Evaluation of triceps surae muscle length and resistance to passive lengthening in patients with acquired brain injury

Gastrocnemius Medialis Muscle Geometry and Extensibility in Typically Developing Children and Children With Spastic Paresis Aged 6-13 Years

Gait of children with spastic paresis (SP) is frequently characterized by a reduced ankle range of motion, presumably due to reduced extensibility of the triceps surae (TS) muscle. Little is known about how morphological muscle characteristics in SP children are affected. The aim of this study was to compare gastrocnemius medialis (GM) muscle geometry and extensibility in children with SP with those of typically developing (TD) children and assess how GM morphology is related to its extensibility. Thirteen children with SP, of which 10 with a diagnosis of spastic cerebral palsy and three with SP of unknown etiology (mean age 9.7 ± 2.1 years; GMFCS: I-III), and 14 TD children (mean age 9.3 ± 1.7 years) took part in this study. GM geometry was assessed using 3D ultrasound imaging at 0 and 4 Nm externally imposed dorsal flexion ankle moments. GM extensibility was defined as its absolute length change between the externally applied 0 and 4 Nm moments. Anthropometric variables and GM extensibility did not differ between the SP and TD groups. While in both groups, GM muscle volume correlated with body mass, the slope of the regression line in TD was substantially higher than that in SP (TD = 3.3 ml/kg; SP = 1.3 ml/kg, p < 0.01). In TD, GM fascicle length increased with age, lower leg length and body mass, whereas in SP children, fascicle length did not correlate with any of these variables. However, the increase in GM physiological cross-sectional area as a function of body mass did not differ between SP and TD children. Increases in lengths of tendinous structures in children with SP exceeded those observed in TD children (TD = 0.85 cm/cm; SP = 1.16 cm/cm, p < 0.01) and even exceeded lower-leg length increases. In addition, only for children with SP, body mass (r = -0.61), height (r = -0.66), muscle volume (r = - 0.66), physiological cross-sectional area (r = - 0.59), and tendon length (r = -0.68) showed a negative association with GM extensibility. Such negative associations were not found for TD children. In conclusion, physiological cross-sectional area and length of the tendinous structures are positively associated with age and negatively associated with extensibility in children with SP.

Robot-Assisted Rehabilitation of Ankle Plantar Flexors Spasticity: A 3-Month Study with Proprioceptive Neuromuscular Facilitation

In this paper, we aim to investigate the effect of proprioceptive neuromuscular facilitation (PNF)-based rehabilitation for ankle plantar flexors spasticity by using a Robotic Ankle-foot Rehabilitation System (RARS). A modified robot-assisted system was proposed, and seven poststroke patients with hemiplegic spastic ankles participated in a 3-month robotic PNF training. Their impaired sides were used as the experimental group, while their unimpaired sides as the control group. A robotic intervention for the experimental group started from a 2-min passive stretching to warming-up or relaxing the soleus and gastrocnemius muscles and also ended with the same one. Then a PNF training session including 30 trials was activated between them. The rehabilitation trainings were carried out three times a week as an addition to their regular rehabilitation exercise. Passive range of motion, resistance torque, and stiffness were measured in both ankles before and after the interventions. The changes in Achilles tendon length, walking speed, and lower limb function were also evaluated by the same physician or physiotherapist for each participant. Biomechanical measurements before interventions showed significant difference between the experimental group and the control group due to ankle spasticity. For the control group, there was no significant difference in the 3 months with no robotic intervention. But for the experimental group, passive dorsiflexion range of motion increased (p < 0.01), resistance torque under different dorsiflexion angle levels (0°, 10°, and 20°) decreased (p < 0.05, p < 0.001, and p < 0.001, respectively), and quasi-static stiffness under different dorsiflexion angle levels (0°, 10°, and 20°) also decreased (p < 0.01, p < 0.001, and p < 0.001, respectively). Achilles's tendon length shortened (p < 0.01), while its thickness showed no significant change (p > 0.05). The robotic rehabilitation also improved the muscle strength (p < 0.01) and muscle control performance (p < 0.001). In addition, improvements were observed in clinical and functional measurements, such as Timed Up-and-Go (p < 0.05), normal walking speed (p > 0.05), and fast walking speed (p < 0.05). These results indicated that the PNF-based robotic intervention could significantly alleviate lower limb spasticity and improve the motor function in chronic stroke participant. The robotic system could potentially be used as an effective tool in poststroke rehabilitation training.

Multivariable static ankle mechanical impedance with relaxed muscles

Quantitative characterization of ankle mechanical impedance is important to understand how the ankle supports lower-extremity functions during interaction with the environment. This paper reports a novel procedure to characterize static multivariable ankle mechanical impedance. An experimental protocol using a wearable therapeutic robot, Anklebot, enabled reliable measurement of torque and angle data in multiple degrees of freedom simultaneously, a combination of inversion-eversion and dorsiflexion-plantarflexion. The measured multivariable torque-angle relation was represented as a vector field, and approximated using a method based on thin-plate spline smoothing with generalized cross validation. The vector field enabled assessment of several important characteristics of static ankle mechanical impedance, which are not available from prior single degree of freedom studies: the directional variation of ankle mechanical impedance, the extent to which the ankle behaves as a spring, and evidence of uniquely neural contributions. The method was validated by testing a simple physical "mock-up" consisting of passive elements. Experiments with young unimpaired subjects quantified the behavior of the maximally relaxed human ankle, showing that ankle mechanical impedance is spring-like but strongly direction-dependent, being weakest in inversion. Remarkably, the analysis was sufficiently sensitive to detect a subtle but statistically significant deviation from spring-like behavior if subjects were not fully relaxed. This method may provide new insight about the function of the ankle, both unimpaired and after biomechanical or neurological injury.

