Characteristics of Lower Extremity Clonus after Human Cervical Spinal Cord Injury

Abstract

Clonus can interfere with self-care and rehabilitation of people with spinal cord injury. Our aim was to characterize clonus and to evaluate factors that influence clonus duration in muscles paralyzed chronically by spinal cord injury. Electromyographic activity was recorded from soleus and 7 other limb muscles (5 ipsilateral, 2 contralateral) during clonus. In 14 subjects, clonus frequency in soleus averaged 5.4 -0.9 Hz and was slower when the reflex path was longer. Contraction frequency slowed at the beginning and end of clonus (sometimes by 2 Hz). The magnitude of one cycle changed the timing and magnitude of the next cycle. These data suggest that afferent input influences the frequency and maintenance of clonus. Recording from many muscles revealed that clonus was prolonged ( > 40 sec) when only ipsilateral triceps surae or triceps surae and tibialis anterior were involved. Therefore, localized inputs to spinal circuits were important to sustain clonus. Clonus was intermediate (median: 21 sec) with activation of three or four ipsilateral muscles and these contractions were associated with greater activation of ipsilateral flexors. Clonus was short ( < 5 sec) when ipsilateral and contralateral muscles were activated (five or six muscles). Activation of extraneous afferent input, particularly contralateral muscles, may provide a way to shorten clonus after spinal cord injury.

Identification and classification of involuntary leg muscle contractions in electromyographic records from individuals with spinal cord injury

“…Bursts of EMG occur at 4 to 12 Hz during clonus, largely dependent on the reflex arc length (Iansek, 1984; Wallace et al, 2012). Contractions repeat at lower frequencies during myoclonus (De Mello et al, 2002; Zucconi et al, 2006) and classification, count and duration discrepancies arose largely from raters grouping versus separating contractions.…”

“…Criteria are also needed to classify different types of involuntary contractions that commonly occur in paralyzed muscles (e.g. clonus, motor unit potentials, tonic EMG, myoclonus; Little et al, 1989; Thomas and Ross, 1997; De Mello et al, 2002; Gorassini et al, 2004; Benz et al, 2005; Wallace et al, 2012; Zijdewind and Thomas, 2012). Continuous recordings of EMG during voluntary contractions have been digitized, partitioned into events and rest intervals, and the length of each contraction and rest measured (Kern et al, 2001; Mork and Westgaard, 2005).…”

Automatic Identification and Classification of Muscle Spasms in Long-Term EMG Recordings

“…Clonus is documented clinically when there are four bursts of EMG [15]. These two criteria were used here to indicate clonus (at least four EMG bursts, with periodicity between 4 and 12 Hz).…”

Restoring Walking after Spinal Cord Injury

“…Exaggerated stretch reflexes in extensor muscles may counteract the remaining dorsiflexion and exacerbate foot drop (Knutsson 1981; Yang and others 1991). Furthermore, hyperactive stretch reflex pathways may limit joint motion (Hornby and others 2006) and may also lead to clonus (Corcos and others 1986; Hidler and Rymer 1999; Wallace and others 2012; Yang and others 1991). …”