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

Despite its potential importance in hand dysfunction, spasticity in the fin ger muscles following stroke has not been well described. To explore this a rea, we assessed the role of finger flexor spasticity, along with that of p assive 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) jo ints. Both maintained and constant-velocity stretches were imposed. For the constant-velocity stretches, eight of the 13 stroke subjects exhibited str ong stretch reflexes, as determined by electromyography and net work. The n et 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 s troke subjects did not possess distinctly greater passive, mechanical resis tance to MCP rotation than control subjects. While extensor spasticity was not observed, stretch of the extrinsic finger flexors also produced some re flex activity in the finger extensors concomitant with reflex excitation of the flexors. These findings suggest that resistance to muscle stretching f ollowing stoke is mediated primarily by neurological rather than biomechani cal disturbances, although changes in muscle fiber length may exaggerate th e resistance. (C) 2000 John Wiley & Sons.