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Kinematics of the knee during gait has mostly been studied using optical motion capture systems (MCS). The presence of soft tissue artifacts (STA) between the skin markers and the underlying bone presents a major impediment to obtaining a reliable joint kinematics assessment. In this study, we determined the effects of STA on the calculation of knee joint kinematics during walking and running, through the combination of high-speed dual fluoroscopic imaging system (DFIS) and magnetic resonance imaging technique. Ten adults walked and ran while data was collected simultaneously from MCS and high-speed DFIS. The study showed that measured STA underestimated knee flexion angle, but overestimated knee external and varus rotation. The absolute error values of the skin markers derived from knee flexion-extension angle, internal-external rotation, and varus-valgus rotation during walking were -3.2 ± 4.3 deg, 4.6 ± 3.1 deg, and 4.5 ± 3.2 deg respectively, and during running were -5.8 ± 5.4 deg, 6.6 ± 3.7 deg, and 4.8 ± 2.5 deg respectively. Average errors relative to the DFIS for flexion-extension angle, internal-external rotation, and varus-valgus rotation were 78 %, 271 %, 265 % during walking respectively, and were 43 %, 106 %, 200 % during running respectively. This study offers reference for the kinematic differences between MCS and high-speed DFIS, and will contribute to optimizing methods for analyzing knee kinematics during walking and running., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier Ltd.)

Background: The purpose of this study was to analyze sagittal-plane knee biomechanics in individuals with ACL reconstructions in bilateral countermovement jumps. This aimed to determine potential knee compensation strategies during a high-demanding symmetrical movement task from pre to six months post-ACL reconstruction., Methods: 20 ACL-reconstructed individuals were tested pre-operatively, and then seven weeks, three months, and six months after reconstruction. Additionally, a matched control group was analyzed. Data were sampled with 3D motion capture and two force plates. The following kinematic data were analyzed: peak knee flexion during countermovement, knee angle at toe-off, and knee flexion excursion during landing. The following kinetic data were analyzed: peak knee extension moments during countermovement and landing., Findings: ACL-reconstructed individuals showed significant increases in knee flexion during countermovement and knee flexion excursion during landing from six weeks to six months after reconstruction but they remained significantly below the level of the controls. The reconstructed knee joint showed increased flexion at toe-off compared to the non-injured leg at all test sessions. Knee extension moments during countermovement increased up to six months after reconstruction, but remained deficient in ACL-reconstructed individuals during countermovement and landing compared to the controls., Interpretation: Although ACL-reconstructed individuals showed increases in most kinematic and kinetic variables, they remained below the controls at six months post-ACL reconstruction. The deficits between contralateral legs and compared to the controls show that six months post-ACL reconstruction, knee joint functionality was still not equal between reconstructed and non-injured legs or in comparison to controls., Competing Interests: Declaration of Competing Interest The authors declare no conflicts of interest. All authors have approved the final article., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Background: Medial and lateral hamstrings are known for their capacity to promote internal or external rotation of the knee. Apart from implant geometry, increased co-contraction to a larger share of either the medial or lateral hamstrings has the potential to contribute to the restricted knee internal rotation especially under consideration of cruciate ligament substituting compared to cruciate ligament retaining knee endoprosthesis designs. Hence, the purpose of the study was to evaluate, whether increased co-contraction of the hamstrings contribute to the impaired knee internal rotation in total and unicondylar knee arthroplasty patients during level and decline walking., Methods: Knee joint angles were calculated using an inverse kinematics model in Anybody. Muscle activity was examined of the semitendinosus and biceps femoris., Findings: Knee internal rotation was constraint in the operated compared to the non-operated limb only in the total knee arthroplasty group during decline slope walking. Co-contraction values revealed no statistically significant differences between the operated and non-operated limb during the limited knee internal rotation period of time (59-94% of stance). Biceps femoris activity was significantly reduced (69-71% of stance) in the operated limb in the total knee arthroplasty group during decline slope walking., Interpretation: Contrary to the proposed mechanism, aspects other than co-contraction between semitendinosus and biceps femoris are involved in the impaired transverse plane knee motion. These include implant congruency and probably friction. Unexpectedly, the biceps femoris did not compensate the absence of the anterior cruciate ligament with increased muscular activity in the operated limb of the total knee arthroplasty group., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Although athletes with unilateral below-the-knee amputations (BKAs) generally use their affected leg, including their prosthesis, as their take-off leg for the long jump, little is known about the spring-like leg behavior and stiffness regulation of the affected leg. The purpose