Analyses of dynamic co-contraction level in individuals with anterior cruciate ligament injury

Higher coactivations of lower limb muscles increase stability during walking on slippery ground in forward dynamics musculoskeletal simulation

The energy efficiency theory of human bipedal locomotion has been widely accepted as a neuro-musculoskeletal control method. However, coactivation of agonist and antagonist muscles in the lower limb has been observed during various limb movements, including walking. The emergence of this coactivation cannot be explained solely by the energy efficiency theory and remains a subject of debate. To shed light on this, we investigated the role of muscle coactivations in walking stability using a forward dynamics musculoskeletal simulation combined with neural-network-based gait controllers. Our study revealed that a gait controller with minimal muscle activations had a high probability of falls under challenging gait conditions such as slippery ground and uneven terrain. Lower limb muscle coactivations emerged in the process of gait controller training on slippery ground. Controllers with physiological coactivation levels demonstrated a significantly reduced probability of falls. Our results suggest that achieving stable walking requires muscle coactivations beyond the minimal level of muscle energy. This study implies that coactivations likely emerge to maintain gait stability under challenging conditions, and both coactivation and energy optimization of lower limb muscles should be considered when exploring the foundational control mechanisms of human walking.

Individuals differ in muscle activation patterns during early adaptation to a powered ankle exoskeleton

Exoskeletons have the potential to assist users and augment physical ability. To achieve these goals across users, individual variation in muscle activation patterns when using an exoskeleton need to be evaluated. This study examined individual muscle activation patterns during walking with a powered ankle exoskeleton. 60% of the participants were observed to reduce medial gastrocnemius activation with exoskeleton powered and increase with the exoskeleton unpowered during stance. 80% of the participants showed a significant increase in tibialis anterior activation upon power addition, with inconsistent changes upon power removal during swing. 60% of the participants that were able to adapt to the system, did not de-adapt after 5 min. Muscle activity patterns differ between individuals in response to the exoskeleton power state, and affected the antagonist muscle behavior during this early adaptation. It is important to understand these different individual behaviors to inform the design of exoskeleton controllers and training protocols.

Responses in knee joint muscle activation patterns to different perturbations during gait in healthy subjects

PURPOSE

To compare the responses in knee joint muscle activation patterns to different perturbations during gait in healthy subjects.

SCOPE

Nine healthy participants were subjected to perturbed walking on a split-belt treadmill. Four perturbation types were applied, each at five intensities. The activations of seven muscles surrounding the knee were measured using surface EMG. The responses in muscle activation were expressed by calculating mean, peak, co-contraction (CCI) and perturbation responses (PR) values. PR captures the responses relative to unperturbed gait. Statistical parametric mapping analysis was used to compare the muscle activation patterns between conditions.

RESULTS

Perturbations evoked only small responses in muscle activation, though higher perturbation intensities yielded a higher mean activation in five muscles, as well as higher PR. Different types of perturbation led to different responses in the rectus femoris, medial gastrocnemius and lateral gastrocnemius. The participants had lower CCI just before perturbation compared to the same phase of unperturbed gait.

CONCLUSIONS

Healthy participants respond to different perturbations during gait with small adaptations in their knee joint muscle activation patterns. This study provides insights in how the muscles are activated to stabilize the knee when challenged. Furthermore it could guide future studies in determining aberrant muscle activation in patients with knee disorders.

Effect of Prophylactic Knee Bracing on Anterior Cruciate Ligament Agonist and Antagonist Muscle Forces During Perturbed Walking

Background:

Anterior cruciate ligament (ACL) injuries most commonly occur after a perturbation. Prophylactic knee braces (PKBs) are off-the-shelf braces designed to prevent and reduce the severity of knee injuries during sports, yet their effectiveness has been debated.

Purpose:

To identify differences in ACL agonist and antagonist muscle forces, during braced and unbraced conditions, while walking with the application of unexpected perturbations.

Study Design:

Controlled laboratory study.

Methods:

A total of 20 recreational athletes were perturbed during walking at a speed of 1.1 m/s, and motion analysis data were used to create patient-specific musculoskeletal models. Static optimization was performed to calculate the lower-limb muscle forces. Statistical parametric mapping was used to compare muscle forces between the braced and unbraced conditions during the stance phase of the perturbed cycle.

Results:

The brace reduced muscle forces in the quadriceps (QUADS), gastrocnemius (GAS), and soleus (SOL) but not in the hamstrings. The peak QUADS muscle force was significantly lower with the brace versus without at 49% to 60% of the stance phase (28.9 ± 12.98 vs 14.8 ± 5.06 N/kg, respectively; P < .001) and again at 99% of the stance phase (1.7 ± 0.4 vs 3.6 ± 0.13 N/kg, respectively; P = .049). The SOL muscle force peak was significantly lower with the brace versus without at 25% of the stance phase (1.9 ± 1.7 vs 4.6 ± 3.4 N/kg, respectively; P = .031) and at 39% of the stance phase (1.9 ± 1.4 vs 5.3 ± 5.6 N/kg, respectively; P = .007). In the GAS, there were no significant differences between conditions throughout the whole stance phase except between 97% and 100%, where the braced condition portrayed a smaller peak force (0.23 ± 0.13 vs 1.4 ± 1.1 N/kg for unbraced condition; P = .024).

