Strategies for muscle activation during isometric torque generation at the human elbow

1. We studied the patterns of electromyographic (EMG) activity in elbow muscles of 14 normal human subjects. The activity of five muscles that act in flexion-extension and forearm supination-pronation was simultaneously recorded during isometric voluntary torque generation, in which torques generated in a plane orthogonal to the long axis of the forearm were voluntarily coupled with torques generated about the long axis of the forearm (i.e., supination-pronation). 2. When forearm supination torques were superimposed on a background of elbow flexion torque, biceps brachii activity increased substantially, as expected; however, brachioradialis and brachialis EMG levels decreased modestly, a less predictable outcome. The pronator teres was also active during pure flexion and flexion coupled with mild supination (even though no pronation torque was required). This was presumably to offset inappropriate torque contributions of other muscles, such as the biceps brachii. 3. When forearm supination torque was superimposed on elbow extension torque, again the biceps brachii was strongly active. The pronator teres also became mildly active during extension with added pronation torque. These changes occurred despite the fact that both the pronator and biceps muscles induce elbow flexion. 4. In these same elbow extension tasks, triceps brachii activity was also modulated with both pronation or supination loads. It was most active during either supination or pronation loads, again despite the fact that it has no mechanical role in producing forearm supination-pronation torque. 5. Recordings of EMG activity during changes in forearm supination-pronation angle demonstrated that activation of the biceps brachii followed classic length-tension predictions, in that less EMG activity was required to achieve a given supination torque when the forearm was pronated (where biceps brachii is relatively longer). On the other hand, EMG activity of the pronator teres did not decrease when the pronator was lengthened. Triceps EMG was also more active when the forearm was supinated, despite its having no direct functional role in this movement. 6. Plots relating EMG activity in biceps brachii, brachialis, and brachioradialis at three different forearm positions revealed that there was a consistent positive near-linear relationship between brachialis and brachioradialis and that biceps brachii is often most active when brachioradialis and brachialis are least active. 7. We argue that, for the human elbow joint at least, fixed muscle synergies are rather uncommon and that relationships between muscle activities are situation dependent.(ABSTRACT TRUNCATED AT 400 WORDS)     

学龄儿童背负不同重量行走时足底压力分布研究

通过Footscan足底压力步态分析系统测试学龄儿童背负不同重量行走时动态足底压力分布进行分析.结果表明,学龄儿童背负4 kg书包行走时,足底第二、三跖趾关节处峰值压力增大,支撑时间延长;压力中心变化曲线呈横向摆动偏大趋势,足中部控制不良需要肢体参与维持平衡;随着背负重量的增加出现足支撑各阶段内外翻的比例加大,造成下肢伤害的可能性增高,说明儿童长期负重行走对足及下肢肌肉负荷较大,足掌跖趾区相应部位易形成胼胝体,将会影响儿童足弓正常发育,应引起社会及家长的重视.建议家长应限制儿童书包重量,避免儿童长时间背负重物行走与站立,应采取有效措施促进学龄儿童身体全面发展.     

The control of arm pointing movements in three dimensions

Summary In this study we investigated pointing movements made with an extended arm. Despite the large number of mechanical degrees of freedom, limb orientation adopted during pointing could be described by rotation axes contained on a two-dimensional curved surface. As a result of the curvature, the orientation of a linear plane approximating a small region of the curved surface was dependent on the location of the movements within the full workspace. These results account for earlier suggestions that limb orientation could be described by coplanar rotation vectors and that the orientation of the plane moved with the workspace. Despite the additional complexity, our results indicate that the number of degrees of freedom used to position the extended forearm is reduced from four to two for normal pointing movements. Contributions to orientation of the wrist and hand by supination/pronation of the forearm were minor for changes in shoulder yaw angle. However, supination/ pronation added significantly to orientation of the hand for changes in shoulder pitch angle.     

Elbow torques and EMG patterns of flexor muscles during different isometric tasks.

