Muscle Activity Before and After Subacromial Injection

Area of Science:

• Orthopedics
• Biomechanics
• Sports Medicine

Background:

• Subacromial impingement syndrome (SIS) presents variable shoulder muscle activation patterns in patients.
• Pain-related normalization artifacts may explain discrepancies in existing literature.
• Limited understanding of SIS pathogenesis hinders effective clinical treatment and functional recovery.

Purpose of the Study:

• To investigate the effects of pain reduction on shoulder muscle activation in patients with SIS.
• To compare muscle activity patterns between patients and healthy controls before and after treatment.

Main Methods:

• Electromyography (EMG) of 7 shoulder muscles was recorded in 21 patients with stage 2 SIS and 21 controls.
• EMG data were collected during arm elevation before and after subacromial bursa injection in patients.

Main Results:

• Following injection, patients showed increased anterior deltoid, middle deltoid, and upper trapezius activity, mirroring control group trends.
• Control subjects exhibited greater latissimus dorsi activation at peak elevation compared to post-injection patients.

Conclusions:

• Reduced subacromial pain is linked to significant changes in shoulder muscle recruitment, especially the deltoid.
• Observed deltoid activity changes may support the role of the rotator cuff in non-tear cases.