Assessment of trunk control and core stability in spinal cord injured subjects

Abstract

Objective measures for evaluating active trunk movements and postural control in sitting are important for the assessment of people with Spinal Cord Injury (SCI) and for tailoring rehabilitative interventions. However, studies addressing this issue are limited [1]. This work fills this gap by proposing a modular protocol for the kinematic and muscular quantitative assessment of trunk control, specifically designed for SCI subjects. We used hunova® (Movendo Technology), a medical robotic device for the sensory-motor assessment and training of postural control in standing and sitting [2]. consisted of two different tests: a reaching (R) and an adaptive exercise (A), both performed while sitting on hunova®. The test R aims to assess the volitional component of trunk control: six reaching exercises, where subjects need to actively tilt the seat platform to move a cursor on the screen and reach targets, are alternating with two different platform inclinations: 3.5 and 5° (1° corresponds to 1 cm of cursor motion on the screen). The test A aims to assess how subjects adapt to predictable perturbations imposed by the seat platform [3]: six repetitions of an adaptive task, where subjects need to stabilize themselves while the seat platform moves following a given infinite-shape trajectory, is repeated once with eyes open (EO) and eyes close (EC), with different inclinations of the seat platform: 3, 5 and 7°. After testing the device and protocol on 18 healthy subjects, 10 SCI subjects (with different lesion level) participated in the study. Both the reaching block and the adaptive block (Fig. 1) started with the easiest testing condition and gradually increases the difficulty of the exercises. This allowed all SCI subjects, with different lesion level, to participate in the assessment. Electromyography (EMG) was recorded bilaterally from the following muscles: obliquus externus abdominis, trapezius descendens, trapezius transversalis, trapezius ascendens, erector spinae longissimus, erector spinae iliocostalis, multifidus, latissimus dorsi, soleus, tibialis anterior, vastus medialis, semitendinosus, gluteus medium. The leg muscles were recorded only for SCI subjects with an incomplete lesion of the spinal cord. For each subject, we characterized postural responses in terms of kinematics and muscular activity, estimating the correspondent spatiotemporal organization of the motoneuronal activity in the spinal cord [4]. All subjects with an incomplete SCI could finish the whole protocol. This was not the case for subjects with a complete lesion. Only one subject (lesion level D12) completed both blocks and had movement performance like SCI subjects with an incomplete lesion. The other subjects (two with lesion level D6 and one D3) performed few repetitions of R as they found difficult to control the seat platform, and the tasks with 3 and 5° of inclination for A. Concerning the performance, for R all subjects, independently on their type of lesion, reached a greater number of targets across repetitions. During A, all subjects had a bigger trunk sway for higher inclinations of the seat platform, with higher values in the repetitions with EC. Each SCI subject used his/her own muscular strategy for reaching the different targets and also for adapting to the seat motion, despite it was continuous and predictable. This assessment highlighted the differences in the muscular control among subjects, also due to the different lesions. This modular protocol evaluated in a quantitative, objective, repeatable, and comprehensive manner the kinematic and muscular strategies adopted by SCI subjects when performing dynamic tasks while sitting. The device hunova® allowed us to evaluate different aspects related to trunk control, the volitional and the feedforward control of balance while adapting to predictable and continuous perturbations. The results of this assessment will be used to tailor specific rehabilitative interventions.