Reliability of biomechanical spasticity measurements at the elbow of people poststroke

Abstract

Objective: To determine the minimum number of measurements required to obtain a reliable estimate of upper-extremity spasticity using biomechanic assessment across multiple testing trials and dates.

Design: Single-center, longitudinal study with repeated measurements of spastic upper-extremity torque measures taken 1 week apart.

Setting: A hospital-based laboratory with an isokinetic testing system.

Participants: Sixteen subjects more than 6 months poststroke with upper-extremity spasticity.

Intervention: Elbow flexor hypertonia was assessed with a custom-made manipulandum attached to a 6-axis load cell and a Biodex System 3 isokinetic testing machine. Movements into extension were imposed at 4 speeds: 6 degrees /s, 30 degrees /s, 60 degrees /s, and 90 degrees /s.

Main outcome measures: The resistive torque and electromyographic response to these imposed movements were measured. The torque response at the slowest speed (6 degrees /s) was attributed solely to the passive elements of the elbow and was subtracted from the torque response at the higher speeds (30 degrees /s, 60 degrees /s, 90 degrees /s), leaving only reflex torque. The reflex torques at 30 degrees /s, 60 degrees /s, and 90 degrees /s were used for further analysis. Peak torque, peak joint stiffness, and onset angle of reflex torque responses were found; repeatability and daily variability of these measures were statistically examined. The variabilities due to the subject, test day, and trial number were computed. The overall reliability of each parameter at the 3 higher test speeds using different testing schemes was also calculated.

Results: Ninety percent reliability in the measurement of all parameters was obtained after at least 2 days of testing during which 3 tests a day were performed. The variability in between-subjects measurements was at least 4 times greater than the intertrial variability when testing at the highest speeds; daily variability that was up to 50% of the intersubject variability was also observed. The biomechanic measures correlated well with the Ashworth Scale (Spearman rho=.84, P<.005), a clinical measure of hypertonia.

Conclusions: We recommend at least 2 test dates to account for the daily variability in the spastic reflex response and to ensure reliable spasticity measurements.