Measurement of passive ankle stiffness in subjects with chronic hemiparesis using a novel ankle robot

Our objective in this study was to assess passive mechanical stiffness in the ankle of chronic hemiparetic stroke survivors and to compare it with those of healthy young and older (age-matched) individuals. Given the importance of the ankle during locomotion, an accurate estimate of passive ankle stiffness would be valuable for locomotor rehabilitation, potentially providing a measure of recovery and a quantitative basis to design treatment protocols. Using a novel ankle robot, we characterized passive ankle stiffness both in sagittal and in frontal planes by applying perturbations to the ankle joint over the entire range of motion with subjects in a relaxed state. We found that passive stiffness of the affected ankle joint was significantly higher in chronic stroke survivors than in healthy adults of a similar cohort, both in the sagittal as well as frontal plane of movement, in three out of four directions tested with indistinguishable stiffness values in plantarflexion direction. Our findings are comparable to the literature, thus indicating its plausibility, and, to our knowledge, report for the first time passive stiffness in the frontal plane for persons with chronic stroke and older healthy adults.

Non-surgical management of ankle contracture following acquired brain injury

BACKGROUND AND PURPOSE

The purpose of this study was to document the outcome of non-surgical management of equinovarus ankle contracture in a cohort of patients with acquired brain injury admitted to a specialist Neurosurgical Rehabilitation Unit.

METHODS

This prospective descriptive study examined all patients with a new diagnosis of moderate to severe acquired brain injury (Glasgow Coma Scale score </=12) admitted for rehabilitation over a 1 year period. Ankle dorsiflexion range and plantarflexor/invertor muscle activity were evaluated weekly during the period of hospitalization. Contracture was defined as maximal passive range of motion </= 0 degrees dorsiflexion, with the knee extended, on a minimum of two measurement occasions. Patients were retrospectively allocated to one of four treatment outcome categories according to ankle dorsiflexion range, type of intervention required and response to treatment.

RESULTS

Ankle contracture was identified in 40 of the 105 patients studied. Contracture resolved with a standard physiotherapy treatment programme, including prolonged weight-bearing stretches and motor re-education, in 23 patients. Contracture persisted or worsened in 17 of 40 cases, all of whom exhibited dystonic muscle overactivity producing sustained equinovarus posturing. Ten of 17 cases required serial plaster casting (+/- injection of botulinum toxin type A) in order to achieve a functional range of ankle motion. Remediation of ankle contracture was not considered a priority in the remaining seven patients due to the severity of their overall disability.

CONCLUSION

The incidence of ankle contracture identified in this population was considerably less than previously reported. Reduced dorsiflexion range was remediated with standard physiotherapy treatment in over half of the cases. Additional treatment with serial casting +/- botulinum toxin type-A injection was required to correct persistent or worsening contracture in one quarter of cases. Dystonic extensor muscle overactivity was a major contributor to persistent or progressive ankle contracture.

Changes in passive mechanical properties of the gastrocnemius muscle at the muscle fascicle and joint levels in stroke survivors

OBJECTIVES

To investigate the ankle joint-level and muscle fascicle-level changes and their correlations in stroke survivors with spasticity, contracture, and/or muscle weakness at the ankle.

DESIGN

To investigate the fascicular changes of the medial gastrocnemius muscle using ultrasonography and the biomechanical changes at the ankle joint across 0 degrees, 30 degrees, 60 degrees, and 90 degrees knee flexion in a case-control manner.

SETTING

Research laboratory in a rehabilitation hospital.

PARTICIPANTS

Stroke survivors (n=10) with ankle spasticity/contracture and healthy control subjects (n=10).

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASUREMENTS

At the muscle fascicle level, medial gastrocnemius muscle architecture including the fascicular length, pennation angle, and thickness were evaluated in vivo with the knee and ankle flexion changed systematically. At the joint level, the ankle range of motion (ROM) and stiffness were determined across the range of 0 degrees to 90 degrees knee flexion.

RESULTS

At comparable joint positions, stroke survivors showed reduced muscle fascicle length, especially in ankle dorsiflexion (P< or =.048) and smaller pennation angle, especially for more extended knee positions (P< or =.049) than those of healthy control subjects. At comparable passive gastrocnemius force, stroke survivors showed higher fascicular stiffness (P< or =.044) and shorter fascicle length (P< or =.025) than controls. The fascicle-level changes of decreased muscle fascicle length and pennation angle and increased medial gastrocnemius fascicle stiffness in stroke were correlated with the joint level changes of increased joint stiffness and decreased ROM (P<.05).

