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Awareness of the possibility of multiple ligament injuries in the traumatized knee is essential for the successful management of an injured knee. Relative infrequency of occurrence, heterogeneous presentation, inconsistent treatment protocols, ambiguity in the timing of surgery, post-surgical rehabilitation protocol, and paucity of literature on the subject make the situation perplexing. This study aims at the evaluation of a multi-staged protocol and determination of various factors having influence on outcome. This study included 39 patients with injury to two or more ligaments of the knee, without associated complications. Staged protocol of ligament surgery included repair or reconstruction of collaterals and corners in the initial stage, followed by reconstruction of posterior cruciate ligament (using Hamstring graft) and anterior cruciate ligament (using Bone Patellar Tendon Bone graft). Rehabilitation included two weeks of immobilization following repair/reconstruction of collaterals/corners followed by protected range of motion exercises. In final IKDC qualification, 10 knees (25.64%) were normal (A), 26 knees (66.6%) were near normal (B), 2 knees (5.1%) were abnormal (C), and 1 knee (2.56%) was severely abnormal (D). Our staged management protocol had good subjective, and objective outcomes, and nearly all patients, but two, returned to their routine activities.

Objective: To clarify the pathophysiology of knee arthropathy, articular sound in the knee joint was recorded using an accelerometer, vibroarthrography (VAG), during standing-up and sitting-down movements in patients with osteoarthropathy (OA) of the knees. Methods: VAG signals and angular changes of the knee joint during standing-up and sitting-down movements were recorded in patients with OA, including 17 knees with OA at Kellgren–Lawrence stage I and II, 16 knees with OA at III and IV stages, and 20 knees of age-matched control subjects. Results: The level of VAG signals was greater in knees with a higher stage of OA at 50–99 and 100–149 Hz among the groups (ANOVA with Tukey–Kramer multiple comparisons test, p < 0.01). The VAG signals did not correlate with WOMAC-pain or physical scores. Conclusions: We considered that the increase in VAG signals in these ranges of frequency corresponded with pathological changes of OA, but not self-reported clinical symptoms. This method of VAG can be used by clinicians during interventions to obtain pathological information regarding structural changes of the knee joint.

Purpose: This study was conducted to histopathologically compare the results of the administration of intra-articular PDRN and HA injections in experimentally induced OA in rats. Methods: Osteoarthritis of the knee joints was induced in a total of 30 rats. Rats were randomly divided into three groups; polydeoxyribonucleic (PDRN) acid group, hyaluronic acid (HA) group, and saline group. The PDRN group was injected with 12 mg/0.05 ccPDRN acid. The HA group was injected with 12 mg/0.05 ccHA, whereas the saline group was injected with 50 $\mu$l (0.05 cc) of 0.9% sodium chloride solution. All rats were sacrificed on postinjection day 29, and the right knee joints were prepared and evaluated histologically using the Mankin scoring system. Results: Total Mankin scores showed a significant difference among all groups ($p$ = 0.001). According to bilateral comparisons performed to identify the group that showed a difference, the total Mankin scores of the PDRN acid and HA groups were found to be significantly lower than those of the saline group. In PDRN acid group, tidemark continuity wasobserved in all specimen. Conclusion: Intra-articular injections of PDRN acid resulted in greater chondroprotective effects and less degeneration than those of HA and saline in experimentally induced OA of the knee joints in rats.

Interaction between articular surfaces at the knee joint allows movement and stability. The knowledge of how this mechanism works in physiological conditions could be very useful for the development of new clinical procedures. The objective of this study was to develop a subject-specific model able to estimate the articular contact area at the tibio-femoral joint avoiding any destructive measurements. Thin plate splines were used to describe articular surfaces and to allow an analytical estimation of the distance between the surfaces. The sensitivity of the model was evaluated and the tibio-femoral contact area was estimated in a living subject. Femoral contact area results were always smaller than the tibial one, whereas tibial contact area results were less repeatable. Increasing the distance threshold, the increase of the contact area was almost linear. High repeatability was obtained sampling each condyle with more than 60 steps. Contact areas, estimated with the loaded knee, were in accordance with physiology and literature showing a good repeatability. The devised model was suitably used to evaluate the articular contact at the knee joint of an healthy living subject and can be a useful clinical tool to suggest procedures aimed at restoring physiological conditions.

