Increased Joint Stiffness Research Articles

Differences in landing biomechanics in the presence of delayed onset muscle soreness following or not active recovery

ObjectiveDelayed onset muscle soreness (DOMS) can reduce joint range of motion and strength, cause edema, and increase joint stiffness. Here we set out to determine whether quadriceps DOMS followed by an active recovery low-intensity exercise alters jump landing biomechanics. Methods3D landing kinematics, kinetics, and DOMS were evaluated in 26 healthy adults (15 women) performing drop and vertical jump landings before and after a squat protocol to induce quadriceps DOMS. In the presence of DOMS, half of the participants (n = 13) performed a low-intensity exercise for active recovery (10-minute treadmill walking), while the other half (n = 13) did not. Descriptive statistics and generalized estimative equations were applied to determine the effects of DOMS and active recovery on landing kinematics and kinetics. ResultsDOMS decreased knee and ankle flexion angles and increased knee and ankle frontal plane angles during vertical jumps. DOMS elicited a longer time to reach peak ground reaction force during drop jumps. Low-intensity exercise for active recovery reduced DOMS perception but did not alter the biomechanics of landing. ConclusionDOMS changes landing strategy. However, including a low-intensity exercise for active recovery before landing practice did not change the kinematics and kinetics of landing.

Design of a mixed robotic machining system and its application in support removal from metal additive manufactured thin-wall parts

Robotic machining could provide a solution for removing supports from metal additive manufactured workpieces, replacing labor-intensive work. However, the robot’s intrinsic weaknesses of low positioning accuracy and structural rigidity primarily restrict its applications. Improving the accuracy of robotic machining remains an unresolved issue. A mixed solution is proposed, in which a portable CNC machine with the capability of visual feature recognition is equipped with a universal industrial robot. The robot implements positioning motions in a large space, while the portable CNC fulfills accurate machining motions on a local feature of the workpiece. A sizeable weight of the portable CNC exerts a moderate load on the industrial robot’s joints, increasing joint stiffness. The mixed machining system exhibits high accuracy and stiffness when milling a steel/titanium alloy workpiece, achieving tolerances up to ±0.04 mm on a 60×80 mm U-shaped path without exciting any structural vibration modes. When the dimension of the workpiece exceeds the machining range of the portable CNC, a combined algorithm of coarse-fine registration based visual identification and robot error compensation is designed to align the spatial coordinates of the machining motion with that of the positioning motion, thereby extending the machining range with high accuracy. Through the proposed mixed robot machining method, experiments of doubling the machining range have been done to verify that the mixed machining robotic system is able to slot a 550 mm-long path with accuracy of ±0.1 mm. Furthermore, the mixed robotic machining system is applied to recognize and remove multiple supports of lattices, grids and ribs from a titanium-alloy additive manufactured thin-wall workpiece with high accuracy and high efficiency.

Proximal Joint Compliance as a Passive Method for Ground Reaction Force Redirection During Legged Locomotion

Abstract Ground reaction forces (GRFs) are a critical component of legged locomotion, and controlling their direction leads to more stable, efficient, and robust performance. The novelty of this work is to studying passive proximal joint (hips/shoulders) compliance for the purpose of redirecting the GRF passively. Previous works have redirected the GRF actively or studied passive proximal joint compliance for purposes such as swing phase efficiency, but passive methods of stance-phase GRF redirection are under-developed. This paper analyzes the relationship between hip compliance and the GRF direction analytically and with simulations of a trotting quadruped. The results show increased GRF redirection, on average, with increased joint stiffness, for a range of cases. An example method of utilizing this relationship to improve locomotion performance is presented by simulating online compliance adaptation. By adapting the compliance parameter during locomotion, the cost of locomotion was reduced toward the known minimum within the parameter space explored. These results support the conclusion that adjusting the hip compliance provides a passive way of redirecting the GRF, which leads to improved locomotion performance. Other systems can utilize this knowledge to passively improve their own performance.

