固前有无血液环境对骨水泥与骨界面稳定性的影响

目的:研究在有血和无血环境下粘合骨水泥和骨,比较两种粘合骨水泥的方式对骨与骨水泥界面稳定性影响的区别。方法:选取新鲜猪肱骨头20块,随机分成两组:实验组在有血的环境下用骨水泥将股骨头与金属粘合;对照组在无血的环境下用骨水泥将肱骨头和金属粘合,再将两组实验材料分别做拉伸试验,至骨与骨水泥界面断裂,最后再沿垂直于截骨面的方向做骨切片,在扫描电镜下观察并测量出每个实验对象中骨水泥的最大浸润深度。比较两组实验过程中拉力的最大载荷和断裂时的拉力以及骨水泥最大浸润深度。结果:实验组10个实验对象拉力最大载荷平均为738.50±262.15 N,断裂时的拉力平均为656.50±242.88N,骨水泥最大浸润深度平均为1.22±0.19 MM;对照组10个实验对象实验过程中拉力最大载平均为739.60±306.98 N,断裂时的拉力平均为658.80±264.56 N,骨水泥最大浸润深度平均为1.22±0.21 MM。20个实验对象在实验过程中均无意外断裂的情况发生,均在骨与骨水泥界面发生断裂。两组实验的拉力最大载荷与断裂拉力以及骨水泥最大浸润深度,均无统计学差异(P0.05)。结论:血液环境不能增加骨与骨水泥界面的不稳定因素。因此,与应用止血带相比,在TKA手术中不用止血带可能不会对骨与骨水泥界面稳定性和假体的寿命产生影响。     

Pre-clinical assessment of total knee replacement anterior-posterior constraint

Pre-clinical, bench-top assessment of Total Knee Replacements (TKR) can provide information about the inherent constraint provided by a TKR, which does not depend on the condition of the patient undergoing the arthroplasty. However little guidance is given by the ASTM standard on test configurations such as medial-lateral (M:L) loading distribution, flexion angle or restriction of secondary motions. Using a purpose built rig for a materials testing machine, four TKRs currently in widespread clinical use, including medial-pivot and symmetrical condyle types, were tested for anterior-posterior translational constraint. Compressive joint loads from 710 to 2000 N, and a range of medial-lateral (M:L) load distributions, from 70:30% to 30:70% M:L, were applied at different flexion angles with secondary motions unconstrained. It was found that TKA constraint was significantly less at 60 and 90° flexion than at 0°, whilst increasing the compressive joint load increased the force required to translate the tibia to limits of AP constraint at all flexion angles tested. Additionally when M:L load distribution was shifted medially, a coupled internal rotation was observed with anterior translation and external rotation with posterior translation. This paper includes some recommendations for future development of pre-clinical testing methods.     

Muscle activation and coactivation during five-time-sit-to-stand movement in patients undergoing total knee arthroplasty

Quadriceps weakness is prevalent with knee osteoarthritis (OA) and after total knee arthroplasty (TKA). To compensate for quadriceps dysfunction, patients often alter movement strategies. Little is known about muscle coordination during sit-to-stand (concentric) and stand-to-sit (eccentric) movements in the acute postoperative period. This investigation characterized the distribution of muscle activation between the concentric and eccentric phases during a five-time-sit-to-stand (FTSTS) movement in late stage OA and one month after TKA. Patients and healthy participants performed a FTSTS while recording bilateral ground reaction forces (GRFs) and electromyography (EMG). Concentric and eccentric ensemble averages of the GRF and EMG were calculated for the concentric and eccentric phases. Coactivation indices, integrated EMG, and GRF were calculated for each limb and phase. Patients demonstrated higher eccentric coactivation than the healthy group. Postoperative loading was higher in the nonsurgical limb. Postoperative quadriceps activity was lower in the concentric phase and higher in the eccentric phase than the healthy group. Higher coactivation in the patients resulted from sustained distribution of quadriceps activity throughout the eccentric phase. This indicated an inability to coordinate muscle firing when rapidly lowering to a chair and occurred despite unloading of the surgical limb. Although these patterns may serve as a protective strategy, they may also impede recovery of muscle function after TKA.     

旋转平台与后稳定固定平台假体在人工膝关节置换术后的临床疗效

目的:探讨旋转平台与后稳定固定平台假体在人工膝关节置换术(TKA)后的临床治疗效果。方法:选择2008年8月到2014年8月在我院接收人工膝关节置换术的218例患者,随机分为对照组和实验组,分别采用后稳定固定平台假体和旋转平台假体行TKA。观察并记录两组患者治疗前和治疗后6个月世界膝关节学会(KSS)评分、美国膝关节学会(HSS)评分和膝关节的屈曲度(ROM),以及治疗后6个月并发症的发生情况。结果:治疗后,两组患者KSS评分、HSS评分及ROM评分均明显高于治疗前,差异有统计学意义(P0.05);两组患者KSS评分、HSS评分及ROM评分相比,差异无统计学意义(P0.05)。实验组患者并发症发生率(9.17%)和对照组患者并发症发生率(10.09%)相比,无统计学意义(P0.05)。结论:旋转平台与后稳定固定平台假体在TKA中均能有效改善膝关节的功能,两者疗效相近,均值得在临床推广应用。     

