Kinematic,kinetic and electromyographic differences between young adults with and without chronic ankle instability during walking

The objective of this study was to quantify the kinematic, kinetic and electromyography differences between individuals with and without chronic ankle instability (CAI) during comfortable (CW) and fast (FW) walking. Twenty-one individuals with CAI and 21 healthy controls were recruited to walk at CW and FW speeds. The dependent variables were gluteus medius, vastus lateralis, gastrocnemius lateralis, gastrocnemius medialis, peroneus longus and tibialis anterior muscles mean activity, ankle and knee angles and moments. Kinematic, kinetic and electromyography variables were compared between groups with a one-dimensional statistical non-parametric mapping analysis. The CAI group exhibited no significant difference for ankle angles and moments compared to the control group. However, the CAI group showed less external knee rotation from 56 to 100% (CW) and 51 to 98% (FW) and more knee abduction moment from 1 to 6% and 7 to 9% (CW) and 1 to 2% (FW) of the stance phase. Less gluteus medius muscle activity was also observed from 6 to 9% and 99 to 100% (CW) of the stance phase for the CAI group. These results suggest proximal biomechanical compensations and will help better understand the underlying deficits associated with CAI. They also indicate that regardless of walking speeds, individuals with CAI exhibit similar differences compared to healthy participants.     

A new method to analyze postural stability during a transition task from double-leg stance to single-leg stance

Time to stabilization (TTS) has been introduced as a method to analyze dynamic postural stability during jump and landing tasks, but has also been applied during the transition task from double-leg stance (DLS) to single-leg stance (SLS). However, the application of the originally described TTS technique during the latter task has some important limitations. The first goal of this study was to present an adapted version of the TTS technique to provide an effective alternative method to better analyze postural stability during the transition from DLS to SLS. The second goal was to study the influence of pathology and different speeds on postural stability outcomes. Fifteen healthy control subjects and 15 subjects with chronic ankle instability (CAI) performed the transition task on their preferred speed and as fast as possible, with eyes open and with eyes closed. Subjects with CAI performed the transition significantly slower when moving at their preferred speed with eyes closed. The time subjects needed to reach a new stability point was not discriminative between groups and largely dependent on movement speed. However, the amount of sway after this new stability point was significantly increased in the CAI group and when eyes were closed. The results of this study suggest that subjects with CAI have a decreased ability to overcome the postural perturbation created by the voluntary movement from DLS to SLS. Focusing only on TTS during the transition from DLS to SLS may lead at least in some cases to misinterpretations when assessing postural stability.     

Copers adopt an altered movement pattern compared to individuals with chronic ankle instability and control groups in unexpected single-leg landing and cutting task

Individuals with chronic ankle instability (CAI) demonstrate altered ankle kinematics during landing compared to uninjured individuals. However, if copers may have adopted unique movement strategy to prevent repeated ankle sprains is unclear. The purpose of this study compares the lower-extremity joint kinematics and muscle activities of CAI (N = 8), coper (COP) (N = 8), and control (CON) (N = 8) groups in unexpected single-leg landing and cutting. Performance time (from initial contact to toe-off), number of mistakes in the jumping direction, low-extremity joint angle are assessed. Muscle activities were recorded from the tibialis anterior, medial gastrocnemius, and peroneus longus (PL), and mean muscle activity, co-contraction index (CI), and PL latency were analyzed. Results of performance time and CI are not significant. Significantly less number of mistakes in the jumping direction and a shorter PL latency were discovered in the COP and CON compared with the CAI group (P < 0.05). The peak hip joint flexion angle is significantly smaller in the COP than in the CON (P = 0.04). In dynamic tasks requiring quick judgments of ankle inclination, the COP may be able to accurately sense the inclination of the foot. Additionally, movement strategies differed between the COP and CON groups in an unexpected single-leg landing and cutting.     