Wave transmission in layered composite rock mass comprising parallel joints and different rock materials

This study investigates wave propagation of layered composite rock mass composed of multiple joints and assorted rock materials. Firstly, the effect of multiple-reflection between joints on wave transmission was explored by modifying the method of characteristics. Secondly, the superposition of direct and indirect transmission induced by multiple-reflection was analyzed. Waveform variations in wave transmission were compared across three different layered composite rock mass. Finally, the effects of wave parameters (frequency), joint parameters (stiffness and number), and rock parameters (wave impedance ratio) on both direct and indirect transmission induced by multiple-reflection were considered. The results indicate that the effect of indirect transmission induced by multiple-reflection on both particle velocity and stress transmission of waves cannot be ignored in many cases. The results further indicate that effect of indirect transmission induced by multiple-reflection on both particle velocity and stress transmission coefficients decreases with increasing incident wave frequency, while it increases with increasing joint numbers. The effect initially increases and subsequently decreases with increasing joint stiffness. Furthermore, the effect of indirect transmission induced by multiple-reflection on the particle velocity transmission coefficient increases while its effect on the stress transmission coefficient decreases with increasing wave impedance ratio.

Combined translational and rotational perturbations of standing balance reveal contributions of reduced reciprocal inhibition to balance impairments in children with cerebral palsy.

Balance impairments are common in cerebral palsy. When balance is perturbed by backward support surface translations, children with cerebral palsy have increased co-activation of the plantar flexors and tibialis anterior muscle as compared to typically developing children. However, it is unclear whether increased muscle co-activation is a compensation strategy to improve balance control or is a consequence of reduced reciprocal inhibition. During translational perturbations, increased joint stiffness due to co-activation might aid balance control by resisting movement of the body with respect to the feet. In contrast, during rotational perturbations, increased joint stiffness will hinder balance control as it couples body to platform rotation. Therefore, we expect increased muscle co-activation in response to rotational perturbations if co-activation is caused by reduced reciprocal inhibition but not if it is merely a compensation strategy. We perturbed standing balance by combined backward translational and toe-up rotational perturbations in 20 children with cerebral palsy and 20 typically developing children. Perturbations induced forward followed by backward movement of the center of mass. We evaluated reactive muscle activity and the relation between center of mass movement and reactive muscle activity using a linear feedback model based on center of mass kinematics. In typically developing children, perturbations induced plantar flexor balance correcting muscle activity followed by tibialis anterior balance correcting muscle activity, which was driven by center of mass movement. In children with cerebral palsy, the switch from plantar flexor to tibialis anterior activity was less pronounced than in typically developing children due to increased muscle co-activation of the plantar flexors and tibialis anterior throughout the response. Our results thus suggest that a reduction in reciprocal inhibition causes muscle co-activation in reactive standing balance in children with cerebral palsy.

Parametric Analysis of “Zollinger Type” Ribbed Timber Shells

The following article presents the study and further development of the roof system developed and patented by Friedrich Zollinger in 1920. The so-called Zollinger construction system is based on short timber components ‐ lamellae, connected by a bolt and a form of decking only for covering purpose. By developing the micro step joint, an increase in joint stiffness can be achieved. In addition, by applying and activating a load-bearing roof covering, a further increase in system stiffness can be achieved and demonstrated. Especially with regard to large spans, the increase of the stiffness and reduction of the deflection becomes inevitable against the background of an economic feasibility. Based on the analysis of the historic Zollinger system, it is possible to evaluate potential for improvements in terms of system stiffness as well as contemporary design, development and manufacturing. Due to the large number of different influencing factors, the system was modeled as a parametric master model. In this, a closed process cycle can be developed from the geometric definition, to the static analysis and to the derivation of the computer-aided manufacturing data. In the present study especially the exact recording, description and modeling of the stiffness and feasibility of the connection details “lamella‐lamella” and “lamella‐planking” was investigated. A parametric finite element model can be used to determine the stiffness parameters as a function of the fasteners used and the spacing of the fasteners. Staple connections are used as the main means of connection between the lamella and the planking. The implementation of the staple connections in the finite element analysis was carried out using spring parameters, which are determined in the course of the development. The analysis and optimization of the connection stiffnesses is presented against the background of an economical structure development. By using digital planning methods and interfaces, a contemporary way of working is presented. In addition, a contribution is made to digitalization in the construction industry.

Fracture related infection (FRI) of the upper extremity correlates with poor bone and soft tissue healing.

