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Deltoid Muscle


- See: Shoulder Abductors

- Discussion:
    - major function of the deltoid muscle is to abduct  arm;
    - it performs this action after   scapula[scapula  has been fixed by its stabilizing muscles and the humeral head  has been
           snubbed to glenoid  by the rotator cuff;
    - it is innervated by axillary nerve (C5);

- Anterior Division:
    - origin: anterior border of the lateral 1/3 of the clavicle;
    - insertion: deltoid tuberosity of the humerus;
    - action: abduction, horizontal flexion and medial rotation of humerus at shoulder;
    - nerve supply: axillary, C5, C6 ;
    - synergists: medial and posterior deltoid divisions, supraspinatus and pectoralis major clavicular division;

- Deltoid: Medial Division:
    - origin: superior surface of the acromion process;
    - insertion: deltoid tuberosity of humerus;
    - action: abduction of the humerus at the shoulder
    - nerve supply: axillary, C5, C6;
    - synergists: anterior and posterior deltoid divisions, supraspinatus;

- Deltoid: Posterior Division:
    - origin: inferior margin of spine of scapula;
    - insertion: deltoid tuberosityy of humerus;
    - action: abduction, horizontal extension & lateral rotation of humerus at shoulder;
    - nerve supply: axillary, C5, C6;
    - synergists: anterior and medial divisions of deltoid, supraspinatus;

- Surgical approach:
    - if deltoid muscle is split anteriorly for > 5 cm, branches of axillary nerve will be damaged, rendering corresponding portion of deltoid muscle deinnervated;
           - however, deltoid is innervated by the axillary nerve, whose branches pass upward as they extend anteriorly & may come as close as 2 cm to acromion;
                 - hence, this anamatomy defies the described 5 cm safe zone;
    - posteriorly: medial edge of the deltoid is too medial to provide useful access to the glenohumeral joint;
           - access must be acheived by splitting deltoid, which is most conveniently done at junction of its middle & posterior thirds;
    - site is favorable for a split because it overlies joint & also because axillary nerve exiting quadrangular space divides into 2 trunks
           (anterior and posterior divisions) in an inferior location;

- Deltoid Contracture:
    - often arises from multiple intra-muscular injections;
    - clinical manifestations:
          - shoulder pain, palpable fibrous band, scapular winging, difficulty in combing hair, and an abduction contracture;
    - radiographs: anterosuperior subluxation of the humeral head;
    - management: distal release;

- Deltoid Paralysis: (most commonly occurs from parsonage turner syndrome)

The sub-deltoid approach to the metaphyseal region of the humerus.

Contracture of the Deltoid Muscle. Results of distal release

A cadaveric study on the anatomy of the deltoid insertion and its relationship to the deltopectoral approach to the proximal humerus.