Conclusion:

These findings suggested that PKBs that restrict knee hyperextension and knee valgus/varus motion can alter neuromuscular patterns, which result in a reduction of QUADS force.

Clinical Relevance:

Understanding the way PKBs alter muscle function and knee mechanics can provide invaluable information that will help in making decisions about their use. Further studies should investigate different types of braces and perturbations to evaluate the effectiveness of PKBs.

Hop Performance After Return to Sport in Anterior Cruciate Ligament-Reconstructed Gaelic Football and Hurling Athletes

PURPOSE

Anterior cruciate ligament (ACL) injuries are among the most severe injuries in the Gaelic Athletic Association. Hop tests measure functional performance after ACL reconstruction as they replicate the key requirements for a match situation. However, research examining functional recovery of ACL-reconstructed Gaelic athletes is lacking. The objective of this study is to determine if athletes restore normal hop symmetry after ACL reconstruction and to examine if bilateral deficiencies persist in hop performance following return to sport.

METHODS

A cross-sectional design was used to evaluate hop performance of 30 ACL-reconstructed Gaelic athletes who had returned to competition and 30 uninjured controls in a battery of hop tests including a single, 6-m, triple, and triple-crossover hop test.

RESULTS

In each test, the mean symmetry score of the ACL reconstruction group was above the cutoff for normal performance of 90% adopted by this study (98%, 99%, 97%, and 99% for the single, 6-m, triple, and triple-crossover hop, respectively). No significant differences in absolute hop scores emerged between involved and control limbs, with the exception of the single-hop test where healthy dominant limbs hopped significantly further than ACL-reconstructed dominant limbs (P = .02). No significant deficits were identified on the noninvolved side.

CONCLUSIONS

The majority of ACL-reconstructed Gaelic athletes demonstrate normal levels of hop symmetry after returning to competition. Suboptimal hop performance can persist on the involved side compared with control limbs. Targeted rehabilitation may be warranted after returning to competition to restore performance to levels of healthy uninjured athletes.

Anterior cruciate ligament agonist and antagonist muscle force differences between males and females during perturbed walking

Anterior cruciate ligament (ACL) injuries most commonly occur following a perturbation. Perturbations make the athlete unbalanced or at loss of control, which ultimately can lead to injury. The purpose of this study was to identify differences in ACL agonist and antagonist muscle forces, between sexes, during unexpected perturbations. Twenty recreational athletes were perturbed during walking at a speed of 1.1 m/s. Motion analysis data were used to create subject-specific musculoskeletal models and static optimization was performed to calculate muscle forces in OpenSim. Statistical parametric mapping (SPM) was used to compare muscle forces between males and females during the stance phase of the perturbed cycle. Females illustrated higher ACL antagonist muscle forces (p < 0.05) and lower ACL agonist muscle forces, compared to their male counterparts. The quadriceps (QUADs) muscle group peak was about 1.4 times higher in females (35.50 ± 8.71 N/kg) than males (22.81 ± 5.83 N/kg during 57%-62% of the stance phase (p < 0.05). Females presented a larger peak of gastrocnemius (GAS) at two instances: 12.42 ± 4.5 N/kg vs. 8.10 ± 2.83 N/kg between 70% and 75% at p < 0.05 and 2.26 ± 0.55 N/kg vs. 0.52 ± 0.09 N/kg between 95% and 100% at p < 0.05. Conversely, males illustrated higher initial hamstrings (HAMS) peak of 10.67 ± 4.15 N/kg vs. 5.38 ± 1.1 N/kg between 8% and 11%. Finally, males showed almost double the soleus (SOL) peak at 30.63 ± 8.64 N/kg vs. 17.52 ± 3.62 N/kg between 83% and 92% of the stance phase at p < 0.001. These findings suggest that females may exhibit riskier neuromuscular control in unanticipated situations, like sports.

Co-Contraction of Lower Limb Muscles Contributes to Knee Stability During Stance Phase in Hemiplegic Stroke Patients

Background

Knee stability has an important role in the gait of hemiplegic stroke patients. However, factors affecting knee stability have not been assessed concerning gait. The purpose of this study was to explore whether co-contraction of the lower limb muscles contributes to the knee stability during the stance phase of the gait cycle in hemiplegic stroke patients.

Material/Methods

A total of 30 hemiplegic stroke patients, ages 36–79 years, were instructed to walk at their natural speed. The root mean square of surface electromyography was used to measure activities of the biceps femoris and rectus femoris muscles, while the co-contraction ratio was computed based on the root mean squares. The peak angle of knee extension was acquired in the stance phase by 3D kinematic analyses. Lower limb function was evaluated using the Fugl-Meyer scale for lower limb motor assessment.

Results

A statistically significant increase of the muscle co-contraction ratio of the involved extremity was observed compared with that of the uninvolved extremity (t=−4.066, P<0.05). The muscle co-contraction ratio was significantly correlated with the peak angle of knee extension (r=0.387, P=0.035), Fugl-Meyer scale (r=−0.522, P=0.003), and Modified Ashworth Scale (r=0.404, P=0.027) during the stance phase of the gait cycle.

