Quantitative evaluation of trunk function and the StartReact effect during reaching in patients with cervical and thoracic spinal cord injury

Changes in thoracic erector spinae regional activation during postural adjustments and functional reaching tasks after spinal cord injury

Many individuals with incomplete spinal cord injury (SCI) exhibit reduced volitional control of trunk muscles, such as impaired voluntary contractions of the erector spinae (ES), due to damage to the neural pathways regulating sensorimotor function. Studies using conventional bipolar electromyography (EMG) showed alterations in the overall, or global, activation of the trunk muscles in people with SCI. However, how activation varied across specific regions within the ES, referred to as regional activation, remains unknown. The aim of the study was to investigate the regional distribution of the ES activity below the level of injury in individuals with incomplete SCI during postural tasks and multidirectional reaching tasks using high-density EMG. Twenty-one individuals with incomplete SCI and age-matched controls were recruited. The EMG amplitude of the thoracic ES and displacement of the arm, trunk, and center of pressure were recorded during the tasks. Activation was more in the lower region of the ES in individuals with SCI than in the controls during the postural tasks. In addition, activation was limited to a small area of the ES during the reaching tasks. The EMG amplitude was greater during reaching forward than returning to the upright posture in the controls; however, this phase-dependent difference in the EMG amplitude was not present in individuals with SCI. Our findings demonstrate changes in regional activation of the thoracic ES during postural and reaching tasks, likely reflecting injury-induced changes in selective neural control to activate residual muscle fibers of the ES for postural control and function after SCI.NEW & NOTEWORTHY We demonstrate that individuals with chronic incomplete spinal cord injury (SCI) recruit lower part of the thoracic erector spinae (ES) for postural control of the trunk. We also show that activation was restricted in a smaller part of the ES, and the discrete control of the ES was lost during functional reaching movements in individuals with SCI. Our study provides evidence of alterations in neural control between vertebral levels in individuals with SCI.

Correlation Between Modified Functional Reach Test and Medio-Lateral Center of Pressure in Paraplegic Individuals With Motor-Complete Spinal Cord Injury

The Modified Functional Reach Test (mFRT) was developed to assess sitting balance in individuals with spinal cord injury (SCI). No studies have explored which mFRT reach directions correlate with the center of pressure (CoP) variables in patients with motor-complete SCI (mcSCI). Addressing this gap is important for improving the clinical usefulness of the mFRT. Thus, this study aims to determine the correlation between seated balance parameters based on CoP and the mFRT in individuals with MCSCI. A total of 10 individuals with mcSCI (9 males and 1 female; range 20-42 years; 4 high paraplegia and 6 low paraplegia). Individuals were tested using a force platform during the sitting postural balance test (SPBT) and the mFRT with/without force plate with three measures of reach: forward (FR), right (RR), and left (LR). The sway parameters investigated were the area CoP sway (CoPSway), the average velocity of CoP displacements along the anterior-posterior (VAP) and medial-lateral (VML) directions, and standard deviation in both directions (SDAP and SDML). The Pearson correlation test was used to analyze the data. Significant correlations were found between the mediolateral reaches of the mFRT and corresponding CoP variables. The rightward and leftward reaches of the mFRT both showed strong correlations with CoP variables during the leftward reach. Additionally, the leftward mFRT exhibited moderate correlations with CoP variables in the same, rightward, and forward directions. The mFRT medio-lateral direction correlates with CoP at medio-lateral directions in paraplegic individuals with mcSCI.

Trunk Posture from Randomly Oriented Accelerometers

Feedback control of functional neuromuscular stimulation has the potential to improve daily function for individuals with spinal cord injuries (SCIs) by enhancing seated stability. Our fully implanted networked neuroprosthesis (NNP) can provide real-time feedback signals for controlling the trunk through accelerometers embedded in modules distributed throughout the trunk. Typically, inertial sensors are aligned with the relevant body segment. However, NNP implanted modules are placed according to surgical constraints and their precise locations and orientations are generally unknown. We have developed a method for calibrating multiple randomly oriented accelerometers and fusing their signals into a measure of trunk orientation. Six accelerometers were externally attached in random orientations to the trunks of six individuals with SCI. Calibration with an optical motion capture system resulted in RMSE below 5° and correlation coefficients above 0.97. Calibration with a handheld goniometer resulted in RMSE of 7° and correlation coefficients above 0.93. Our method can obtain trunk orientation from a network of sensors without a priori knowledge of their relationships to the body anatomical axes. The results of this study will be invaluable in the design of feedback control systems for stabilizing the trunk of individuals with SCI in combination with the NNP implanted technology.