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The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a common shoulder muscle, particularly in animals such as domestic cats. The deltoid gets its name from its shape, which resembles the inverted Greek letter delta. The muscle is responsible for elevating the arm in the scapular plane and plays a key role in shoulder stability and motion. It is a superficial muscle, lying over the glenohumeral joint, and is one of the six intrinsic muscles of the shoulder. The deltoid is also a common site for intramuscular injections, including vaccinations.
| Characteristics | Values |
|---|---|
| Muscle shape | Triangular |
| Muscle type | Superficial |
| Muscle size | Large |
| Muscle function | Shoulder abduction, flexion and extension |
| Muscle parts | Anterior or clavicular, middle or acromial, and posterior or spinal |
| Muscle fibres | Pennate |
| Muscle insertion | Deltoid tuberosity of the humerus |
| Muscle origin | Clavicle, acromion and spine of scapula |
| Muscle blood supply | Axillary artery, posterior humeral circumflex artery, profunda brachii artery |
| Muscle innervation | Axillary nerve |
| Muscle nerve roots | C5 and C6 |
| Muscle nerve branches | Anterior and posterior |
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What You'll Learn
The deltoid muscle is a large, triangular-shaped muscle
The deltoid is a thick muscle with a broad origin and a narrow base. It has three functionally and anatomically distinct parts: the anterior or clavicular, middle or acromial, and posterior or spinal. These three parts correspond to the muscle's three areas of origin. The anterior portion originates from the lateral third of the clavicle, the acromial portion from the acromion of the scapula, and the posterior part from the spine of the scapula. The deltoid's fibres are pennate muscle, and it has a very broad origin, spanning the clavicle, acromion, and spine of the scapula.
The deltoid muscle is a key player in shoulder stability and motion. It is responsible for elevating the arm in the scapular plane, and its contraction elevates the humeral head. It is one of the main abductors of the shoulder, helping to lift the arm when reaching for objects or brushing hair, and is also active when carrying heavy weights to prevent dislocation of the glenohumeral joint. The deltoid also compensates for weak shoulder abduction due to rotator cuff tears. The deltoid receives its blood supply from various branches of the axillary artery and is innervated by the axillary nerve.
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It is a common shoulder muscle
The deltoid muscle is a common shoulder muscle. It is a large, thick, triangular-shaped muscle that forms the rounded contour of the shoulder. It gets its name from its shape, which resembles the inverted Greek letter delta (Δ). The deltoid muscle is responsible for the shoulder's range of motion and stability. It is involved in lifting the arm, such as when reaching for objects or carrying heavy weights, and it helps prevent dislocation of the glenohumeral joint.
The deltoid muscle is divided into three distinct parts: the anterior or clavicular, middle or acromial, and posterior or spinal. These parts originate from different regions of the shoulder and each performs a unique function. The anterior deltoid flexes and medially rotates the arm, assisting in movements like brushing hair. The middle or acromial part is the largest and strongest, and it abducts the arm, lifting it away from the body. The posterior or spinal part extends and laterally rotates the arm.
The deltoid muscle is a powerful muscle used in various activities of daily living (ADLs) and athletic activities. For example, it is active when playing sports such as netball, swimming, and water polo, as well as when performing repetitive overhead activities like painting or pitching. However, these types of activities can also lead to deltoid pain and injuries. Common abnormalities affecting the deltoid include tears, fatty atrophy, and enthesopathy, often related to traumatic shoulder dislocation or rotator cuff tears.
The deltoid muscle is innervated by the axillary nerve, which provides motor and sensory innervation to the shoulder. It receives its blood supply from various branches of the axillary artery, including the thoracoacromial artery, the circumflex humeral arteries, and the deep brachial artery. The deltoid muscle is a common site for intramuscular injections, including vaccinations, due to its superficial nature.
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The deltoid is a key shoulder stabiliser
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the shoulder. It is comprised of three distinct portions: the anterior or clavicular, the middle or acromial, and the posterior or spinal. The deltoid is a key shoulder stabiliser, providing stability and motion to the shoulder joint.
The deltoid muscle is responsible for elevating the arm in the scapular plane, with its contraction also elevating the humeral head. It is the prime mover of arm abduction along the frontal plane, with its fibres contracting simultaneously to assist in abducting the arm past 15 degrees. The deltoid cannot initiate abduction as it contracts parallel to the humeral axis. However, it plays a crucial role in preventing inferior glenohumeral joint displacement during activities such as deadlift exercises.
The anterior deltoid has several important functions, including flexion, internal rotation, and horizontal adduction. To stretch this muscle, the reverse action of extension, external rotation, and horizontal abduction can be performed. The therapist typically stands behind the patient, holding the testing shoulder. The anterior deltoid also works in tandem with the subscapularis, pecs, and lats to internally (medially) rotate the humerus. Additionally, it assists the pectoralis major in flexing the shoulder and the arm when walking.