The angular jerk cost (AJC) was proposed to objectively represent the smoothness of joint movement by calculating the time-dependent changes in acceleration during motion. There are currently no reports focusing on smoothness using AJC measurements of the knee joint movement during the stance phase of gait. The purpose of this study was to verify whether a reduced walking speed affects the smoothness of the knee joint movement during the stance phase of gait. The gaits of 12 healthy adults were assessed. A slower walker showed a significant reduction in the AJC value in the period between the initial contact and the loading response, as compared with someone walking at a comfortable speed.

The maximum ground reaction force of the stance phase at a comfortable walking speed was significantly larger than that at a slower walking speed. Thus, although the smoothness of the knee joint was impaired by a rapid load in the early stance phase, a slower walking speed reduced the ground reaction force and angular acceleration of the knee joint and created a smoother movement. The AJC can be an important index for understanding the smoothness of the knee joint in the early stance phase.

The objective of the present study is to investigate the stiffness of the knee joint, in order to provide a basis for developing a biofidelic pedestrian legform impactor. A biofidelic lower limb model was employed to replicate structural responses of the human knee joint by finite element simulations. In the simulation, a single displacement was imposed on the thigh or leg, and constrained six freedoms of the other part. As a result, nonlinear load-displacement data were approximated by a linear regression to determine the stiffness. Considering knee joint kinematics under lateral car-pedestrian impacts, a stiffness matrix was established including lateral bending, lateral shearing and torsion effects that significantly influence pedestrian lower limb injuries. Then, this stiffness matrix was applied in a developed legform model. The structural responses of the legform were obtained by the impact with a family car model. Finally, the legform biofidelity was evaluated by comparing the global kinematics of the pedestrian lower limb.

The articular cartilage in the human knee plays an important role to ensure a lifetime knee function for an individual. Due to damage of the cartilage in the knee, the coefficient of friction (COF) increases even after treatments for the cartilage, due to the poor self-healing ability of the cartilage, resulting in decreased knee life. As the mechanism of the function of the knee joint is similar to a bearing, a model based on the regression model of cylindrical bearing life has been developed. The model is used to evaluate the effect of the COF on the lifetime of the knee. The results show the correlation between the life of the knee and the COF of the knee cartilage. The knee lifetime depends on the ratio of the COF of the healthy cartilage to the damaged cartilage. The results demonstrate the effect of the COF on the knee lifetime, which is an exponential decrease in the life of the knee for both males and females.

Knee joint is the hub of human lower limb movement and it is also an important weight-bearing joint, which has the characteristics of load-bearing and heavy physical activities. So the knee joint becomes the predilection site of clinical disease. Once people have the cartilage lesions, their daily life will be affected seriously. The simulation of the knee joint lesions could provide help for clinical knee-joint treatment. Based on the complete model of knee joint, this paper use the finite element method to analyze the biomechanical characteristics of the defective knee joint. The results of simulation show that the stress of cartilages when standing on single leg is approximately doubled than that of standing on two legs. When standing on single leg, the 8-mm diameter osteochondral defect in femur cartilage can generate maximal changes in von-mises stress (by 36.74%), while the von-mises stress on tibia cartilage with 8-mm defect increase by 87%. The stress distribution of cartilages is almost the same, there is no obvious stress concentration when in defect. Increasing the defective diameter, femoral cartilage, meniscus and tibial all present an increasing trend towards stress. When increasing the applied load, the stress of the femoral cartilage, the meniscus and the tibial cartilage all increased.

