Estimation of Ligament Loading and Anterior Tibial Translation in Healthy and ACL-Deficient Knees During Gait and the Influence of Increasing Tibial Slope Using EMG-Driven Approach

The purpose of this study was to develop a biomechanical model to estimate anterior tibial translation (ATT), anterior shear forces, and ligament loading in the healthy and anterior cruciate ligament (ACL)-deficient knee joint during gait. This model used electromyography (EMG), joint position, and force plate data as inputs to calculate ligament loading during stance phase. First, an EMG-driven model was used to calculate forces for the major muscles crossing the knee joint. The calculated muscle forces were used as inputs to a knee model that incorporated a knee–ligament model in order to solve for ATT and ligament forces. The model took advantage of using EMGs as inputs, and could account for the abnormal muscle activation patterns of ACL-deficient gait. We validated our model by comparing the calculated results with previous in vitro, in vivo, and numerical studies of healthy and ACL-deficient knees, and this gave us confidence on the accuracy of our model calculations. Our model predicted that ATT increased throughout stance phase for the ACL-deficient knee compared with the healthy knee. The medial collateral ligament functioned as the main passive restraint to anterior shear force in the ACL-deficient knee. Although strong co-contraction of knee flexors was found to help restrain ATT in the ACL-deficient knee, it did not counteract the effect of ACL rupture. Posterior inclination angle of the tibial plateau was found to be a crucial parameter in determining knee mechanics, and increasing the tibial slope inclination in our model would increase the resulting ATT and ligament forces in both healthy and ACL-deficient knees.     

Relationship between leg extensor muscle strength and knee joint loading during gait before and after total knee arthroplasty

ObjectiveThe aim of the present study was to evaluate an isometric maximal voluntary contraction (MVC) force of the leg extensor muscles and its relationship with knee joint loading during gait prior and after total knee arthroplasty (TKA).MethodsCustom-made dynamometer was used to assess an isometric MVC force of the leg extensor muscles and 3-D motion analysis system was used to evaluate the knee joint loading during gait in 13 female patients (aged 49–68 years) with knee osteoarthritis. Patients were evaluated one day before, and three and six months following TKA in the operated and non-operated leg.ResultsSix months after TKA, MVC force of the leg extensor muscles for the operated leg did not differ significantly as compared to the preoperative level, whereas it remained significantly lower for the non-operated leg and controls. The knee flexion moment and the knee joint power during mid stance of gait was improved six months after TKA, remaining significantly lowered compared with controls. Negative moderate correlation between leg extensor muscles strength and knee joint loading for the operated leg during mid stance was noted three months after TKA.ConclusionsThe correlation analysis indicates that due to weak leg extensor muscles, an excessive load is applied to knee joint during mid stance of gait in patients, whereas in healthy subjects stronger knee-surrounding muscles provide stronger knee joint loading during gait.Level of Evidence: III (correlational study)     

A potential animal model for creating a controlled and reversible anterior cruciate ligament insufficiency

We developed and tested a device to manipulate the axial position of the tibial anterior cruciate ligament (ACL) insertion in vitro to create a potential animal model that could simulate both ACL insufficiency and 'optimal' ACL reconstruction. This model is based on the concept that controlled incremental proximal displacement of the tibial ACL insertion simulates ACL insufficiency. Replacing the insertion at the joint level and then adjusting its position until the forces recorded equaled those in the ACL-intact knee can simulate 'optimal' ACL reconstruction. Anterior tibial translation (ATT) was quantified in vitro in 24 sheep cadaver knees with the ACL intact and after the ACL was cut or detached (ACL insufficiency). In 8 knees, a bone plug including the tibial ACL insertion was detached, mounted in a specially designed device, and adjusted to reproduce ATT of the ACL-intact knee. ATT was then measured after proximal displacement of the tibial ACL insertion in calibrated 1 mm increments. The results revealed that detaching the ACL increased ATT by 132-700%. Controlled 3 mm proximal displacement of the insertion using this device increased ATT by more than 100%. Comparing the increase in ATT due to controlled displacement of the ACL insertion to that due to detaching the ACL, in only one case was the same magnitude of ACL insufficiency reproduced. Despite the variability between knees, the device was able to reproduce ATT of the ACL-intact knee and to substantially increase ATT with controlled proximal displacement of the tibial ACL insertion. Use of this device, if successful in an in vivo ACL reconstruction model, could help define any quantitative association between altered joint kinematics and degenerative changes in the joint.     

