Which of the following muscles carries out shoulder abduction from 15 to 90 degrees?
Ans. is 'c' i.e., Deltoid Abduction of shoulder* Abduction is initiated by supraspinatus, which is responsible abduction upto 15 degrees.* After that deltoid (acromial or middle fibers) is the major abductor upto 90 degrees of abduction. These two muscles, supraspinatus and deltoid are the prime movers for abduction.* Overhead abduction (> 90 degrees) is caused by trapezius and serratus anterior, which act by causing upward rotation of glenoid cavity.* In abduction, out of total 180 degree elevation, humerus moves 120o at the shoulder joint and the remaining 60 degree is done by rotation of scapula. In every 15o elevation, shoulder joint contributes lOo and scapular rotation 5o, in the ratio of 2:1. Rotation of scapula is facilitated by movements at sternoclavicularand acromioclavicular joints. In higher ranges of abduction there is lateral rotation of humerus. Lateral rotation of scapulaincreases the range of humeral elevation.
Suprapinatus
Trapezius
Deltoid
Serratus Anterior
Upper Extremity