Mechanobiological simulations of prenatal joint morphogenesis

Joint morphogenesis is the process in which prenatal joints acquire their reciprocal and interlocking shapes. Despite the clinical importance of the process, it remains unclear how joints acquire their shapes. In this study, we simulate 3D mechanobiological joint morphogenesis for which the effects of a range of movements (or lack of movement) and different initial joint shapes are explored. We propose that static hydrostatic compression inhibits cartilage growth while dynamic hydrostatic compression promotes cartilage growth. Both pre-cavitational (no muscle contractions) and post-cavitational (with muscle contractions) phases of joint development were simulated. Our results showed that for hinge type motion (planar motion from 45° to 120°) the proximal joint surface developed a convex profile in the posterior region and the distal joint surface developed a slightly concave profile. When 3D movements from 40° to −40° in two planes were applied, simulating a rotational movement, the proximal joint surface developed a concave profile whereas the distal joint surface rudiment acquire a rounded convex profile, showing an interlocking shape typical of a ball and socket joint. The significance of this research is that it provides new and important insights into normal and abnormal joint development, and contributes to our understanding of the mechanical factors driving very early joint morphogenesis. An enhanced understanding of how prenatal joints form is critical for developing strategies for early diagnosis and preventative treatments for congenital musculoskeletal abnormalities such as developmental dysplasia of the hip.     

Chronic softening of cartilage without thickening of underlying bone in a joint trauma model

We have recently developed a trauma model to study degradation of the rabbit patello-femoral joint. Our current working hypothesis is that alterations in retropatellar cartilage and underlying bone in our model are initiated independently by acute overstresses developed in each tissue during blunt insult to the joint, and that the processes of chronic degradation in each tissue are not related in a mechanical sense. The current study was conducted in an attempt to help validate our hypothesis by impacting the patello-femoral joint with a padded interface. Based upon earlier human cadaver experiments, we believe this would reduce the acute overstresses in patellar bone while the stresses developed in the overlying retropatellar cartilage would be sufficient enough to initiate a chronic softening of the tissue. Twenty-four animals received an impact to the patello-femoral joint and were sacrificed at either 0, 4.5, or 12 months post-insult. Three acute animals were impacted to develop a simplified computational model to estimate the stresses in joint tissues. The study showed there was a significant softening of the retropatellar cartilage at 4.5 and 12 months post-trauma, compared to unimpacted controls. However, no thickening of the underlying subchondral bone was documented at any timepoint. This was consistent with a reduction of stress in the bone compared to earlier studies, which document thickened subchondral bone post-insult at the same applied impact load. In conclusion, this study helped validate our hypothesis by documenting chronic softening of cartilage without remodeling of the underlying subchondral bone. Furthermore, this study, along with our earlier studies, suggest that impact load alone, which is currently used by the automobile industry to certify new automobiles, is not a good predictor of chronic injuries to a diarthrodial joint, and that simply the addition of padding to impact interfaces may not be adequate to protect occupants from chronic injuries.     

Development and validation of a kinematically-driven discrete element model of the patellofemoral joint

Quantifying the complex loads at the patellofemoral joint (PFJ) is vital to understanding the development of PFJ pain and osteoarthritis. Discrete element analysis (DEA) is a computationally efficient method to estimate cartilage contact stresses with potential application at the PFJ to better understand PFJ mechanics. The current study validated a DEA modeling framework driven by PFJ kinematics to predict experimentally-measured PFJ contact stress distributions. Two cadaveric knee specimens underwent quadriceps muscle [215 N] and joint compression [350 N] forces at ten discrete knee positions representing PFJ positions during early gait while measured PFJ kinematics were used to drive specimen-specific DEA models. DEA-computed contact stress and area were compared to experimentally-measured data. There was good agreement between computed and measured mean and peak stress across the specimens and positions (r = 0.63–0.85). DEA-computed mean stress was within an average of 12% (range: 1–47%) of the experimentally-measured mean stress while DEA-computed peak stress was within an average of 22% (range: 1–40%). Stress magnitudes were within the ranges measured (0.17–1.26 MPa computationally vs 0.12–1.13 MPa experimentally). DEA-computed areas overestimated measured areas (average error = 60%; range: 4–117%) with magnitudes ranging from 139 to 307 mm² computationally vs 74–194 mm² experimentally. DEA estimates of the ratio of lateral to medial patellofemoral stress distribution predicted the experimental data well (mean error = 15%) with minimal measurement bias. These results indicate that kinematically-driven DEA models can provide good estimates of relative changes in PFJ contact stress.     