of this study was to investigate vertical stiffness during one-legged hopping in an elite-level long jump athlete with a unilateral BKA. We used the spring-mass model to calculate vertical stiffness, which equals the ratio of maximum vertical ground reaction force to maximum center of mass displacement, while the athlete with a BKA hopped on one leg at a range of frequencies. Then, we compared the vertical stiffness of this athlete to seven non-amputee elite-level long-jumpers. We found that from 1.8 to 3.4 Hz, the vertical stiffness of the unaffected leg for an athlete with a BKA increases with faster hopping frequencies, but the vertical stiffness of the affected leg remains nearly constant across frequencies. The athlete with a BKA attained the desired hopping frequencies at 2.2 and 2.6 Hz, but was unable to match the lowest (1.8 Hz) and two highest frequencies (3.0 and 3.4 Hz) using his affected leg. We also found that at 2.5 Hz, unaffected leg vertical stiffness was 15% greater than affected leg vertical stiffness, and the vertical stiffness of non-amputee long-jumpers was 32% greater than the affected leg vertical stiffness of an athlete with a BKA. The results of the present study suggest that the vertical stiffness regulation strategy of an athlete with a unilateral BKA is not the same in the unaffected versus affected legs, and compared to non-amputees., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

The low cost and ease of use of inertial measurement units (IMUs) make them an attractive option for motion analysis tasks that cannot be easily measured in a laboratory. To date, only a limited amount of research has been conducted comparing commercial IMU systems to optoelectronic systems, the gold standard, for everyday tasks like stair climbing and inclined walking. In this paper, the 3D joint angles of the lower limbs are determined using both an IMU system and an optoelectronic system for twelve participants during stair ascent and descent, and inclined, declined and level walking. Three different datasets based on different hardware and anatomical models were collected for the same movement in an effort to determine the cause and quantify the errors involved with the analysis. Firstly, to calculate software errors, two different anatomical models were compared for one hardware system. Secondly, to calculate hardware errors, results were compared between two different measurement systems using the same anatomical model. Finally, the overall error between both systems with their native anatomical models was calculated. Statistical analysis was performed using statistical parametric mapping. When both systems were evaluated based on the same anatomical model, the number of trials with significant differences decreased markedly. Thus, the differences in joint angle measurement can mainly be attributed to the variability in the anatomical models used for calculations and not to the IMU hardware., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Perturbation training is an emerging approach to reduce fall risk in the elderly. This study examined potential differences in retention of improvements in reactive gait stability over 14 weeks resulting from unexpected trip-like gait perturbations. Twenty-four healthy middle-aged adults (41-62 years) were assigned randomly to either a single perturbation group (SINGLE, n = 9) or a group subjected to eight trip-like gait perturbations (MULTIPLE, n = 15). While participants walked on a treadmill a custom-built brake-and-release system was used to unexpectedly apply resistance during swing phase to the lower right limb via an ankle strap. The anteroposterior margin of stability (MoS) was calculated as the difference between the anterior boundary of the base of support and the extrapolated centre of mass at foot touchdown for the perturbed step and the first recovery step during the first and second (MULTIPLE group only) perturbation trials for the initial walking session and retention-test walking 14 weeks later. Group MULTIPLE retained the improvements in reactive gait stability to the perturbations (increased MoS at touchdown for perturbed and first recovery steps; p < 0.01). However, in group SINGLE no differences in MoS were detected after 14 weeks compared to the initial walking session. These findings provide evidence for the requirement of a threshold trip-perturbation dose if adaptive changes in the human neuromotor system over several months, aimed at the improvement in fall-resisting skills, are to occur., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

The inclusion of muscle forces into the analysis of joint contact forces has improved their accuracy. But it has not been validated if such force and activity calculations are valid during highly dynamic multidirectional movements. The purpose of this study was to validate calculated muscle activation of a lower extremity model with a spherical knee joint for running, sprinting and 90°-cutting. Kinematics, kinetics and lower limb muscle activation of ten participants were investigated in a 3D motion capture setup including EMG. A lower extremity rigid body model was used to calculate the activation of these muscles with an inverse dynamics approach and a cubic cost function. Correlation coefficients were calculated to compare measured and calculated activation. The results showed good correlation of the modelled and calculated data with a few exceptions. The highest average correlations were found during walking (r = 0.81) and the lowest during cutting (r = 0.57). Tibialis anterior had the lowest average correlation (r = 0.33) over all movements while gastrocnemius medius had the highest correlation (r = 0.9). The implementation of a spherical