Anterolateral ligament reconstruction as an augmented procedure for double-bundle anterior cruciate ligament reconstruction restores rotational stability: Quantitative evaluation of the pivot shift test using an inertial sensor

PurposeThe purpose of this study was to investigate the biomechanical function of the anterolateral structures (ALS) of the knee regarding rotational stability, and to attempt to verify the effectiveness of anterolateral ligament (ALL) reconstruction concomitant with double-bundle anterior cruciate ligament (ACL) reconstruction by quantifying the pivot shift test (PST) using an inertial sensor.MethodsSix knees of the fresh-frozen cadavers were evaluated during the following phases: (1) [Intact]; (2) ACL-deficient [ACL-D]; (3) ACL-reconstructed [ACL-R]; (4) ACL-reconstructed + ALS-deficient [ACL-R + ALS-D]; and (5) combined ACL and ALL reconstructed [ACL-R + ALL-R]. We evaluated knee rotational instability during each phase using the PST. We used an inertial sensor to calculate tibial external rotational angular velocity (ERAV) and tibial acceleration. Data were analyzed using repeated-measures analysis of variance; statistical significance was accepted as P < 0.05.ResultsRelative to [Intact], [ACL-D] caused a significant increase in ERAV and acceleration. However, there was no difference in these parameters between [ACL-R] and [Intact]. [ACL-R + ALS-D] increased ERAV significantly compared with [ACL-R], and there was a significant difference between ERAV during [ACL-R + ALS-D] and [Intact]. However, ERAV was significantly reduced during [ACL-R + ALL-R] compared with [ACL-R + ALS-D], and there was no significant difference in ERAV or acceleration between [ACL-R + ALL-R] and [Intact].ConclusionsALS controlled rotational instability in cooperation with the ACL in a cadaveric model. In cases of combined injury of ACL and ALS, concomitant ACL and ALL reconstruction may restore knee stability comparable with the intact state.     

A novel technique,dynamic intraligamentary stabilization creates optimal conditions for primary ACL healing: A preliminary biomechanical study

BackgroundAnterior cruciate ligament (ACL) rupture is a common lesion. Current treatment emphasizes arthroscopic ACL reconstruction via a graft, although this approach is associated with potential drawbacks. A new method of dynamic intraligamentary stabilization (DIS) was subjected to biomechanical analysis to determine whether it provides the necessary knee stability for optimal ACL healing.MethodsSix human knees from cadavers were harvested. The patellar tendon, joint capsule and all muscular attachments to the tibia and femur were removed, leaving the collateral and the cruciate ligaments intact. The knees were stabilized and the ACL kinematics analyzed. Anterior–posterior (AP) stability measurements evaluated the knees in the following conditions: (i) intact ACL, (ii) ACL rupture, (iii) ACL rupture with primary stabilization, (iv) primary stabilization after 50 motion cycles, (v) ACL rupture with DIS, and (vi) DIS after 50 motion cycles.ResultsAfter primary suture stabilization, average AP laxity was 3.2 mm, which increased to an average of 11.26 mm after 50 movement cycles. With primary ACL stabilization using DIS, however, average laxity values were consistently lower than those of the intact ligament, increasing from an initial AP laxity of 3.00 mm to just 3.2 mm after 50 movement cycles.ConclusionsDynamic intraligamentary stabilization established and maintained close contact between the two ends of the ruptured ACL, thus ensuring optimal conditions for potential healing after primary reconstruction. The present ex vivo findings show that the DIS technique is able to restore AP stability of the knee.     