The purpose of this study was to evaluate the specific course and complication profile following the development of FRI in the upper extremity. An IRB-approved retrospective review was conducted on a consecutive series of operatively managed patients within an academic medical center between 1/2010 and 6/2022. Included patients met the following criteria: (1) upper extremity fracture definitively treated with internal fixation (2) development of criteria for suggestive or confirmatory FRI (as per the FRI Consensus Group) and (3) age ≥ 18years. Baseline demographics, medical history, injury information, infection characteristics, hospital quality measures, and outcomes were recorded. A 3:1 propensity-matched control cohort of patients without FRI was obtained using the same dataset. Univariable analysis was performed to compare the outcomes (rate of nonunion, time to bone healing, need for soft tissue coverage, patient reported joint stiffness at final follow-up) of the FRI vs Non-FRI cohorts. Of 2827 patients treated operatively for an upper extremity fracture, 43 (1.53%) met criteria for suggestive of confirmatory FRI. The successful propensity match (43 FRI, 129 Non-FRI) revealed no differences in demographics, baseline health status, or fracture location. FRI patients underwent more reoperations (p < 0.001), experienced an increased rate of removal of hardware (p < 0.001), and were admitted more frequently following index operation (p < 0.001). The FRI cohort had higher rates of fracture nonunion (p = 0.003), and a prolonged mean time to bone healing in months (8.37 ± 7.29 FRI vs. 4.14 ± 5.75 Non-FRI, p < 0.001). Additionally, the FRI cohort had a greater need for soft tissue coverage throughout their post-operative fracture treatment (p = 0.014). While there was no difference in eventual bone healing (p = 0.250), FRI patients experienced a higher incidence of affected joint stiffness at final follow-up (p < 0.001). Patients who develop an FRI of the upper extremity undergo more procedures and experience increased complications throughout their treatment, specifically increased joint stiffness. Despite this, ultimate outcome profiles are similar between patients who experience FRI and those who do not following operative repair of an upper extremity fracture. III.

THU471 Resolution Of Elevated Alkaline Phosphatase After Joint Replacement In Severe Osteoarthritis

Abstract Disclosure: J. Rakholiya: None. S. Nagaraj: None. P. Sharma: None. Introduction: Alkaline phosphatase (ALP) elevation is commonly seen in hepatobiliary disorders. Conditions of high turnover such as healing fractures, hyperparathyroidism, Pagets’ disease of the bone, also lead to ALP elevation (1). Osteoarthritis (OA), characterised by degeneration of articular cartilage, joint space narrowing, and osteophyte formation, rarely causes ALP elevation. We present a case of ALP elevation that resolved after the arthritic joint was replaced. Case Presentation: A 60-year-old female with history of bilateral knee OA presented to the endocrinology clinic due to elevated ALP for over a year. She reported chronic fatigue, sleep disturbance, dry skin, hair loss, inability to lose weight and anxiety. ALP level at presentation was 165 U/L. An extensive work-up showed unremarkable serum and ionized calcium, serum phosphorus, parathyroid hormone, vitamin D 25-OH, calcitriol, 24-hour urine calcium, serum protein electrophoresis, and 24-hour urine protein electrophoresis. Dual x-ray absorptiometry (DXA) scan was normal with Fracture risk assessment tool (FRAX) score 5.9% for major osteoporotic fracture and 0.2% for hip fracture. Patient underwent total left knee arthroplasty following which ALP improved from 165 U/L to 135 U/L within 9 weeks of the procedure. Five months later, ALP was elevated (164 U/L) again. She then underwent right knee arthroplasty and ALP dropped to normal level (114 U/L) within 1 week post-surgery. Discussion: We report the rare phenomenon of ALP elevation in severe OA, that resolved after joint replacement. OA is characterised by inflammation mediated cartilage destruction, subchondral bone change, osteophyte formation, and alterations of ligaments and meniscuses. Bone change in severe OA is associated with increased synovial fluid ALP level. However, there is a paucity of literature studying the association of ALP with OA. A cross-sectional study of 3060 patients demonstrated higher serum ALP with symptomatic knee OA. Another study showed higher ALP levels with increased joint stiffness. The ALP elevation was attributed to low grade inflammation causing an inflammatory response in chondrocytes, and osteoarthritic pain. There is a need for more studies to evaluate the utility of serum ALP as a biomarker for severe OA. Presentation: Thursday, June 15, 2023

