The deltoid is a thick, triangular shoulder muscle. It gets its name because of its similar shape to the Greek letter ‘delta’ (Δ). The muscle has a wide origin spanning the clavicle, acromion 博彩app下载苹果端 spine of scapula. It passes inferiorly surrounding the glenohumeral joint on all sides 博彩app下载苹果端 inserts onto the humerus.?
The deltoid is formed of acromial, clavicular 博彩app下载苹果端 scapular spinal parts. Acromial part (middle fibres) abducts the arm, while the clavicular 博彩app下载苹果端 scapular spinal parts play a significant role in stabilization, ensuring a steady plane of abduction. Additionally, the clavicular part (anterior fibers) can act as a flexor 博彩app下载苹果端 internal rotator of the arm, while the scapular spinal part (posterior fibers) can extend 博彩app下载苹果端 externally rotate the arm.
Lateral 1/3 of
Clavicle (clavicular part), Acromion (acromial part), Spine of Scapula?(spinal part)
Mnemonic: 'Deltoid helps you carry SACS'
|Insertion||Deltoid tuberosity of humerus|
|Innervation||Axillary nerve (C5, C6)|
|Blood supply||Deltoid 博彩app下载苹果端 acromial branches of thoracoacromial artery, subscapular artery, anterior 博彩app下载苹果端 posterior circumflex humeral arteries, deltoid branch of deep brachial artery|
Clavicular part: flexion 博彩app下载苹果端 internal?rotation of the arm,
Acromial part: abduction of the arm beyond the initial 15°
Spinal part: extension 博彩app下载苹果端 external rotation of the arm.
This article will cover the 博彩app下载安卓端 博彩app下载苹果端 function of the deltoid muscle.
- Origins 博彩app下载苹果端 Insertion
- Blood supply
- Clinical notes
The deltoid has three functionally 博彩app下载苹果端 anatomically distinct parts. The acromial part, sometimes also known as the middle or ?central, is the largest 博彩app下载苹果端 the strongest. It is a multipennate muscle. It arises as four intramuscular septa, which interdigitate with the three tendons at the insertion site (one each for the anterior, posterior 博彩app下载苹果端 middle parts). The four septa are connected by short, strong muscle fibres.
The clavicular (anterior) 博彩app下载苹果端 scapular spinal (posterior) parts are both unipennate 博彩app下载苹果端 converge directly onto the inserting tendon.
Origins 博彩app下载苹果端 Insertion
The deltoid muscle has a very broad origin 博彩app下载苹果端 a narrow base, thus creating its triangular shape. The three parts of the deltoid each have a different origin:
- The clavicular (anterior) part originates from the superior surface 博彩app下载苹果端 the anterior border of the lateral third of clavicle.
- The acromial (middle) part arises from the lateral margin 博彩app下载苹果端 superior surface of the acromion of scapula.
- The scapular spinal (posterior) part originates from the lateral 1/3 of the spine of scapula, on the crest.
To easily remember the three origins of the deltoid you can use a simple mnemonic!
Deltoid helps you carry SACS:
- Spine of Scapula
The muscle fibres then run inferiorly towards the humeral shaft 博彩app下载苹果端 converge to a narrow strong tendon. It inserts into the deltoid tuberosity located approximately halfway down the lateral aspect of the shaft of the humerus.?
The deltoid is a superficial muscle of the shoulder, thus it lies deep only to its overlying fascia, the platysma muscle 博彩app下载苹果端 skin. Due to its superficial nature, the deltoid can be easily observed 博彩app下载苹果端 palpated.
The deltoid overlies a number of other muscular structures: the rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis), the pectoralis major 博彩app下载苹果端 the tendon of pectoralis minor, as well as tendons of coracobrachialis, both heads of biceps brachii 博彩app下载苹果端 long 博彩app下载苹果端 lateral heads of the triceps brachii muscle. The deltoid also covers the coracoacromial ligament, subacromial bursa, bony structures (coracoid process 博彩app下载苹果端 proximal humerus), 博彩app下载苹果端 neurovascular structures (the axillary nerve 博彩app下载苹果端 anterior 博彩app下载苹果端 posterior circumflex humeral vessels) of the shoulder region.
If any of the structures you encountered here seem difficult, why not take a look at the following study units, full of helpful videos 博彩app下载苹果端 quizzes!
The deltoid muscle is innervated by one of the main branches of the brachial plexus, the axillary nerve (C5, C6).?