This paper examines the torque responses and EMG activity levels in four muscles acting at the elbow joint during different combinations of one- and two- degree of freedom isometric torque production (single and dual tasks, respectively). Flexor and supinator/pronator torques and surface EMG signals from m. biceps brachii, m. brachialis, m. brachioradialis and m. triceps brachii were measured in 16 male subjects while they performed maximal effort isometric contractions of pure flexion, pure supination, pure pronation, combined flexion and supination and combined flexion and pronation. In the single tasks, the torque responses were consistent with task requirements, but the dual task results were surprising in that flexor torque levels were reduced as compared to pure flexion, while supinator/pronator torque levels were as high or higher than in pure supination or pronation. Muscle activity levels varied with task, and could not always explain the differences observed in torque responses. These data are discussed within the framework of subpopulations of task-specific motor units within each muscle. The implications of such task-specific muscle units are related to musculoskeletal modelling and previous EMG - torque relationships found at the elbow.     

Functional Anatomy,Pathomechanics, and Pathophysiology of Lateral Ankle Instability

OBJECTIVE: To describe the functional anatomy of the ankle complex as it relates to lateral ankle instability and to describe the pathomechanics and pathophysiology of acute lateral ankle sprains and chronic ankle instability. DATA SOURCES: I searched MEDLINE (1985-2001) and CINAHL (1982-2001) using the key words ankle sprain and ankle instability. DATA SYNTHESIS: Lateral ankle sprains are among the most common injuries incurred during sports participation. The ankle functions as a complex with contributions from the talocrural, subtalar, and inferior tibiofibular joints. Each of these joints must be considered in the pathomechanics and pathophysiology of lateral ankle sprains and chronic ankle instability. Lateral ankle sprains typically occur when the rearfoot undergoes excessive supination on an externally rotated lower leg. Recurrent ankle sprain is extremely common; in fact, the most common predisposition to suffering a sprain is the history of having suffered a previous ankle sprain. Chronic ankle instability may be due to mechanical instability, functional instability, or most likely, a combination of these 2 phenomena. Mechanical instability may be due to specific insufficiencies such as pathologic laxity, arthrokinematic changes, synovial irritation, or degenerative changes. Functional instability is caused by insufficiencies in proprioception and neuromuscular control. CONCLUSIONS/RECOMMENDATIONS: Lateral ankle sprains are often inadequately treated, resulting in frequent recurrence of ankle sprains. Appreciation of the complex anatomy and mechanics of the ankle joint and the pathomechanics and pathophysiology related to acute and chronic ankle instability is integral to the process of effectively evaluating and treating ankle injuries.     

The dynamics of isometric bimanual coordination

Eight right-handed subjects performed rhythmic isometric applications of torque in the directions of pronation and supination of the forearm, in single limb and bimanual conditions. Bimanual movements were executed in either in-phase (homologous muscles simultaneously active) or anti-phase (non-homologous muscles active simultaneously) modes of coordination, in self-paced and frequency-scaled conditions. In the inphase (frequency-scaled) condition, subjects were required to synchronise (applications of torque) with each beat of a metronome, either in the direction of pronation or supination. In the anti-phase (frequency-scaled) condition, subjects were required to synchronise (applications of torque) with each beat of the metronome, either to the left or to the right. Departures from the anti-phase mode of coordination were observed as pacing frequency was increased. However, these departures were of short duration and the anti-phase mode was always re-established. These findings are in marked contrast to those obtained when there is free motion of the limbs. There also existed systematic differences between the stability of the pronation and supination phases of torque application. These differences were, in turn, modified through coincidence with the pacing signal. These results are discussed with reference to the constraints imposed upon the coordination dynamics by the intrinsic properties of the neuromuscular-skeletal system.     