Differences in muscle synergies between skilled and unskilled athletes in power clean exercise at various loads

ABSTRACT The purpose of this study was to determine the differences in muscle synergy between skilled and unskilled participants using various loading conditions for power clean. Nineteen participants (ten skilled and nine unskilled) performed power clean at 60–90% one repetition maximum (1RM), while measured 12 muscles across the entire body. The vertical impulse was calculated for the unweighting associated with the double-knee bend (DKB) manoeuvre in power clean. Muscle synergies were extracted using non-negative matrix factorization. The weighting of muscle synergies was subsequently compared between the two groups for all loads, and confidence intervals were calculated. The number of muscle synergies in both groups was three, and the functions of all muscle synergies were similar. Muscle synergy 1 involved the first pull, muscle synergy 2 involved the transition and the second pull, and muscle synergy 3 involved DKB. No significant difference in either muscle synergy was observed at 60–80% 1RM weight, while the 90% 1RM showed significantly active in the ankle plantar flexor and knee extensor muscles for muscle synergy 3, which involved DKB only in the skilled group. This indicates that increased joint stiffness during DKB may minimize unweighting. Unskilled individuals may acquire such muscle synergies to lift greater weights.

Dose–response effect of incremental lateral-wedge hardness on the lower limb Biomechanics during typical badminton footwork

ABSTRACT Badminton footwork has been characterised with jump-landing, cross step, side side and lunges, which requires movement agility to facilitate on-court performance. A novel badminton shoe design with systematic increase of lateral wedge hardness (Asker C value of 55, 60, 65, and 70) was developed and investigated in this study, aiming to analyse the dose–response effect of incremental wedge hardness on typical badminton footwork. Stance time and joint stiffness were employed to investigate the footwork performance, and the factorial Statistical non-Parametric Mapping and Principal Component Analysis (PCA) were used to quantify the biomechanical responses over the stance. As reported, shorter contact times (decreased by 8.9%–13.5%) and increased joint stiffness (in side step) of foot-ankle complex were found, suggesting improved footwork stability and agility from increased hardness. Time-varying differences were noted during the initial landing and driving-off phase of cross and side steps and drive-off returning of lunges, suggesting facilitated footwork performance. The reconstructed modes of variations from PCA further deciphered the biomechanical response to the wedge dosage, especially during drive-off, to understand the improved footwork agility and stability.

New genicular joint angle criteria for flexor muscle (Musculus Semimembranosus) during the terrestrial mammals walking.

The genicular or knee joint angles of terrestrial mammals remain constant during the stance phase of walking; however, the angles differ among taxa. The knee joint angle is known to correlate with taxa and body mass among extant mammals, yet several extinct mammals, such as desmostylians, do not have closely related descendants. Furthermore, fossils lose their soft tissues by the time they are unearthed, making body mass estimates difficult. These factors cause significant problems when reconstructing the proper postures of extinct mammals. Terrestrial mammals use potential and kinetic energy for locomotion; particularly, an inverted pendulum mechanism is used for walking. This mechanism requires maintaining the rod length constant, therefore, terrestrial mammals maintain their joint angle in a small range. A muscle reaction referred to as co-contraction is known to increase joint stiffness; both the agonist and antagonist muscles work simultaneously on the same joint at the same time. The musculus semimembranosus flexes the knee joint and acts as an antagonist to muscles that extend it. Twenty-one species of terrestrial mammals were examined to identify the elements that constitute the angle between the m. semimembranosus and the tibia based on the period between the hindlimb touching down and taking off from the ground. Measurements were captured from videos in high-speed mode (420 fps), selecting 13 pictures from the first 75% of each video while the animals were walking. The angles between the main force line of the m. semimembranosus and the tibia, which were defined as θsm-t, were measured. The maximum and minimum angles between the m. semimembranosus and the tibia (θsm-t) of the stance instance (SI) were successfully determined for more than 80% of the target animals (17 out of 21 species) during SI-1 to SI-13 within ±10° from the mean. The difference between each successive SI was small and, therefore, the θsm-t transition was smooth. According to the results of the total stance differences among the target animals, θsm-t was relatively constant during a stance and, therefore, average θsm-t (θave) can represent each animal. Only Carnivora had a significant difference in the correlation between body mass and θave. In addition, there were significant differences in θave between plantigrade and unguligrade locomotion. Our measurements show that θave was 100 ± 10° regardless taxon, body mass, and locomotor mode. Thus, only three points on skeletons need to be measured to determine θave. This offers a new approximation approach for understanding hindlimb posture that could be applied to the study of the hindlimbs of extinct mammals with no closely related extant descendants.