Fluid movement and joint capsule strains due to flexion in rabbit knees

Diarthrodial joints are freely moveable joints containing synovial fluid (SF) within a connective tissue joint capsule that allows for low-friction and low-wear articulation of the cartilaginous ends of long bones. Biomechanical cues from joint articulation regulate synoviocyte and cartilage biology via joint capsule strain, in turn altering the composition of SF. Joint flexion is clinically associated with pain in knees with arthritis and effusion, with the nociception possibly originating from joint capsule strain. The hypothesis of this study was that knee fluid volume distribution and joint capsule strain are altered with passive flexion in the rabbit model. The aims were to (a) determine the volume distribution of fluid in the joint at different total volumes and with flexion of rabbit knees ex vivo, (b) correlate the volume distribution for the ex vivo model to in vivo data, and (c) determine the strains at different locations in the joint capsule with flexion. During knee flexion, ～20% of anteriorly located joint fluid moved posteriorly, correlating well with the fluid motion observed in in vivo joints. Planar joint capsule principal strains were ～100% (tension) in the proximal-distal direction and ～-40% (shortening) in the circumferential direction, relative to the femur axis and 30° strain state. The joint capsule strains with flexion are consistent with the mechanics of the tendons and ligaments from which the capsule tissue is derived. The movement and mixing of SF volume with flexion determine the mechanical and biological fluid environment within the knee joint. Joint fluid movement and capsular strains affect synovial cell biology and likely modulate trans-synovial transport.     

Gender differences exist in the hip joint moments of healthy older walkers

Gender differences in the incidence of symptomatic hip osteoarthritis (OA), changes in hip cartilage volume and hip joint space and rates hip arthroplasty of older people are reported in the literature. As the rate of progression of OA is in part mechanically modulated it is possible that this gender bias may be related to inherent differences (if they exist) in walking mechanics between older males and females. The purpose of this study was to examine potential mechanisms for gender differences in hip joint mechanics during walking by testing the hypotheses that females would exhibit higher hip flexion, adduction and internal rotation moments but not significantly greater normalized ground reaction forces (GRFs). Forty-two healthy subjects (21 male, 21 female), ages 50–79 yr were recruited for gait analysis. In support of the hypotheses, greater external hip adduction and internal rotation along with hip extension moments were found for females compared to males after normalizing for body size for all self-selected walking speeds. Differences in walking style (kinematics) were the main determinants in the joint kinetic differences as no differences in the normalized GRFs were found. As external joint moments are surrogate measures of the joint contact forces, the results of this study suggest the hip joint stress for the female population is higher compared to male population. This is in favor of a hypothesis that the increased joint contact stress in a female population could contribute to a greater joint degeneration at the hip in females as compared with males.     

Experimental and finite element analysis for prediction of kidney injury under blunt impact

Kidneys are third most injured organs in abdominal trauma after liver and spleen; this study therefore is an attempt to understand the behaviour of kidneys under blunt trauma. Dynamic impact tests were performed on 20 fresh porcine kidneys to study the injury propagation in the organ, and the acceleration of the impactor was measured. A kidney model was developed with structural details like capsule and cortex. The kidney cortex was modelled with solid hexahedral elements and the capsule was modelled with quadratic shell elements. The material models for the capsule and cortex were used from the experimental data reported in our previous study. The developed model was calibrated using previous and current experimental results to reproduce the injuries of the organ in terms of acceleration of the impactor, and the injuries sustained by the organ during the experiments. The developed kidney model is observed to be robust and can be integrated with the available human body finite element models to simulate accidents and to predict or simulate injuries.     