The posterior deltoid is responsible for extension, external rotation, and horizontal abduction. To stretch this muscle, the reverse action of flexion, internal rotation, and horizontal adduction can be performed. The therapist will initially stand in front of the patient and then move behind them for a better length assessment. The posterior fibres assist the latissimus dorsi in extending the shoulder.
The deltoid muscle is susceptible to various pathologies, including tears, fatty atrophy, and enthesopathy. Deltoid tears are often associated with traumatic shoulder dislocations or massive rotator cuff tears. Rotator cuff tears place significant strain on the deltoid, as it compensates for the loss of strength to prevent abduction motion loss. Deltoid pain can affect individuals who perform repetitive overhead activities or those who carry heavy loads.
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It is innervated by the axillary nerve
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is a key shoulder stabilizer and is responsible for elevating the arm in the scapular plane. The deltoid is a very powerful muscle and is used in many everyday activities, such as putting on clothes, carrying shopping bags, or washing hair, as well as athletic activities like swimming, water polo, and netball.
The deltoid muscle is innervated by the axillary nerve, which is a mixed nerve carrying both motor and sensory information. The axillary nerve originates from the brachial plexus, specifically the anterior rami of the cervical nerves C5 and C6, and travels through the quadrangular space to innervate the deltoid and teres minor. It enters the quadrilateral space, curves around the humerus deep to the deltoid muscle, and then divides into anterior and posterior branches to supply the deltoid muscle and the skin over the deltoid. The anterior branch provides the most consistent innervation for the deltoid muscle, containing all the fibres that innervate the anterior and middle deltoid muscle. The posterior branch supplies the posterior part of the deltoid and the teres minor.
The axillary nerve is susceptible to injury, particularly in anterior-inferior dislocations of the shoulder joint, compression of the axilla with a crutch, or fracture of the surgical neck of the humerus. Injury to the axillary nerve can result in paralysis of the deltoid muscle, leading to a loss of arm abduction, weak flexion, extension, and rotation of the shoulder, and flat shoulder deformity.
The deltoid muscle is also supplied by the thoracoacromial branch of the axillary artery, as well as minor contributions from the posterior humeral circumflex and profunda brachii arteries.
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The deltoid is susceptible to injury
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the shoulder. It is responsible for lifting the arm and giving the shoulder its range of motion. The deltoid is susceptible to injury due to its function and anatomy.
The deltoid is a powerful muscle that is frequently used in activities of daily living (ADLs) and athletic activities. It is involved in movements such as putting on clothes, carrying shopping bags, and washing hair, as well as sports like swimming and water polo. This frequent and repetitive use of the deltoid muscle makes it susceptible to overuse injuries, strains, and tears.
Overuse of the deltoid muscle without adequate rest can lead to deltoid strain, causing pain, swelling, and loss of function. Additionally, a forced eccentric contraction of the shoulder, such as during weight lifting, can also result in a deltoid strain. In more severe cases, direct traumatic blows to the shoulder or accidents can cause tears in the deltoid muscle, leading to severe pain, swelling, and muscle bulge or gap.
The deltoid muscle is also susceptible to injury due to its role in compensating for weaknesses in the rotator cuff. Rotator cuff tears or injuries can place more strain on the deltoid, increasing the risk of deltoid fatigue, injury, or tears. Furthermore, the deltoid can be indirectly affected by conditions such as enthesitis, calcific tendinitis, myositis, infection, tumors, and chronic avulsion injury.
To prevent deltoid injuries, it is essential to warm up, cool down, and stretch properly. Gradual strength training and conditioning can also help to prevent strain and injury. When recovering from a deltoid injury, gentle stretching can aid in reducing pain and improving flexibility. For mild injuries, a doctor may recommend adjusting exercise routines and using over-the-counter anti-inflammatories to manage symptoms. More severe injuries may require physical therapy and restricted activities to promote healing and regain function.
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Frequently asked questions
The deltoid muscle is a large, triangular-shaped muscle that lies over the glenohumeral joint in the shoulder.
The deltoid muscle is one of the main abductors of the shoulder, helping lift the arm when reaching for objects. It also helps to prevent dislocation of the glenohumeral joint when carrying heavy weights.
The deltoid muscle is made up of three distinct sets of muscle fibres, which can be further divided into seven neuromuscular segments. The three main parts are the anterior or clavicular, middle or acromial, and posterior or spinal.
The deltoid muscle is impacted by common injuries and clinical procedures. Issues can include tears, atrophy, enthesopathy, and infection.
