Hip-phase-dependent flexion reflex modulation and expression of spasms in patients with spinal cord injury

Abstract

The flexion reflex in human spinal cord injury (SCI) is believed to incorporate interneuronal circuits that consist elements of the stepping generator while ample evidence suggest that hip proprioceptive input is a controlling signal of locomotor output. In this study, we examined the expression of the non-nociceptive flexion reflex in response to imposed sinusoidal passive movements of the ipsilateral hip in human SCI. The flexion reflex was elicited by low-intensity stimulation (300 Hz, 30 ms pulse train) of the right sural nerve at the lateral malleolus, and recorded from the tibialis anterior (TA) muscle. Sinusoidal hip movements were imposed to the right hip joint at 0.2 Hz by a Biodex system while subjects were supine. The effects of leg movement on five leg muscles along with hip, knee, and ankle joint torques were established simultaneously with the modulation pattern of the flexion reflex during hip oscillations. Phase-dependent modulation of the flexion reflex was present during hip movement, with the reflex to be significantly facilitated during hip extension and suppressed during hip flexion. The phase-dependent flexion reflex modulation coincided with no changes in TA pre-and post-stimulus background ongoing activity during hip extension and flexion. Reflexive muscle and joint torque responses, induced by the hip movement and substantiated by excitation of flexion reflex afferents, were entrained to specific phases of hip movement. Joint torque responses were consistent with multi-joint spasmodic muscle activity, which was present mostly during the transition phase of the hip from flexion to extension and from mid-to peak extension. Our findings provide further evidence on the interaction of hip proprioceptors with spinal interneuronal circuits engaged in locomotor pathways, and such interaction should be considered in rehabilitation protocols employed to restore sensorimotor function in people with SCI.

Locomotor training modifies soleus monosynaptic motoneuron responses in human spinal cord injury

“…This has been linked to changes in the electrical, biophysical, physiological, and morphological properties of spinal moto-neurons and interneurons (Cope et al 1986; Hochman and McCrea 1994a, b; Bennett et al 2001; Beaumont et al 2004; Heckmann et al 2005; Button et al 2008). Similar changes have been reported in humans after spinal cord injury (SCI) (Hornby et al 2003; Knikou 2007; Knikou et al 2009). While these changes may represent spontaneous plasticity underlying recovery (Wolpaw 2007), training-mediated neuronal changes may play a key role.…”

“…The soleus H-reflex was evoked according to methods we have previously employed in both healthy subjects and people with SCI (Knikou 2007, 2008; Knikou et al 2009). With the subject seated, relaxed, and both feet supported by a foot rest, a stainless steel plate of 4 cm 2 in diameter (anode electrode) was secured proximal to the patella of the right and/or left leg.…”

Parallel facilitatory reflex pathways from the foot and hip to flexors and extensors in the injured human spinal cord

“…6) could be potentially interpreted to indicate that spinal locomotor pathways were activated by the stimulation. We have previously observed a similar behavior when group Ia afferents (but not Ib afferents) from the common peroneal nerve or flexion reflex afferents were excited during imposed hip movements in the same SCI subjects (Knikou et al, 2006a;Knikou, 2007b). In those cases, oscillatory activity was observed during hip extension and flexion, but its amplitude was half of that observed here (compare Fig.…”

“…The TA flexion reflex was elicited and recorded according to procedures identical to those previously employed in the same SCI subjects (Knikou, 2007b;Knikou et al, 2006b). Briefly, the flexion reflex was evoked following sural nerve stimulation by a 30-ms train of 1-ms pulses delivered at 300 Hz using a constant current stimulator (DS7A, Digitimer, UK), and recorded from the TA muscle.…”

Locomotor training alters the behavior of flexor reflexes during walking in human spinal cord injury

“…These new findings support the adaptive capability of the injured nervous system to return to a prelesion excitability and integration state. locomotor training; neuroplasticity; SCI; reorganization; spinal circuits TWO OF THE REFLEX CHANGES observed in the human spinal cord following injury are impaired excitability of pathways mediating early flexor reflexes and increased excitability of pathways mediating late long-lasting flexor reflexes (Roby-Brami and Bussel 1987;Knikou and Conway 2005;Knikou 2007b; Conway and Knikou 2008;Dietz et al 2009). Specifically, the early flexor reflexes are reduced or can be completely absent at the chronic stage of spinal cord injury (SCI) in humans (Roby-Brami and Bussel 1987;Knikou and Conway 2005;Knikou 2007a), while their increased presence has been linked to improved mobility in individuals with SCI (Hubli et al 2012).…”