Influence of landmark and surgical variability on virtual assessment of total knee arthroplasty

Given advances in recent years in imaging modalities and computational hardware/software, virtual analyses are increasingly valuable and practical for evaluating total knee arthroplasty (TKA). However, the influence of variabilities at each step in computational analyses on predictions of TKA performance for a population has not yet been thoroughly investigated, nor the relationship between these variabilities and expected variations in surgical practice. Understanding these influences is nevertheless essential for ensuring the clinical relevance of theoretical predictions. Here, a morphological analysis of proximal tibial resections within TKA is proposed and investigated. The goals of this analysis are to quantify the influence of variability in landmark detection on resection parameters and to evaluate this sensitivity relative to expected clinical variability in TKA resections. Results here are directly applicable to population-level computational analyses of morphological and functional TKA performance.     

A new registration method for three-dimensional knee nearthrosis model using two X-ray images

The purpose of this study is to develop a method to analyse the pose of the knee nearthrosis mounted and to automate the registration procedure for easy use in clinical applications. The proposed registration method is essentially a model-based method, in which the CAD model is acquired by reverse engineering. The CAD model is converted into a two-dimensional (2D) image by a rendering technique, and the compatibility of the X-ray image and the image of the CAD model is investigated. To avoid the optimisation of six unknown parameters with respect to the relative pose between the condyle and tibial models, a 2D coordinate system is set on each component of the X-ray images. A 3D coordinate system is also set on each of the two nearthrosis components. With such a setup, there is only one unknown rotational angle on each component, which is determined by an optimum algorithm in accordance with the contour error between the X-ray image and the image of the CAD model. Extensive computer simulation and in vitro experiments using real X-ray images have been implemented to investigate the feasibility of the proposed registration method.     

Approximation of the functional kinematics of posterior stabilised total knee replacements using a two-dimensional sagittal plane patello-femoral model: comparing model approximation to in vivo measurement

Previous in vivo studies have observed that current designs of posterior stabilised (PS) total knee replacements (TKRs) may be ineffective in restoring normal kinematics in Late flexion. Computer-based models can prove a useful tool in improving PS knee replacement designs. This study investigates the accuracy of a two-dimensional (2D) sagittal plane model capable of predicting the functional sagittal plane kinematics of PS TKR implanted knees against direct in vivo measurement. Implant constraints are often used as determinants of anterior–posterior tibio-femoral positioning. This allowed the use of a patello-femoral modelling approach to determine the effect of implant constraints. The model was executed using motion simulation software which uses the constraint force algorithm to achieve a solution. A group of 10 patients implanted with Scorpio PS implants were recruited and underwent fluoroscopic imaging of their knees. The fluoroscopic images were used to determine relative implant orientation using a three-dimensional reconstruction method. The determined relative tibio-femoral orientations were then input to the model. The model calculated the patella tendon angles (PTAs) which were then compared with those measured from the in vivo fluoroscopic images. There were no significant differences between the measured and calculated PTAs. The average root mean square error between measured and modelled ranged from 1.17° to 2.10° over the flexion range. A sagittal plane patello-femoral model could conceivably be used to predict the functional 2D kinematics of an implanted knee joint. This may prove particularly useful in optimising PS designs.     

AdipoRon reduces TGFβ1-mediated collagen deposition in vitro and alleviates knee stiffness in vivo

Arthrofibrosis, which causes joint motion restrictions, is a common complication following total knee arthroplasty (TKA). Key features associated with arthrofibrosis include myofibroblast activation, knee stiffness, and excessive scar tissue formation. We previously demonstrated that adiponectin levels are suppressed within the knee tissues of patients affected by arthrofibrosis and showed that AdipoRon, an adiponectin receptor agonist, exhibited anti-fibrotic properties in human mesenchymal stem cells. In this study, the therapeutic potential of AdipoRon was evaluated on TGFβ1-mediated myofibroblast differentiation of primary human knee fibroblasts and in a mouse model of knee stiffness. Picrosirius red staining revealed that AdipoRon reduced TGFβ1-induced collagen deposition in primary knee fibroblasts derived from patients undergoing primary TKA and revision TKA for arthrofibrosis. AdipoRon also reduced mRNA and protein levels of ACTA2, a key myofibroblast marker. RNA-seq analysis corroborated the anti-myofibrogenic effects of AdipoRon. In our knee stiffness mouse model, 6 weeks of knee immobilization, to induce a knee contracture, in conjunction with daily vehicle (DMSO) or AdipoRon (1, 5, and 25 mg/kg) via intraperitoneal injections were well tolerated based on animal behavior and weight measurements. Biomechanical testing demonstrated that passive extension angles (PEAs) of experimental knees were similar between vehicle and AdipoRon treatment groups in mice evaluated immediately following immobilization. Interestingly, relative to vehicle-treated mice, 5 mg/kg AdipoRon therapy improved the PEA of the experimental knees in mice that underwent 4 weeks of knee remobilization following the immobilization and therapy. Together, these studies revealed that AdipoRon may be an effective therapeutic modality for arthrofibrosis.