CONCLUSIONS

This study evaluated specific muscle fascicular changes as mechanisms underlying spasticity, contracture, and joint-level impairments, which may help improve stroke rehabilitation and outcome evaluation.

In vivo biomechanical evaluations of the medial gastrocnemius: changes in muscle properties in stroke survivors

Patients post stroke showed substantial changes in biomechanical properties of the ankle and knee joints. However, it is not clear what the underlying mechanisms are in the hypertonic calf muscles in stroke survivors. Biomechanical properties of the medial gastrocnemius muscle in both stroke survivors and healthy subjects were investigated in vivo and noninvasively. A programmable electrical stimulator was used to activate the medial gastrocnemius selectively and a GE LOGIQ-9 ultrasound machine was used to register the muscle images across the fiber lengths to examine its biomechanical properties in vivo. It was found that 1) stroke survivors showed shorter muscle fiber length; 2) stroke survivors' muscles had smaller pennation angles both anteriorly and posteriorly; 3) stroke survivors demonstrated an active torque-angle curve shifted towards dorsi-flexion, compared with healthy control subjects.

Biomechanic changes in passive properties of hemiplegic ankles with spastic hypertonia11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the author(s) or upon any organization with which the author(s) is/are associated

OBJECTIVE

To investigate quantitatively biomechanic changes in the passive properties of hemiplegic spastic ankles.

DESIGN

Evaluation of spastic hypertonia by moving the ankle joint slowly between dorsiflexion and plantarflexion extreme positions under controlled joint torque and position.

SETTING

Institutional research center.

PARTICIPANTS

Twenty-four stroke patients with spastic ankles and 32 healthy controls.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURES

Passive resistance torque at controlled dorsiflexion and plantarflexion positions, dorsiflexion and plantarflexion range of motion (ROM) at controlled torques, and quasistatic stiffness and energy loss in dorsiflexion and plantarflexion.

RESULTS

Spastic hypertonic ankles showed significant alterations of the passive properties in plantarflexion (P=.041) as well as in dorsiflexion (P=.016) directions. Compared with healthy controls, spastic ankles showed higher resistance torque (9.51+/-4.79Nm vs 6.21+/-3.64Nm, P=.016), higher quasistatic stiffness (.54+/-.19Nm/deg vs .35+/-.20Nm/deg, P=.001) at 10 degrees of dorsiflexion, larger normalized dorsiflexion energy loss (.068+/-.04J/deg vs .04+/-.02J/deg, P=.037), and decreased dorsiflexion ROM at 10Nm of resistance torque (10.77 degrees +/-8.69 degrees vs 20.02 degrees +/-11.67 degrees , P=.014). The resistance torque, ROM, and stiffness of spastic hypertonic ankles in plantarflexion showed similar changes (P<.05) to those in dorsiflexion. The passive ROM, joint stiffness, and resistance torque at controlled positions correlated with each other and also correlated with the Modified Ashworth Scale (P<.01).

CONCLUSIONS

Various biomechanic changes in both plantar- and dorsiflexors are associated with spastic hypertonia of chronic stroke patients, and they can be evaluated quantitatively under well-controlled conditions. With simplifications, the various measures in this study can potentially be used to obtain more comprehensive and quantitative evaluations of spastic hypertonia in a clinical setting.

Velocity dependent passive plantarflexor resistive torque in patients with acquired brain injury

OBJECTIVES

This study sought to determine whether factors other than stretch reflex excitability contribute to velocity dependent passive plantarflexor resistive torque following brain injury.

BACKGROUND

In patients with acquired brain injury increased resistance to passive muscle lengthening commonly results from abnormal muscle contraction, secondary to disinhibition of descending motor pathways, in addition to rheologic changes within the musculo-tendinous unit. Hyper-excitable tonic stretch reflex responses (spasticity) have traditionally been considered to be the main factor influencing resistance that is velocity dependent.

METHODS

Ten adults with brain injury and eighteen age matched controls were studied. A computer controlled torque measurement system was utilised to evaluate resistance to dorsiflexion stretches at two velocities (5 degrees and 25 degrees s(-1)). Only stretches which did not evoke muscle contraction were included in the data analysis. The mean difference and 95% confidence limits in passive plantarflexor resistive torque at two stretch velocities, measured over a defined portion of the test movement, were compared between subject groups.

RESULTS

A velocity dependent increase in passive plantarflexor resistive torque was evident when the ankle was dorsiflexed past the neutral position in both subjects with brain injury and controls. However, the mean difference was approximately 10 times greater in neurologically impaired limbs compared with control values.

CONCLUSIONS

These data indicate that an important component of velocity dependent resistance to passive muscle lengthening in adults with brain injury can be mechanical, and unrelated to stretch induced reflex muscle contraction.

RELEVANCE

Increased resistive torque during rapid muscle lengthening may represent a compensatory adaptation for reduced distal motor control following brain injury. A velocity dependent increase in passive plantarflexor resistive torque has the potential to improve stability during gait and provide mechanical resistance to sudden external perturbations.