A toolkit for objective clinical outcome measures of muscle tone

Research Objectives: To evaluate a wearable sensor-based toolkit for quantifying muscle tone in patients with upper motor neuron syndrome (UMNS). Design: Cross-sectional, multi-site, beta trial to test and validate a new technology. Setting: Neurorehabilitation clinics at tertiary care hospitals. Participants: Patients >6mo post acquired brain injury, spinal cord injury, multiple sclerosis and cerebral palsy. Excluded were patients with orthopedic, rheumatic, or other co-morbidity affecting muscle and joint function. All patients provided signed informed consent before participating. Interventions: N/A. Main Outcome Measure(s): Strength: grip, elbow flexor and extensor, and knee extensor; Range of Motion (RoM): Passive RoM (contracture) and passive-active RoM (paresis); Objective spasticity: Stretch-reflex test for elbow, and pendulum test for knee; Subjective spasticity: Modified Ashworth Scale scores for elbow and knee. Results: Measures were acquired for 103 patients from three rehabilitation clinics. Grip strength correlated significantly with elbow muscle strength (r=.8, p<.001). Strength and paresis were correlated for elbow (r=-.38, p<.001) and knee (r=-.47, p<.001) but neither correlated with contracture. For the knee, objective measures of spasticity correlated with strength (r=.32, p<.001), and subjective spasticity correlated with contracture (r=.26, p=.002). Objective measures of spasticity correlated with strongly with MAS scores for elbow muscles (r=.54 to .82, <.001), but less strong for knee muscles (range: r=.23, p=.01 to r=.52, p<.001). Conclusions: A wearable sensor system can provide valid, objective measures of muscle tone in a clinical setting. Weakness and paresis were related to both objective and subjective clinical measures of spasticity for the elbow, but for the knee there was a weak but significant relationship between subjective spasticity and contracture. Comparison of objective and subjective measures of spasticity suggest the clinical MAS score measures elbow spasticity but may be confounded by contracture for knee extensors.