Examining Variability In M-wave Max And Probe Positioning: A Reliability Study

Appropriate assessment of nerve function is vital to establish the outcomes of neuromuscular excitability, muscle activation, and the standardization of electromyographic data. Further, the determination of this measure has clinical relevance in the diagnosis of nerve disorders. However, factors such as probe orientation and pressure may lead to inconsistencies in the accurate assessment of nerve function. PURPOSE: The purpose of this study was to determine the interrater reliability of varying probe orientations and pressures on the maximal m-wave (M-wavemax). METHODS: Fourteen females and ten males (age: 20.9 ± 2.2 yrs) underwent electrical stimulation to the median nerve and M-wavemax was recorded in the abductor pollicis brevis. Two raters administered five conditions on separate visits to evaluate the effects of varying probe orientations and pressures on the M-wavemax response. Measures included a 1) parallel (PAR) probe nerve orientation with a pressure of 4-6 N; 2) PAR probe nerve stimulation with a pressure of 9-11 N; 3) perpendicular (PERP) nerve orientation with a pressure of 9-11 N, 4) stimulation disc electrodes in the PAR and 5) PERP direction. The intraclass correlation coefficient (ICC) was calculated for interrater reliability. The reliability of two raters was assessed using a two-way mixed model (ICC[2,1]). RESULTS: Regarding the PERP orientation, there was moderate reliability for the 9-11 N and stimulation disc electrodes (ICC(2,1) = 0.57, p = 0.003, M = 14.77, SE = 5.02; ICC(2,1) = 0.65, p = 0.211, M = 14.88, SE = 4.30; respectively). Similarly, in the PAR orientation, there was moderate reliability for the 9-11 N and stimulation patches (ICC(2,1) = 0.53, p = 0.952, M = 14.20, SE = 5.02; ICC (2,1) = 0.56, p = 0.889, M = 14.52, SE = 5.13; respectively). Lastly, in the PAR orientation, there was poor reliability for 4-6 N (ICC(2,1) = 0.33, p = 0.821, M = 13.61, SE = 5.99). CONCLUSIONS: The poor and moderate reliability indicate varying levels of consistency between the measurements acquired. This is meaningful in clinical applications because measurement reliability is crucial in the effectiveness of diagnosis and treatment. These findings suggest appropriate standardization should be emphasized to increase reliability in common peripheral nerve stimulation.