Influence of Anthropometric and Mechanical Variations on Functional Instability in the ACL-Deficient Knee

Individual variations in joint anatomy, tissue mechanical properties, and muscle strength of the knee are believed to affect the clinical outcome of ACL-deficient patients, but the effects have not been studied systematically. The impact of individual anthropometric and mechanical variation on functional stability of the ACL-deficient knee was investigated in this study using a two-dimensional mathematical knee model. The model included the tibiofemoral and the patellofemoral articulations, four ligaments, the medial capsule, and four muscle units surrounding the knee. Simulations were conducted to determine tibial anterior translation as well as tibiofemoral and patellofemoral joint loading at a single selected position during early stance phase of gait. Incremental hamstring muscle forces were applied to the modeled ACL-deficient knee in order to examine the level of the hamstring muscle forces required to prevent abnormal tibial anterior translation relative to the femur. Simulations were repeated using incremental variations in the selected anthropometric and mechanical properties of the ACL-deficient knee. It was found that bony geometry of the knee joint, especially the slope of tibial plateau, strongly affected both the tibial translations in the ACL-deficient knee and the effectiveness of the hamstring muscles to compensate for the ACL deficiency. For instance, simulations indicated that, due to ACL deficiency, the tibial anterior displacement increased by 9.1 mm for a tibial slope angle of 4° compared to 15.2 mm for a tibial slope angle of 12°. Future outcome studies for ACL-deficient knee may be required to include individual anthropometric and mechanical parameters of the knee as covariants. © 2003 Biomedical Engineering Society. PAC2003: 8719Rr, 8719Ff, 8719St     

There is significant load sharing and physical interaction between the anteromedial and posterolateral bundles of the ovine ACL under anterior tibial loads

IntroductionThe ovine stifle joint is an ideal preclinical model to test the ability of double-bundle reconstruction techniques in providing superior joint stability and less osteoarthritis (OA) compared with single-bundle techniques. However, knowledge of the normal ovine ACL and more specifically the load sharing and physical interaction between the two main bundles of the ovine ACL is currently limited.MethodsSix ovine stifle joints were tested using a robotic testing system. Each joint was cyclically loaded to 200 N in the anterior tibial direction between 30° and 90° flexion and the force-displacement data were recorded for both the intact ACL, and when the anteromedial (AM, n = 3) or the posterolateral bundle (PL, n = 3) was transected.ResultsThe load shared by the AM bundle increased from 30° to 75° of flexion at all loading levels (25–200 N); whereas, the load shared by the PL bundle decreased between full extension and mid flexion (60°) and then increased again. The load borne by the AM bundle did not change in response to increasing Anterior Tibial Loads (ATL) at each flexion angle, in contrast to the PL bundle (P = 0.004). Physical interaction between bundles was greatest at 60° and under 50 N ATL.ConclusionThese data will help create double-bundle ACL reconstructions in sheep which are functionally similar to intact native ACL. In turn, this model can be used to examine the success of anatomically accurate double-bundle reconstructions to prevent the development of OA. Level of evidence: III.     

Pattern generation for walking and searching movements of a stick insect leg. I. Coordination of motor activity

During walking, the six legs of a stick insect can be coordinated in different temporal sequences or gaits. Leg coordination in each gait is controlled and stabilized by coordinating mechanisms that affect the action of the segmental neuronal networks for walking pattern generation. At present, the motor program for single walking legs in the absence of movement-related coordinating intersegmental influences from the other legs is not known. This knowledge is a prerequisite for the investigation of the segmental neuronal mechanisms that control the movements of a leg and to study the effects of intersegmental coordinating input. A stick insect single middle leg walking preparation has been established that is able to actively perform walking movements on a treadband. The walking pattern showed a clear division into stance and swing phases and, in the absence of ground contact, the leg performed searching movements. We describe the activity patterns of the leg muscles and motoneurons supplying the coxa-trochanteral joint, the femur-tibial joint, and the tarsal leg joints of the middle leg during both walking and searching movements. Furthermore we describe the temporal coordination between them. During walking movements, the coupling between the leg joints was phase-constant; in contrast during searching movements, the coupling between the leg joints was dependent on cycle period. The motor pattern of the single leg generated during walking exhibits similarities with the motor pattern generated during a tripod gait in an intact animal. The generation of walking movements also drives the activity of thoraco-coxal motoneurons of the deafferented and de-efferented thoraco-coxal leg joint in a phase-locked manner, with protractor motoneurons being active during swing and retractor motoneurons being active during stance. These results show that for the single middle leg, a basic walking motor pattern is generated sharing similarities with the tripod gait and that the influence of the motor pattern generated in the distal leg joints is sufficient for driving the activity of coxal motoneurons so an overall motor pattern resembling forward walking is generated.     

