Dominic Stone
The deltoid is a large, triangular-shaped muscle that covers the shoulder joint and gives it its rounded contour. It is a very powerful muscle that is used in many everyday actions, such as lifting, pushing, and pulling, as well as athletic activities. The deltoid is a superficial muscle, meaning it lies deep only to its overlying fascia, the platysma muscle, and skin. It is a main muscle group in the upper body and is connected to many other muscles and bones in the upper back, neck, and shoulder region. The deltoid is responsible for elevating the arm in the scapular plane and plays a significant role in shoulder abduction, as well as smaller roles in flexion and extension movements of the arm.
| Characteristics | Values |
|---|---|
| Name | Deltoid Muscle |
| Other Names | Delt, Deltoideus, Common Shoulder Muscle |
| Description | A thick, large, triangular-shaped muscle that forms the rounded contour of the shoulder |
| Location | Shoulder, where the upper arm meets the torso |
| Function | Abduction, flexion, and extension movements of the arm; stabilizes the glenohumeral joint |
| Blood Supply | Axillary Artery, Thoracoacromial Artery, Circumflex Humeral Arteries, Deep Brachial Artery |
| Innervation | Axillary Nerve (C5, C6), Brachial Plexus |
| Muscle Parts | Anterior/Clavicular, Lateral/Acromial, Posterior/Spinal |
| Muscle Attachments | Clavicle, Acromion, Spine of Scapula, Humerus |
| Prone to Injuries | Yes, due to high mobility and minimal bone attachments |
| Common Injuries | Strains, Tears, Bursitis, Tendonitis, Rotator Cuff Tears |
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What You'll Learn
Deltoid muscle structure
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the shoulder. It is comprised of three distinct parts: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). These three parts form a U-shaped proximal attachment, mirroring the trapezius muscle's distal insertion.
The deltoid muscle is a key player in shoulder stability and motion, working alongside other shoulder muscles such as the rotator cuff muscles. It helps to elevate the arm in the scapular plane, with its contraction also elevating the humeral head. The deltoid is responsible for arm abduction, which is raising the arm out to the side of the body, as well as flexion (moving the arm forward) and extension (moving the arm backward). It also assists in stabilization of the shoulder joint to prevent dislocations, especially when lifting the arm or carrying weight.
The deltoid muscle is supplied by the thoracoacromial artery and its branches, as well as the circumflex humeral arteries and the profunda brachii artery. It is innervated by the axillary nerve, which originates from the anterior rami of the cervical nerves C5 and C6. Studies have shown that there are seven neuromuscular segments to the deltoid muscle, with three lying in the anatomical anterior head, one in the middle head, and three in the posterior head. These neuromuscular segments work in coordination with other muscles of the shoulder girdle, such as the pectoralis major and supraspinatus.
The deltoid muscle is a common site for intramuscular injections, including vaccinations. Conditions affecting the deltoid muscle include tears, fatty atrophy, and enthesopathy, which can be caused by trauma or chronic wear and tear. Deltoid pathologies can lead to functional disfunction of the shoulder complex, and rotator cuff tears can place additional strain on the deltoid.
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Deltoid muscle function
The deltoid muscle is a large, thick, triangular-shaped muscle that covers the top of the shoulder. It gets its name from its shape, which resembles the inverted Greek letter delta (Δ). The deltoid is a key shoulder stabilizer, providing stability and motion to the shoulder joint. It helps lift the arm to the front, side, and back, and also assists in forward elevation.
The deltoid muscle has three functionally and anatomically distinct parts: the anterior or clavicular part (front delt), the posterior or scapular part (rear delt), and the intermediate or acromial part (side delt). These parts work together to perform a variety of movements. The anterior deltoid is responsible for flexion, internal rotation, and horizontal adduction, while the posterior deltoid is responsible for extension, external rotation, and horizontal abduction. The acromial part, or the middle deltoid, is the largest and strongest part of the deltoid muscle. It is responsible for abducting the arm, or raising it out to the side of the body.
The deltoid muscle is a powerful muscle that is used in many everyday activities, such as putting on clothes, carrying shopping bags, or washing hair. It is also used in athletic activities such as swimming, water polo, and netball. The deltoid muscle can compensate for lost arm strength due to injuries such as rotator cuff tears. However, overuse or repetitive overhead arm movements can lead to deltoid muscle pain and injuries such as tears, tendonitis, and strains.
The deltoid muscle is supplied by the axillary nerve, which originates from the anterior rami of the cervical nerves C5 and C6. Damage to the axillary nerve can lead to paralysis of the deltoid muscle and affect its function. To test the function of the deltoid muscle, the arm must be raised beyond 15 degrees of abduction, and the patient then pushes against resistance. If the muscle is functioning properly, contraction should be felt near the acromion of the scapula.
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Deltoid muscle injuries
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is divided into three distinct portions or heads: the anterior (front), middle, and posterior (back). The deltoid muscle is responsible for lifting the arm out to the side of the body and assisting in lifting the arm forward. It is a powerful muscle that is needed for various athletic activities and everyday activities such as putting on clothes, carrying shopping bags, etc.