Conclusions

Our results showed that co-contraction of the rectus femoris muscle contributes to the stability of the knee and lower limb function in hemiplegic stroke patients, and suggests that co-contraction should be considered in the rehabilitation of knee stability during gait in hemiplegic stroke patients. Appropriate rehabilitation assessment planning with hemiplegic stroke patients, such as muscle co-contraction or knee stability of, might be created based on our results.

Objective parameters to measure (in)stability of the knee joint during gait: A review of literature

BACKGROUND

Instability of the knee joint during gait is frequently reported by patients with knee osteoarthritis or an anterior cruciate ligament rupture. The assessment of instability in clinical practice and clinical research studies mainly relies on self-reporting. Alternatively, parameters measured with gait analysis have been explored as suitable objective indicators of dynamic knee (in)stability.

RESEARCH QUESTION

This literature review aimed to establish an inventory of objective parameters of knee stability during gait.

METHODS

Five electronic databases (Pubmed, Embase, Cochrane, Cinahl and SPORTDiscuss) were systematically searched, with keywords concerning knee, stability and gait. Eligible studies used an objective parameter(s) to assess knee (in)stability during gait, being stated in the introduction or methods section. Out of 10717 studies, 89 studies were considered eligible.

RESULTS

Fourteen different patient populations were investigated with kinematic, kinetic and/or electromyography measurements during (challenged) gait. Thirty-three possible objective parameters were identified for knee stability, of which the majority was based on kinematic (14 parameters) or electromyography (12 parameters) measurements. Thirty-nine studies used challenged gait (i.e. external perturbations, downhill walking) to provoke knee joint instability. Limited or conflicting results were reported on the validity of the 33 parameters.

SIGNIFICANCE

In conclusion, a large number of different candidates for an objective knee stability gait parameter were found in literature, all without compelling evidence. A clear conceptual definition for dynamic knee joint stability is lacking, for which we suggest : "The capacity to respond to a challenge during gait within the natural boundaries of the knee". Furthermore biomechanical gait laboratory protocols should be harmonized, to enable future developments on clinically relevant measure(s) of knee stability during gait.

Anticipation modulates neuromechanics of drop jumps in known or unknown ground stiffness

With an emphasis on ballistic movements, an accurately anticipated neural control is an essential prerequisite to deliver a motor response coincidentally with the event of ground contact. This study investigated how previous knowledge of the ground condition affects proactive and reactive motor control in drop jumps (DJ). Thereby, human anticipatory capacity of muscle activation was investigated regarding neuromuscular activation, joint kinematics and peak forces associated with DJ performance. In 18 subjects, the effect of knowledge of two different surface conditions during DJs was evaluated. Peak force, ground-contact-time (GCT), rate of force development (RFD) and jump height were assessed. Electromyographic (EMG) activities of the m. soleus (SOL) and gastrocnemius medialis (GM) were assessed for 150ms before (PRE) and during ground contact (GC) for the short-, medium-, and long-latency responses. Ankle and knee joint kinematics were recorded in the sagittal plane.In the unknown conditions peak force, RFD and jump height declined, GCT was prolonged, proactive EMG activity (PRE) in SOL and GM was diminished (P<0.05). During GC, a decline in EMG activity in the unknown condition was manifested for SOL and GM for the SLR, MLR and LLR (P<0.05). Ankle and knee joint deflections during GC were increased in the unknown vs. known condition (P<0.05). Peak force, RFD and jump height were positively correlated to GM-EMG in PRE, SLR, MLR and LLR (P<0.05). Results revealed that proactive and reactive modulations in muscle activity prior and during GC are interrelated to the force-time characteristics and height of the jumps. The unknown condition revealed a comparable neuromuscular activity during pre-activation for both conditions, followed by an inhibition in the subsequent phase after touch down. These findings underline that anticipation is a determining factor influencing timing and adjustment of motor responses to accomplish ballistic movements regarding precision and performance.

Do cognitive tasks during gait increase the risk of accidents with pedestrians? A study based on electromyographic parameters

Abstract Introduction Accidents involving pedestrians are responsible for many cases of serious injuries and deaths. Crossing streets safely requires complex planning and cognitive demand because it is necessary to perform more than one task at a time. Objective The aim of this study was to identify electromyographic changes during gait in young subjects who performed the cognitive tasks concurrently. Methods The study included 17 younger women aged between 18 and 25 years. Data collection was performed on a treadmill. The volunteers were instructed to walk in four different conditions: normal gait (NG), gait with dual easy task (DET), gait with dual hard task (DHT) and gait with dual mixed task (DMT). Results Significant differences were found between the MN condition to the other conditions for all muscles and, during the NG, smaller values of muscle activation were found. Muscle co-contraction between muscles VM / BF showed a significant difference between the conditions of NG and DMT (p = 0.04) and, during the NG, smaller values of co-contraction were observed. Conclusion The data of this study permits to conclude that the competition between motor and cognitive resources significantly affects the levels of muscle activation and co-contraction during gait in young adult women. Thus, we conclude that the performance of dual cognitive tasks while driving can be considered a risk factor for safe driving.