腓骨短肌腱外侧韧带重建术治疗慢性踝关节外侧不稳的临床疗效

目的:研究外侧副韧带重建手术结合关节镜检查治疗慢性踝关节外侧不稳的临床疗效。方法:选取2012年7月-2014年7月我院收治的慢性踝关节外侧不稳患者60例,随机分为研究组和对照组,每组30例。对照组患者给予保守治疗,研究组患者采取踝关节镜探查清理联合腓骨短肌腱外侧韧带重建手术进行治疗。应用美国足踝外科裸-后足功能评分系统(AOFAS)评价两组患者治疗前后的踝关节功能评分,并比较两组的优良率、复发率以及并发症的发生率。结果:两组治疗前的AOFAS功能评分比较无统计学差异(P0.05),两组治疗后的AOFAS功能评分均较治疗前显著升高,且研究组显著高于对照组,差异具体统计学意义(P0.05)。研究组的优良率为96.7%(29/30),显著高于对照组的73.3%(22/30);研究组的复发率为0.0%(0/30),显著低于对照组的13.3%(4/30);研究组并发症的发生率为3.3%(1/30),显著低于对照组的20.0%(6/30),两组比较差异均具有统计学意义(P0.05)。结论:外侧副韧带重建手术结合关节镜检查治疗慢性踝关节外侧不稳具有较好的临床疗效,且复发率较低,并发症较少。     

Neural excitability of lower extremity musculature in individuals with and without chronic ankle instability: A systematic review and meta-analysis

This systematic review and meta-analysis examined differences in lower extremity neural excitability between ankles with and without chronic ankle instability (CAI). We searched the literature for studies that compared corticomotor or spinal reflexive excitability between a CAI group and controls or copers, or between limbs of a CAI group. Random effects meta-analyses calculated pooled effect sizes for each outcome. Nineteen studies were included. Meta-analyses of motor thresholds of the fibularis longus (Z = 1.17, P = 0.24) and soleus (Z = 0.47, P = 0.64) exhibited no differences between ankles with and without CAI. Pooled data indicate that ankles with CAI had reduced soleus spinal reflexive excitability (Z = 2.18, P = 0.03) and significantly less modulation of the soleus (Z = 6.96, P < 0.01) and fibularis longus (Z = 4.75, P < 0.01) spinal reflexive excitability when transitioning to more challenging stances. Pre-synaptic inhibition was facilitated in ankles with CAI (Z = 4.05, P < 0.01), but no difference in recurrent inhibition existed (Z = 1.50, P = 0.13). Soleus spinal reflexive activity is reduced in those with CAI. Reduced ability of ankles with CAI to modulate soleus and fibularis longus reflexive activity may contribute to impaired balance.     

Chromatin perturbations during the DNA damage response in higher eukaryotes

The DNA damage response is a widely used term that encompasses all signaling initiated at DNA lesions and damaged replication forks as it extends to orchestrate DNA repair, cell cycle checkpoints, cell death and senescence. ATM, an apical DNA damage signaling kinase, is virtually instantaneously activated following the introduction of DNA double-strand breaks (DSBs). The MRE11-RAD50-NBS1 (MRN) complex, which has a catalytic role in DNA repair, and the KAT5 (Tip60) acetyltransferase are required for maximal ATM kinase activation in cells exposed to low doses of ionizing radiation. The sensing of DNA lesions occurs within a highly complex and heterogeneous chromatin environment. Chromatin decondensation and histone eviction at DSBs may be permissive for KAT5 binding to H3K9me3 and H3K36me3, ATM kinase acetylation and activation. Furthermore, chromatin perturbation may be a prerequisite for most DNA repair. Nucleosome disassembly during DNA repair was first reported in the 1970s by Smerdon and colleagues when nucleosome rearrangement was noted during the process of nucleotide excision repair of UV-induced DNA damage in human cells. Recently, the multi-functional protein nucleolin was identified as the relevant histone chaperone required for partial nucleosome disruption at DBSs, the recruitment of repair enzymes and for DNA repair. Notably, ATM kinase is activated by chromatin perturbations induced by a variety of treatments that do not directly cause DSBs, including treatment with histone deacetylase inhibitors. Central to the mechanisms that activate ATR, the second apical DNA damage signaling kinase, outside of a stalled and collapsed replication fork in S-phase, is chromatin decondensation and histone eviction associated with DNA end resection at DSBs. Thus, a stress that is common to both ATM and ATR kinase activation is chromatin perturbations, and we argue that chromatin perturbations are both sufficient and required for induction of the DNA damage response.     

