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The purpose of this paper was to investigate the anatomical location of the main axes of rotation of the knee, that is the axes of flexion-extension and longitudinal rotation. We compared 4 hypotheses on the correlation between the axis of flexion-extension and the femoral anatomy and 4 hypotheses on the correlation between the axis of longitudinal rotation and the tibial anatomy in 6 normal human knees. The methods used for the study were:. digitization by an electrogoniometer; computer reconstruction of motion and bone geometry, and an original geometrical interpolation to identify axes location. Our results suggest that: (a) the axis of flexion-extension lies in a cone spanned by the transepicondylar line and the so called FFc line;¹⁹ (b) the axis of longitudinal rotation can be represented by a line parallel to the tibial anatomical axis intersecting the flexion axis in a fixed point of the medial compartment.

This study presents the validation of the tensioning device that applies a constant load to the medial and lateral compartments of knee joint separately, which can collapse or expand on each side independently, and that should be able to provide a better evaluation of ligament tension and allow the computer software to better plan the appropriate bone cuts or ligament release, and reports the first phase of the clinical validation of the tensioning device, including first qualitative comparison with standard navigated technique and consideration on the use of the device.

A randomized study, involving five experienced orthopedic surgeons with 58 complete data sets, revealed that there is no statistical difference between the gaps obtained with standard navigated technique and tensioning device in extension, while in flexion there is an average difference 1.4 mm.

This paper reports an extensive analysis of the articular surfaces of the femur and the tibia in sagittal, frontal and coronal sections, obtained by digitizing the bones with a precise electrogoniometer (FARO Arm) and elaborated off-line fitting the profiles with least square curves. Within the method resolution, we show that the tibio-femoral joint can be described as consisting of two different compartments rigidly connected. The femoral medial side can be represented by an ellipsoid with its main axis in the AP direction, semi-axes equal to 30 and 23 ± 2 mm (posteriorly spherical) and circular ML section with a radius equal to 20 ± 2 mm, which articulates on a (tibial) semi-cylinder with its main axis in the AP direction and conform circular ML section (radius equal 22 ± 1.3 mm). The femoral lateral side can be represented by a ellipsoid with lower eccentricity and a shorter AP size than the medial side, semi-axes equal to 26 and 20 ± 4 mm. It has an elliptic ML section with a sloped major axis parallel to the tibial spine, which forms an angle around 160° with the lateral tibial plateau. This study integrates a previous study by two of the authors with further data on tibia and femur, explaining when the sagittal view of femoral condyles can be better fitted by ellipses than two circles and when it is equivalent. This work represents a systematic numerical study of the tibio-femoral joint in six cadaveric knees, integrates the known anatomical data and provides updated and quantitative 3D information useful for mathematical knee models, prosthesis design, further understanding of knee biomechanics and the function of knee anatomical structures.

Injuries to the knee joint are common and often have an adverse impact on a patient's quality of life. It is therefore important to understand the load transfer mechanism of the knee, especially with regard to the loading of the menisci in different positions and under different conditions.

To date, only contact pressure between joint surfaces and menisci, as well as circumferential strain, have been measured by pressure sensors and strain gauges. Therefore, the aim of this study was to investigate the spread of axial load within the menisci and the effect of the knee flexion angle on the axial load within the menisci.

Intrameniscal forces were measured with Fiber Bragg Grating (FBG) sensors and conductive rubber sensors in porcine knee joint specimens. The changes in pressure were measured under different loading conditions. Measurement of the intrameniscal pressure is feasible. Although, there is some existence of variations in readings, some trends can be inferred. From the overall trend, it was observed that higher stress occurs at lateral central and lateral posterior regions. As the occurrences of injuries are mainly at the medial meniscus, this may imply that the level of stress is secondary to the mobility of the meniscus in incidents of injuries. It was found that the posterior meniscofemoral ligament plays a crucial role in the mechanics of the lateral meniscus.

The purpose of this study was to create a kinematic model of the knee joint with six degrees of freedom (DOF) and evaluate the effect of medial collateral ligament (MCL) and lateral collateral ligament (LCL) rupture on cartilage contact point distribution on the tibia during flexion. We hypothesized that collateral ligament contributions vary over six DOF of knee joint articulation and affect the cartilage contact point distribution during joint articulation. The ligament contributions and distribution of joint cartilage contact points cannot be fully assessed with simplified joint models or invasive experiments. Therefore, we developed a new model in which the tibia and femur centers of mass were determined from their surface geometry, and the displacement of the moving tibia was determined from the displacements of the attached ligaments. Compared to the intact knee, the tibia with the LCL removed had higher medial translation and lower valgus rotation. The tibia with the MCL removed had higher lateral translation and higher valgus rotation than the intact knee. At 0${}^{\circ }$, 30${}^{\circ }$, and 60${}^{\circ }$, the tibia with the LCL removed had more internal rotation than the intact knee. Understanding six DOF knee joint kinematics with integration of ligament contributions and cartilage contact positions is useful for the diagnosis of ligament injuries and the design of articulating surfaces for total arthroplasty.

