23.23 Abduction

• Abduction requires several muscles… no muscle is individually responsible

• Three stages:

  • Scapulo-humeral roation

    • Allows for 90\(^{\circ}\) of abduction by the combined action of deltoid, superior stabilizers (supraspinatus, long head of the biceps), and lateral stabilizers (subscapularis, infraspinatus, pectoralis major,a nd latissimus dorsi

  • Rotation and scapular tilt give an additional arc of 60 \(^{\circ}\) (150\(^{\circ}\) total)

    • Muscles of serratus anterior and superior trapezius orientating the glenoid upwards, backwards, and outwards

  • Contralateral inclination of the spine from 150\(^{\circ}\)-180\(^{\circ}\)

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