Neuromuscular-skeletal constraints upon the dynamics of unimanual and bimanual coordination

In the first of three experiments, 11 participants generated pronation and supination movements of the forearm. in time with an auditory metronome. The metronome frequency was increased in eight steps (0.25 Hz) from a base frequency of 1.75 Hz. On alternating trials, participants were required to coordinate either maximum pronation or maximum supination with each beat of the metronome. In each block of trials, the axis of rotation was either coincident with the long axis of the forearm, above this axis, or below this axis. The stability of the pronate-on-the-beat pattern, as indexed by the number of pattern changes, and the time of onset of pattern change, was greatest when the axis of rotation of the movement was below the long axis of the forearm. In contrast, the stability of the supinate-on-the-beat pattern was greatest when the axis of rotation of the movement was above the long axis of the forearm. In a second experiment, we examined how changes in the position of the axis of rotation alter the activation patterns of muscles that contribute to pronation and supination of the forearm. Variations in the relative dominance of the pronation and supination phases of the movement cycle across conditions were accounted for primarily by changes in the activation profile of flexor carpi radialis (FCR) and extensor carpi radialis longus (ECR). In the final experiment we examined how these constraints impact upon the stability of bimanual coordination. Thirty-two participants were assigned at random to one of four conditions, each of which combined an axis of rotation configuration (bottom or top) for each limb. The participants generated both inphase (both limbs pronating simultaneously, and supinating simultaneously) and antiphase (left limb pronating and right limb supinating simultaneously, and vice versa) patterns of coordination. When the position of the axis of rotation was equivalent for the left and the right limb, transitions from antiphase to inphase patterns of coordination were frequently observed. In marked contrast, when the position of the axis of rotation for the left and right limb was contradistinct, transitions from inphase to antiphase patterns of coordination occurred. The results demonstrated that when movements are performed in an appropriate mechanical context, inphase patterns of coordination are less stable than antiphase patterns.     

一种新型撕脱性骨折固定装置在踝关节周围撕脱性骨折手术治疗中的应用*

目的 评估一种新型撕脱性骨折固定装置固定踝关节周围撕脱性骨折的临床疗效。方法 2019年1月至2020年4月,以一种新型撕脱性骨折固定装置固定踝关节周围撕脱性骨折18例,其中男12例、女6例。按照Lauge-Hansen分型,旋后内收型4例,旋后外旋型9例,旋前外旋型5例。撕脱性骨折固定装置用于固定内踝撕脱性骨折13例,用于固定外踝撕脱性骨折5例。术后进行随访,随访满1年者按照AOFAS踝-后足评分系统行踝关节功能评定并记录并发症。结果 18例患者随访12 ～ 27个月,骨折均I期愈合,末次随访AOFAS踝-后足评分93.6分（80 ～ 100分）。1例内踝骨折患者和1例外踝骨折患者偶感内/外踝轻微刺痛,1例内踝骨折患者和1例外踝骨折患者感长距离行走后内/外踝轻微疼痛,行内固定取出术。结论 新型撕脱性骨折固定装置固定踝关节周围撕脱性骨折有固定稳定、软组织友好的特点,可作为踝关节周围撕脱性骨折固定的一种选择。     

Coordination and inhomogeneous activation of human arm muscles during isometric torques

1. In this study we have recorded the activity of motor units of the important muscles acting across the elbow joint during combinations of voluntary isometric torques in flexion/extension direction and supination/pronation direction at different angles of the elbow joint. 2. Most muscles are not activated homogeneously; instead the population of motor units of muscles can be subdivided into several subpopulations. Inhomogeneous activation of the population of motor units in a muscle is a general finding and is not restricted to some multifunctional muscles. 3. Muscles can be activated even if their mechanical action does not contribute directly to the external torque. For example, m. triceps is activated during supination torques and thus compensates for the flexion component of the m. biceps. On the other hand, motor units in muscles are not necessarily activated if their mechanical action contributes to a prescribed torque. For example, there are motor units in the m. biceps that are activated during flexion torques, but not during supination torques. 4. The relative activation of the muscles depends on the elbow angle. Changing the elbow angle affects the mechanical advantage of different muscles differently. In general, muscles with the larger mechanical advantage receive the larger input. 5. We have calculated the relative contributions of some muscles to isometric torques. These contributions depend on the combination of the torques exerted. 6. Existing theoretical models on muscle coordination do not incorporate subpopulations of motor units and therefore need to be amended.     