Loss of neuromuscular control related to motion in the acutely ACL-injured knee: an experimental study

Ligamentomuscular and muscular stretch reflexes are known to contribute to knee joint stability. After anterior cruciate ligament (ACL) injury, a more intense and adjusted muscular response is required to maintain joint stability, but this neuromuscular control of the knee has not been clearly proved. The aim of the study is to record electromyography (EMG) signal and muscular fibre length variations in quadriceps and hamstrings of the knee with and without ACL, and to analyze and integrate the ligament strain and the muscular reaction to forced anterior tibial translation (ATT). In 17 knees from 12 cats, EMG electrodes and ultrasonomicrometry crystals were inserted into four main periarticular muscles, with strain gauges on periarticular ligament insertions. Their output signal was compared before and after ACL surgical section in series of ATT (at 90 degrees and 30 degrees knee flexion), and also during knee flexion and extension. Linear regression analysis was performed between the EMG signal and muscular fibre length variations, and between the EMG signal and the strain on ligament insertions, in the search of this reflex neuromuscular response. In the ACL deficient knees, the studied muscles showed a poor adjustment to motion of EMG firing, inversely to controls. The muscle stretch reflexes showed poorer correlation with post-peak EMG activity than the ligaments. ATT control depended mainly on hamstrings activity in control knees, whereas in unstable knees, quadriceps activity was associated with more tibial translation. Acute ACL-deficient knees showed poor neuromuscular control with weak ligamentomuscular reflexes and no muscular stretch reflexes, suggesting the ineffectiveness of acute muscular reaction to provide early mechanical knee stabilization after injury.     

Relationships between early postoperative gait biomechanical factors and patient-reported outcome measures 6 months after total knee arthroplasty

BackgroundThis study was focused on the gait parameters of the knee extensor and hip abductor muscle groups, which are believed to contribute to knee joint function improvement in early postoperative TKA. The associations between patient-reported outcome measures (PROMs) 6 months after total knee arthroplasty (TKA) and the early postoperative internal knee extension moment, knee extension negative joint power, and internal hip abduction moment while walking were investigated.MethodsTwenty-one patients who underwent primary TKA for knee osteoarthritis were included. Three weeks after TKA, gait at a comfortable speed was measured by three-dimensional motion analysis. The lower limb joint angle, internal joint moment, and joint power parameters on the operated side while standing were calculated. The PROMs 6 months after TKA were assessed using the Japanese Knee Osteoarthritis Measure (JKOM). The relationship between each gait biomechanical parameter and the JKOM was determined.ResultsThe maximum internal knee extension moment and maximum knee extension negative joint power during the early stance showed moderate negative correlations with the JKOM scores. The maximum internal hip abduction moment was not correlated with the JKOM scores. The maximum internal hip extension moment during the early stance and internal hip flexion moment during the late stance showed moderate negative correlations with the total JKOM scores.ConclusionThe early postoperative internal knee extension moment, maximum knee extension negative joint power, and internal hip extension and flexion moment are associated with patient PROMs 6 months after TKA.     

Evaluation of anteroposterior accelerometric change after bi-cruciate stabilized total knee arthroplasty and posterior stabilized total knee arthroplasty

