Quantitative parameters to define the angle and severity of the catch in children with spastic cerebral palsy

Abstract

Introduction: The angle at which a clinician encounters a catch sensation during a fast stretch of a spastic muscle is called the angle of catch (AOC). The AOC is commonly measured using the Tardieu Scale (TS) [1], a subjective scale whose reliability or validity have been questioned [2]. Biomechanical techniques based on individual signal data (angular deceleration [2] and torque [3]) have recently been suggested as objective alternatives to define the AOC. However, we believe that integration of all signals may provide an improved quantification of the AOC, as well as additional measures for the severity of a catch. A new objective definition and severity indicator, which combines both torque and angular velocity, is introduced: the angle corresponding to the time ofmaximal power absorption. The psychometric properties of different AOC definitions and severity indicators were explored in two spastic muscles in children with cerebral palsy (CP). Patients/materials andmethods:Thegastrocnemius (GAS) and medial hamstrings (MEH) of 46 children with CP (9±3.3 years, 22 males) were stretched by passively moving the knee or ankle joint through the full range of motion (ROM) as fast as possible. Twelve children were re-tested after 11.6±7.9 days. During the stretches, joint angle characteristics, torque, and surface EMG (sEMG) were simultaneously collected. AOC 1, 2 and 3 were estimated based on maximum angular deceleration [2], maximum change in torque (dT/dt) [3] and maximal power absorption respectively. AOC 1, 2 and 3 were expressed as a percentage of the full ROM. Between session repeatability was calculated by ICC (1, k) and SEM [4]. To explorevalidity, parameterswere comparedusingSpearman’s rank order correlations to the averaged root mean square sEMG (rms EMG) and to the value of the TS [1]. Results: For both muscles, repeatability of all three AOC definitions was high with the exception of AOC2 in the MEH. Neither muscle showed a correlation between maximum deceleration and maximum dT/dt. AOC3 significantly correlated to the TS in both muscles. For theMEH, AOC3 showed the highest correlation to rms EMG (Table 1). Discussion and conclusions: The AOC can be quantified in a repeatableway in a clinical setting for the GAS andMEH of children with CP. The low correlation between maximum deceleration and maximum dT/dt emphasizes the need to define and quantify the severity of the AOC based on an integration of signals. A change in the direction of the power best represents the definition of theAOC. In addition, low correlations between signals indicate the need to examine EMG information in order to fully understand theAOC and link it to spasticity. The sensitivity of AOC3 to spasticity treatment should be explored.