Upper limb impairments associated with spasticity in neurological disorders

Abstract

Background: While upper-extremity movement in individuals with neurological disorders such as stroke and spinal cord injury (SCI) has been studied for many years, the effects of spasticity on arm movement have been poorly quantified. The present study is designed to characterize the nature of impaired arm movements associated with spasticity in these two clinical populations. By comparing impaired voluntary movements between these two groups, we will gain a greater understanding of the effects of the type of spasticity on these movements and, potentially a better understanding of the underlying impairment mechanisms.

Methods: We characterized the kinematics and kinetics of rapid arm movement in SCI and neurologically intact subjects and in both the paretic and non-paretic limbs in stroke subjects. The kinematics of rapid elbow extension over the entire range of motion were quantified by measuring movement trajectory and its derivatives; i.e. movement velocity and acceleration. The kinetics were quantified by measuring maximum isometric voluntary contractions of elbow flexors and extensors. The movement smoothness was estimated using two different computational techniques.

Results: Most kinematic and kinetic and movement smoothness parameters changed significantly in paretic as compared to normal arms in stroke subjects (p < 0.003). Surprisingly, there were no significant differences in these parameters between SCI and stroke subjects, except for the movement smoothness (p < or = 0.02). Extension was significantly less smooth in the paretic compared to the non-paretic arm in the stroke group (p < 0.003), whereas it was within the normal range in the SCI group. There was also no significant difference in these parameters between the non-paretic arm in stroke subjects and the normal arm in healthy subjects.

Conclusion: The findings suggest that although the cause and location of injury are different in spastic stroke and SCI subjects, the impairments in arm voluntary movement were similar in the two spastic groups. Our results also suggest that the non-paretic arm in stroke subjects was not distinguishable from the normal, and might therefore be used as an appropriate control for studying movement of the paretic arm.

Figures

Figure 1

The apparatus including the height adjustable chair, and force and position sensors.

Figure 2

A typical movement trajectory of rapid elbow extension generated by a normal and a stroke subject. Normal: A1 Position; B1 Velocity; and C1 Acceleration. Stroke: A2 Position; B2 Velocity; and C2 Acceleration. Circles in B2, C2 represent zero-crossings in the acceleration. MT: movement time, AROM: active range of motion, Vp: peak velocity, Ap: peak acceleration, TVp: the latency to peak velocity, TAp: the latency to peak acceleration.

Figure 3

A Movement trajectories of elbow angular position, velocity and acceleration of the paretic arm (dotted-line) and the non-paretic arm (solid-line) in a typical stroke subject; B Kinematic, kinetic and smoothness parameters which are significantly different between the paretic and non-paretic arms: MT: movement time; Vp: Peak velocity; Ap: peak acceleration; AROM: active range of motion; MVC: isometric muscle strength of elbow extensors; NJS: normalized jerk score; NMU: number of movement unit. Group average ± Standard deviation.

Figure 4

Movement trajectories of elbow angular position, velocity and acceleration of the non-paretic arm (dotted-line) in a typical stroke subject and the normal arm in a typical healthy subject (normal; solid-line).

Figure 5

A Movement trajectories of elbow angular position, velocity, and acceleration of the spastic arm in a typical SCI subject (spastic SCI; dotted-line) and the normal arm in a typical healthy subject (Normal; solid-line); B Kinematic, kinetic and smoothness variables which are significantly different between the spastic SCI and Normal arms: MT: movement time; TVp: latency to peak velocity; Vp: Peak velocity; Ap: peak acceleration; AROM: active range of motion; MVC: isometric muscle strength of elbow extensors. Group average ± Standard deviation.

Figure 6

Movement trajectories of paretic in stroke (dotted-line) and of spastic in SCI (solid-line) arms.