Surface-EMG analysis for the quantification of thigh muscle dynamic co-contractions during normal gait

The research purpose was to quantify the co-contraction patterns of quadriceps femoris (QF) vs. hamstring muscles during free walking, in terms of onset-offset muscular activation, excitation intensity, and occurrence frequency. Statistical gait analysis was performed on surface-EMG signals from vastus lateralis (VL), rectus femoris (RF), and medial hamstrings (MH), in 16315 strides walked by 30 healthy young adults. Results showed full superimpositions of MH with both VL and RF activity from terminal swing, 80 to 100% of gait cycle (GC), to the successive loading response (≈0-15% of GC), in around 90% of the considered strides. A further superimposition was detected during the push-off phase both between VL and MH activation intervals (38.6±12.8% to 44.1±9.6% of GC) in 21.9±13.6% of strides, and between RF and MH activation intervals (45.9±5.3% to 50.7±9.7 of GC) in 32.7±15.1% of strides. These findings led to identify three different co-contractions among QF and hamstring muscles during able-bodied walking: in early stance (in ≈90% of strides), in push-off (in 25-30% of strides) and in terminal swing (in ≈90% of strides). The co-contraction in terminal swing is the one with the highest levels of muscle excitation intensity. To our knowledge, this analysis represents the first attempt for quantification of QF/hamstring muscles co-contraction in young healthy subjects during normal gait, able to include the physiological variability of the phenomenon.

Dynamic knee muscle co-contraction quantified during walking

The purpose of the present study was the quantification of the co-activation patterns of the knee extensor and flexor muscles during walking at self-selected speed and cadence. To this aim, the Statistical Gait Analysis, a recent methodology providing a statistical characterization of gait, was performed on surface EMG signals from Vastus Lateralis (VL) and Medial Hamstrings (MH) in 14 healthy young adult subjects. Muscular co-contraction was assessed as the overlapping period between activation intervals of agonist and antagonist muscles. Superimpositions between VL and MH activity were detected from terminal swing to the following loading response in 100% of the considered strides. This superimposition could be intended as an actual co-contraction of VL and MH, working across the same joint, the knee. It occurs in this gait phase likely in order to assist knee extension, developing muscle tension for weight acceptance during loading response, and to control knee flexion. A further less frequent (28.9±13.6% of the strides, P<;0.001) superimposition was detected in terminal stance; this superimposition, however, should not be considered a real co-contraction, because VL and MH work on different joints. These findings have the merit to provide a novel data on the variability of the reciprocal role of VL and MH during walking, allowing a deeper insight in the physiological mechanisms that regulate the knee flexion/extension.

A new muscle co-activation index for biomechanical load evaluation in work activities

Low-back disorders (LBDs) are the most common and costly musculoskeletal problem. Muscle co-activation, a mechanism that stabilises the spine, is adopted by the central nervous system to provide added protection and avoid LBDs. However, during high-risk lifting tasks, the compressive load on the spine grows owing to increased co-activation. The aim of this study was to develop a method for the sample-by-sample monitoring of the co-activation of more than two muscles, and to compare this method with agonist-antagonist methods. We propose a time-varying multi-muscle co-activation function that considers electromyographic (EMG) signals as input. EMG data of 10 healthy subjects were recorded while they manually lifted loads at three progressively heavier conditions. The repeated measures ANOVA revealed a significant effect of lifting condition on our co-activation index. Heavier conditions resulted in higher muscle co-activation values. Significant correlations were found between the time-varying multi-muscle co-activation index and other agonist-antagonist methods. Practitioner Summary: We have developed a method to quantify muscle co-activation during the execution of a lifting task. To do this we used surface electromyography. Our algorithm provides a measure of time-varying co-activation between more than two muscles.

Assessment of the ankle muscle co-contraction during normal gait: a surface electromyography study

The study was designed to assess the co-contractions of tibialis anterior (TA) and gastrocnemius lateralis (GL) in healthy young adults during gait at self-selected speed and cadence, in terms of variability of onset-offset muscular activation and occurrence frequency. Statistical gait analysis (SGA), a recent methodology performing a statistical characterization of gait by averaging spatio-temporal and EMG-based parameters over numerous strides, was performed in twenty-four healthy young adults. Co-contractions were assessed as the period of overlap between activation intervals of TA and GL. Results showed that GL and TA act as pure agonist/antagonists for ankle plantar/dorsiflexion (no co-contractions) in only 21.3 ± 8.2% of strides. In the remaining strides, statistically significant (p < 0.05) co-contractions appear in early stance (29.2 ± 1.7%), mid-stance (32.1 ± 18.3%) and swing (62.2 ± 2.0%). This significantly increased complexity in muscle recruitment strategy beyond the activation as pure ankle plantar/dorsiflexors, suggests that co-contractions are likely functional to further physiological tasks as foot inversion, balance improvement, control of ankle stability and knee flexion. This study represents the first attempt for the development in healthy young adults of a "normality" reference frame for GL/TA co-contractions, able to include the physiological variability of the phenomenon and eliminate the confounding effect of age.