The main purpose of our study was to evaluate the biomechanics of different posterior cruciate ligament (PCL) reconstruction techniques. Seven fresh cadaver knees were collected. A 6-DOF robot arm was used to test the biomechanical parameters, including the posterior stability, the lateral stability and the rotation stability of different PCL reconstruction techniques. Each group was tested at the knee flexion of 0, 30${}^{\circ }$, 60${}^{\circ }$, 90${}^{\circ }$ and 120${}^{\circ }$, under the following conditions respectively: a posterior force of 134N, an internal and external rotation torque of 5$\mathrm{\text{N}}\cdot \mathrm{\text{m}}$, a varus and valgus torque of 10$\mathrm{\text{N}}\cdot \mathrm{\text{m}}$, and a combination of 100N posterior force and 5$\mathrm{\text{N}}\cdot \mathrm{\text{m}}$ external rotation torque. The posterior tibia translation and the rotational angle of the 4-tunnel double-bundle PCL reconstruction group were significantly lower than that of 3-tunnel double-bundle group and the single-bundle group; the posterior tibia translation valgus–varus-angle were lower at some specified flexion angle. No statistical difference was found between the anatomic 4-tunnel bundle group and the intact knee group concerning the posterior tibia translation, the rotational angle, and the valgus–varus-angle. This study showed that the biomechanics of PCL of 4-tunnel double-bundle reconstruction was closer to the intact knees than the other two reconstruction methods.

Reduced muscle strength is an important fall risk factor. The fall occurs more in elderly women than in elderly men. The aim of this study is to investigate muscle strength and the ability to generate rapid torque for knee joint in elderly men and women. Twenty healthy elderly participants (10 men and 10 women) performed maximal voluntary knee extension and flexion during concentric, isometric and eccentric conditions. The peak torque and rate of torque development (RTD) was normalized by each subject’s body mass. Independent $t$-tests were employed in the comparison of elderly women with elderly men. Elderly women exhibited weaker isometric flexion and eccentric extension strength compared to elderly men ($p<0.05$). Although there was no significant gender difference in isometric extension peak torque, RTD of elderly women was slower than it of elderly men ($p<0.05$). In contrast, no significant gender differences were observed in concentric contraction condition ($p>0.05$). These results indicate that the deteriorated RTD as well as muscle strength per body mass may be associated with a higher frequency of falls in elderly women than in elderly men. This study suggests that training of specific-contraction type should be considered for fall prevention in elderly women.

Complication rates of anterior cruciate ligament reconstruction (ACL-R) were reported to be around 15%. Although it is a very common arthroscopic surgery with good outcomes, breakage and migration of fixators are still possible to occur due to stability issue. One of the factors that affects the mechanical stability of fixators is its length. Therefore, the aim of this paper is to analyze the biomechanical effects of different lengths of fixators (cross-pin technique) towards the stabilities of the knee joint after ACL-R. Finite element analyses of knee joint with DST grafts and fixators were carried out. Mimics and 3-Matic were used in the development of knee joint models, while the grafts and fixators were designed by using SolidWorks software. All models were remeshed in the 3-Matic and numerical analysis was performed via MSC.Marc Mentat software. A 100 N anterior tibial load was applied onto the tibia to simulate the anterior drawer test after the surgery and proximal femur was fixed at all degrees of freedom. Based on the findings, cross-pin with 40mm in length provided the most favorable option for better treatment of ACL-R, where it could promote osseointegration and preventing fracture.

