Contribution of Different Impairments to Restricted Knee Flexion during Gait in Individuals with Cerebral Palsy.

The coexistence of overlapping impairments modulates the knee pattern in the swing phase of walking in children with cerebral palsy (CP). The impact and contribution of each impairment to the reduction of knee range-of-motion is unknown. The aim of the study was to establish the gradation of the impact of individual coexisting impairments on the knee flexion range-of-motion. Passive range-of-motion, selective motor control, strength, and spasticity from 132 patients (Male = 76, Female = 56, age:11 ± 4 years) with spastic CP were tested with clinical tools. Knee flexion range-of-motion at terminal stance, pre-swing, and initial swing phases were assessed by gait analysis. Hypertonia (ß = −5.75) and weakness (ß = 2.76) of knee extensors were associated with lower range of knee flexion (R2 = 0.0801, F = 11.0963, p < 0.0001). The predictive factors (R2 = 0.0744, F = 7.2135, p < 0.0001) were strength (ß = 4.04) and spasticity (ß = −2.74) of knee extensors and strength of hip flexors (ß = −2.01); in swing those were knee extensors hypertonia (ß = −2.55) and passive range of flexion (ß = 0.16) (R2 = 0.0398, F = 3.4010, p = 0.01). Hypertonia of knee extensors has the strongest impact on knee flexion range-of-motion; secondary is the strength of knee extensors. The knee extensors strength with knee extensors hypertonia and strength of hip flexors contributes in stance. Knee extensors hypertonia with passive knee flexion range-of-motion contributes in swing.

Visual and proprioceptive feedback improves knee joint position sense.

Joint position sense (JPS), one method to assess proprioception, is the ability to replicate a target limb position. Feedback is commonly used to improve motor performance but it has not been demonstrated to improve JPS. The purpose of this study was to determine if feedback decreases error associated with knee JPS at three movement velocities. Healthy volunteers sat with their hip and knees flexed. The knee was passively extended at three velocities (0.5, 2, and 10 degrees/s). Subjects were instructed to stop knee motion, via a thumb switch, at a 20 degrees knee flexion target. Following movement, each subject received visual and proprioceptive feedback indicating final leg position relative to the target position. Movement velocities and times (4 s, 5 s, 6 s) were randomly presented so subjects could not predict the target position. Measures of JPS included constant error (CE), absolute error (AE), variable error (VE), and percent correct (%CORR). Significant decreases in CE, AE, and VE as well as an increase in %CORR were demonstrated. The majority of JPS improvement (85%) occurred by the tenth trial. Short-term improvements in JPS may be the result of temporary CNS adaptations via feedback that was provided to subjects. Long-term learning of JPS enhancement needs further investigation.

The popliteal angle tests in patients with cerebral palsy.

The aims were to determine during the popliteal angle (PA) tests whether particular knee muscles are activated and whether the position of pelvis affects the level of muscles activation. Twenty-two patients with cerebral palsy were recruited (age: 14±4.94 years). Knee muscle activities and range of motion were measured during PA. Knee flexors were active during tests, with fivefold increase of activation of ipsilateral hamstring. Higher and more frequent activation of muscles only in the contralateral limb was seen. Muscles activation should be considered as a confounding factor during tests. PA should not be relied upon as a major criterion for the treatment selection in cerebral palsy.

Human body shape index based on an experimentally derived model of human growth.

OBJECTIVES: To test the assumption of geometrically similar growth by developing experimentally derived models of human body growth during the age interval of 5 to 18 years; to use these derived growth models to establish a new human body shape index (HBSI) based on natural age-related changes in human body shape (HBS); and to compare various metrics of relative body weight (body mass index [BMI], ponderal index [PI], and HBSI) in a sample of 5- to 18-year-old children. STUDY DESIGN: Nondisabled Polish children (n = 847) participated in this descriptive study. To model growth, the best fit between body height (H) and body mass (M) was calculated for each sex using the allometric equation M = m(i) H(chi). HBSI was calculated separately for girls and boys, using sex-specific values for chi and a general HBSI from combined data. The customary BMI and PI were calculated and compared with HBSI values. RESULTS: The models of growth were M = 13.11H(2.84) (R2 = 0.90) for girls and M = 13.64H(2.68) (R2 = 0.91) for boys. HBSI values contained less inherent variability and were less influenced by growth (age and height) compared with BMI and PI. CONCLUSIONS: Age-related growth during childhood is sex-specific and not geometrically similar. Therefore, indices of HBS formulated from experimentally derived models of human growth are superior to customary geometric similarity-based indices for characterizing HBS in children during the formative growth years.