The role of muscle activation in cruciate disease

Traditional investigations into the etiopathogenesis of canine cranial cruciate ligament (CCL) disease have focused primarily on the biological and mechanical insults to the CCL as a passive stabilizing structure of the stifle. However, with recent collaboration between veterinarians and physical therapists, an increased focus on the role of muscle activity and aberrant motor control mechanisms associated with anterior cruciate ligament (ACL) injuries and rehabilitation in people has been transferred and applied to dogs with CCL disease. Motor control mechanisms in both intact and cruciate-deficient human knees may have direct translation to canine patients, because the sensory and motor components are similar, despite moderate anatomic and biomechanical differences. Components of motor control, such as muscle recruitment and the coordination and amplitudes of activation are strongly influenced by afferent proprioceptive signaling from peri- and intra-articular structures, including the cruciate ligaments. In people, alterations in the timing or amplitude of muscle contractions contribute to uncoordinated movement, which can play a critical role in ACL injury, joint instability and the progression of osteoarthritis (OA). A better understanding of motor control mechanisms as they relate to canine CCL disease is vitally important in identifying modifiable risk factors and applying preventative measures, for development of improved surgical and rehabilitative treatment strategies. The purpose of this review article is to analyze the influence of altered motor control, specifically pelvic limb muscle activation, in dogs with CCL disease as evidenced by mechanisms of ACL injury and rehabilitation in people.

Tibial rotation in single- and double-bundle ACL reconstruction: a kinematic 3-D in vivo analysis

PURPOSE

The effect of double-bundle ACL reconstruction on knee kinematics has recently been studied by several authors under controlled laboratory conditions however little evidence has been derived from dynamic in vivo evaluations. This study hypothesized that tibial rotation during pivoting motor tasks would be better restored after double-bundle ACL reconstructions when compared with single-bundle procedures.

METHODS

Twenty patients with a chronic ACL rupture were randomly assigned to receive a single- or double-bundle ACL reconstruction. Both knees were evaluated pre-operatively by kinematic 3-D gait analysis while performing low- and high-demand motor tasks, including pivoting. At 6 months post-operatively, measurements were repeated in 16 patients. Ten healthy, sex- and age-matched subjects with no history of lower limb pathology formed the control group. The tibial rotational excursion was set as the dependent variable.

RESULTS

The results indicate that at 6 months after surgery both "anatomic" single- and double-bundle ACL reconstruction are able to restore tibial rotational excursion when compared with the contralateral knees and with control knees from uninjured subjects. Chronic ACL-deficient patients show an increase in tibial rotation in both knees during high-demand pivoting tasks.

CONCLUSIONS

Both "anatomic" single- and double-bundle ACL reconstruction adequately restore tibial rotational excursion in a human, "in vivo" kinematic model. As knee stability measurements by in vivo kinematic 3-D analysis more accurately represent actual knee loading during activities, the results of this study might better correlate with functional outcome after ACL reconstructions compared with static knee stability tests or ex vivo laboratory experiments. In such, the results of this dynamic study do not support the theoretical advantage of a double-bundle ACL reconstruction over an "anatomic" single-bundle ACL reconstruction.

Muscle co-contraction after anterior cruciate ligament reconstruction: Influence of functional level

BACKGROUND

ACL reconstruction is recommended to improve function in subjects with ligament injuries. However, after surgery, some individuals are not able to return to their pre-injury functional level. The mechanisms related to this incapacity are not well understood.

STUDY DESIGN

Cross-sectional study.

METHODS

Co-contraction levels were assessed in individuals who returned to their pre-injury functional level and in 10 individuals who were not able to return to full activity after unilateral ACL reconstruction. Electromyography of the vastus lateralis and biceps femoris muscles before and after sudden perturbations applied during the stance phase of walking was used to calculate co-contraction.

RESULTS

The involved limb had lower co-contraction pre-perturbation than the non-involved limb in both groups (p=0.049). The co-contraction level post-perturbation was significantly higher in the limited return group than in the full return group (p=0.03).

CONCLUSION

Decreased co-contraction in the involved limb before perturbation may be caused by sensorial changes resulting from surgery or injury. Increased co-contraction levels observed in the limited return group after perturbation may be a compensatory mechanism to make up for possible decreased intrinsic stability of the knee joint.

CLINICAL RELEVANCE

Increased co-contraction after perturbation does not contribute to knee stability.

Risk factors for a contralateral anterior cruciate ligament injury

Contralateral anterior cruciate ligament (ACL) injuries are together with the risk of developing osteoarthritis of the knee and the risk of re-rupture/graft failure important aspects to consider after an ACL injury. The aim of this review was to perform a critical analysis of the literature on the risk factors associated with a contralateral ACL injury. A better understanding of these risk factors will help in the treatment of patients with unilateral ACL injuries and in the development of interventions designed to prevent contralateral ACL injuries. A Medline search was conducted to find studies investigating risk factors for a contralateral ACL injury, as well as studies where a contralateral ACL injury was the outcome of the study. Twenty studies describing the risk of a contralateral ACL rupture, or specific risk factors for a contralateral ACL injury, were found and systematically reviewed. In 13 of these studies, patients were followed prospectively after a unilateral ACL injury. The evidence presented in the literature shows that the risk of sustaining a contralateral ACL injury is greater than the risk of sustaining a first time ACL injury. Return to a high activity level after a unilateral ACL injury was the most important risk factor of sustaining a contralateral ACL injury. There was inconclusive evidence of the relevance of factors such as female gender, family history of ACL injuries, and a narrow intercondylar notch, as risk factors for a contralateral ACL injury. Risk factors acquired secondary to the ACL injury, such as altered biomechanics and altered neuromuscular function, affecting both the injured and the contralateral leg, most likely, further increase the risk of a contralateral ACL injury. This literature review indicates that the increased risk of sustaining a contralateral ACL injury should be contemplated, when considering the return to a high level of activity after an ACL injury.