Objective: To explore the clinical value of high-frequency ultrasound in the detection of chronic knee injuries in miners. Methods: A total of 53 Chinese coal miners from the China, as well as 33 nonminers without history of knee conditions were prospectively examined using high-frequency ultrasound. Blood flow was observed using color Doppler flow imaging (CDFI) and power Doppler ultrasound (PDUS). In the event of slow blood flow, parameters for color Doppler were set to maximal gain and minimal noise. Results: Chronic knee joint injuries were detectable as lesions in bursa around the joint and infrapatellar soft tissues. Various proportions of miners had nodular, finger-like or focal protrusions extending from the bursa synovium into the synovial cavity. Such protrusions were observed in the suprapatellar bursa (15, 28.3%), prepatellar bursa (17, 32.1%), and deep infrapatellar bursa (4, 7.5%). Infrapatellar soft tissues were significantly thicker in miners ($9.00\pm 2.85$mm) than of controls ($4.47\pm 0.55$mm; $t=11.25$, $P<0.001$). Miners showed substantial thickening of the synovia, as well as nodular, finger-like and focal protrusions in the synovia of suprapatellar bursa and/or prepatellar bursa (infrapatellar bursa). Synovium in miners showed more blood flow signals, especially in the supra- and prepatellar bursae, than synovium in controls. Echoes from the interior of infrapatellar soft tissues were enhanced and uneven in 47 of 53 miners, showing hyperecho patterns of scattered dots, short lines or flakes. Conclusion: Ultrasound can complement X-ray imaging and magnetic resonance imaging for detecting and characterizing chronic knee joint injuries in miners.

In this paper, we develop a control law for Functional Electrical Stimulation (FES) application fields. This work aims to command the knee joint movement of patients in the seated position suffering from neurological disorders that lead to a partial or total paralysis of the limb. For this purpose, we propose the synthesis of an adaptive continuous control that permits to the knee joint the tracking of a time-varying desired angle. The knee movement is represented by the dynamical model of the lower limb. The designed control ensures an asymptotic stability while considering constraints such as unknown model parameters, unknown perturbation effects and unknown spasticity and fatigue parameters. The applicability and the effectiveness of the designed control law are shown through the simulation results.

Preface: Understanding knee kinematics is a fundamental prerequisite to address restoration in pathological joints; these performances represent the goal to achieve after the treatment. Experimental activities addressing knee kinematics often involve Motion Capture systems to acquire information, both for in vivo and ex vivo studies. This technique allows a complete analysis of the joint kinematics and is able to provide useful results for the comparison mentioned above. Objectives: The definition of a reproducible and straightforward protocol represents a beneficial factor to improve both reliability and the time required: in this study a new protocol for kinematics experimental activities on ex vivo knee specimens was developed, validated and tested. Methods: Synthetic bones were chosen for the analysis and different Total Knee Arthroplasties models were selected (a Cruciate Retaining, a Posterior Stabilized, a Constrained Condylar Knee and a Rotating Hinge). A dedicated frame was used to support and secure the knee specimens and pair the extensor mechanism to a motor. The Motion Capture System was assembled and paired with dedicated marker-sets to be fixed to the specimens. A post-processing tool was developed to analyze the outputs and was validated with a goniometer. A series of force-driven tasks were defined, implemented and run in the motor system for all the different prosthesis configurations and kinematics output were analyzed, comparing the outputs with the expected results. Results: The validation of the system returned satisfying results in terms of correspondence between the angles imposed and the ones measured, with an average error below $3^{\circ }$ and a standard deviation below $1^{\circ }$ for each kind of rotation. The results from the different testing were coherent with the type of specimens and prostheses tested. Conclusions: This study proved that the protocol and testing set-up developed for knee kinematics in vitro analysis are able to provide reliable and coherent data, as proven by the post-processing validation and by the testing campaign on synthetic specimens.

