Maria K. Lebiedowska

Definition and Classification of Negative Motor Signs in Childhood

In this report we describe the outcome of a consensus meeting that occurred at the National Institutes of Health in Bethesda, Maryland, March 12 through 14, 2005. The meeting brought together 39 specialists from multiple clinical and research disciplines including developmental pediatrics, neurology, neurosurgery, orthopedic surgery, physical therapy, occupational therapy, physical medicine and rehabilitation, neurophysiology, muscle physiology, motor control, and biomechanics. The purpose of the meeting was to establish terminology and definitions for 4 aspects of motor disorders that occur in children: weakness, reduced selective motor control, ataxia, and deficits of praxis. The purpose of the definitions is to assist communication between clinicians, select homogeneous groups of children for clinical research trials, facilitate the development of rating scales to assess improvement or deterioration with time, and eventually to better match individual children with specific therapies. “Weakness” is defined as the inability to generate normal voluntary force in a muscle or normal voluntary torque about a joint. “Reduced selective motor control” is defined as the impaired ability to isolate the activation of muscles in a selected pattern in response to demands of a voluntary posture or movement. “Ataxia” is defined as an inability to generate a normal or expected voluntary movement trajectory that cannot be attributed to weakness or involuntary muscle activity about the affected joints. “Apraxia” is defined as an impairment in the ability to accomplish previously learned and performed complex motor actions that is not explained by ataxia, reduced selective motor control, weakness, or involuntary motor activity. “Developmental dyspraxia” is defined as a failure to have ever acquired the ability to perform age-appropriate complex motor actions that is not explained by the presence of inadequate demonstration or practice, ataxia, reduced selective motor control, weakness, or involuntary motor activity.

Invariant sway properties in children

The ability to maintain upright body posture depends on the biomechanical properties of a body and on the execution of control programs. The aim of this study was to determine how the structural growth of the human body, between ages 7-18, affects spontaneous sway parameters and to determine how the visual feedback positional task changes body sway parameters. The selected parameters of postural sway were evaluated in 57 children aged 7-18, while they stood with their feet together for 30 s. The experiment consisted of two different tasks: free standing with no feedback (No feedback), and free standing with additional visual feedback (Feedback). No statistically significant correlation between sway parameters and developmental factors (body height, body mass, and age) in the No Feedback task was found. Statistically significant correlations were found between age and most of the sway parameters in the Feedback task. The execution of voluntary feedback resulted in an increase in the total sway (20%), while the total area decreased nearly two-times. The invariance of sway amplitude supports the view that the same activation patterns can be utilized by children aged 7-18, despite the changes in body dimensions.

Quantitative evaluation of reflex and voluntary activity in children with spasticity

OBJECTIVE To determine whether increased reflexes are related to functional impairment in children with spasticity. DESIGN Descriptive measurement study. SETTING Rehabilitation department in Poland. PARTICIPANTS Sixteen able-bodied children and 29 children with spasticity. INTERVENTIONS Not applicable. MAIN OUTCOME MEASURES Measurement of modulation function of knee tendon reflexes by isometric knee extension, maximum isometric knee flexion, and extension torques, and scoring of ambulation in patients. RESULTS In able-bodied children, the reflex modulation function increased with voluntary knee extension, reached maximum at 5% to 20% of voluntary extension, and then decreased. The reflex modulation function in patients fell into 2 major categories. In the majority of affected limbs, the modulation function was inverse, with maximum reflex response at relaxation, and decreased with an increase of voluntary extension. In the remaining limbs, the shape of the reflex modulation function was normal, although other parameters changed. Isometric torques decreased more in flexion (65%) than in extension (39%). A torque decrease was a result of cocontraction more often during knee flexion (65%) than in knee extension (24%). The larger the reflexes, the more flexion torque decreased and ambulation deteriorated. This pattern occurred in patients with inverse modulation function but not in those with normal modulation function. The reciprocal inhibition from knee flexors to extensors could be affected in patients with inverse modulation function and cocontraction during flexion, whereas other mechanisms occurred in other patients. CONCLUSIONS The experimental design has potential as a quantitative measure of abnormal control in children with spasticity and can lead to more precise treatment selection criteria.