The kinematic consequences of invariant dynamics in children 6-18 years of age.

The effect of limb dynamics on trajectory formation is unclear. The natural frequency of a limb is the major factor in its dynamics. It has previously been shown with an indirect measurement method that the natural frequency of body segments is invariant during human growth from the age of 6 to 18. The aim of our study was to determine, using a direct measurement method, whether human growth affects: (1) lower limb dynamics (i.e. the natural frequency of the lower leg) and (2) the maximum velocities of the knee during selected motor tasks. In 20 non-disabled children, 6-18 years of age, measurements were taken of the natural frequency of the lower leg (including the foot), and the maximum velocities of knee flexion and extension during voluntary movement (MVV) and at initial and terminal swing phases of self-paced walking (WAL). The velocities were also estimated using a dynamic model and the results were compared to the measured velocities with a paired t-test. Correlations among the frequencies, velocities, and body height (an indicator of growth) were calculated. The natural frequency of the lower leg (mean+/-standard deviation, omega(0)=6.58+/-0.54s(-1)), maximum velocities of knee extension and flexion during voluntary movement (MVV(e)=10.1+/-1.8rads(-1) and MVV(f)=7.8+/-1.3rads(-1), respectively), and maximum velocities of knee flexion and extension during the swing phase of walking (WAL(f)=5.4+/-0.6rads(-1) and WAL(e)=6.3+/-0.87rads(-1), respectively) were each found to be independent of body height. The MVV measured velocities were 22% larger and WAL(f) measured velocities were 25% smaller than the velocities predicted from the dynamic model (p<0.05). The study found that a segment's dynamic properties, as well as selected kinematics, may be considered invariant with human growth.

Validation of Manual Muscle Testing (MMT) in children and adolescents with cerebral palsy.

BACKGROUND: Weakness is a major impairment in many movement disorders, including cerebral palsy (CP), which presents as a decrease in muscle strength. Manual muscle testing (MMT) is very popular in clinical practice, however it has many limitations. OBJECTIVE: (1) Whether maximum voluntary contraction (MVC) measures differ across clinical MMT groups; (2) Whether an association exists between clinical MMT score groups and instrumental MVC measures. METHODS: Twenty-one participants with spastic CP were recruited (11 females and 10 males; age = 13.46±3.62 years). To achieve the aims of the study, we investigated the relationship between qualitative (MMT) and instrumental (MVC) measures of knee flexor muscles' strength in patients with CP. RESULTS: MVC values increased somewhat proportionally with increasing MMT score group (p = 0.032, MS = 207.54, F = 3.75). The differences in MVC values was only statistically significant between score groups 3 and 5. A weak correlation (R = 0.4, MVC = -2.54 + 4.50 MMT, p < 0.01) was found between measured MVCs and the MMT score groups. CONCLUSIONS: In pediatric research studies, instrumental MVC should be preferred over MMT scoring. Also, MMT score groups higher than 3 should be modified in clinical testing of children and adolescents with cerebral palsy.

Assessment of selective motor control in clinical Gillette's test using electromyography.

BACKGROUND: Selective motor control (SMC), the ability to isolate selected muscle activation during a functional task, is often impaired. Gillette's SMC scale is commonly used to classify the impairment level; however it may not be sensitive to muscle coactivation. AIM: To characterize differences in muscle activation levels and coactivation incidence in Gillette's SMC grade levels. DESIGN: Non-randomized observational study. SETTING: Participants were recruited and examined in the motion analysis laboratory of a university hospital. POPULATION: Forty-two participants were enrolled: 23 patients with CP (13 females, 10 males; 15±5.59 years, range: 7-28 years; bilateral involvement; GMFCS levels I to III) and 19 able-bodied volunteers (14 females, 5 males; 22±1.54 years, range: 20-24 years). METHODS: Participants flexed each knee three times at self-paced velocity. Each limb was classified into one of three types using Gillette's SMC scale: Type 0 (CP limbs with no ability to isolate movement), Type 2 (CP limbs with complete isolation of movement) and Type C (Control limbs of able-bodied volunteers). Surface electromyography recorded muscle activation levels of hamstring, rectus femoris, hip adductor, gastrocnemius and tibialis anterior muscles. We applied the Friedman ANOVA χ2 Test to analyze muscle co-activation incidence and Kruskal-Wallis ANOVA and Median Tests to analyze muscle activation levels. We used the Wilcoxon Matched-Pairs Test to compare results between SMC Types. RESULTS: Comparing mean activation levels of the majority of muscles, we found: CP limbs (Type 0+2) > Control limbs (P<0.001); Type 0 > Type 2 (P<0.05); and Type 2 > Type C (P<0.01). The incidence of muscle co-activation was affected by CP (P=0.008) and differed by SMC type (P<0.001). CONCLUSIONS: Our quantitative study confirmed that SMC is worse in Gillette's Type 0 limbs than in Type 2 limbs. We also found that the SMC of Type 2 limbs of CP patients in CP patents is not equivalent to that of Type 2 limbs in able-bodied volunteers. CLINICAL REHABILITATION IMPACT: A better characterization of this clinical test will help gauge its usefulness in evaluating the effectiveness of rehabilitation treatments.

