Neurophysiological characterization of motor recovery in acute spinal cord injury

Abstract

Study design: Prospective cohort study.

Objective: This study was designed to neurophysiologically characterize motor control recovery after spinal cord injury (SCI).

Setting: University of Louisville, Louisville, Kentucky, USA.

Material: Eleven acute SCI admissions and five non-injured subjects were recruited for this study.

Methods: The American Spinal Injury Association Impairment Scale (AIS) was used to categorize injury level and severity at onset. Multimuscle surface electromyography (sEMG) recording protocol of reflex and volitional motor tasks was initially performed between the day of injury and 11 days post onset (6.4±3.6, mean±s.d. days). Follow-up data were recorded for up to 17 months after injury. Initial AIS distribution was as follows: 4 AIS-A; 2 AIS-C; 5 AIS-D. Multimuscle activation patterns were quantified from the sEMG amplitudes of selected muscles using a vector-based calculation that produces separate values for the magnitude and similarity of SCI test-subject patterns to those of non-injured subjects for each task.

Results: In SCI subjects, overall sEMG amplitudes were lower after SCI. Prime mover muscle voluntary recruitment was slower and multimuscle patterns were disrupted by SCI. Recovery occurred in 9 of the 11 subjects, showing an increase in sEMG amplitudes, more rapid prime mover muscle recruitment rates and the progressive normalization of the multimuscle activation patterns. The rate of increase was highly individualized, differing over time by limb and proximal or distal joint within each subject and across the SCI group.

Conclusions: Recovery of voluntary motor function can be quantitatively tracked using neurophysiological methods in the domains of time and multimuscle motor unit activation.

Figure 1

Biceps Brachi sEMG during three repeated trials of voluntary elbow flexion (auditory cue at up arrow) and extension (down arrow) performed in the supine position by subject #5 (C4, AIS-D). Serial recordings made 9, 22, and 36 days after injury show typical characteristics of changing motor control in the prime mover muscle for the task. Note that at first, only a few motor units can be fired, but with recovery, an increase in motor unit firing occurs with a progressive decrease in the time from the onset of activity to the peak of activation. Also, note the antagonistic co-activation of this muscle during the elbow extension phase of the motor task that developed over time.

Figure 2

Voluntary right ankle dorsiflexion performed by a subject (#9) with an initial injury level at C5, who improved to the level of L2. Serial recordings made 11, 27, 45, and 135 days post onset show the evolution of control in which the prime mover (RTA) amplitude increases, at first along with coactivation of other muscles followed by the reduction of activation in all but the prime mover. The Cue mark is 5 seconds.

Figure 3

Profile of Similarity Index increase over time within an individual (subject #2) for all voluntary motor tasks. Note that recovery occurred at different rates for each task with elbow flexion being the slowest.

Figure 4

Profile of SI changes for all 11 SCI subjects and all 6 tasks. Note the diverse distribution of initial values and change patterns.