BackgroundIn conventional total knee arthroplasty (TKA), the anterior cruciate ligament (ACL) is resected. ACL dysfunction causes knee instability and is regarded as one factor in poor TKA outcomes. In bi-cruciate stabilized (BCS) TKA, the implant reproduces ACL function and provides anterior stability. The objective of this study was to evaluate preoperative and postoperative X-rays and accelerometer gait measurements in patients who underwent BCS TKA and posterior-stabilized (PS) TKA to assess the postoperative acceleration changes of knees after these procedures and to compare them in terms of joint range of motion (ROM) and the New Knee Society Score (New KSS).MethodsThe subjects were 60 patients, 30 of whom underwent BCS TKA and 30 PS TKA. Joint ROM, New KSS, lateral X-rays of the standing extended knee, and accelerometer data were evaluated 12 months postoperatively.ResultsThere was no significant difference in joint ROM between the groups. Both had good New KSS results, but the functional activity score was significantly higher after BCS TKA than after PS TKA. X-rays showed a lower posterior offset ratio after BCS TKA than after PS TKA, with anteroposterior positioning closer to that of the normal knee.Accelerometer data showed that postoperative anteroposterior acceleration on the femoral side in the stance phase and swing phase was lower after BCS TKA than after PS TKA.ConclusionCompared with PS TKA, BCS TKA resulted in a higher functional activity score, closer positioning to that of the normal knee on lateral X-ray, and lower anteroposterior acceleration on the femoral side.     

Anterior cruciate ligament (ACL) repair using cortical or anchor fixation with suture tape augmentation vs ACL reconstruction: A comparative biomechanical analysis

BackgroundThe purpose was to compare knee kinematics in a cadaveric model of anterior cruciate ligament (ACL) repair using an adjustable-loop femoral cortical suspensory (AL-CSF) or independent bundle suture anchor fixation (IB-SAF) with suture tape augmentation to a bone-patellar tendon-bone (BPTB) ACL reconstruction.MethodsTwenty-seven cadaveric knees were randomly assigned to one of three surgical techniques: (1) ACL repair using the AL-CSF technique with suture tape augmentation, (2) ACL repair using the IB-SAF technique with suture tape augmentation, (3) ACL reconstruction using a BPTB autograft. Each specimen underwent three conditions according to the state of the ACL (native, proximal transection, repair/reconstruction) with each condition tested at four different angles of knee flexion (0°, 30°, 60°, 90°). Anterior tibial translation (ATT) and internal tibial rotation (ITR) were evaluated using 3-dimensional motion tracking software.ResultsACL transection resulted in a significant increase in ATT and ITR when compared to the native state (P < 0.001, respectively). ACL repair with the AL-CSF or IB-SAF technique as well as BPTB reconstruction restored native ATT and ITR at all tested angles of knee flexion, while showing significantly less ATT at 0°, 30°, 60°, and 90° as well as significantly less ITR at 30°, 60°, and 90° of knee flexion when compared to the ACL-deficient state. There were no significant differences in ATT and ITR between the three techniques utilized.ConclusionACL repair using the AL-CSF or IB-SAF technique with suture tape augmentation as well as BPTB ACL reconstruction each restored native anteroposterior and rotational laxity, without significant differences in knee kinematics between the three techniques utilized.Level of EvidenceControlled Laboratory Study.     

Biomechanics of the knee joint in flexion under various quadriceps forces

Bioemchanics of the entire knee joint including tibiofemoral and patellofemoral joints were investigated at different flexion angles (0° to 90°) and quadriceps forces (3, 137, and 411 N). In particular, the effect of changes in location and magnitude of restraining force that counterbalances the isometric extensor moment on predictions was investigated. The model consisted of three bony structures and their articular cartilage layers, menisci, principal ligaments, patellar tendon, and quadriceps muscle. Quadriceps forces significantly increased the anterior cruciate ligament, patellar tendon, and contact forces/areas as well as the joint resistant moment. Joint flexion, however, substantially diminished them all with the exception of the patellofemoral contact force/area that markedly increased in flexion. When resisting extensor moment by a force applied on the tibia, the force in cruciate ligaments and tibial translation significantly altered as a function of magnitude and location of the restraining force. Quadriceps activation generated large ACL forces at full extension suggesting that post ACL reconstruction exercises should avoid large quadriceps exertions at near full extension angles. In isometric extension exercises against a force on the tibia, larger restraining force and its more proximal location to the joint substantially decreased forces in the anterior cruciate ligament at small flexion angles whereas they significantly increased forces in the posterior cruciate ligament at larger flexion angles.     