The coordination of upper and lower arm rotation

We tested the hypothesis that the upper and lower arm act as a coordinative structure coupled through a higher order control system. Five healthy participants moved their hand between two targets in ten conditions via internal/external rotation of the shoulder. In eight conditions, the task required concurrent rotation of the lower arm (180° pronation/supination). Movements were stereotypical within a condition but plotting the upper and lower arm angle against each other produced an asymmetrical pattern. With internal rotation, the upper arm reached peak angular velocity slower than the lower arm but this was reversed with external rotation. In two conditions, participants were asked to move faster and slower than their normal speed. The peak speed, time to peak speed and duration were predictable for the different tasks. Internal and external asymmetries decreased with faster movements. In addition a decrease in upper arm amplitude (from 90° to 30°) removed the asymmetry. The asymmetry was unaffected by initial posture but was exaggerated when external rotation was paired with pronation rather than supination, and internal rotation combined with supination (versus pronation). However, the presence of the same fundamental pattern suggests that the asymmetry is not due to biomechanical factors but might arise because of the difficulties involved in visually monitoring the hand when it is close to the body. The results support the idea that functional coupling can occur between upper and lower arm rotations and thus provides further evidence for a higher order control system which is responsible for coordination of arm segment movement.     

Prophylactic ankle braces and knee varus-valgus and internal-external rotation torque

Context: Although prophylactic ankle bracing has been shown to be effective in reducing the incidence of ankle sprains,how these ankle braces might affect the other joints of the lower extremity is not clearly understood.Objective: To determine the effects of a prophylactic ankle brace on knee joint varus-valgus and internal-external rotation torque during a drop landing onto a slanted surface.Design: A repeated-measures design.Setting: Biomechanics research laboratory. Patients or Other Participants: Twenty-four physically active college students.Intervention(s): Participants were tested in a brace and no brace condition. Main Outcome Measure(s): We measured 3 dependent variables:(1) peak ankle inversion-eversion torque, (2) peak knee varus-valgus torque, and (3) peak knee internal-external rotation torque. A force plate was used to collect ground reaction force data, and 6 motion analysis cameras collected kinematic data during the unilateral drop landing. An adjustable bar was hung from the ceiling, and a slant board was positioned over the center of the force plate, so that the ankle of the participant's dominant leg would invert upon landing. Peak torque was measure din both the brace and no-brace conditions. The average of the peak values in 3 trials for both conditions was used for the statistical analysis.Results: Ankle eversion torque was significantly greater in the brace condition (F1,23 19.75, P < .01). Knee external rotation torque was significantly greater in the brace condition(F1,23 4.33, P <.05). Valgus knee torque was smaller in the brace condition, but the difference was not statistically significant(F1,23 3.45, P .08).Conclusions: This study provides an important first step in understanding the effects of prophylactic ankle bracing on other joints of the lower extremity. We found that prophylactic ankle bracing did have an effect on knee torque when the subject was landing on a slanted surface. Specifically, knee external rotation torque increased when the ankle was braced.     

A surgical ankle sprain pain model in the rat: effects of morphine and indomethacin

Ankle sprain is a frequent injury in humans that results in pain, swelling and difficulty in walking on the affected side. Currently a suitable animal model resembling human ankle sprain is lacking. Here, we describe an animal ankle sprain model induced by ankle ligament injury (ALI) in rats. Cutting combinations of the lateral ankle ligament complex produced pain, edema and difficulty of weight bearing, thereby mimicking severe (grade III) ankle sprain in humans. Analgesic compounds, morphine and indomethacin, significantly reversed the reduced weight bearing, thus indicating that reduction of weight bearing is partially due to pain. The ALI model is a new ankle sprain model that may be useful for the study of ankle sprain pain mechanisms and treatments, as well as for the screening of new analgesic drugs.     

