Kinematical measure for spastic reaching in children with cerebral palsy

Abstract

Background. Practitioners need more sensitive measure to quantify reaching movement for judgment of the treatment effects and reflecting the degrees of motor impairment in upper extremities. The purposes of this study were to identify the specific kinematic characteristics between normal and spastic reaching under different levels of accuracy, and to determine the most sensitive kinematic variable for quantifying the interference of spasticity on reaching.

Methods. Ten normal subjects as control group and ten subjects with spastic cerebral palsy as experimental group were studied. Participants were asked to reach, at a self-selected pace, toward two different sizes of buttons (one with accuracy constraint and the other with non-accuracy constraint) away from normalized distance. Motion analysis system was used to record the trajectory of reaching performance. Kinematic variables of reaching movement were computed and analyzed.

Findings. Measure for movement smoothness presented larger effect size (0.24–0.43) than other kinematic variables adopted in this study. Under high-accuracy reaching, children with spastic cerebral palsy had a prolonged movement time than normal children (P < 0.05). Modified Ashworth score was significantly correlated to normalized jerk score, number of movement unit and movement time (r = 0.56–0.75). Number of movement unit was the most sensitive kinematic variable to discriminate between normal and spastic reaching.

Interpretation. Development of reliable, valid, and sensitive multi-joint biomechanical evaluation is required, particularly for natural and goal-oriented reaching movement. It is concluded that measure of movement smoothness may be applied as valid and sensitive index to quantify the level of coordinative motor performance for subjects with spastic movement disorder.

Introduction

Reach and grasp movements are basic and important upper arm motor components in completing daily living activities such as self-feeding, opening a door, operation of a button or switch, etc. Children with cerebral palsy (CP) often demonstrate unique motor impairments, such as spastic or athetoid movement, in the upper extremity during executing daily living activities. These impairments, from mild to severe, may restrict the patient from learning adaptive skills (e.g., manipulating in new environments and controlling electronic aids). Reaching has been defined as the voluntary positioning of the hand at or near a desired location so that it may interact with the environment. Performance of reach movement may be used to reflect the coordination of multiple joints and involvement of both the musculoskeletal and neural system (Edwards and Humphreys, 1999). Thus, it is very important to evaluate reaching with quantitative method for rehabilitation practitioners and researchers to objectively describe the coordination and functional status of the impaired upper limb.

Kinematic analysis in reaching performance would provide a more sensitive way to evaluate treatment and progression of a wide variety of motor disorder conditions. The forward reaching movements in children with CP with quantitative measures of the elbow kinematics, and found ataxic subjects were characterized by lower peak velocities, prolonged durations, and increased variability compared with normal subjects (Ramos et al., 1997). Treatment effect study used kinematic evaluation to assess the effect of neurodevelopment treatment on reach movement for spastic CP and found both movement time (MT) and movement units were reduced after treatments (Fetters and Kluzik, 1996). A movement unit is defined as one crossing of the zero line in the acceleration trace. Another kinematics study also showed that providing a task with natural and functional context for reach movement would elicit better quality of reaching for the non-affected, particularly the affected arm for children with spastic hemiparesis (Volman et al., 2002). Other studies have examined the reaching kinematics in normal, Parkinson’s disease (Alberts et al., 2000; Castiello et al., 2000; Poizner et al., 2000), and stroke subjects (Trombly, 1993; Wu et al., 2000). These kinematic studies in reaching performance have generally found that subjects with movement disorders have increased movement duration, decreased velocity, increased segmentation, and increased variability in path trajectory. Additionally, subjects with movement disorders significantly show less smooth and continuous in path trajectory when reaching to an object with more accuracy constraints (Alberts et al., 2000).

Assessment of reaching with kinematic analysis is considered as “a strategy level assessment” in upper arm and hand function (Duff et al., 2001). There are many kinematic variables, which will be utilized to reflect the characteristics of reaching. By quantification of specific kinematic reaching parameters, key component can be identified and the influence of motor impairment on reaching can be carefully analyzed. Consequently, specific kinematic parameters with large effect size can provide therapists with a sensitive way to measure the treatment efficacy, and to analyze the influence of different levels of motor dysfunction on upper arm control during carrying out activities with various accuracy demanded. A better understanding of this information will give insight to evaluate treatment and progression of a wide variety of motor disorder conditions, such as CP, stroke, and Parkinson’s diseases (Kluzik et al., 1990; Ramos et al., 1997; Rash et al., 1999).

It is well known that spasticity is one of the major motor problems for patient with upper motor neuron disease. Few researches have been conducted to determine the sensitivity of kinematic variables for detecting the influences of spasticity on control of functional reaching. The purposes of this study were to assess the differences in kinematics between normal and spastic reaching under different levels of accuracy constraint, to analyze the relationships between levels of spasticity and significant kinematic variables, and finally to find parsimonious measures for quantifying impact of spasticity on reaching in children with CP.