Estimation of bone-on-bone contact forces in the tibiofemoral joint during walking

In this study, the tibiofemoral contact forces were estimated from standard gait analysis data of adult walking. Knee angles, ground reaction forces, and external flexion-extension knee moments together with lines of action and moment arms of the force bearing structures in the knee previously determined were used to obtain bone-on-bone contact forces. The heel strike, the onset of single limb stance and terminal extension before toe-off each corresponded to a significant turning point on the force versus gait cycle curve. The tibiofemoral bone-on-bone peak forces calculated reached an estimated three times bodyweight. The estimated joint loads are clinically relevant and can either be used directly for evaluation of subjects in a gait analysis, or indirectly in studies of the knee joint where models simulating loading conditions are used to investigate various pathologies.     

Sex differences in ACL loading and strain during typical athletic movements: a musculoskeletal simulation analysis

Purpose

Female athletes experience anterior cruciate ligament (ACL) injuries at a much greater rate than males, yet the mechanisms responsible for this are not well-understood. The current investigation aimed using a musculoskeletal simulation-based approach, to examine sex differences in ACL loading parameters during cut and hop movements.

Methods

Fifteen male and fifteen female participants completed 45° cut and maximal one legged hop movements. Three-dimensional motion capture and ground reaction force data during the stance phase of the cut movement and landing phase of the one legged hop were obtained. Lower extremity muscle forces, ACL forces and ACL strains were extracted via a simulation-based approach using a musculoskeletal model, with an ACL insertion into the femur and tibia.

Results

During the hop movement, females were associated with significantly greater peak ACL forces (male = 15.01 N/kg and female = 15.70 N/kg) and strains (male = 6.87% and female = 10.74%). In addition, for both the cut (male = 4.45 and female = 1.45) and hop (male = 2.04 and female = 1.46) movements, the soleus/gastrocnemius ratio was significantly larger in males.

Conclusions

The current investigation provides new information regarding sex differences during athletic movements that provide further insight regarding the increased incidence of ACL injuries in females.

     

The amplitude modulation of the Quadriceps H-reflex in relation to the knee joint action during walking

Previously the modulation of the quadriceps H-reflex has only been investigated in the initial part of the gait cycle, and it was suggested that the quadriceps H-reflex modulates with relative high reflex gain at heel contact and decreases during the subsequent part of stance (Dietz et al. 1990b). The objectives of the present study was to elaborate on the previous results by increasing the measurement resolution around heel contact and include additional measures in order to relate the H-reflex modulation to the mechanical function of the knee extensors throughout the gait cycle. EMG profiles were measured in quadriceps and the antagonistic hamstring muscles simultaneously with the knee joint kinematics in ten subjects during treadmill walking at preferred speed. H-reflex excitability was measured in vastus lateralis (VL) and rectus femoris (RF) at 11 selected positions during the gait cycle. The resulting excitability curves showed a significant modulation of the quadriceps H-reflex during the gait cycle. The H-reflex amplitude increases shortly after heel contact and reflex inhibition is present in the remaining part of stance and most of the swing phase. The modulation of the quadriceps H-reflex during walking does not follow the classical pattern of reciprocal inhibition between antagonistic muscles. It is suggested that at least during the stance phase the modulation of the quadriceps H-reflex is controlled by presynaptic inhibition. The present results confirm the idea that the excitability of the quadriceps H-reflex is controlled to comply with the different mechanical demands on the muscle during the gait cycle in humans.     

An EMG-driven model to estimate muscle forces and joint moments in stroke patients

Individuals following stroke exhibit altered muscle activation and movement patterns. Improving the efficiency of gait can be facilitated by knowing which muscles are affected and how they contribute to the pathological pattern. In this paper we present an electromyographically (EMG) driven musculoskeletal model to estimate muscle forces and joint moments. Subject specific EMG for the primary ankle plantar and dorsiflexor muscles, and joint kinematics during walking for four subjects following stroke were used as inputs to the model to predict ankle joint moments during stance. The model's ability to predict the joint moment was evaluated by comparing the model output with the moment computed using inverse dynamics. The model did predict the ankle moment with acceptable accuracy, exhibiting an average R² value ranging between 0.87 and 0.92, with RMS errors between 9.7% and 14.7%. The values are in line with previous results for healthy subjects, suggesting that EMG-driven modeling in this population of patients is feasible. It is our hope that such models can provide clinical insight into developing more effective rehabilitation therapies and to assess the effects of an intervention.     