踝关节骨折的治疗与踝关节功能预后影响因素分析

目的：探讨踝关节骨折的治疗方法及影响踝关节功能的预后因素。方法：对自2005年1月至2008年12月以来采用手法复位石膏固定和切开复位手术治疗并得到随访的40例踝关节骨折者的临床资料进行回顾分析。按Lauge—Hansen分型,旋后外旋型27例,旋后内收型3例,旋前外展型2例,旋前外旋型6例,垂直压缩型（pilon骨折）2例。采用保守治疗10例,切开复位内固定治疗30例。按照美国足踝骨科协会（AOFAS）推荐的足踝评分系统评估治疗结果。对患者年龄、性别、合并伤、受伤至治疗时间、骨折类型等5个可能的相关因素进行多因素分析。结果：40例术后均获平均15个月（6～20个月）随访。按AOFAS评分平均97分。单因素Logistic回归分析发现年龄和骨折类型的差异有统计学意义,多因素Logistic逐步回归分析发现骨折类型的差异有统计学意义。结论：影响踝关节骨折后踝关节功能的主要预后因素是骨折类型,应主要根据这个因素采取个体化的治疗方法。     

桡尺远侧关节在体MRI运动学研究

目的　利用MRI轴位图像分析正常桡尺远侧关节（DRUJ）旋转运动。 方法　健康志愿者30名（男、女各15名）,共60个正常DRUJ,在腕关节完全旋外、旋外60 °、旋外30 °、中立位、旋内30 °、旋内60 °及完全旋内7个体位行DRUJ的MRI扫描。在DRUJ轴位图上,选取桡骨乙状切迹掌侧顶点（A）及背侧顶点（B）作一连线,利用工作站工具取得尺骨头中心点（C）,过C点作AB垂线,相交于D点,计算AD/AB比值（桡尺比值）;尺骨头-尺骨茎突背侧缘顶点E、F连线,测量EF与AB相交指向掌侧夹角（桡尺夹角）;由两名放射科医生独立完成测量、取其平均值,并评价该方法可信度。 结果　60个正常DRUJ完全旋外、旋外60°、旋外30°、中立位、旋内30°、旋内60°及完全旋内桡尺比值分别为（0.29±0.05）,（0.36±0.06）,（0.42±0.07）,（0.49±0.05）,（0.53±0.06）,（0.56±0.06）,（0.61±0.07）;桡尺夹角分别为（38.41±3.71）°,（48.74±5.54）°,（63.31±4.98）°,（105.56±5.63）°,（138.68±6.04）°,（162.45±6.00）°,（178.46±2.09）°。桡尺比值与桡尺夹角呈正相关,有统计学意义（r=0.97,P<0.05）,腕关节从完全旋外向完全旋内旋转过程中,桡尺比值随桡尺夹角增大而增大。不同体位两项测量指标观察者间相关系数（ICC）范围为0.83~0.96。 结论　通过建立DRUJ在不同体位下桡骨的不同旋转角度所对应桡尺比值正常范围,可以为桡尺远侧关节不稳的诊断提供更多参考依据。     