Periarticular muscle stimulation controls anterior tibial laxity after experimental ACL section: an experimental study

BACKGROUND AND PURPOSE

Besides current strategies to treat potentially disabling anterior cruciate ligament (ACL) injury, a new and innovative approach was designed based on electrical stimulation of the muscle to prevent unwanted displacement of the tibia relative to the femur. Our aim was to measure muscular strain and anterior tibial translation (ATT) in a controlled study using an animal model of ACL-deficient knee undergoing muscular electric stimulation.

METHODS

Seventeen cat knees under tibial anterior traction of 24.5 N were studied before and after ACL transection. Muscular fiber length variation was obtained by ultrasonomicrometry and ATT by video recordings at the beginning, during, and at the end of the movement. Square pulses of 0.2 ms with 5 V were applied in trains of 500, 100, and 20 ms simultaneously to both the quadriceps and hamstrings before and immediately after traction.

RESULTS

Electric stimulation of ACL-deficient knees normalized muscular strain to values of control knees. An increased resistance to muscular lengthening was observed in stimulated knees. Stimulation before traction maintained similar ATT than control knees during the subsequent traction.

DISCUSSION

Electric muscular stimulation in the ACL-deficient knee provoked periarticular muscle contraction, controlling ATT when time-adjusted stimulus (before traction) was used. This suggested that artificially inducing the muscular response could help to control anterior knee laxity after ACL injury.

Applicability of the coactivation method in assessing synergies of the scapular stabilizing muscles

HYPOTHESIS

This study investigated the feasibility of quantifying the coactivation levels in the evaluation of synergisms of the scapular stabilizing muscles during the elevation and lowering of the arms. This method, which quantifies the overlapping area of the normalized electromyographic (EMG) activity, could be applicable in assessing such muscular synergies.

MATERIALS AND METHODS

Both shoulders of 10 healthy volunteers were assessed. The coactivation of 3 synergic muscular groups (upper, middle and lower trapezius; upper trapezius and serratus anterior; middle trapezius and serratus anterior) and the isolated electromyographic activity of each muscle were analyzed.

RESULTS

Analysis of variance revealed that the coactivation values between the synergic groups were different from the isolated levels of each respective muscle for both movements (24.42 < F < 40.12; df=6; p < 0.001). The coactivation values of all groups during elevation were different from those during the lowering of the arms (13.31 <F < 959.92; df=1; p <or= 0.002), with progressive increases in EMG activity during the elevation and decreases during the lowering of the arms.

CONCLUSION

The significant differences in EMG activity between the isolated and the coactivation methods indicated that the coactivation method was adequate to assess the scapular muscular synergies.

Changes in lower limb co-contraction and stiffness by toddlers with Down syndrome and toddlers with typical development during the acquisition of independent gait

During gait acquisition, children learn to use their changing resources to meet the requirements of the task. Compared to typically developing toddlers (TD), toddlers with Down syndrome (DS) have functionally different musculoskeletal characteristics, such as hypotonia, and joint and ligament laxity, that could produce a reduced passive stiffness. The interplay between this inherently lower passive stiffness and the demands of walking may result in different strategies during gait acquisition. This study compared normalized global stiffness and lower limb's co-contraction indices (CCI) used by toddlers with TD (n=12) and with DS (n=12), during the early stages of gait acquisition. Stiffness and CCI were normalized by gravitational torque (mLg) in both phases of gait (stance, swing). Five longitudinal evaluations were conducted from the onset of locomotion until three months post-acquisition. All children were video taped and had electromyographic (EMG) recordings from muscle pairs of one leg, which were used to calculate CCI of hip, knee, ankle, and total leg CCI. Body and lower limb stiffness were calculated according to a hybrid pendulum resonance equation. Results from ANOVAs revealed no group differences on stiffness or on CCI's during stance but children with DS showed greater CCI during swing. Despite the structural musculoskeletal differences between toddlers with TD and with DS, the similarities observed in their processes of gait development suggest functional equivalences.

Scapular muscular activity with shoulder impingement syndrome during lowering of the arms

OBJECTIVE

To compare isolated electromyographic (EMG) activity of the serratus anterior, upper, middle, and lower trapezius, as well as the coactivation of the upper and middle trapezius/serratus anterior in subjects with and without shoulder impingement syndrome (IS), during lowering of the arms.

DESIGN

Cross-sectional study.

SETTING

University laboratory.

