Quantitative features of the stretch response of extrinsic finger muscles in hemiparetic stroke

Abstract

Despite its potential importance in hand dysfunction, spasticity in the finger muscles following stroke has not been well described. To explore this area, we assessed the role of finger flexor spasticity, along with that of passive mechanical forces, in resisting finger movement in 13 chronic stroke subjects. Subjects were tested with a device that stretched the extrinsic finger muscles through imposed rotation of the metacarpophalangeal (MCP) joints. Both maintained and constant-velocity stretches were imposed. For the constant-velocity stretches, eight of the 13 stroke subjects exhibited strong stretch reflexes, as determined by electromyography and net work. The net work of this reflex response, calculated from the integral of the torque-angle plots, increased proportionally with increasing velocity, indicating a contribution from flexor muscle spasticity. Conversely, nine of the 13 stroke subjects did not possess distinctly greater passive, mechanical resistance to MCP rotation than control subjects. While extensor spasticity was not observed, stretch of the extrinsic finger flexors also produced some reflex activity in the finger extensors concomitant with reflex excitation of the flexors. These findings suggest that resistance to muscle stretching following stoke is mediated primarily by neurological rather than biomechanical disturbances, although changes in muscle fiber length may exaggerate the resistance.

The Effect of Motor Imagery on Spinal Segmental Excitability

“…Stretches were provided by a servomotor (1.4 horsepower; PMI Motion Technologies, Radford, VA) as described previously (Kamper and Rymer, 2000). Briefly, the subject was positioned on an adjustable chair such that the shoulder was abducted ϳ50°a nd the elbow was flexed ϳ90°.…”

Hand Spring Operated Movement Enhancer (HandSOME): A Portable, Passive Hand Exoskeleton for Stroke Rehabilitation

“…This was accomplished by basing the design on the biomechanics of the hand after stroke. Kamper et al examined the torque required to extend hypertonic finger joints and found a nearly linear relationship between metacarpophalangeal (MCP) joint extension angle and applied extension torque [16], [17]. They also found that stretching of the flexors elicited muscle activity in the paretic extensors.…”

“…The HandSOME design uses elastic cords as springs to assist with finger and thumb extension, and provide assistance profiles that emulate the torque versus extension angle profiles for passive movement reported by Kamper et al [17]. Changes in the spring location and stiffness used allow the therapist to vary the assistance profile and magnitude.…”

Exploratory design of a compliant mechanism for a dynamic hand orthosis: Lessons learned

“…An exact value, however, is almost impossible to determine because there exists a large variety in severity between individuals [18]. As an initial exploration of the presented concept which is able to accommodate hypertonic muscles with similar scores on the Ashworth scale, a stiffness of 0.5 Nm/rad with equilibrium position at 60…”