Muscle activation patterns in patients with recurrent shoulder instability.

Area of Science:

• Orthopedics
• Neuroscience
• Sports Medicine

Background:

• Recurrent shoulder instability is a common clinical problem.
• Understanding the underlying muscle activation patterns is crucial for effective treatment.

Purpose of the Study:

• To identify and analyze muscle activation patterns in patients with recurrent shoulder instability.
• To correlate these patterns with the direction of instability.

Main Methods:

• Retrospective review of 131 fine wire dynamic electromyography (DEMG) studies.
• EMG analysis of pectoralis major (PM), latissimus dorsi (LD), anterior deltoid (AD), and infraspinatus (IS) during shoulder movements.
• Comparison of EMG findings with clinical diagnosis and direction of instability.

Main Results:

• Abnormal muscle activation patterns were identified in 93% of the tested shoulders.
• Increased latissimus dorsi (LD) activation was observed in 81% of anterior and 80% of posterior instability cases.
• Increased pectoralis major (PM) activation was noted in 60% of anterior instability cases, while infraspinatus (IS) was inappropriately inactive in 25% of posterior instability cases.

Conclusions:

• Dynamic electromyography (DEMG) is valuable in diagnosing muscle dysfunction associated with shoulder instability.
• Increased latissimus dorsi (LD) activation may contribute to both anterior and posterior shoulder instability.
• Increased pectoralis major (PM) activation is implicated in anterior shoulder instability.