PARTICIPANTS

Twenty young adults, 10 with unilateral IS degree I or II (mean age 28.6 +/- 5.89 years) and 10 without any complaints or history of previous shoulder lesions (mean age 29.0 +/- 5.35 years), matched by gender, age, and levels of physical activity.

MAIN OUTCOME MEASUREMENTS

Isolated EMG activity of the serratus anterior, upper, middle, and lower trapezius, as well as the coactivation of the upper trapezius and middle trapezius/serratus anterior. The EMG activity was quantified by root mean square calculations and normalized by maximal voluntary isometric contractions.

RESULTS

Significant differences between groups were found only for the coactivation of the middle trapezius/serratus anterior (F = 6.81; P = 0.02). No significant differences were found between sides (F = 0.05; P = 0.83) nor for interactions between sides and groups (F = 3.85; P = 0.07).

CONCLUSIONS

These findings pointed out the importance of evaluating the lowering of the arms in individuals with IS and suggested that measures of coactivation, besides reflecting the real purpose of the muscular actions during functional activities, are more sensitive to detect changes between groups. The evaluation of the coactivation of the middle trapezius/serratus anterior should be included in clinical assessment of individuals with IS and investigations on the etiology and progression of IS.

Landing mechanics between noninjured women and women with anterior cruciate ligament reconstruction during 2 jump tasks

BACKGROUND

Women with anterior cruciate ligament reconstruction have different neuromuscular strategies than noninjured women during functional tasks after ligament reconstruction and rehabilitation.

HYPOTHESIS

Landing from a jump creates high loads on the knee creating dynamic instability in women with anterior cruciate ligament reconstruction, whereas noninjured women have stable knee landing mechanics.

STUDY DESIGN

Controlled laboratory study.

METHODS

Fifteen noninjured women and 13 women with anterior cruciate ligament reconstruction performed 5 trials of a single-legged 40-cm drop jump and 2 trials of a 20-cm up-down hop task. Multivariate analyses of variance were used to compare hip and knee joint kinematics, knee joint moments, ground-reaction forces, and electromyographic findings between the dominant leg in noninjured women and reconstructed leg in women with anterior cruciate ligament reconstruction.

RESULTS

No statistically significant differences between groups were found for peak hip and knee joint angles for the drop jump task. Statistically significant differences in neuromuscular activity (P = .001) and anterior-posterior knee shear forces (P < .001) were seen in women with anterior cruciate ligament reconstruction compared with noninjured women in the drop jump task. However, no statistically significant differences (P > .05) between groups were found for either peak hip and knee joint angles, peak joint kinetics, or electromyographic findings during the up-down hop task.

CONCLUSION

Women with anterior cruciate ligament reconstruction have neuromuscular strategies that allow them to land from a jump similar to healthy women, but they exhibit joint moments that could predispose them to future injury if they participate in sports that require jumping and landing.

Knee instability after acute ACL rupture affects movement patterns during the mid-stance phase of gait

The purpose of this study was to identify gait asymmetries during the mid-stance phase of gait among subjects with knee instability ("non-copers") after acute anterior cruciate ligament (ACL) rupture. Twenty-one non-copers with acute, isolated ACL injury ambulated at their intentional walking speed as kinetic, kinematic, and electromyographic (EMG) data were collected bilaterally. Lower extremity movement patterns and muscle activity were analyzed during the mid-stance and weight acceptance phases of stance. When compared to the uninjured limb, subjects exhibited lower sagittal plane knee excursions and peak knee angles, and higher muscle co-contraction on the injured limb. There was a lower knee flexion moment at peak knee extension, a trend for the knee contribution to the total support moment to be lower, and a higher ankle contribution to the total support moment on the injured limb. There were differences in the magnitude of muscle activity which included higher hamstring activity and lower soleus activity on the injured limb. Changes in quadriceps, soleus, and hamstring muscle activity on the injured limb were identified during weight acceptance that had not previously been reported, while hip compensation for a lower knee contribution to the total support moment has been described. Non-copers consistently stabilize their knee with a stiffening strategy involving less knee motion and higher muscle contraction. The variable combination of muscle adaptations that produce joint stiffness, and the ability of both the ankle and the hip to compensate for lower knee control indicate the non-coper neuromuscular system may be more malleable than previously believed.

Análise da freqüência mediana do sinal eletromiográfico de indivíduos com lesão do ligamento cruzado anterior em exercícios isométricos de cadeia cinética aberta e fechada

Indivíduos com lesão do ligamento cruzado anterior (LCA) possuem importantes alterações funcionais na musculatura periarticular do joelho. Sendo assim, é de suma importância caracterizar tais alterações, bem como enfatizar um efetivo protocolo de reabilitação para esses indivíduos, com conseqüente retorno às atividades físicas. O objetivo deste estudo foi analisar o comportamento da freqüência mediana (Fmed) em indivíduos com lesão do LCA durante contrações isométricas em exercícios de cadeia cinética aberta (CCA) e fechada (CCF). Entre lesados e não lesados, 40 indivíduos realizaram a extensão do joelho através da contração isométrica voluntária máxima (CIVM) nos aparelhos leg extension e leg press a 30°, 60° e 90° de flexão do joelho. Os resultados revelaram valores da Fmed menores para indivíduos com lesão do LCA quando comparados com o membro contralateral e grupo controle em CCA (p < 0,05). Já exercícios em CCF não apresentaram diferença estatística significativa (p > 0,05) na comparação entre os grupos, não evidenciando esse tipo de lesão. Portanto, a Fmed parece ser uma ferramenta eletromiográfica eficaz na caracterização da lesão crônica do LCA. Além disso, exercícios em CCF parecem ser os mais indicados para a reabilitação desses indivíduos.