Passive dynamics of the knee joint in healthy children and children affected by spastic paresis

OBJECTIVE The purposes of this study were (1) to evaluate how changes in biomechanical parameters affect segment dynamics in children and (2) to determine whether the biomechanical parameters were changed in children with spastic paresis. DESIGN In vivo measurements were collected of knee viscoelastic properties. Background. It is unknown if the inertial and viscoelastic properties of a human growing limb should be considered in motor performance. Also unclear are whether changes in passive dynamics might be responsible for abnormal control in human spastic paresis. METHOD Small oscillation techniques were used to measure moment of inertia of lower leg, stiffness and viscous damping of the knee joint. Eighty seven healthy children and 32 children with spastic paresis participated. RESULTS Moment of inertia, stiffness and the damping changed with the fifth power of childs height. Dynamic equation of motion parameters were a constant, independent of the childs height. Passive viscoelastic parameters were not changed in spastic patients. CONCLUSIONS Inertial and viscoelastic properties of a growing limb segment should not be considered in motor performance. Passive viscoelastic properties were not changed in patients with spastic paresis and, therefore, cannot be responsible for abnormal control in human spastic paresis. RELEVANCE There is no need to adapt control patterns in children (ages 6-18). Passive viscoelastic parameters cannot be used as a descriptor of spasticity.

Quantifying repeatability of the Wartenberg pendulum test parameters in children with spasticity

The Wartenberg (pendulum) test is commonly used in a variety of studies involving healthy subjects, patients with CP, stroke patients, and other neurological conditions. There is some evidence that the Wartenberg test may be able to differentiate healthy people from patients with spasticity. The aim of the study was to explore the within-session repeatability of primary outcome measures, i.e. relaxation indices derived from the Wartenberg test when test was performed by single investigator. Patients were lying supine, thigh along the horizontal line. The lower legs were allowed to hang freely over the table edge, and the knee motion in response to leg drop from the horizontal position was measured using motion system VICON with external markers attached to each leg at greater trochanter, lateral knee epicondyle, and lateral malleolus. Data from four consecutive trials were collected at 1 min intervals. The set of relaxation indices and maximum velocity was calculated for each trial. Data of 21 children (42 limbs) who underwent the evaluation due to spasticity problem were analysed. The repeated measure ANOVA test, one way analysis of variance, coefficients of correlation and determination were used to determine the repeatability of the relaxation indices, the association between the indices in time, and influence of the spasticity origin on the variability. The results show that relaxation indices, did not differ between the trails in statistically significant way in our group of patients with spasticity, however they exhibited high within-session variability in the individual patients (16-90%). Therefore the variability of the relaxation indices may restrict the clinical usefulness of the indices to monitor the changes of spasticity over time. Further, our findings do not seem to conform to the earlier reports demonstrating a systematic, time-dependent, change in the relaxation indices when repeated measures were taken within a session. In conclusion, this study demonstrates that although the Wartenberg test is repeatable in groups of patients, it does not provide us with repeatable measures in individual patients, thus if it is to be used as a replacement for other clinical tests of spasticity further investigations are needed to explain the substantial variability of the indices.

Knee resistance during passive stretch in patients with hypertonia.

The aims of the study were to determine by a portable method (1) whether velocity-dependent changes in knee resistance in patients with spastic paresis differ from those in non-disabled subjects, and (2) whether biomechanical measures of resistance can differentiate between neural and other factors that contribute to hypertonia (increased resistance). Biomechanical (hand-hold dynamometer, electrogoniometer) and bioelectrical (EMG) measures of resistance were evaluated under static (slow stretch) and dynamic (fast stretch) conditions in twenty patients with hypertonia and 19 non-disabled subjects. Measures calculated for non-disabled subjects (control limbs) were compared to those calculated for patients (spastic limbs). Biomechanical measures of resistance did not differ strongly between groups of spastic and control limbs and between spastic limbs having different origins of knee hypertonia (neural vs. other), due to substantial variability. In contrary the static and dynamic bioelectrical measures of muscles activation were substantially larger in spastic limbs than in control limbs (p<0.05). The variability of biomechanical measures of resistance was due to varied patterns of muscle activation in response to stretch. We concluded that the biomechanical measures of hypertonia did not discriminate spastic patients from non-disabled subjects. To classify various types of knee hypertonia, the portable method should include not only analysis of biomechanical but also EMG characteristics of hypertonia. It is expected that the functional status of patients would be better predicted using clinical and quantitative measures of impairment if different classes of hypertonia (defined by different patterns of activation) were analyzed separately rather than analyzing the heterogeneous patient population as a whole.

Application of biomechanical growth models of the quantitative evaluation of the motor system in children.