Background: During the process of aerobic exercise, there are a lot of jumping and split movements, which can easily cause anterior cruciate ligament (ACL) injury in the knee joint. After undergoing ACL reconstruction (ACLR) surgery, postoperative recovery is crucial. Currently, many methods have been applied, but research on water exercise is still limited. Purpose: This paper aims to understand the role of water exercise in the recovery of athletic ability after ACLR and provide guidance for athletes’ postoperative rehabilitation. Methods: Forty athletes with ACL injuries caused by aerobics practice or competition and undergoing surgery were randomly assigned to either group A or group B. The former received six weeks of a conventional postoperative recovery program, and the latter received six weeks of a water exercise postoperative recovery program. Knee joint range of motion (ROM), swelling value, visual analog scale (VAS) score, knee joint function score, and passive angle reproduction (PAR) were measured before and after the experiment. Results: After six weeks of recovery, the knee ROM was $127.84\pm 9.12^{\circ }$, the swelling value was $0.92\pm 0.53$cm, the VAS score was $1.86\pm 0.21$, the Lysholm score was $88.67\pm 5.62$, and the International Knee Documentation Committee (IKDC) score was $83.56\pm 13.64$ in group B, which were significantly lower than those before recovery and those in group A ($p<0.01$). After recovery, the PAR of the affected side was still different from that of the healthy side in the two groups ($p<0.01$), but the PAR of group B was better than that of group A ($p<0.01$). Conclusion: Compared to the conventional program, the water exercise-based postoperative recovery program demonstrates better performance in improving knee joint ROM, functionality, and proprioception, and can be used for practical post-ACLR rehabilitation.

In order to study the three jump training and competition on knee joint impact damage degree, left knee joint of one healthy male athletes is used as the research object, a complete knee three-dimensional model was established based on the jumper’s knee CT scan and magnetic resonance imaging (MRI), including the femur, tibia, fibula, patella and knee major cartilage, ligaments. The multi-body dynamics analysis (MDA) and finite element analysis (FEA) method are used to calculate the three jump, jump starting, landing process of athletes knee joint impact, the state should change the status of stress, strain and displacement. The results show that in the three jump process, the load on the lateral contact area of the knee joint is the largest, the displacement is the largest, and it increases with the impact of jump and landing. This exacerbated the degree of wear and tear of the tibia, it tends to induce knee injury in athletes. The results show that the combination of finite element and MDA can better study the knee joint’s shock and vibration during the three-level jump training and competition, and these open up a new research method for the knee joint injury. It also provides a certain reference for the prevention and treatment of knee joint injury.

In this study, we adopt different material models to study the strength and stiffness of menisci of the knee joint using finite element method. The three-dimensional (3-D) knee joint finite element model is constructed based on the Magnetic Resonance (MR) images of a human knee joint, and the strength of menisci is analyzed under a specific vertical loading case. In this paper we categorize and implement three types of appropriate material properties, namely isotropic linearly elastic, transversely isotropic elastic and isotropic hyperelastic for menisci of the knee joint. Different strain energy models are also studied and compared under hyperelastic category. The comparative study demonstrates that the hyperelastic model with Ogden form is more appropriate in modeling menisci of the knee joint. By referring to the test data of different material properties from earlier studies by various researchers, we hope to provide a comparative study leading to appropriate menisci material models and properties for finite element analyses of knee joint structures.

Degenerative osteoarthritis is the consequence of impact force applied to articular cartilage that results in surface fissuring. Soft cushions and flexed posture are two important factors to reduce the impact force; however, no quantitative information of how soft should the cushion be to prevent the injury and the mechanism of force attenuation of knee joint at neutral and flexed posture was not well documented yet. The objective of current study is hence to find the quantitative shock attenuation of knee joint using different stiffness of cushions when the knee is at neutral posture and flexed posture. A “drop-tower type” impact apparatus was used for testing. Nineteen fresh porcine knee joints were divided into two posture groups, i.e. neutral and flexed posture. All specimens were tested using stiff, medium, and soft cushions. The axial reaction force, anteroposterior shear force, and flexion bending moment were recorded for analysis. We found the flexed posture decreased the axial reaction force and anterior shear force but increased the flexion bending moment. The effect of stiffness of cushions on the mechanical response of knee joint during impact loading was significant for neutral posture but not for flexed posture.