Purpose: The aim of this study is to evaluate the muscular activation of the deltoid after deltopectoral approach for treatment of proximal humerus fractures (PHF) with a superficial electromyographic (EMS) study.

Material and Methods: Twenty three consecutive patients (9 men – 14 women; mean age 56) with displaced PHF (3 and 4 part) treated with locking plate osteosynthesis (18 Phillos and 5 Numelock) were enrolled in this study.  Inclusion criteria were no postoperative complications, satisfactory bony union and no removal of hardware. Using EMG parameters, muscular strength and fatigability was investigated in the three portions of the deltoid muscle during active 90º elevation on scapular plane. The study included evaluation of constant score and was performed between 12 and 16 months after operation. The non operated shoulder was used as control group.

Results: The medium portion of the deltoid showed the higher values of EMG activation in both shoulders (PHF: 8,8 mV; control 9,3 mV) with no significant differences. The posterior deltoid showed higher values in control group, although not statistical significant. Anterior deltoid activation was similar in both groups, and no fatigue was recorded. Age and sex adjusted constant score was 78 (range 44 – 100)

Conclusion: The electromyographic function parameters of the deltoid muscle after deltopectoral approach for  treatment of PHF are not statistically different from the healthy shoulder after 1 year postoperative time. Deltopectoral approach preserves good function of the deltoid muscle.