Isolated Infraspinatus Atrophy Secondary to Suprascapular Nerve Neuropathy Results in Altered Shoulder Muscles Activity.
Isolated infraspinatus atrophy (IIA) is a common condition among overhead-activity athletes, which affects the hitting shoulder and is caused by suprascapular nerve injury. The loss of infraspinatus function could lead to altered activity of the glenohumeral and scapulothoracic muscles and compromise the optimal shoulder function.OBJECTIVE
To assess the surface electromyographic (sEMG) activity patterns, relationships, and response latencies of relevant shoulder girdle muscles in professional volleyball players with IIA and in healthy control players.DESIGN
Research laboratory.PATIENTS OR OTHER PARTICIPANTS
Twenty-four male professional volleyball players (12 players with diagnosed IIA and 12 healthy players) recruited from local volleyball teams.INTERVENTION(S)
sEMG activity of anterior, middle and posterior deltoid, upper, middle and lower trapezius, and serratus anterior was recorded and evaluated during a movement of shoulder abduction in the scapular plane, monitored with an optoelectronic motion capture system.MAIN OUTCOME MEASURE(S)
sEMG activity, relationships, and response latencies of the selected muscles were analyzed with ANOVA models, to highlight statistical differences within and between groups.RESULTS
Athletes with IIA demonstrated significant higher deltoid and trapezius muscles activity, and lower serratus anterior activity, compared with the contralateral shoulder and with healthy athletes. The shoulder with IIA also showed a higher activity ratios between the upper trapezius and the other scapulothoracic muscles, in addition to anticipated activation of the upper trapezius and delayed activation of the serratus anterior, with regard to the onset of shoulder movement.CONCLUSIONS
The present study highlighted altered shoulder muscle activity levels, scapulothoracic muscles imbalances, and abnormal scapulothoracic recruitment patterns in the hitting shoulder of professional volleyball players with IIA, secondary to suprascapular nerve neuropathy. Such shoulder girdle muscles impairments may compromise the optimal scapulhoumeral rhythm and function, increasing the risk of acute and overuse shoulder injuries.