Variable Stiffness and Antagonist Actuation for Cable-Driven Manipulators Inspired by the Bird Neck

Abstract This paper discusses stiffness and antagonistic actuation in light-weight cable-driven bio-inspired manipulators suitable for safe interactions. Manipulators under study are built upon arranging in series several tensegrity joints, called “modules.” A comparative study of several modules revealed that the X module, in contrast to modules based on pivots, allows one to increase joint stiffness by increasing antagonistic input forces like during muscle coactivation. For a planar manipulator with N modules, antagonistic actuation schemes with 2N and N + 1 cables are proposed and compared. It is shown that the N + 1 cable actuation scheme allows controlling both the manipulator configuration and joint stiffness satisfactorily. As compared with a manipulator with 2N active cables, one on each side of each module, higher forces are required to achieve the manipulator configuration. However, the N + 1 cable actuation scheme is a reasonable solution that allows reducing the moving masses and cost.

Upscaling poromechanical models of coalbed methane reservoir incorporating the interplay between non-linear cleat deformation and solvation forces

We construct herein a three-scale coupled mechanical model for naturally fractured coalbed methane reservoir with the ability of describing the stress balance between the solvation force, arising from the gas adsorption in nanopores, and the restoration stress stemming from the elastic response of the cleats. To determine the cleat porosity, the non-linear hyperbolic Barton–Bandis (BB) law, which captures increase in joint stiffness induced by the cleat closure due to matrix swelling, is postulated for the fracture mechanical response. At the microscale, the theory incorporates the coupling between the effects of the solvation force and the elastic response of the matrix. Such system of governing equations is coupled with the fluid pressure in the discrete cleat system with dependency of aperture with the normal stress dictated by the aforementioned BB-model. A reiterated homogenized procedure is pursued and capable of providing the constitutive response of the homogenized poromechanical parameters on gas pressure. Numerical simulations illustrate the performance of the proposed model.

The Effects of Vertical vs. Horizontal plyometric Training on Sprinting Kinetics in Post Peak Height Female Student Athletes

Plyometric training is a form of jump training that is a useful method to improve sprinting speed due to its propensity to improve neural efficiency, increase joint stiffness and contraction speed. While research has shown that plyometrics can improve jumping and sprinting performance, no studies have compared the effects of different types of plyometric training on sprinting speed in young females. Therefore, the aim of the study was to compare different forms of plyometric training (horizontal and vertical) on sprinting performance in young females. Thirty young females from a private girls college were randomly divided into two groups and trained for seven weeks, twice a week; vertical plyometric (n=11, age 13.50 ± 0.96, peak heigh velocity-PHV: 1.60 ± 1.14), horizontal plyometric training (n=10, 13.40 ± 0.92, PHV:1.60 ± 0.93), and a physical education class as a control (n=15, age, 15.60 ± 0.31, PHV: 2.90 ± 0.55). Participants were tested for sprinting kinetics i.e. force (Fo), maximum power (Pmax), theoretical velocity (Vo), maximal velocity (Vmax), 10, 20 and 30 m split times using a radar gun over 30 m, isometric strength, vertical jump height and horizontal jump distance before and after the intervention. Both the intervention groups significantly improved all performance variables (g= 0.32- 1.30; p&lt;0.05). The vertical group improved all kinetic variables except Fo and Pmax whereas the horizontal group improved all kinetic variables with a greater effect size g= 0.40-1.30. In comparison to the control group, the vertical group significantly improved Vo, Vmax, vertical and broad jump scores whereas the horizontal group significantly improved broad jump and 20 m split time scores (p&lt;0.05). The findings of this study suggest that horizontal plyometric training is more effective in improving sprinting kinetics.