兔食管静脉曲张模型的建立

目的建立新西兰兔的食管静脉曲张模型,为下一步的临床研究提供可靠的小型动物模型。方法采用门静脉左支完全夹闭法造模,并通过外观、超声、胃镜等检查检验手段对造模结果加以评估。结果术后8周存活动物100%可见食管静脉曲张。结论通过门静脉左支夹闭法,基本可以建立兔食管静脉曲张模型。     

Aging in the musculoskeletal system of rhesus monkeys: I. Passive joint excursion

In order to describe ontogenetic change in the musculoskeletal system of rhesus monkeys, 126 Macaca mulatta from Cayo Santiago, ranging in age from 7 months to 21 years, were examined under anesthesia. Passive joint excursions were measured at the wrist, elbow, shoulder, hip, and knee. Mean ranges of excursion at these joints differed significantly between age groups and by sex. The potential for most movements appeared to decrease approximately 25 degrees over the first two decades of the macaque life span, and males generally showed less potential for movement than females in all age groups. These results are similar to those obtained for humans and are consistent with patterns of positional behavior, trauma, and osteoarthritis observed in this rhesus monkey population. Thus, to fully describe the locomotor strategy of rhesus monkeys, age- and sex-related variation in locomotor anatomy and functional capacity must be considered.     

兔下颌骨慢性化脓性骨髓炎动物模型的建立

目的 探讨下颌骨慢性化脓性骨髓炎的造模方法.方法 成年新西兰兔22只,于下颌骨体外侧近正中联合处开骨窗注入0.1 mL5％鱼肝油酸钠和0.1 mL5.0×108 CFU/mL金黄色葡萄球菌悬液,术后常规回笼饲养.于6周开始采用以下方法检测:①肉眼大体观察;②双能X线骨密度检测;③CBCT(锥束CT)放射学形态观察;④局部细菌培养;⑤组织病理学评价.结果 所有新西兰兔早期精神状况较差,手术区域肉眼观有瘘管并有脓性分泌物.双能X线骨密度检测发现手术区骨密度(BMD)值变化不具有统计学意义(P＞0.05).CBCT显示骨缺损区边缘模糊,有骨破坏迹象.局部取材细菌培养有金黄色葡萄球菌生长.病理切片显示有不同程度的淋巴细胞、中性粒细胞、桨细胞浸润,死骨形成.结论 采用兔下颌骨体外侧近正中联合处造骨缺损并注射一定量细菌悬液的方法能够获得理想的慢性化脓性骨髓炎模型.     

The impact of adding trunk motion to the interpretation of the role of joint moments during normal walking

Biomechanical model assumptions affect the interpretation of the role of the muscle or joint moments to the segmental power estimated by induced acceleration analysis (IAA). We evaluated the effect of modeling the pelvis and trunk segments as two separate segments (8 SM) versus as a single segment (7 SM) on the segmental power, support of the body, knee and hip extension acceleration produced by the joint moments during the stance phase of normal walking. Significant differences were observed in the contribution of the stance hip abductor and extensor moments to support, ipsilateral knee and hip acceleration, and ipsilateral thigh and upper body power. The primary finding was that the role of the stance hip moment in generating ipsilateral thigh and upper body power differed based on degrees of freedom in the model. Secondarily, the magnitude of contributions also differed. For example, the hip abductor and extensor moments showed greater contribution to support, hip and knee acceleration in the 8 SM. IAA and segment power analysis are sensitive to the degrees of freedom between the pelvis and trunk. There is currently no gold standard by which to evaluate the accuracy of IAA predictions. However, modeling the pelvis and trunk as separate segments is closer to the anatomical architecture of the body. An 8 SM appears to be more appropriate for estimating the role of joint moments, particularly to motion of more proximal segments during normal walking.     

Use of dual Euler angles to quantify the three-dimensional joint motion and its application to the ankle joint complex

This paper presents a modified Euler angles method, dual Euler angles approach, to describe general spatial human joint motions. In dual Euler angles approach, the three-dimensional joint motion is considered as three successive screw motions with respect to the axes of the moving segment coordinate system; accordingly, the screw motion displacements are represented by dual Euler angles. The algorithm for calculating dual Euler angles from coordinates of markers on the moving segment is also provided in this study. As an example, the proposed method is applied to describe motions of ankle joint complex during dorsiflexion–plantarflexion. A Flock of Birds electromagnetic tracking device (FOB) was used to measure joint motion in vivo. Preliminary accuracy tests on a gimbal structure demonstrate that the mean errors of dual Euler angles evaluated by using source data from FOB are less than 1° for rotations and 1 mm for translations, respectively. Based on the pilot study, FOB is feasible for quantifying human joint motions using dual Euler angles approach.     