Muscular co-contraction during walking and landing from a jump: Comparison between genders and influence of activity level

BACKGROUND

Women have higher rates of knee ligament injury than men. Co-contraction of knee muscles is proposed to be an important mechanism to protect the joint from injuries.

HYPOTHESIS

Females have lower co-contraction levels when compared to males.

STUDY DESIGN

Exploratory, cross-sectional design.

METHODS

Thirty-six men and women equally divided into four groups according to gender and activity level (sedentary and athletic) were compared in relation to vastus lateralis and biceps femoris co-contraction before heel strike during level walking and before floor contact during landing from a jump. Muscular co-contraction was assessed by surface electromyography. Correlations between co-contraction and ligament laxity, extensor and flexor work, and flexion/extension torque ratio were also analyzed.

RESULTS

No differences between genders were found in the studied situations (p0.381). During walking, co-contraction was greater in sedentary women compared to athletic women (p=0.002). A moderate inverse correlation was found between co-contraction during walking and women extensor (r=-0.613; p=0.007) and flexor (r=-0.575; p=0.012) work. During landing from a jump, no variables correlated to co-contraction in any of the groups tested (r0.477; p0.061).

CONCLUSION

Co-contraction levels were not different between genders. Results suggest that women compensate strength deficits by means of increasing activation levels, possibly to generate adequate joint stiffness to meet stabilization demands. However, this is not evident in a more stressful activity like landing from a jump.

CLINICAL RELEVANCE

This study contributes to a better understanding of the factors related to joint protection in females, who are at a greater risk of ligament injuries.

Co-contraction during static and dynamic knee extensions in ACL deficient subjects

Co-contraction of the muscles is proposed in the literature as one of the strategies that anterior cruciate ligament deficient (ACLD) subjects can use to compensate the loss of ACL function. This study examined the response of ACLD and control subjects to different shear forces in isometric and slow-dynamic knee extensions. Twelve chronic ACLD and 10 control subjects performed submaximal positioning and slow-dynamic knee extensions (between 45 degrees and 5 degrees of knee flexion) with two external flexion moments both applied at two distances on the lower leg. The shear force was controlled by changing the moment arm without changing the moment. Electromyographic data were collected from knee flexor and extensor muscles. In the analysis of variance, no significant effect of subject group was found in positioning or slow-dynamic tasks across all muscles. The effect of knee angle was significantly different between the subject groups for biceps femoris in positioning and for rectus femoris in slow-dynamic tasks, but these effects were very small and will not have a great impact on the resulting shear forces. There was no interaction between moment arm and subject group. Therefore, the hypothesis that ACLD subjects increase co-contraction in situations with an increased shear load in positioning and slow-dynamic knee extensions could not be confirmed.

Kinematic analysis of functional lower body perturbations

BACKGROUND

Sudden changes in direction on a single weight-bearing-limb are commonly associated with injury to the lower extremity. The purposes of this study were to assess the between day reliability of hip, knee, and ankle kinematic displacements achieved with internal and external femur-on-weight-bearing-tibia rotation perturbations and to determine the effect of these perturbations on three dimensional hip, knee and ankle kinematics.

METHODS

Twenty recreationally active, healthy college students with no history of significant orthopedic injury (10 male, 10 female) were subjected to a forward and either internal or external rotary perturbation of the trunk and thigh on the weight-bearing-tibia while three dimensional kinematics were simultaneously collected. The protocol was repeated 24-48 h later to assess reliability.

FINDINGS

External perturbations resulted in significant internal rotation (IR) of the tibia on the femur (mean 7.3 (SD 3.9 degrees)) and IR of the femur on the pelvis (mean 6.8 (SD 5.4 degrees)) (P<0.05). Internal perturbations resulted in significant external rotation (ER) of the tibia on the femur (mean 6.8 (5.9 degrees)) and ER of the femur on the pelvis (mean 10.7 (SD 96.1 degrees)) (P<0.05). Additionally the external perturbation results in a significantly greater knee valgus (mean 3.6 (SD 2.2 degrees)) position while the internal perturbation results in a significantly greater knee varus position (mean 2.3 (SD 3.5 degrees)) (P<0.05). External perturbation hip and knee total joint displacements revealed moderate to strong reliability (Intraclass Correlation Coefficient(2,k)=0.67-0.94) while internal perturbations revealed slightly higher Intraclass Correlation Coefficients(2,k)(0.80-0.96).

INTERPRETATION

The lower extremity perturbation device provides a consistent external and internal perturbation of the femur on the weight-bearing-tibia. The observed transverse and frontal plane kinematics are similar to motions observed during cross-over and side-stepping tasks.