Background: Adequate research is not reported so far to underline the influence of commonly used polycentric knee joints on gait performance of subjects with trans-femoral amputation. Objective: The intent of this investigation is to analyze prosthetic gait of unilateral traumatic trans-femoral amputees with polycentric four-bar linkage knee and compare it with normal subjects for evaluating any asymmetry in gait performance. Methods: Objective three-dimensional gait analysis of 15 subjects [mean (age): 36.4 (10.7) years] were performed in gait lab through force plate and optoelectronic devices to measure temporal-spatial parameters, kinematic and kinetic performances. Gait patterns of amputees were compared with those of 15 individuals with normal gait to analyze distinct functionalities of existing polycentric knee. Results: Asymmetry in gait was observed between amputees and normal subjects for all variables concerned ($p<0.05$). Amputee gait was with significantly lesser velocity, cadence with shorter step and stride length. There was significantly less hip, knee and pelvic motions, however, pelvic obliquity and rotation did not show significant difference from the normal subjects. The vertical component of the ground reaction force differed significantly between prosthetic and intact limb [49.7 (8.5)% and 90.4 (7.4)% body weight] and also from normal subjects [107.5 (2.4)% body weight] during stance ($p<0.05$). Interpretation and Conclusion: This difference may be attributed to nonproportionate loading of limbs and mechanical adaptations for counteracting deficiencies of prosthetic side. This study will help to explain gait asymmetry in trans-femoral amputees and to identify underlying mechanisms to enhance the quality of the existing design of prosthetic knee through optimizing design parameters and utilizing appropriate materials.

Background: Knee joint stability is enhanced by ligamentus structures such as anterior cruciate (ACL), posterior cruciate (PCL), medial collateral (MCL) and lateral collateral ligaments (LCL). Rupture of ACL is the most common knee injuries, especially in sport related activities. The aim of this study is to evaluate the stress developed in knee joint structures in various degrees of knee flexion in ACL ruptured compared to normal condition.

Method: CT scan images of knee joint were used to create 3d model of knee joint by use of Mimics software. Abaqus software was used to evaluate the stress developed in knee joint in normal and in ACL reconstructed conditions in various degrees of knee flexion.

Results: The stress developed in ACL and other knee joint structures increased significantly by increase in knee joint flexion. The stress of knee joint structures (especially in ACL) in ACL reconstructed condition was more than that of normal condition.

Conclusion: It is recommended to immobilize the knee joint in extension up to $15^{\circ }$ of knee flexion in those with ACL injuries. The stress of ACL increased due to an increase in tibia translation associated with knee flexion.

The aim of this experiment was to provide insight into the immediate influence of both semi-custom insoles and knee sleeves in recreational male runners/athletes suffering from patellofemoral pain and also to explore the association between the extent of patellofemoral pain and psychological wellbeing. Experiment 1 examined 17 male recreational runners with patellofemoral pain, in semi-custom insole and no-insole conditions. Experiment 2 examined 13 male recreational athletes with patellofemoral pain, undertaking run, $45^{\circ }$ cut and single-leg hop movements in knee sleeve and no-sleeve conditions. In both experiments, motion capture and ground reaction forces were collected, allowing kinetics and three-dimensional kinematics to be calculated alongside patellofemoral joint loading quantified using musculoskeletal modeling. In both experiments, patellofemoral pain symptoms were examined using the KOOS patellofemoral pain subscale and psychological wellbeing using the COOP-WONCA questionnaire. The findings from both experiments showed that pain symptoms significantly predicted psychological wellbeing ($R^2=0.29$ in experiment 1 and $R^2=0.33$ in experiment 2). Experiment 1 showed that orthoses significantly reduced tibial internal rotation range of motion (no-$\mathrm{\text{insole}}=7.59^{\circ }$ and $\mathrm{\text{insole}}=6.87^{\circ }$) whilst also increasing the peak knee adduction moment (no-$\mathrm{\text{insole}}=1$N$\cdot$m/kg and $\mathrm{\text{insole}}=1.09$N$\cdot$m/kg). The findings from experiment 2 revealed that the knee sleeve reduced the peak patellofemoral force (no-$\mathrm{\text{sleeve}}=3.40$BW and $\mathrm{\text{sleeve}}=3.10$BW) in the run movement and the patellofemoral load rate in the cut movement (no-$\mathrm{\text{sleeve}}=135.18$BW/s and $\mathrm{\text{sleeve}}=111.24$BW/s). Overall, the findings confirm that pain symptoms are predictive of psychological wellbeing in recreational male athletes with patellofemoral pain. Furthermore, the findings suggest that both insoles and knee sleeves may provide immediate biomechanical benefits in recreationally active individuals with patellofemoral pain, although when wearing insoles this may be at the expense of an increased knee adduction moment during running.