桡尺远侧关节在体MRI运动学研究

目的　利用MRI轴位图像分析正常桡尺远侧关节（DRUJ）旋转运动。 方法　健康志愿者30名（男、女各15名）,共60个正常DRUJ,在腕关节完全旋外、旋外60 °、旋外30 °、中立位、旋内30 °、旋内60 °及完全旋内7个体位行DRUJ的MRI扫描。在DRUJ轴位图上,选取桡骨乙状切迹掌侧顶点（A）及背侧顶点（B）作一连线,利用工作站工具取得尺骨头中心点（C）,过C点作AB垂线,相交于D点,计算AD/AB比值（桡尺比值）;尺骨头-尺骨茎突背侧缘顶点E、F连线,测量EF与AB相交指向掌侧夹角（桡尺夹角）;由两名放射科医生独立完成测量、取其平均值,并评价该方法可信度。 结果　60个正常DRUJ完全旋外、旋外60°、旋外30°、中立位、旋内30°、旋内60°及完全旋内桡尺比值分别为（0.29±0.05）,（0.36±0.06）,（0.42±0.07）,（0.49±0.05）,（0.53±0.06）,（0.56±0.06）,（0.61±0.07）;桡尺夹角分别为（38.41±3.71）°,（48.74±5.54）°,（63.31±4.98）°,（105.56±5.63）°,（138.68±6.04）°,（162.45±6.00）°,（178.46±2.09）°。桡尺比值与桡尺夹角呈正相关,有统计学意义（r=0.97,P<0.05）,腕关节从完全旋外向完全旋内旋转过程中,桡尺比值随桡尺夹角增大而增大。不同体位两项测量指标观察者间相关系数（ICC）范围为0.83~0.96。 结论　通过建立DRUJ在不同体位下桡骨的不同旋转角度所对应桡尺比值正常范围,可以为桡尺远侧关节不稳的诊断提供更多参考依据。     

护踝对功能性踝关节不稳患者下肢运动生物力学特征的影响

目的 探究护踝对功能性踝关节不稳(functional ankle instability,FAI)患者的保护作用,为其护踝的选择提供依据。 方法 15 名 FAI 患者随机佩戴半刚性、弹性护踝及无护踝以自选速度步行和跑步,运用红外光点运动捕捉系统和三维测力台采集其下肢运动生物力学参数。 通过 3×2 重复设计的双因素方差分析检验护踝和运动模式对下肢运动学、动力学和能量吸收的影响。 结果 护踝与运动模式对本研究中所有指标均无交互作用(P>0. 05)。不论运动模式,与无护踝相比,弹性护踝显著减少了 FAI 患者踝关节内翻角峰值、内翻角速度和踝关节能量吸收(P<0. 05),同时增加了踝关节外翻力矩( P < 0. 001);而半刚性护踝增加了踝关节内翻角峰值和内翻角速度(P<0. 05)。 此外,弹性护踝可降低着地时刻的膝关节内旋力矩和外旋力矩峰值(P<0. 05)。 结论 与无护踝相比,弹性护踝通过减小踝关节内翻角、内翻角速度和能量吸收,增大踝关节外翻力矩,继而起到预防踝关节扭伤的作用。 FAI 患者佩戴半刚性护踝后需定时关注踝关节慢性损伤风险。 整体来看,弹性护踝的防护效果可能更有效,且未引起膝关节功能补偿,可作为预防 FAI 患者踝关节扭伤的有效措施。     

The Radioulnar Distance at the Level of the Radial Tuberosity

Ruptures of the distal biceps brachii tendon are generally treated operatively due to their loss of supination and flexion force. A mechanical impingement at the insertion of the tendon at the radial tuberosity is discussed to play a role in the etiology of this injury. The aim of this study was to present a detailed, three-dimensional anatomical analysis of the radioulnar space at the radial tuberosity. A total of 166 imprints of the radioulnar space in neutral rotation and pronation from 84 cadaveric specimens of both arms using silicone impression material were produced for this study. Imprints were cut in slices of 3 mm and digitally measured after picture acquisition using a high-resolution digital camera. Distances were grouped into a proximal, central, and distal groups and used for correlation to morphometric data at the elbow (radial head diameter, ulna and radius length) as well as volume calculation. The mean radioulnar distance was 8.8 ± 4.0 mm in neutral rotation and 7.8 ± 3.9 mm in pronation. In pronation, the central zone was the smallest whereas in neutral rotation the proximal zone was the smallest. The volume of the radioulnar space did not reduce significantly during pronation. Little space is provided for the insertion of the distal biceps brachii tendon especially during pronation. This could play a role in the etiology of distal biceps brachii tendon ruptures and should be considered in the fixation after rupture of the tendon. Clin. Anat., 33:661–666, 2020. © 2019 Wiley Periodicals, Inc.     