Deltoid strains are graded based on their severity, ranging from Grade I to Grade III. Grade I strains cause mild pain and minor tears, with patients still being able to use their arms with minimal pain. Grade II strains represent a partial tear of the deltoid muscle, resulting in increased pain and difficulty lifting the arm. Grade III strains are the most severe, with complete tearing of the muscle, causing severe pain and dysfunction in the arm.
Diagnosis of deltoid strains involves examining the mechanism of injury and the patient's symptoms. A physical examination is crucial, and range-of-motion and strength testing are performed to confirm the diagnosis. Treatment for deltoid strains depends on the grade of the injury. Grade I injuries usually require minimal treatment, while Grade II and Grade III injuries may take longer to recover, requiring rest and, in some cases, conservative treatment or surgery.
Other conditions affecting the deltoid muscle include adhesive capsulitis (frozen shoulder), axillary nerve palsy, bursitis, deltoid fibrosis, rotator cuff tears, shoulder impingement syndrome, shoulder separation, tendonitis, and various other pathologies.
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Deltoid muscle pain
The deltoid muscle is a large, triangular-shaped muscle that covers the top of the shoulder and gives it its rounded contour. It is responsible for lifting the arm and moving it to the front, side, and back. The deltoid muscle is susceptible to various injuries and conditions that can cause pain and affect its function.
One of the most common causes of deltoid muscle pain is a strain, which can range from mild tightness to severe, restricting pain. Strains can occur suddenly due to forceful movements or develop gradually from repetitive motions and overuse. They can be graded from 1 to 3 based on their severity, with grade 3 strains causing severe pain, swelling, and muscle bulge or gap.
Another cause of deltoid muscle pain is a rotator cuff tear, which occurs when one of the tendons in the rotator cuff becomes detached from the arm bone. This can lead to pain, stiffness, and soreness in the shoulder and may require the deltoid muscle to work harder to compensate for the loss of function. Additionally, shoulder impingement syndrome, which is caused by friction between the shoulder muscles or tendons and bones, can result in deltoid muscle pain and inflammation.
Other conditions that can affect the deltoid muscle include adhesive capsulitis, also known as frozen shoulder, which causes shoulder pain, muscle spasms, and stiffness. Axillary nerve palsy, which involves compression or damage to the axillary nerve, can also lead to deltoid muscle pain and weakness. Bursitis, an inflammation of the bursa in the shoulder, may cause muscle irritation and make it difficult to move the joint. Deltoid fibrosis, which can occur due to repeated shoulder muscle injections, can cause the muscle to stop repairing itself.
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Deltoid muscle stabilisation
The deltoid muscle is the muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'. It is a large, triangular-shaped muscle that lies over the glenohumeral joint, giving the shoulder its rounded contour. The deltoid muscle is made up of three distinct sets of muscle fibres: the anterior or clavicular part (commonly known as the front delt), the posterior or scapular part (commonly known as the rear delt), and the intermediate or acromial part (commonly known as the side delt). These fibres are pennate muscle, but electromyography suggests that the deltoid consists of at least seven groups that can be independently coordinated by the nervous system.
The deltoid muscle is responsible for elevating the arm in the scapular plane, and its contraction in doing this also elevates the humeral head. It is the prime mover of shoulder abduction and helps lift the arm to the front, side, and back. The deltoid muscle works alongside other shoulder muscles, such as the rotator cuff muscles, to help perform a variety of movements.
An important function of the deltoid is the stabilisation of the shoulder joint, preventing subluxation or dislocation of the head of the humerus, particularly when carrying a load. All heads of the deltoid work together to produce abduction of the shoulder joint. It compensates for the loss of strength in the rotator cuff. The deltoid's role in stabilisation is particularly important for people who do repetitive overhead activities, such as swimmers, pitchers, and painters, as well as those carrying objects like suitcases.
Deltoid strengthening exercises can help improve the strength of the deltoid muscles and prevent injuries. Some examples of these exercises include:
- Standing next to a wall with your back and elbow straight, then gently pushing your arm to the side against the wall as hard as possible without pain. Hold for 5 seconds and repeat 10 times on each side.
- Using a suitable dumbbell weight, perform arm raises anterior, lateral, and posterior. Repeat 10 times on each side without pain.
- Resistance band forward raises, lateral raises, and pullbacks. Repeat 10 times on each side without pain.
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Frequently asked questions
The deltoid muscle is a large, triangular-shaped muscle that forms the rounded contour of the human shoulder. It is also known as the 'common shoulder muscle'.
The deltoid muscle is responsible for elevating the arm in the scapular plane. It is also one of the main abductors of the shoulder, helping to lift the arm when reaching for objects. It also helps to prevent dislocation of the glenohumeral joint.
The deltoid muscle is anatomically divided into three parts: the anterior, or clavicular; lateral, or acromial; and posterior, or spinal.
The deltoid muscle can be injured by repeated overhead activities, sports injuries, and motor vehicle crashes. Deltoid muscle tears are uncommon and usually associated with rotator cuff tears or traumatic shoulder dislocations.