To evaluate the effectiveness of rehabilitation methods, and to assess the progress of the rehabilitation process in an individual patient, quantitative methods are necessary. The large number of motor system parameters makes the problem of data collection time-consuming and expensive. A quantitative evaluation of the childs motor system is an assessment of a combination of the growth and rehabilitation processes. The aim of the study was to establish methods of differentiation between these two processes. The chosen anthropometric measures, biomechanical parameters of the lower leg segment, maximal voluntary extension and flexion torques of lower leg and chosen gait parameters, were measured in various groups of healthy children 6-18 years old. Mathematical functions were calculated describing these parameters against developmental parameters (body mass, body stature, age). Using the maximal correlation criterion the best growth parameters were established. Normalized databases for these parameters were developed. It is suggested that, using their approach, differentiation between the influences of growth and rehabilitation processes can be achieved, thus eliminating the need for tedious data collection.

Changes in the lower leg moment of inertia due to child's growth

During growth the size and shape of the childs body changes. It is not clear whether the shape of a body segment changes proportionally in children between the age 5 and 18 years. The aim of this study is to describe these changes for the lower leg moment of inertia in a population of children. The segment moment of inertia describes the mass distribution along the body segment axis. The moment of inertia of the lower leg (including the foot) was measured by the free oscillation technique in 90 healthy children (61 boys and 29 girls) between and 5 and 18 years of age. The period of free oscillation was measured with and without external mass loading. The moment of inertia was calculated using a relation between the mass and the period of oscillation. A two-cylinder model of constant body density was used to predict the moment of inertia. Anthropometric measurements of length of the lower leg and foot, the circumference of the knee, ankle and foot were made. Experimental and model data of the lower leg of inertia were described by a fifth power function of body height. The experimental and model data showed high degree of convergence, confirming that the segment growth of the human body can be treated like the volume growth of a cylindrical object of constant body density. Thus it was experimentally confirmed that the lower leg segment growth between age 5 and 18 years may be considered as proportional.

THE INFLUENCE OF FOOT POSITION ON BODY DYNAMICS

During locomotion, the human body exhibits inherent dynamic properties such as mass (M), stiffness (K) and damping (B). During the gait cycle, foot contact with the ground progresses from the heel to the toe. Contact forces between the foot and ground are defined as ground reaction forces (GRF). It is unclear how body dynamics are affected by foot landing position. If the shape of GRF is indicative of body dynamics, our understanding of gait patterns in normal and pathologic conditions may improve. The aims of this study were to determine:(1) whether foot landing position affects the inherent dynamics of the human body and (2) the extent to which the GRF curve reflects the response of inherent body dynamics to sudden loading. Eight non-disabled control volunteers performed a series of small jumps and landed on one leg with a fully extended knee in three foot landing positions: heel, mid-foot, and toe. They then walked at self-paced velocity over force plates. For each foot landing position, values of K, B and the dimensionless damping coefficient, xi, were calculated from the period of vertical body oscillations, T, and compared with an ANOVA test. In addition, the time between the two peaks of the vertical GRF, T(GRF), was compared with T. We found that that K and B decreased and xi did not change (p<0.01) between heel to toe-landing positions. T(GRF) was not different than T for the toe-landing position, which suggests that the dynamic body response has major impact on the shape of GRF.

Knee joint angular velocities and accelerations during the patellar tendon jerk.

Tendon jerk (TJ) is one of the most commonly used clinical tests in differential diagnosis of human motor disorders. There remains some ambiguity in the physiological interpretation of the test, especially with respect to its association to the functional status of patients. The TJ test inputs a non-physiological stimuli, but it is unclear to what degree the kinematics generated during the TJ test exceed the ranges that muscles encounter in activities of daily living (ADLs). The aim of our pilot study was to determine the range of angular knee kinematics (angular velocities and accelerations) corresponding to the muscle stretch elicited by TJ. We measured the longitudinal kinematics (velocities and accelerations) of the rectus femoris muscle in vivo using vector tissue Doppler imaging, an ultrasound-based method, and measured the angular kinematics of the knee in response to tendon taps with an electrogoniometer. We concluded that muscle longitudinal elongation accelerations elicited during the standard TJ test exceed angular accelerations (104.40-4534.20 rads⁻²) encountered in typical ADLs, but the velocities (0.82-6.21 rads⁻¹) elicited do not exceed those elicited by ADLs.