Evaluation of a subject-specific finite-element model of the equine metacarpophalangeal joint under physiological load

The equine metacarpophalangeal (MCP) joint is frequently injured, especially by racehorses in training. Most injuries result from repetitive loading of the subchondral bone and articular cartilage rather than from acute events. The likelihood of injury is multi-factorial but the magnitude of mechanical loading and the number of loading cycles are believed to play an important role. Therefore, an important step in understanding injury is to determine the distribution of load across the articular surface during normal locomotion. A subject-specific finite-element model of the MCP joint was developed (including deformable cartilage, elastic ligaments, muscle forces and rigid representations of bone), evaluated against measurements obtained from cadaver experiments, and then loaded using data from gait experiments. The sensitivity of the model to force inputs, cartilage stiffness, and cartilage geometry was studied. The FE model predicted MCP joint torque and sesamoid bone flexion angles within 5% of experimental measurements. Muscle–tendon forces, joint loads and cartilage stresses all increased as locomotion speed increased from walking to trotting and finally cantering. Perturbations to muscle–tendon forces resulted in small changes in articular cartilage stresses, whereas variations in joint torque, cartilage geometry and stiffness produced much larger effects. Non-subject-specific cartilage geometry changed the magnitude and distribution of pressure and the von Mises stress markedly. The mean and peak cartilage stresses generally increased with an increase in cartilage stiffness. Areas of peak stress correlated qualitatively with sites of common injury, suggesting that further modelling work may elucidate the types of loading that precede joint injury and may assist in the development of techniques for injury mitigation.     

A geometric approach to study the contact mechanisms in the patellofemoral joint of normal versus patellofemoral pain syndrome subjects

The biomechanics of the patellofemoral (PF) joint is complex in nature, and the aetiology of such manifestations of PF instability as patellofemoral pain syndrome (PFPS) is still unclear. At this point, the particular factors affecting PFPS have not yet been determined. This study has two objectives: (1) The first is to develop an alternative geometric method using a three-dimensional (3D) registration technique and linear mapping to investigate the PF joint contact stress using an indirect measure: the depth of virtual penetration (PD) of the patellar cartilage surface into the femoral cartilage surface. (2) The second is to develop 3D PF joint models using the finite element analysis (FEA) to quantify in vivo cartilage contact stress and to compare the peak contact stress location obtained from the FE models with the location of the maximum PD. Magnetic resonance images of healthy and PFPS subjects at knee flexion angles of 15°, 30° and 45° during isometric loading have been used to develop the geometric models. The results obtained from both approaches demonstrated that the subjects with PFPS show higher PD and contact stresses than the normal subjects. Maximum stress and PD increase with flexion angle, and occur on the lateral side in healthy and on the medial side in PFPS subjects. It has been concluded that the alternative geometric method is reliable in addition to being computationally efficient compared with FEA, and has the potential to assess the mechanics of PFPS with an accuracy similar to the FEA.     

Accuracy and repeatability of a pressure measurement system in the patellofemoral joint

The objective of this study was to assess how accurately and repeatably the Iscan system measures force and pressure in the natural patellofemoral joint. These measurements must be made to test widely held assumptions about the relationships between mechanics, pain and cartilage degeneration. We assessed the system's accuracy by using test rigs in a materials testing machine to apply known forces and force distributions across the sensor. The root mean squared error in measuring resultant force (for five trials at each of seven load levels) was 6.5±4.4% (mean±standard deviation over all trials at all load levels), while the absolute error was −5.5±5.6%. For force distribution, the root mean squared error (for five trials at each of five force distributions) was 0.86±0.58%, while the absolute error was −0.22±1.03%. We assessed the repeatability of the system's measurements of patellofemoral contact force, pressure and force distribution in four cadaver specimens loaded in continuous and static flexion. Variability in measurement (standard deviation expressed as a percentage of the mean) was 9.1% for resultant force measurements and 3.0% for force distribution measurements for static loads, and 7.3% for resultant force and 2.2% for force distribution measurements for continuous flexion. Cementing the sensor to the cartilage lowered readings of resultant force by 31±32% (mean±standard deviation), area by 24±13% and mean pressure by 9±34% (relative to the uncemented sensor). Maximum pressure measurement, however, was 24±43% higher in the cemented sensor than in the uncemented sensor. The results suggest that the sensor measures force distribution more accurately and repeatably than absolute force. A limitation of our work, however, is that the sensor must be cemented to the patellar articular surface to make the force distribution measurements, and our results suggest that this process reduces the accuracy of force, pressure and area measurements. Our results suggest that the Iscan system's pressure measurement accuracy and repeatability are comparable to that of Fuji Prescale film, but its advantages are that it is thinner than most Fuji Prescale film, it measures contact area more accurately and that it makes continuous measurements of force, pressure and area.     

