A site for medical students - Practical,Theory,Osce Notes

The serratus anterior and winging of scapula

This muscle is not strictly a muscle of the pectoral region. 
Origin of Serratus anterior
This muscle arises by eight digitations from the upper eight ribs, and from the fascia covering the intervening intercostal muscles.
Insertion of Serratus anterior
The muscle is inserted into the costal surface of the scapula along its medial border
The first digitation is inserted from the superior angle to the root of the spine. 
The next two or three digitations are inserted lower down on the medial border. 
The lower four or five digitations are inserted into a large triangular area over the inferior angle.
Nerve Supply of Serratus anterior
The nerve to the serratus anterior is Long thoracic nerve a branch of the brachial plexus.It arises from roots C5. C6 and C7.
Actions of Serratus anterior
  • Serratus anterior helps in pushing and punching movements.Along with the pectoralis minor it pulls the scapula forwards around the chest wall to protract the upper limb 
  • The fibres inserted into the inferior angle of the scapula pull it forwards and rotate the scapula so that the glenoid cavity is turned upwards. This action of the serratus anterior is helped by the trapezius muscle which pulls the acromion upwards and backwards.
  • When the serratus anterior is paralysed the medial margin of the scapula gets raised specially when pushing movements are attempted. The patient is unable to do any pushing action, nor can he raise his arm above the head. Any attempt to do these movements makes the inferior angle of the scapula still more prominent.It is called winging of the scapula.
  • The muscle_steadies the scapula during weight carrying.
  • It helps in forced inspiration. Serratus anterior is an accessory muscle of respiration
Clinical testing of  Serratus anterior
Forward pressure with the hands against a wall, or against resistance offered by the examiner makes the inferior angle of the scapula prominent (winging scapula) if the serratus anterior is paralyzed.