Ankle kinematics,center of pressure progression,and lower extremity muscle activity during a side-cutting task in participants with and without chronic ankle instability

This study assessed ankle kinematics, surface electromyography, and center-of-pressure (COP) progression relative to the medial border of the foot during a side-cutting task in individuals with and without chronic ankle instability (CAI). Thirty participants (CAI = 15; Controls = 15) performed a side-cutting task on a force platform while 3-dimentional ankle kinematics, COP position, and surface electromyography from the tibialis anterior, medial gastrocnemius, fibularis longus, fibularis brevis, vastus medialis, and semitendinosus were recorded on the testing leg. Ankle kinematics, root-mean-square muscle activity and COP position relative to the medial boarder of the foot were compared between CAI and healthy controls (p < 0.05). Significantly greater ankle internal rotation from 35–54% of the stance phase (p = 0.032) was found for the CAI group compared to controls. Furthermore, significantly greater tibialis anterior muscle activity from 86–94% of the stance phase (p = 0.022) and a more medial COP position from 81–100% (p < 0.05) and of the stance phase was also observed in the CAI group. Less lateral COP progression and increased tibialis anterior activation in the CAI group could reflect a protective movement strategy during anticipated side-cutting to avoid recurrent injury. However, greater ankle internal rotation during mid-stance highlights a potential ‘giving way’ mechanism in individuals with CAI.     

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

PurposeTo compare the responses in knee joint muscle activation patterns to different perturbations during gait in healthy subjects.ScopeNine 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.ResultsPerturbations 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.ConclusionsHealthy 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.     

Activation of Lyn Tyrosine Kinase through Decreased Membrane Cholesterol Levels during a Change in Its Membrane Distribution upon Cell Detachment

Cellular membranes, which can serve as scaffolds for signal transduction, dynamically change their characteristics upon cell detachment. Src family kinases undergo post-translational lipid modification and are involved in a wide range of signaling events at the plasma membrane, such as cell proliferation, cell adhesion, and survival. Previously, we showed the differential membrane distributions among the members of Src family kinases by sucrose density gradient fractionation. However, little is known about the regulation of the membrane distribution of Src family kinases upon cell detachment. Here, we show that cell detachment shifts the main peak of the membrane distribution of Lyn, a member of Src family kinase, from the low density to the high density membrane fractions and enhances the kinase activity of Lyn. The change in Lyn distribution upon cell detachment involves both dynamin activity and a decrease in membrane cholesterol. Cell detachment activates Lyn through decreased membrane cholesterol levels during a change in its membrane distribution. Furthermore, cholesterol incorporation decreases Lyn activity and reduces the viability of suspension cells. These results suggest that cell detachment-induced Lyn activation through the change in the membrane distribution of Lyn plays an important role in survival of suspension cells.     

An effective balancing response to lateral perturbations at pelvis level during slow walking requires control in all three planes of motion

In this study we investigated balancing responses to lateral perturbations during slow walking (0.85 m/s). A group of seven healthy individuals walked on an instrumented treadmill while being perturbed at the level of waist at left heel strike in outward and inward lateral directions. Centre of mass (COM) and centre of pressure (COP), rotation of pelvis around vertical axis, step lengths, step widths and step times were assessed. The results have shown that beside control of COP in lateral direction, facilitated by adequate step widths, control of COP in sagittal direction, slowing down movement of COM was present after commencement of lateral perturbations. Sagittal component of COM was significantly retarded as compared to unperturbed walking for both inward (4.32 ± 1.29 cm) and outward (9.75 ± 2.17 cm) perturbations. This was necessary since after an inward perturbation first step length (0.29 ± 0.04 m compared to 0.52 ± 0.02 m in unperturbed walking) and step time (0.45 ± 0.05 s compared to 0.61 ± 0.04 s in unperturbed walking) were shortened while after an outward perturbation first two step lengths (0.36 ± 0.05 m and 0.32 ± 0.11 m compared to 0.52 ± 0.03 m in unperturbed walking) were shortened that needed to be accommodated by the described modulation of COP in sagittal plane. In addition pronounced pelvis rotation assisted in bringing swing leg to new location. The results of this study show that counteracting lateral perturbations at slow walking requires adequate response in all three planes of motion.