Muscles Of The Shoulder Region.
Learning Objectives:
Shoulder Region
§ It is the proximal part of upper limb.
§ Surrounds the shoulder joint.
§ Providing round counter at proximal end of upper extremity.
§ Bony land marks are:
Ø spine of scapula,
Ø acrominon,
Ø Inferior angle of scapula.
Muscles Of Shoulder Region
Group of six muscles, converge from scapula on to the humerus and surround the shoulder joint, Includes:
Ø Deltoid.
Ø Supraspinatus.
Ø Infraspinatus.
Ø Teres Minor.
Ø Teres major.
Ø Subscapularis.
Most of part of these muscles
are under the cover of Deltoid
and Trapezius.
Deltoid:
§ A powerful muscle.
§ Has longer leaner origin.
§ Has three groups of muscle fibers
Ø Anterior,
Ø Middle &
Ø Posterior.
§ Tip:
§ Principle abductor of the arm.
§ But it cannot initiate this action.
§ Assisted by the supraspinatus muscles.
Greek- delta triangular shaped
§ Origin: Lateral 1/3 of clavicle, acromion process, scapular spine.
§ Insertion: deltoid tuberosity at shaft of humerus.
§ Nerve Supply: Axillary Nerve (C5-C6).
Deltoid consists of three groups of muscle fibers:
q Anterior Fibers:
Ø arising from clavicle,
Ø fibers are parallel.
q Posterior Fibers:
Ø arising from spine of scapula,
Ø parallel fibers.
q Middle fibers:
Ø arising from the acromion, multipennate,
Ø most powerful muscle fibers,
Ø having seven septa inside mass, make the muscle multipennate.
Actions:
§ Anterior fibers:
Ø flexes and medially rotates shoulder.
§ Middle fibers:
Ø Abducts the shoulder.
§ Posterior fibers:
Ø extends and laterally rotates the shoulder.
§ Tip: Anterior & Posterior fibers act like guy ropes to steady the arm in abducted position .
q Common site for Intramuscular Injection (IM)
q On lateral side of bulge of shoulder.
q Axillary nerve is under the cover of deltoid,
q It winds around the posteriolateral aspect of shaft of humerus below the 5-6 cm of acromion.
q If IM injection is given using wrong technique may produce damage to axillary nerve.
Supraspinatus
Latin- supra above spinatus spine
q Bipennate muscle.
q Provide great force pull to the muscle.
§ Origin: Supraspinatus fossa of the scapula.
§ Insertion: Greater tubercle of the humerus.
§ Nerve Supply: Suprascapular nerve (C5-C6)
§ Action:
§ Initiate the abduction at shoulder joint for first 15 degree.
§ Assists deltoid muscle in abducting arm at shoulder.
§ Stabilizes the head of the humerus.
§ Tip: The supraspinatus is the only muscle in the rotator cuff groups that does not actually rotate the humerus
Infraspinatus
Latin- infra beneath spinatus spine
q Multipennate muscle.
q A bursa lies between the muscle and scapula,
q This bursa usually communicates with cavity of shoulder joint.
§ Origin: Infrsapsinatus fossa of the scapula.
§ Insertion: Greater tubercle of the humerus.
§ Nerve Supply: Suprascapular nerve from the brachial plexus (C5-C6).
§ Action: Lateral rotation of the shoulder, and stabilizes the head of the humerus.
Teres Minor
Latin- teres round
§ Origin: superior half of the lateral border.
§ Insertion: Greater tubercle of the humerus.
§ Nerve Supply: axillary nerve (C5 C6).
§ Actions:
§ Weak adductor of humerus,
§ Laterally rotates the shoulder and
§ Stabilizes the head of humerus on glenoid.
Tip:
q It is synergist to Infraspinatus.
q Teres minor may sometimes fuse with infraspinatus.
Latin- teres round
q An offspring of subscapularis.
q It has migrated to the dorsal surface of Scapula.
§ Origin: Inferior part of lateral border and inferior angle of the scapula.
§ Insertion: medial lip intertubercular groove of the humerus.
§ Nerve Supply: lower subscapular nerve (C5 C6).
§ Action: It extends the shoulder, medially rotates the shoulder, Adducts the shoulder.
§ Tip: Its tendon can be transplanted posteriorly to provide lateral rotation.