Electrophysiological Assessment of the Deltoid Muscle after Minimally Invasive Treatment of Proximal Humerus Fractures - A Clinical Observation

The minimal anterolateral acromial approach offers a less invasive access to the proximal humerus. Functional impairment following this procedure may be caused by paresis of the deltoid muscle as a result of iatrogenic injury to the axillary nerve. It was addressed whether electromyography (EMG) of the deltoid muscle gives evidence for an axillary nerve lesion in association with the minimal anterolateral acromial approach.Twenty-three patients (14 men, 9 women; average age 58 years) with proximal humerus fractures were included in this clinical observation. Follow-up was performed 6 weeks (6w), 6 months (6m) and 12 months (12m) postoperatively. EMG changes indicating either lesion of the axillary nerve or direct muscle trauma were distinguished in "acute", "chronic" and "combined" and semi quantified in "slight", "moderate" and "severe". Patients were examined clinically (standard neurological examination and Constant Score).Three cases of incomplete axillary nerve lesion with limited functional impairment were detected. Subclinical EMG signs of neural impairment of the deltoid muscle were observed frequently (6w, N = 8; 6m, N = 8; 12m, N = 7). Functional outcome did not show an association with EMG.Most patients presented with subclinical and most likely trauma- related neurogenic lesions of the deltoid muscle following the anterolateral acromial approach. Despite the fact that the axillary nerve does not function normally following this less-invasive approach for fixation of proximal humerus fractures, this does not appear to affect the clinical outcome. Prospective studies with larger sample sizes are required to determine the effect of axillary nerve retraction in the more commonly used deltopectoral approach.