A conservative approach towards idiopathic chondrolysis of hip: a case report

Chondrolysis of the hip causes pain and a limping as articular cartilage space is gradually lost due to an unknown but suspected inflammatory process. It could be idiopathic or due to another hip condition, such as slipped capital femoral epiphysis. It is a well-known complication of a slipped capital femoral epiphysis, although it can also occur as a result of trauma, septic arthritis, immobilization, or juvenile idiopathic arthritis. Idiopathic chondrolysis of the hip is a disorder that causes the articular cartilage of the hip joint to degrade spontaneously. The most common clinical manifestation is pain at the affected hip joint, which is linked to increasing joint stiffness and a significant loss of range of motion and function. Idiopathic chondrolysis of hip is a rare condition with Incidence around 8.2% percent. In this case report we are presenting a 12-year-old boy came with complaint of pain, stiffness and restricted range of movement at left hip joint followed by trauma. On the basis of physical and investigatory findings, the patient was diagnosed as a case of idiopathic chondrolysis of hip associated with avascular necrosis grade 4 according to Ficat and Arlet classification. Radiological findings were evident of reduced joint space of left hip and slipped capital epiphysis, this is known to be the hallmark finding to confirm the diagnosis of idiopathic chondrolysis of hip. The patient was conservatively managed with non-steroidal anti-inflammatory medicines, vigorous physiotherapy. Chrondolysis is usually managed with bed rest, traction and non-steroidal anti-inflammatory drugs, hence the aim of this case report was to incorporate an elaborate and efficiency of physical Therapy along with medical management to promote the recovery, aid early return to activities of daily living and improve quality of life.

Effect of nylon fabric reinforcement on the mechanical performance of adhesive joints made between glass and GFRP

The use of reinforcements in adhesive joints makes the stress distribution more uniform, improving their mechanical performance and adhesion. The present paper aims to verify the effectiveness and efficiency of the insertion of nylon 6 fabric in the adhesive layer, to study their applicability and functionality in building components. The increase in stiffness achieved by applying nylon 6 fabric in the adhesive layer between glass and GFRP pultruded profiles and steel laminates applied to GFRP beams is investigated. Three different epoxy adhesives and one epoxy resin are used and compared. Three different types of tests are carried out in order to study the different properties of the reinforcement system: tensile tests on GFRP/GFRP single-lap adhesive joints, with and without nylon fabric reinforcement; tensile tests on double-lap adhesive joints between float glass and pultruded GFRP profiles reinforced with nylon fabric according to four configurations (in the middle plane of the adhesive layer, on the glass surfaces, on the GFRP surfaces, on both GFRP and glass configurations) to verify the influence of its position; three-point bending tests on long GFRP tubular profiles reinforced with steel plates and nylon fabric in different configurations, to study resistance to bending loads. The results from the experimental campaign show the effectiveness of the reinforcement system using nylon fabric 6. In general, both a reduction in ultimate strength and an increase in joint stiffness compared to unreinforced configurations are observed.

DATSURYOKU Sensor—A Capacitive-Sensor-Based Belt for Predicting Muscle Tension: Preliminary Results

Excessive muscle tension is implicitly caused by inactivity or tension in daily activities, and it results in increased joint stiffness and vibration, and thus, poor performance, failure, and injury in sports. Therefore, the routine measurement of muscle tension is important. However, a co-contraction observed in excessive muscle tension cannot be easily detected because it does not appear in motion owing to the counteracting muscle tension, and it cannot be measured by conventional motion capture systems. Therefore, we focused on the physiological characteristics of muscle, that is, the increase in muscle belly cross-sectional area during activity and softening during relaxation. Furthermore, we measured muscle tension, especially co-contraction and relaxation, using a DATSURYOKU sensor, which measures the circumference of the applied part. The experiments showed high interclass correlation between muscle activities and circumference across maximal voluntary co-contractions of the thigh muscles and squats. Moreover, the circumference sensor can measure passive muscle deformation that does not appear in muscle activities. Therefore, the DATSURYOKU sensor showed the potential to routinely measure muscle tension and relaxation, thus avoiding the risk of failure and injury owing to excessive muscle tension and can contribute to the realization of preemptive medicine by measuring daily changes.

