Deltoid muscle

Source: Wikipedia, the free encyclopedia.
Deltoid muscle
Latissimus dorsi
Identifiers
Latinmusculus deltoideus
MeSHD057645
TA98A04.6.02.002
TA22452
FMA32521
Anatomical terms of muscle]

The deltoid muscle is the

muscle fibers
, namely the

  1. anterior or clavicular part (pars clavicularis)
  2. posterior or scapular part (pars scapularis)
  3. intermediate or acromial part (pars acromialis)

However, electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.[1]

It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). Deltoid is also further shortened in slang as "delt".

A study of 30 shoulders revealed an average mass of 191.9 grams (6.77 oz) in humans, ranging from 84 grams (3.0 oz) to 366 grams (12.9 oz).[2]

Structure

Origin

  1. The
    anterior or clavicular fibers arise from most of the anterior border and upper surface of the lateral third of the clavicle.[3] The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.[4]
  2. Intermediate or acromial fibers arise from the superior surface of the acromion process of the scapula.[3]
  3. Posterior or spinal fibers arise from the lower lip of the
    spine of the scapula.[3]
Side
Side.
Front
Front.
Back
Back.
Animation
Animation.
Deltoid muscle.
  Anterior part of deltoid (arises from most of the anterior border and upper surface of the lateral third of the clavicle.)
  Intermediate part of deltoid (arises from the superior surface of the acromion process.)
  Posterior part of deltoid (arises from the lower lip of the posterior border of the spine of the scapula.)
Deltoid Muscle Labelled

Insertion

From this extensive origin the fibers converge toward their insertion on the

lateral aspect of the shaft of the humerus
; the intermediate fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.

Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally gives off extensions to the

lateral intermuscular septa
.
[5]

Blood supply

The deltoid is supplied by the thoracoacromial artery (acromial and deltoid branches), the circumflex humeral arteries, and the profunda brachii artery (deltoid branch).[6]

Nerve supply

The deltoid is innervated by the

cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.[8]

Studies have shown that there are seven neuromuscular segments to the deltoid muscle. Three of these lie in the anatomical anterior head of the deltoid, one in the anatomical middle head, and three in the anatomical posterior head of the deltoid.[9] These neuromuscular segments are supplied by smaller branches of the axillary nerve, and work in coordination with other muscles of the shoulder girdle include pectoralis major and supraspinatus.[9]

The axillary nerve is sometimes damaged during surgical procedures of the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus.[10]

Function

Deltoid muscle with superior limb in abduction

When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect.

teres minor
, also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats.

An important function of the deltoid in humans is preventing the

glenohumeral joint needed for hand and arm manipulation.[2] The intermediate fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers.[12]

The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the

infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.[2]

Clinical significance

The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy may result from various causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoideal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation.[13]

Other animals

The deltoid is also found in members of the

knuckle walking apes for the purpose of supporting the entire body weight.[2]

The deltoid muscle is a main component of both the bat and pterosaur wing musculature,[14] but in crown-group birds it is strongly reduced, as they favour sternum attached muscles. Some Mesozoic flying theropods, however, had more developed deltoideus.[15]

References

  • Standring, S. (2005). Gray's Anatomy: The Anatomical Basis of Clinical Practice (39th ed.). Elsevier Churchill Livingstone.
  1. PMID 16458022
    .
  2. ^ .
  3. ^ a b c "Deltoid Muscle". Wheeless' Textbook of Orthopaedics. December 2011. Retrieved January 2012.
  4. PMID 19094189
    .
  5. PMID 19186076. Archived from the original
    (PDF) on 2012-09-04.
  6. ^ Standring, 2005
  7. ^ Anatomy photo:03:03-0103 at the SUNY Downstate Medical Center
  8. ^ "Deltoid muscle". Kenhub. Retrieved 2019-09-21.
  9. ^
    PMID 16458022
    .
  10. .
  11. ^ Radiography of the Upper Extremities: 24 ARRT Category A. CE4RT, 2014. 201. Print.
  12. ^ "Lateral Deltoid Raise - Shoulder Exercise & Workout | MG". Archived from the original on 2012-06-25. Retrieved 2013-06-17.
  13. ^ Arend CF. Ultrasound of the Shoulder. Master Medical Books, 2013. Chapter on deltoideal enthesopathy available at ShoulderUS.com
  14. .
  15. .