An empirical Bayes' approach to joint analysis of multiple microarray gene expression studies

With the prevalence of gene expression studies and the relatively low reproducibility caused by insufficient sample sizes, it is natural to consider joint analysis that could combine data from different experiments effectively to achieve improved accuracy. We present in this article a model-based approach for better identification of differentially expressed genes by incorporating data from different studies. The model can accommodate in a seamless fashion a wide range of studies including those performed at different platforms by fitting each data with different set of parameters, and/or under different but overlapping biological conditions. Model-based inferences can be done in an empirical Bayes' fashion. Because of the information sharing among studies, the joint analysis dramatically improves inferences based on individual analysis. Simulation studies and real data examples are presented to demonstrate the effectiveness of the proposed approach under a variety of complications that often arise in practice.     

分枝杆菌所致家兔皮肤液化病理模型研究

目的 建立卡介苗( BCG) 、H37Ra 和耻垢分枝杆菌感染的新西兰兔皮肤模型, 为肺结核干酪样坏死和继而发生的液化提供研究模型。方法 新西兰兔皮内分别注射BCG、H37Ra 和耻垢分枝杆菌的5 ×10⁶CFU、5 ×10⁴CFU、5 ×10²CFU/ml 菌液, 6 周后在病灶周围再次以相同剂量皮内注射,14 d 后病变明显时取材, 制作切片, 行HE 染色, 显微镜下观察。结果新西兰兔分别经皮内接种BCG、H37Ra 或耻垢分枝杆菌后, 高剂量组观察到明显的炎症反应和脓肿液化、破溃等改变。再次免疫可观察到郭霍现象。引起病变的严重程度依次为BCG 强于H37Ra, 后者又强于耻垢分枝杆菌。显微改变可具典型的结核结节样病灶。皮肤模型处取材, 行细菌抗酸染色, 结果阳性。BCG 中、低剂量组再次免疫可诱导小结节样病变, 但不发生液化溃疡, 其余中剂量组及低剂量组没有观察到明显改变。结论 BCG、H37Ra 和耻垢分枝杆菌均可引起皮肤干酪样坏死和液化,病理损伤与感染细菌剂量密切相关, 5 ×10⁶CFU/ml 浓度的分枝杆菌可有效诱导液化和坏死, 其中BCG 引起的病理改变最明显。     

Identification of Fibroblast Growth Factor-18 as a Molecule to Protect Adult Articular Cartilage by Gene Expression Profiling

To identify genes that maintain the homeostasis of adult articular cartilage and regenerate its lesions, we initially compared four types of chondrocytes: articular (AA) versus growth plate (AG) cartilage chondrocytes in adult rats, and superficial layer (IS) versus deep layer (ID) chondrocytes of epiphyseal cartilage in infant rats. Microarray analyses revealed that 40 and 186 genes had ≥10-fold higher expression ratios of AA/AG and IS/ID, respectively, and 16 genes showed ≥10-fold of both AA/AG and IS/ID ratios. The results were validated by real-time RT-PCR analysis. Among them, Hoxd1, Fgf18, and Esm1 were expressed more strongly in AA than in IS. Fgf18 was the extracellular and secreted factor that decreased glycosaminoglycan release and depletion from the cartilage, and enhanced proliferation of articular chondrocytes. Fgf18 was strongly expressed in the articular cartilage chondrocytes of adult rats. In a surgical rat osteoarthritis model, a once-weekly injection of recombinant human FGF18 (rhFGF18) given 3 weeks after surgery prevented cartilage degeneration in a dose-dependent manner at 6 and 9 weeks after surgery, with significant effect at 10 μg/week of rhFGF18. As the underlying mechanism, rhFGF18 strongly up-regulated Timp1 expression in the cell and organ cultures, and inhibition of aggrecan release by rhFGF18 was restored by addition of an antibody to Timp1. In conclusion, we have identified Fgf18 as a molecule that protects articular cartilage by gene expression profiling, and the anticatabolic effects may at least partially be mediated by the Timp1 expression.     

