Evaluation of a novel elbow joint torque measurement device in healthy subjects and stroke patients: a randomized trial

Abstract

Current clinical practice lacks quantitative assessment methods for elbow joint movements. In response to existing research limitations, this study introduces the innovative elbow joint torque measurement device (EJTMD), which concurrently measures muscle strength and active range of motion (AROM) using a five-bar linkage system governed by a sliding mode control algorithm. Healthy subjects (n = 22) and stroke patients (n = 22) were recruited in a randomized trial. Each participant underwent two measurement. EJTMD or traditional tools like a protractor and a muscle strength tester. Participants were randomly allocated to EJTMD first or traditional tools first. The efficacy of EJTMD was assessed by comparing muscle strength and AROM with traditional tools. Integrated electromyography (iEMG) and root mean square (RMS) were used to assess the intensity of muscle activity during elbow movements. The peak torque (PT) and the ratio of peak torque to body weight (PT/BW) were examined to explore the differences in mechanical characteristics of bilateral elbow joints. Motor evoked potential (MEP) and central motor conduction time (CMCT) were employed to investigate the potential mechanisms underlying motor discrepancies post-stroke. EJTMD demonstrates superior muscle strength, AROM, iEMG, and RMS during elbow movements compared to traditional tools (P < 0.05). Repeated EJTMD measurement outcomes have a good correlation on the same day (r ≥ 0.999, P < 0.001). EJTMD exhibits significant differences in measurement outcomes among stroke patients before and after treatment (P < 0.05), compared to traditional tools. Stroke patients exhibit reduced PT and PT/BW on the lesion side across low, medium, and high-speed tests, with a more pronounced decline observed during low-speed testing (P < 0.001). Stroke patients show decreased iEMG and RMS on the affected side during elbow movements (P < 0.05), with prolonged MEP latency and CMCT (P < 0.001), and reduced MEP amplitude (P < 0.001). Based on the results, EJTMD demonstrates reliability and effectiveness in assessing elbow movements in both healthy subjects and stroke patients, showing sensitivity to minor joint changes. Stroke patients exhibit reduced flexor and extensor function on the lesion side, potentially resulting from impaired corticospinal tract conduction.

Keywords: Elbow joint; Healthy subjects; Motor evoked potential; Stroke; Surface electromyography.

Fig. 1

(a) A novel Elbow Joint Torque Measurement Device. (b) The mechanical structure diagram of the device. (c) Data collection using EJTMD in healthy subjects.

Fig. 2

(a) Electrodes positioning during sEMG testing. (b) Representative sEMG signals during elbow flexion and extension in healthy subjects. (c) Representative sEMG signals during elbow flexion and extension on the healthy side of stroke patients. (d) Representative sEMG signals during elbow flexion and extension on the lesion side of stroke patients.

Fig. 3

(a) Localization of the primary motor cortex (M1). (b) Neuro-electrophysiological testing. O signifies the MEP onset time, N indicates the wave crest, and P represents the wave trough.

Fig. 4

(a) Representative contralesional MEP waveforms from the M1 and C7 regions in a stroke patient. O signifies the MEP onset time, N indicates the wave crest, and P represents the wave trough. Each small square corresponds to 50 ms in length and 500 µV in height. (b) Representative ipsilesional MEP waveforms from the M1 and C7 regions in a stroke patient. (c) Comparison of bilateral MEP latency results in stroke patients. Latency corresponds to the duration from the stimulation onset to the MEP onset (O point). (d) Comparison of bilateral MEP amplitude results in stroke patients. Amplitude refers to the longitudinal gap between the wave crest (N point) and the wave trough (P point) in the MEP waveforms. (e) Comparison of bilateral CMCT results in stroke patients. The CMCT is calculated as the difference in MEP latency between the cortical site and the C7 level. n = 22/group.