Effect of medial foot loading self-practice on lower limb kinematics in young individuals with asymptomatic varus knee alignment

BackgroundVarus alignment of the knee is a risk factor for developing knee osteoarthritis. Recently, voluntary shifting the plantar pressure distribution medially (medial foot loading) during gait has been found to reduce knee adduction angle during stance, which may lower the joint load. However, it is not yet known whether such effect would persist after long-term self-practice. This study aimed to determine whether medial foot loading can be an effective self-care protocol for reducing the knee adduction angle.MethodsEight subjects with asymptomatic varus knee alignment were trained on medial foot loading once in a laboratory, then carried out as self-practice for 8 weeks outside the laboratory. Spatiotemporal gait parameters and lower limb joint kinematics data were collected during natural walking prior to the training (baseline walking), during the practice session immediately after the initial training (trained walking), and during natural walking after the self-practice period (post-practice walking).ResultsParticipants walked significantly faster after the self-practice period with longer step length compared with the baseline. The knee adduction angle at initial contact, maximum angle during stance, and mean angle during a gait cycle were significantly decreased during both the trained and post-practice walking compared with baseline. The 8-week self-practice caused larger decrements in the three angles than the single training, but no significant differences were found between the two conditions.ConclusionsSelf-practice of medial foot loading walking could be an effective gait strategy to reduce the knee adduction angle. The effect could be sustained for individuals with asymptomatic varus knee alignment.     

Design and validation of a cadaveric knee joint loading device compatible with magnetic resonance imaging and computed tomography

PurposeDesign and validation of a magnetic resonance and computed tomography compatible device capable of applying physiologically relevant muscle forces to cadaveric knee joints with high levels of repeatability and reproducibility.MethodsRepeatability and reproducibility were assessed with two porcine stifle joints. Load was applied to joints at full extension, five and 15 degrees of flexion through two cables simulating the lines of action of the quadriceps and hamstrings muscles. Five repeatability and five reproducibility trials were performed at each flexion angle. Standard deviations (SDs) of joint angle and load were recorded.ResultsFor repeatability, the maximum SDs for joint angle were 1.26° (flexion), 1.54° (ab/adduction) and 0.90° (in/external rotation). The maximum SDs for joint load were 4.60 N (anterior/posterior), 7.36 N (medial/lateral), and 42.6 N (axial). For reproducibility, the maximum SDs for joint angle were 0.84° (flexion), 0.66° (ab/adduction) and 0.92° (in/external rotation). The maximum SDs for joint load were 6.40 N (anterior/posterior), 11.7 N (medial/lateral), and 39.7 N (axial).ConclusionsThis level of repeatability and reproducibility is within intra-subject variability of measured gait kinematics. Therefore, this device is considered to be an effective tool for in vitro testing of knee soft tissue repair.     

Effect of isolated hip abductor fatigue on single-leg landing mechanics and simulated ACL loading

BackgroundAltered movement biomechanics are a risk factor for ACL injury. While hip abductor weakness has been shown to negatively impact landing biomechanics, the role of this musculature and injury risk is not clear. The aim of this musculoskeletal simulation study was to determine the effect of hip abductor fatigue-induced weakness on ACL loading, force production of lower extremity muscles, and lower extremity biomechanics during single-leg landing.MethodsBiomechanical data from ten healthy adults were collected before and after a fatigue protocol and used to derive subject-specific estimates of muscle forces and ACL loading using a 5-degree of freedom (DOF) model.ResultsThere were no significant differences in knee joint angles and ACL loading between pre and post-fatigue. However, there were significant differences, due to fatigue, in lateral trunk flexion angle, total excursion of trunk, muscle forces, and joint moments.ConclusionAltered landing mechanics, due to hip abductor fatigue-induced weakness, may be associated with increased risk of ACL injury during single-leg landings. Clinical assessment or screening of ACL injury risk will benefit from subject-specific musculoskeletal models during dynamic movements. Future study considering the type of the fatigue protocols, cognitive loads, and various tasks is needed to further identify the effect of hip abductor weakness on lower extremity landing biomechanics.