knee joint increased the agreement between measured and modelled activation compared to studies using a hinge joint knee. Although some stabilizing muscles showed low correlations during dynamic movements, the investigated model calculates muscle activity sufficiently., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Background: Heterogeneous distribution of tendon strain is considered to contribute to the development of the Achilles tendon overuse injuries. Force distribution between the three portions of the triceps surae muscle and position of the calcaneus might affect the extent of strain differences within the Achilles tendon. Purpose of this study was to determine the effect of changes in force distribution within the triceps muscle and changes in calcaneus position on intratendinous strain distribution of the Achilles tendon., Methods: Five cadaveric Achilles tendons including complete triceps surae and calcaneus were dissected. Specimens were mounted in a loading simulator allowing independent force application for the three parts of triceps muscle and changes calcaneus eversion and inversion position. Strain was determined in different aspects of the Achilles tendon., Findings: Changes of calcaneus position resulted in intratendinous strain differences up to 15%, changes in force distribution within the triceps muscle resulted in strain differences up to 2.5%. Calcaneal eversion was connected to a higher degree of strain in medial tendon portions, while inversion increased strain in lateral tendon portions., Interpretation: Medio-lateral, proximo-distal and dorsal-ventral distribution of tendon strain is rather influenced by kinematics of the subtalar joint than by muscular imbalances within the triceps muscle. Clinical movement analyses should focus on motion pattern combining rearfoot eversion with high Achilles tendon load. The results indicate that twist of the Achilles tendon fascicles seems of paramount importance in balancing tendon strain. To get more insight into the Achilles tendon injuries pathogenesis future research should focus on methods monitoring heterogeneous distribution of strain in vivo., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Background: Increased mechanical load is one risk factor for osteoarthritis. One possible treatment for this disorder is the use of knee braces in order to redistribute joint loading, which may inhibit the progression of the disease. The hypothesis was: knee adduction moment can be reduced with the use of a dedicated knee orthosis, which applies an abduction moment at the knee., Methods: Sixteen healthy male subjects with varus alignment were analysed during walking and running while using an adjustable valgus orthosis. Peak knee adduction moments and knee adduction angular impulses were evaluated through inverse dynamics. Additionally, the abduction moment produced by the orthosis was measured in three different adjustments of valgus angulations (neutral, 4 degrees and 8 degrees valgus) using a strain gauge device., Findings: During walking, mean reductions of 25% and 36% in the knee adduction angular impulse were found between the conditions without orthosis and 4 degrees and between without orthosis and 8 degrees, respectively. For the running trials mean reductions of 18% and 23% were observed between these same conditions. The first and second peak knee adduction moments also decreased during walking with different orthosis adjustments (changes from 5% to 33%). During running, a significant reduction was observed only between the conditions without orthosis and 8 degrees valgus adjustments (change of 11%)., Interpretation: The orthosis tested in this study was effective in reducing the knee adduction moments during walking and running. This reduction of knee adduction moments during locomotion should contribute to decelerate osteoarthritis progression.

Background: It is of paramount importance to know the magnitude and the distribution of joint contact stress within the most heavily loaded structures of the human foot. In the talocrural joint role of external loading and loading applied by muscles on joint contact stress is not extensively studied. The purpose was to determine the distribution of joint contact stress of the talocrural joint with varying axial tibia loading and extrinsic tendon loading., Methods: Five cadaveric feet were studied in the intact condition and following transsection of ligaments under seventeen different loading conditions. Joint contact stress was determined from capacitive pressure sensors implanted in the talocrural joint when the specimens were loaded in a specially designed loading simulator. Different axial tibia and extrinsic tendon loads were applied. Motions of the bony structures were assessed by an optical motion analysis system., Findings: The anterior aspect of the joint is predominantly stressed in all loading conditions. The influence of muscle force on the internal joint contact stress distribution is higher than the axial shank loading. The biggest effect on joint contact stress was initiated by the tibialis posterior muscle. The flexor hallucis homogenizes the pressure distribution in intact joint conditions. Joint angles were not substantially changed by muscle force applications., Interpretation: The functions of the muscles of the lower leg are important for maintaining physiologic joint contact stress. Reducing the force potentials of certain muscle tendon units through surgeries, immobilization, fatigue or inappropriate footwear should change the joint contact stress. Such information is helpful to understand the physiological function of the foot. It might also explain the development and manifestation of certain foot pathologies.