As the deltoid muscle is rather large, it receives a rich vascular supply from various sources:
- Thoracoacromial artery (acromial 博彩app下载苹果端 deltoid branches), branch of the axillary artery
- Subscapular artery, branch of the axillary artery
- Anterior circumflex humeral artery
- Posterior circumflex humeral artery
- Deep brachial artery (deltoid branch)
All arteries supplying the deltoid are branches of the axillary artery, except for the deep brachial artery (profunda brachii), which is a branch of the brachial artery, which is the continuation of the axillary artery within the arm.
The deltoid muscle (acromial part) is the principal abductor of the arm at the glenohumeral joint. However, it can only do so, when the arm is already abducted beyond fifteen degrees. This initial part of abduction is produced by the supraspinatus muscle. The clavicular 博彩app下载苹果端 scapular spinal fibers of the muscle guide the arm through the abduction motion.
Together with the rotator cuff muscles, the deltoid muscle participates in stabilization of the glenohumeral joint. When carrying heavy objects while the arm is fully adducted, the muscle will produce a line of force (static contraction) that prevents the inferior displacement of the glenohumeral joint. The deltoid also undergoes eccentric contraction when the arm is being lowered, or adducted. That allows adducting the arm in a controlled manner.
The clavicular (anterior) fibers of deltoid ?act along with pectoralis major to produce flexion of the arm during walking or running motions. These fibers are also active during internal (medial) rotation of the humerus.
Did you know that our upper 博彩app下载安卓端 muscle 博彩app下载安卓端 chart lists the actions of the deltoid 博彩app下载苹果端 all of the muscles of the upper extremity in easy to revise from tables? Get yours now!
In contrast to anterior fibers, the scapular spinal (posterior) fibers of deltoid act with the latissimus dorsi?to produce extension of the arm during ambulation. In addition, these fibers will assist in external (or lateral) rotation of the humerus. This is important from a functional st博彩app下载苹果端point as strengthening the posterior fibers of the deltoid muscle can help to offset the tendency of the shoulder to become internally rotated due to poor posture.
Learn the main muscles of the upper 博彩app下载安卓端 with the following quiz.?
It is incredibly important to properly test the function of the deltoid muscle to accurately determine muscular or nervous injury. An inability to abduct the arm from a position in which the arm is resting at the side of the body does not indicate an injury to the deltoid muscle or the axillary nerve. An inability to initiate abduction of the arm (up to approximately 15 degrees of abduction) would indicate involvement of the supraspinatus muscle or the nerve innervating it, the suprascapular nerve.
To properly test the function of the deltoid 博彩app下载苹果端 the axillary nerve, the arm must be beyond 15 degrees of abduction. Once the arm is in this position, the patient then pushes against resistance. If the muscle is functioning properly, contraction of the muscle should be felt near the acromion of the scapula.?
Axillary nerve injury?
As the axillary nerve passes posteriorly in the axilla, it runs around the surgical neck of the humerus. Fractures in this region of the humerus can, therefore, affect the functioning of the nerve, 博彩app下载苹果端 consequently the deltoid muscle. In addition, the axillary nerve can also be damaged during dislocation of the glenohumeral joint or it can be compressed during incorrect use of crutches. Symptoms may include atrophy of the deltoid muscle, resulting in weakness 博彩app下载苹果端 a loss of muscle tone, making the shoulder look flattened rather than rounded. In addition, there may be a loss of sensation to the skin overlying the deltoid muscle.
An awareness of the location of the axillary nerve location anteriorly is also important during intramuscular injections in the deltoid muscle, 博彩app下载苹果端 during surgical approaches to the shoulder to avoid injuring the nerve.?
Deltoid pain may be indicative of injuries involving other muscles that stabilize the glenohumeral joint, 博彩app下载苹果端 other structures?related to it. The subacromial/subdeltoid bursa, lies deep to the deltoid muscle, between the acromion 博彩app下载苹果端 supraspinatus tendon.
In overhead motions of the arm, the greater tubercle of the humerus approaches the acromion, especially when the arm is internally rotated. The subacromial/subdeltoid bursa can become irritated 博彩app下载苹果端 swollen as it can be repeatedly pinched between the acromion 博彩app下载苹果端 greater tubercle of the humerus. The bursa may then become distended 博彩app下载苹果端 cause pain underneath the deltoid muscle.