Optimized Thickness of Meniscal Component in Partial Knee Replacement Analysed with Computer Simulation

Computer simulation with programming and Matlab graphics was used to analyse effects of meniscal component thickness on lengths of ligament fibres in partially replaced human knee with uni-compartmental arthroplasty. A circular femoral, a flat tibial and a matching meniscal component were modelled in the sagittal plane with four intact ligaments represented as fibres that showed non-linear elastic behaviour. Shapes of the prosthetic components, attachments of the ligament fibres and their material properties were from anatomical studies in the literature. The components when placed on respective bones with surgical guidelines and an optimized thickness of the meniscal insert achieved nearly fixed lengths of ligament fibres during motion. Changes in thickness of the insert either stretched or slackened the fibres with variable effects during flexion of the joint. For example, a 2 mm thicker insert stretched a fibre of anterior cruciate ligament by 4.7% at 30° and 3.2% at 120° flexion. Such variations in component selection are probable due to surgical judgments. Stretched ligaments could increase joint stiffness, while slack ligaments could increase joint laxity – either of these effects has potential for affecting the joint kinematics. Computer models of the replaced knee validated with anatomical studies allow insight in the mechanics of the replaced knee and effects of surgical errors.

Leaning the Trunk Forward Decreases Patellofemoral Joint Loading During Uneven Running.

AminiAghdam, S, Epro, G, James, D, and Karamanidis, K. Leaning the trunk forward decreases patellofemoral joint loading during uneven running. J Strength Cond Res 36(12): 3345-3351, 2022-Although decline surfaces or a more upright trunk posture during running increase the patellofemoral joint (PFJ) contact force and stress, less is known about these kinetic parameters under simultaneous changes to the running posture and surface height. This study aimed to investigate the interaction between Step (10-cm drop-step and level step) and Posture (trunk angle from the vertical: self-selected, ∼15°; backward, ∼0°; forward, ∼25°) on PFJ kinetics (primary outcomes) and knee kinematics and kinetics as well as hip and ankle kinetics (secondary outcomes) in 12 runners at 3.5 ms -1 . Two-way repeated measures analyses of variance ( α = 0.05) revealed no step-related changes in peak PFJ kinetics across running postures; however, a decreased peak knee flexion angle and increased joint stiffness in the drop-step only during backward trunk-leaning. The Step main effect revealed significantly increased peak hip and ankle extension moments in the drop-step, signifying pronounced mechanical demands on these joints. The Posture main effect revealed significantly higher and lower PFJ kinetics during backward and forward trunk-leaning, respectively, when compared with the self-selected condition. Forward trunk-leaning yielded significantly lower peak knee extension moments and higher hip extension moments, whereas the opposite effects occurred with backward trunk-leaning. Overall, changes to the running posture, but not to the running surface height, influenced the PFJ kinetics. In line with the previously reported efficacy of forward trunk-leaning in mitigating PFJ stress while even or decline running, this technique, through a distal-to-proximal joint load redistribution, also seems effective during running on surfaces with height perturbations.

Load to Failure of the Ankle Joint Complex After Fusion of the Subtalar and Talonavicular Joints: A Cadaveric Study

Recent literature has proposed that restriction of joints in the rearfoot secondary to coalitions may lead to increased risk for severe ankle fracture after trauma. There is a paucity of literature regarding the rigidity of the ankle joint after arthrodesis of the subtalar and talonavicular joints. In this study, load-to-failure testing of cadaveric ankle joints with and without fusion of the subtalar and talonavicular joints was performed to determine if clinically relevant fracture patterns could be reproduced. Of the 3 fixation patterns studied, combined subtalar and talonavicular joint fusion resulted in a measurable increase in joint stiffness; however, this was not statistically significant. Clinical and radiographic examination postloading revealed that all tested ankle joints sustained a dislocation type injury rather than a specific bone fracture pattern. It was determined that a pure low-speed bending and compression model does not produce clinically relevant fracture patterns, and that higher energy mechanisms are required.