Development of a statistical shape-function model of the implanted knee for real-time prediction of joint mechanics

Outcomes of total knee arthroplasty (TKA) are dependent on surgical technique, patient variability, and implant design. Non-optimal design or alignment choices may result in undesirable contact mechanics and joint kinematics, including poor joint alignment, instability, and reduced range of motion. Implant design and surgical alignment are modifiable factors with potential to improve patient outcomes, and there is a need for robust implant designs that can accommodate patient variability. Our objective was to develop a statistical shape-function model (SFM) of a posterior stabilized implanted knee to instantaneously predict joint mechanics in an efficient manner. Finite element methods were combined with Latin hypercube sampling and regression analyses to produce modeling equations relating nine implant design and six surgical alignment parameters to tibiofemoral (TF) joint mechanics outcomes during a deep knee bend. A SFM was developed and TF contact mechanics, kinematics, and soft tissue loads were instantaneously predicted from the model. Average normalized root-mean-square error predictions were between 2.79% and 9.42%, depending on the number of parameters included in the model. The statistical shape-function model generated instantaneous joint mechanics predictions using a maximum of 130 training simulations, making it ideally suited for integration into a patient-specific design and alignment optimization pipeline. Such a tool may be used to optimize kinematic function to achieve more natural motion or minimize implant wear, and may aid the engineering and clinical communities in improving patient satisfaction and surgical outcomes.     

狂犬病小鼠模型的制作

目的建立狂犬病病毒感染动物疾病模型。方法狂犬病病毒CVS-B2C毒株以10LD50剂量腿部肌肉注射接种4~6周龄的BALB/c小鼠,0.2 mL/只,于BSL2实验室负压IVC设备内饲养观察,并对其模型进行评价。结果小鼠接种狂犬病病毒后一周左右就出现临床症状,表现为饮食量下降,毛皮慢慢失去原先的光泽,体重下降,并出现麻痹等症状,进而死亡,部分小鼠出现躁狂的症状或抽搐性和强直性痉挛,而对照组小鼠则表现正常。DFA法检测结果：感染上狂犬病毒的小鼠脑组织涂片中出现特异性荧光抗体染色反应,而对照组动物的小鼠脑组织涂片未出现荧光抗体染色反应。RT-PCR法检测结果：从感染小鼠脑组织标本中提取病毒RNA,引物扩增出的目的基因片段,大小约为1kb,为N蛋白。免疫组化法检测结果：感染狂犬病毒的小鼠脑切片显示出棕色阳性颗粒,对照组小鼠脑切片染色阴性。病理检测结果：HE染色可见感染小鼠脑组织炎性细胞浸润,神经细胞胞质内出现内基体以及神经细胞退行性病变。结论成功的复制出小鼠狂犬病病毒感染模型,为研究和控制狂犬病奠定了基础。     

A two-part joint model for the analysis of survival and longitudinal binary data with excess zeros

Summary .   Many longitudinal studies generate both the time to some event of interest and repeated measures data. This article is motivated by a study on patients with a renal allograft, in which interest lies in the association between longitudinal proteinuria (a dichotomous variable) measurements and the time to renal graft failure. An interesting feature of the sample at hand is that nearly half of the patients were never tested positive for proteinuria (≥1g/day) during follow-up, which introduces a degenerate part in the random-effects density for the longitudinal process. In this article we propose a two-part shared parameter model framework that effectively takes this feature into account, and we investigate sensitivity to the various dependence structures used to describe the association between the longitudinal measurements of proteinuria and the time to renal graft failure.