Lack of Hypertonia in Thumb Muscles After Stroke

Abstract

Towles JD, Kamper DG, Rymer WZ. Lack of hypertonia in thumb muscles after stroke. J Neurophysiol 104: 2139 -2146, 2010. First published June 28, 2010 doi:10.1152/jn.00423.2009. Despite the importance of the thumb to hand function, little is known about the origins of thumb impairment poststroke. Accordingly, the primary purpose of this study was to assess whether thumb flexors have heightened stretch reflexes (SRs) following stroke-induced hand impairment. The secondary purpose was to compare SR characteristics of thumb flexors in relation to those of finger flexors since it is unclear whether SR properties of both muscle groups are similarly affected poststroke. Stretch reflexes in thumb and finger flexors were assessed at rest on the paretic side in each of 12 individuals with chronic, severe, stroke-induced hand impairment and in the dominant thumb in each of eight control subjects also at rest. Muscle activity and passive joint flexion torques were measured during imposed slow (SS) and fast stretches (FS) of the flexors that span the metacarpophalangeal joints. Putative spasticity was then quantified in terms of the peak difference between FS and SS joint torques and electromyographic changes. For both the hemiparetic and control groups, the mean normalized peak torque differences (PTDs) measured in thumb flexors were statistically indistinguishable (P ϭ 0.57). In both groups, flexor muscles were primarily unresponsive to rapid stretching. For 10 of 12 hemiparetic subjects, PTDs in thumb flexors were less than those in finger flexors (P ϭ 0.03). Paretic finger flexor muscle reflex activity was consistently elicited during rapid stretching. These results may reflect an important difference between thumb and finger flexors relating to properties of the involved muscle afferents and spinal motoneurons.

The Effects of Upper-Limb Training Assisted with an Electromyography-Driven Neuromuscular Electrical Stimulation Robotic Hand on Chronic Stroke

“…The abductor pollicis brevis (APB) and ED muscles were used as voluntary neuromuscular drives to control robot assistance and NMES assistance from the system to facilitate performance of phasic and sequential limb tasks, namely, hand closing and hand opening. The APB was selected as the driving muscle in the hand closing phase, since the EMG signals from the APB of the paretic limb after stroke are less affected by spasticity and are relatively easier to be controlled than the flexor digitorum (FD) muscle for finger movements in chronic stroke ( 31 ). EMG-triggered control was used in this study.…”

The effects of post-stroke upper-limb training with an electromyography (EMG)-driven hand robot

“…Commonly, the flexors have more spasticity and the extensors have more weakness. However, the APB is a thumb flexor that had been found lack of spasticity after stroke (Towles et al, 2010). Therefore, in the design of the robot hand, the APB and ED were selected for controlling the open and close of the robot hand with less contamination of spastic EMG.…”

Involuntary Neuromuscular Coupling between the Thumb and Finger of Stroke Survivors during Dynamic Movement

“…Thus, it appears that coupling may be greater between thumb and finger flexors, as we observed in the passive condition ( 29 ). It should be noted that rapid stretch of thumb muscles in passive stroke survivors failed to elicit a spastic stretch reflex ( 30 ). Limited APB reflex may also be attributed to a reduction in heterogeneous extrinsic–intrinsic connections ( 7 ).…”