Design and validation of a smart wearable device to prevent recurrent ankle sprain

Abstract

Lateral ankle sprain is one of the most common ankle injuries, especially in sports. When not treated properly, chronic ankle instability (CAI) may develop causing recurrent sprains and permanent damage to ankle ligaments. In this study, the design, implementation and validation of a smart wearable device connected to a smartphone application is described. This device can predict and prevent the occurrence of ankle sprain. Prediction of potentially harmful motion is achieved by continuous monitoring of ankle kinematics using inertial motion sensors. Detection of such a motion immediately triggers electrical stimulation of the peroneal muscles causing foot dorsiflexion, and hence prevents potential injury. The proposed device has the advantage of having a very short response time of eight milliseconds which is sufficient to halt the sprain motion. Laboratory validation testing using a custom designed trapdoor showed an accuracy of 96% in detecting and correcting hazardous motion. Furthermore, this device complies well with the design constrains of a wearable device such as small size and low power consumption. It is also low cost and unobtrusive due to the wireless connection between all components. Future work is recommended to test the clinical effectiveness of the proposed device in patients with CAI.     

Joint Stability Characteristics of the Ankle Complex in Female Athletes With Histories of Lateral Ankle Sprain,Part II: Clinical Experience Using Arthrometric Measurement

Context:

This is part II of a 2-part series discussing stability characteristics of the ankle complex. In part I, we used a cadaver model to examine the effects of sectioning the lateral ankle ligaments on anterior and inversion motion and stiffness of the ankle complex. In part II, we wanted to build on and apply these findings to the clinical assessment of ankle-complex motion and stiffness in a group of athletes with a history of unilateral ankle sprain.

Objective:

To examine ankle-complex motion and stiffness in a group of athletes with reported history of lateral ankle sprain.

Design:

Cross-sectional study.

Setting:

University research laboratory.

Patients or Other Participants:

Twenty-five female college athletes (age = 19.4 ± 1.4 years, height = 170.2 ± 7.4 cm, mass = 67.3 ± 10.0 kg) with histories of unilateral ankle sprain.

Intervention(s):

All ankles underwent loading with an ankle arthrometer. Ankles were tested bilaterally.

Main Outcome Measure(s):

The dependent variables were anterior displacement, anterior end-range stiffness, inversion rotation, and inversion end-range stiffness.

Results:

Anterior displacement of the ankle complex did not differ between the uninjured and sprained ankles (P = .37), whereas ankle-complex rotation was greater for the sprained ankles (P = .03). The sprained ankles had less anterior and inversion end-range stiffness than the uninjured ankles (P < .01).

Conclusions:

Changes in ankle-complex laxity and end-range stiffness were detected in ankles with histories of sprain. These results indicate the presence of altered mechanical characteristics in the soft tissues of the sprained ankles.Key Words: ankle instability, joint laxity measurement, ankle sprains

Key Points

• Ankles with histories of lateral sprain showed more ankle-complex inversion rotation and less anterior and inversion stiffness than uninjured ankles.
• The mechanical property of stiffness might be important to understanding how lateral ankle sprain affects ligamentous elasticity and joint stability.
• These clinically important findings indicate that increased ankle-complex laxity is not the only identifiable mechanical tissue characteristic that changes after lateral ankle sprain.

