EMG and MRI are Independently Related toShoulderExternal Rotation Function inNeonatalBrachial Plexus Palsy

Abstract

Few studies exist with regard to the ability of electromyography (EMG) and volumetric magnetic resonance imaging (MRI) of the infraspinatus muscle to complement the physical assessment of active global shoulder external rotation (GER) in the neonatal brachial plexus palsy (NBPP) population. Therefore, the purpose of this study was to evaluate the relationships of EMG and MRI with active GER based on analysis of the infraspinatus muscle. Seventy-four NBPP patients (mean age, 5 y 1 m; range, 1 y 1 m to 13 y 3 m) who had undergone physical examination of the shoulder, EMG evaluation of the infraspinatus muscle, and shoulder MRI were included in this study. The outcome variable active GER was dichotomized into <0 degree active GER (poor) and ≥0 degree active GER (good). The interference pattern on EMG of the infraspinatus muscle was graded on a 6-point scale and dichotomized into ≤4 and ≥5. On shoulder MRI, infraspinatus muscle volume was measured. The infraspinatus muscle interference pattern and volume were compared with active GER. Interference pattern on EMG of the infraspinatus muscle was significantly related to the Mallet Score (P=0.0022), with a poor interference pattern associated with an approximately 7 times higher likelihood [odds ratio=7.391; 95% confidence interval (2.054, 26.588)] of poor active GER. Infraspinatus muscle volume decrease on MRI was also significantly related to active GER (P=0.0413), with each percent volume decrease corresponding to an increase of 0.094 in the odds of having a poor Mallet Score for active GER [odds ratio=1.094; 95% confidence interval (1.004, 1.193)]. The interference pattern of the infraspinatus muscle on EMG and the infraspinatus muscle volume on MRI are strongly related to active GER as assessed by the Mallet Score. Integrating clinical assessment with electrophysiological and imaging findings may improve the accuracy in evaluating shoulder dysfunction in NBPP and provide improved guidance in selecting interventions specific to the patient's pattern of deficits. Diagnostic study, level II.