The role of exaggerated patellar tendon reflex in knee joint position sense in patients with cerebral palsy.

The aim of this pilot study was to determine if exaggerated patellar tendon jerk affects knee joint position sense (JPS) in cerebral palsy (CP) patients, by comparing JPS of the knee between participants with normal and exaggerated reflexes. The thresholds for reflex classification were based upon the data from able-bodied volunteers. JPS was measured as the ability of a subject (with eyes closed) to replicate a knee joint position demonstrated by an examiner. Tendon jerk was measured as the moment of force in response to patellar tendon taps. Data was collected from 27 limbs of CP patients (N=14) and 36 limbs of able-bodied volunteers (N=18). JPS was less accurate (p=0.014) in limbs with non-exaggerated reflexes (50.28±43.63%) than in control limbs (11.84±10.85%). There was no significant difference (p=0.08) in JPS accuracy between limbs with exaggerated reflexes (18.66±15.50%) and control limbs. Our data suggests that one component of sensorimotor impairment, JPS, is not as commonly affected in CP patients as previously reported. JPS of the knee is reduced in limbs with non-exaggerated reflexes; however in limbs with exaggerated reflexes which is seen in the majority of CP patients, JPS is not affected.

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.

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.

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.

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.

Gastrocnemius fascicle length changes with two-joint passive movements.

Predicting muscle fascicle length changes during passive movements may lead to a better understanding of muscle function. The purpose of this study was to experimentally compare fascicle length changes in the gastrocnemius during two-joint passive movements with a previously derived kinematic model based on anatomical measures from a cadaver. The ratio of passive ankle to knee motion was manipulated to generate medial gastrocnemius fascicle elongation and lateral gastrocnemius fascicle shortening. Ultrasound images from both heads of the gastrocnemius fascicles were acquired at 10 degrees knee flexion increments and compared with this kinematic model. Our results suggest that the two-joint kinematic model from which we originally based our knee and ankle movements did not adequately reflect fascicle length changes during any of the movement conditions in this study. From our data, we propose that for every degree of ankle motion the medial and lateral gastrocnemius changes 0.42 mm and 0.96 mm, respectively, whereas changes of 0.14 mm and 0.22 mm are observed for the medial and lateral gastrocnemius, respectively, during knee movements.

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.

Biomechanic characteristics of patients with spastic and dystonic hypertonia in cerebral palsy.

OBJECTIVE: To determine what biomechanic characteristics of knee joint motion and walking show potential to quantitatively differentiate spasticity and dystonia in cerebral palsy (CP). DESIGN: Descriptive measurement study. SETTING: University hospital. PARTICIPANTS: Seventeen pediatric and adult patients with CP. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: We measured the resistance of the knee joint at different velocities and positions, maximum muscle activation during external motion, amplitude of knee tendon reflexes, maximum isometric flexion and extension torques, velocity of walking, and knee kinematics during the gait cycle. Patients were classified into 2 groups (dystonia or spasticity) if at least 2 of 3 physicians agreed that a prominent component of dystonia was present. RESULTS: Patients with dystonia had a greater degree of co-contraction and an increased resistance to external motion at slow velocities. The tendon reflexes were almost normal in patients with dystonia, whereas they were increased in patients with spasticity. Muscle strength was more impaired in patients with dystonia, probably as a result of greater muscle co-contraction. They also walked slower, with smaller knee ranges of motion, during the stance phase of walking. CONCLUSIONS: The measurement of resistance and of muscle activation during passive motion and tendon reflexes shows potential to differentiate dystonia from spasticity in CP patients with a mixed form of hypertonia. More studies are needed to confirm these results.