The aim of this study is to investigate the effect of knee extensors fatigue on joint position sense. Fifteen healthy participants, all males, with no history of previous musculoskeletal lesions were recruited. Evaluation of the knee joint position sense and the muscle fatigue protocol had been performed using an isokinetic dynamometer. Fatigue was considered when the maximum torque was reduced by 50%. The joint position sense was analyzed by the absolute error and the variable error. The paired t-test was used to compare the mean in pre and during muscle fatigue conditions. The level of significance was 5%. Absolute and variable errors were not significantly affected by muscle fatigue. Knee joint position sense does not seem to be affected by fatigue of knee joint extensors.

A prosthetic knee is predominantly subjected to cyclic action leading to fatigue failure during its operation. However, cyclic failure is more severe as it occurs below the yield strength and may happen even without prior indication. This study presents a cyclic structural analysis of an existing polycentric mechanical prosthetic knee by finite element simulation and its experimental validation as per the ISO 10328:2016 standard. The three-dimensional (3D) model is imported to the ANSYS 20.1 workbench to study stress distribution and fatigue life in the knee for ensuring its safety performance. The maximum von-Mises stresses developed at the front and back joint bars made of A390.0-T5 and A390.0-T6 cast aluminium are 100 and 89MPa, respectively, in both loading conditions compared to their mechanical fatigue strength of 89MPa. The maximum deformation and average number of cycles for fatigue failure are 2.66 and 2.53mm and $2.95\times 10^6$ and $2.81\times 10^6$ for simulation and experimental results, respectively. These results suggest that this polycentric knee unit has poor fatigue strength and thereby does not meet the ISO structural standard. A validation test has been performed with an average error of 4.75% between the simulation and experiments results showing higher reliability.

Wear is one of the main mechanical factors that limits the lifetime duration of total knee replacements (TKRs) and it is known to be highly dependent on the local kinematics of the knee joint. In this study, a novel hybrid wear model is introduced to model the wear distribution between the lateral and medial side of any commercially available TKRs. The major aim is to be able to rate TKRs, based on their wear properties that are obtained from numerical simulations, whether in long term they are able to maintain a modest and closely equal wear propagation on both of the tibial compartments. For the simulations, three TKR geometries were used with the augmented Archard’s law which involves the effect of slide-roll under squat motion. Squat was chosen due to its importance both in sport and everyday life. By this model, it is demonstrated on different TKRs how wear is built up on both sides of the tibial tray from 20 to 120 degree of flexion angle.

Climbing stairs is relatively challenging for seniors, post-stroke individuals or even healthy young men when carrying heavy objects. In this paper, we have developed a rigid-soft hybrid exosuit that helps the wearer to climb the stairs by offering a driving torque to the knee joint. By combining the advantage of rigid and soft exoskeletons, the exosuit is more comfortable when assisting wearers at a high level of assistance. To simplify the detection system, but keep it versatile, only the surface electromyography sensor is used to detect human movement. This paper uses a hierarchical control strategy based on gait detection and force tracking. To verify the capability of this exosuit system, we conducted experiments with four healthy users walking upstairs in different levels of assistance and climbing speeds. By comparing the muscle activity of participants with exosuit and without exosuit, the vastus lateralis activity was reduced by 3% to 15%, depending on the subject. This research shows the assisting capability of this exosuit under different assistance levels and climbing speeds.

Background: Combining arthroscopic microfractures (MF) with platelet-rich plasma (PRP) complexes is a potential approach for treating knee cartilage injuries. However, effective treatment of cartilage injuries in the knee joint remains a challenge. Objective: To evaluate the clinical effects of a platelet-rich complex based on MF surgery for treating knee cartilage injuries. Methods: We selected 120 patients with knee cartilage injury and divided them into observation and experimental groups according to the use of a platelet-rich complex. Preoperative and postoperative follow-up visit data were retrospectively collected and analyzed. Results: Preoperative visual acuity scores between the two groups were comparable ($P>0.05$). At 3 and 6 months postoperatively, the scores were lower in the experimental group than in the control group ($P<0.05$). The preoperative Lysholm knee scores and Tegner activity were similar ($P>0.05$) but greater in the experimental group at 3 and 6 months postoperatively ($P<0.05$). Postoperative complications were similar between the two groups according to Fisher’s exact test ($P=1.00$). Conclusion: The platelet-rich complex based on MF surgery treatment of knee cartilage injuries exhibited a better clinical effect and is an easy-to-operate and effective method worthy of clinical consideration.