A new electrode placement for recording the compound motor action potential of the first dorsal interosseous muscle

Variable innervation of the first dorsal interosseous muscle: an electrophysiological study

Background

The first dorsal interosseous muscle (FDI) is usually innervated by the deep branch of the ulnar nerve. However, as was first noted by Sunderland in 1946, some individuals have variable innervation of the FDI. This study investigated the incidence of variable innervation of the FDI by using electrophysiological examination and further evaluated the relevance of this variation in patients with cubital tunnel syndrome (CuTS).

Methods

This study included 211 patients who underwent peripheral nerve surgery in Huashan hospital, Fudan University, between October, 2012 and February, 2014. The patients were divided into three groups: the carpal tunnel syndrome (CTS) group, the CuTS group and the control group. During surgery, electromyography was used to determine FDI variation, and a hand function instrument was employed to estimate the pinch strength between the thumb and index finger in both hands of the CuTS patients.

Results

The electromyogram test showed that 22 of the patients enrolled had variable innervation of the FDI. Compared with the CTS group and the control group, the incidence of variable innervation of the FDI was much higher in the CuTS group (P<0.05). Patients under the age of 60 years old in the CuTS group were more likely to have the variation (P=0.043). A higher pinch strength ratio was significantly associated with variable innervation of the FDI in the CuTS patients (P=0.030).

Conclusions

Using electromyography, our study demonstrated that the variable innervation of the FDI could be innervated by the median nerve. In the CuTS patients, the higher incidence of FDI variation was possibly related to age. This variation might lead to a better prognosis for CuTS patients.

Guidelines to electrode positioning for human and animal electrical impedance myography research

The positioning of electrodes in electrical impedance myography (EIM) is critical for accurately assessing disease progression and effectiveness of treatment. In human and animal trials for neuromuscular disorders, inconsistent electrode positioning adds errors to the muscle impedance. Despite its importance, how the reproducibility of resistance and reactance, the two parameters that define EIM, are affected by changes in electrode positioning remains unknown. In this paper, we present a novel approach founded on biophysical principles to study the reproducibility of resistance and reactance to electrode misplacements. The analytical framework presented allows the user to quantify a priori the effect on the muscle resistance and reactance using only one parameter: the uncertainty placing the electrodes. We also provide quantitative data on the precision needed to position the electrodes and the minimum muscle length needed to achieve a pre-specified EIM reproducibility. The results reported here are confirmed with finite element model simulations and measurements on five healthy subjects. Ultimately, our data can serve as normative values to enhance the reliability of EIM as a biomarker and facilitate comparability of future human and animal studies.

Thumb performance of elderly users on smartphone touchscreen

This study investigated the relationship between thumb muscle activity and thumb operating tasks on a smartphone touchscreen in elderly users (right hand posture). Three thumb muscles were targeted in the experiment, namely, abductor pollicis brevis, abductor pollicis longus (APL) and first dorsal interosseous (FDI). The results showed that the elderly participants developed fatigue rapidly and tapped more slowly when operating on smaller buttons (diameter 3.0 mm compared with 9.0 mm) and moving in the flexion–extension (compared with adduction–abduction) orientation. Meanwhile, electromyography and perceived exertion evaluation revealed significant increases in FDI in the small button task, and results for APL were significantly greater in the flexion–extension task. This study suggests that the use of small touch-buttons and flexion–extension movement should be minimised in the handheld touchscreen interface design for elderly users.

Ulnar motor study to first dorsal interosseous: Best reference electrode position and normative data

INTRODUCTION

Reference electrode position affects nerve conduction study results. This study was undertaken to determine the optimal reference electrode position for ulnar motor recording from the first dorsal interosseous (FDI) muscle and to develop normative data.

METHODS

Fifty-one subjects were tested using reference electrode positions on the thumb, index, and little fingers. Latencies were compared with a needle recording from the FDI. Analysis was performed to determine the surface placement that most closely matched the needle recording latency. A normative database was then derived on 100 healthy subjects.

RESULTS

Placing the reference electrode on the thumb yielded results closest to the "gold standard" needle recording latency. The 97th percentile (upper limit of normal) for latency was 4.0 ms. The 3rd percentile values (lower limit of normal) for amplitude were 9.0 mV for men and 9.3 mV for women.

CONCLUSIONS

The reference position on the thumb yields latencies that most closely approximate needle recording. Normative data are presented.

An ergonomics study of thumb movements on smartphone touch screen

This study investigated the relationships between thumb muscle activity and thumb operating tasks on a smartphone touch screen with one-hand posture. Six muscles in the right thumb and forearm were targeted in this study, namely adductor pollicis, flexor pollicis brevis, abductor pollicis brevis (APB), abductor pollicis longus, first dorsal interosseous (FDI) and extensor digitorum. The performance measures showed that the thumb developed fatigue rapidly when tapping on smaller buttons (diameter: 9 mm compared with 3 mm), and moved more slowly in flexion-extension than in adduction-abduction orientation. Meanwhile, the electromyography and perceived exertion values of FDI significantly increased in small button and flexion-extension tasks, while those of APB were greater in the adduction-abduction task. This study reveals that muscle effort among thumb muscles on a touch screen smartphone varies according to the task, and suggests that the use of small touch buttons should be minimised for better thumb performance.