Ankle sprain is one of the most common injuries encountered during sporting activity.¹ Lateral ankle sprain injury can result in changes to the ligaments and surrounding soft tissues that often lead to mechanical instability and functional insufficiencies.^2–7 Equally concerning is the recurrence rate after an initial sprain.⁸ A search of epidemiologic and cohort studies identified history of lateral ankle sprain as a consistent risk factor associated with ankle sprain in sport.^8–12 Our understanding of the connection between history of ankle sprain and mechanical measures of ankle stability is unclear because not all ankles develop mechanical instability after 1 or more ankle sprains.^7,13Increased ligament laxity can result from a tear or lengthening of the involved ligamentous structures supporting the joint or less-than-optimal healing of the injured tissues.² Individuals with histories of ankle sprain present with increased joint laxity and persistent symptoms, such as the feeling of or actual giving way of the ankle during jumping and cutting activities.^14–16 However, some authors have not reported findings of increased laxity in the sprained ankles despite the presence of functional insufficiencies, such as impaired proprioception, altered neuromuscular control, strength deficits, and diminished postural control.^6,17The passive stiffness characteristics of a joint are created in part by the viscoelastic properties of the soft tissues that surround and support the joint.¹⁸ Leardini et al¹⁹ reported that passive stiffness provided by the soft tissue structures is a vital component of joint stability. Thus, the mechanical property of stiffness may be important to understanding joint stability after injury. Only Wikstrom et al²⁰ have investigated passive ankle-joint stiffness in people who reported experiencing ankle sprains. They found no differences in anterior laxity or anterior stiffness of the ankle between individuals with or without reported functional ankle instability. In a later study, Wikstrom et al⁷ reported that patients who had histories of ankle sprain and presented with no signs or symptoms of chronic ankle instability (CAI) and patients with CAI had increased anterior ankle-joint stiffness relative to uninjured control participants. When jointly examined, these previous reports appear specious because laxity and stiffness are inversely related. We wanted to build on the work of Wikstrom et al^7,20 and also examine the effects of previous lateral ankle sprain on inversion ankle-complex motion and stiffness. Therefore, the purpose of our clinically based study was to determine ankle-complex motion and stiffness in a group of athletes with a reported history of lateral ankle sprain. We hypothesized that ankles with histories of lateral sprain would demonstrate altered motion and stiffness characteristics when compared with the uninjured ankles.     

Control of grasp stability during pronation and supination movements

 We analyzed the control of grasp stability during a major manipulative function of the human hand: rotation of a grasped object by pronation and supination movement. We investigated the regulation of grip forces used to stabilize an object held by a precision grip between the thumb and index finger when subjects rotated it around a horizontal axis. Because the center of mass was located distal to the grip axis joining the fingertips, destabilizing torque tangential to the grasp surfaces developed when the grip axis rotated relative to the field of gravity. The torque load was maximal when the grip axis was horizontal and minimal when it was vertical. An instrumented test object, with a mass distribution that resulted in substantial changes in torque load during the rotation task, measured forces and torques applied by the digits. The mass distribution of the object was unpredictably changed between trials. The grip force required to stabilize the object increased directly with increasing torque load. Importantly, the grip force used by the subjects also changed in proportion to the torque load such that subjects always employed adequate safety margins against rotational slips, i.e., some 20–40% of the grip force. Rather than driven by sensory feedback pertaining to the torque load, the changes in grip force were generated as an integral part of the motor commands that accounted for the rotation movement. Subjects changed the grip force in parallel with, or even slightly ahead of, the rotation movement, whereas grip force responses elicited by externally imposed torque load changes were markedly delayed. Moreover, blocking sensory information from the digits did not appreciably change the coordination between movement and grip force. We thus conclude that the grip force was controlled by feedforward rather than by feedback mechanisms. These feedforward mechanisms would thus predict the consequences of the rotation movement in terms of changes in fingertip loads when the orientation of the grip axis changed in the field of gravity. Changes in the object’s center of mass between trials resulted in a parametric scaling of the motor commands prior to their execution. This finding suggests that the sensorimotor memories used in manipulation to adapt the motor output for the physical properties of environmental objects also encompass information related to an object’s center of mass. This information was obtained by somatosensory cues when subjects initially grasped the object with the grip axis vertical, i.e., during minimum tangential torque load. Received: 16 October 1998 / Accepted: 1 February 1999