Deltoid muscle anatomy Origin, Insertion, Function, Exercise

 

Deltoid Muscle

The deltoid muscle is a large, triangular muscle located in the shoulder region. It is named for its shape, which resembles a delta or the Greek letter delta (Δ). The deltoid muscle is composed of three distinct regions or heads: the anterior (front), middle, and posterior (back) heads.

The anterior head originates from the lateral third of the clavicle, while the middle head originates from the acromion process of the scapula. The posterior head originates from the spine of the scapula. All three heads converge to form a single tendon, which inserts into the deltoid tuberosity of the humerus bone.

The deltoid muscle is innervated by the axillary nerve, which arises from the brachial plexus. It is responsible for several movements of the shoulder joint, including abduction (lifting the arm away from the body), flexion (raising the arm in front of the body), and extension (moving the arm backward). Additionally, it assists in medial and lateral rotation of the arm.

Overall, the deltoid muscle is an important muscle for the stability and mobility of the shoulder joint.

Origin of Deltoid muscle

The deltoid muscle has three distinct regions or heads that have different origins:

1. The anterior (front) head originates from the lateral third of the clavicle.
2. The middle head originates from the acromion process of the scapula and the lateral border of the spine of the scapula.
3. The posterior (back) head originates from the inferior edge of the crest of the spine of the scapula.

All three heads of the deltoid converge to form a single tendon, which inserts into the deltoid tuberosity of the humerus bone. The deltoid muscle is innervated by the axillary nerve, which arises from the brachial plexus.

Insertion

The deltoid muscle inserts into the deltoid tuberosity of the humerus bone, which is located on the lateral side of the shaft of the humerus, about one-third of the distance from the proximal end (shoulder end) to the distal end (elbow end) of the bone.

The deltoid muscle's tendon is broad and flat, and it covers the superior and lateral aspects of the humeral head. It is important for the stability and mobility of the shoulder joint, and it helps to hold the humeral head in the glenoid fossa of the scapula during shoulder movement.

In addition to the deltoid tuberosity of the humerus, the deltoid muscle also has some weak insertions into the capsule of the shoulder joint, the acromion process of the scapula, and the spine of the scapula. These additional insertions may provide some extra stability to the shoulder joint.

Nerve supply

The deltoid muscle is innervated by the axillary nerve, which arises from the posterior cord of the brachial plexus. The axillary nerve arises from the spinal nerves C5 and C6, and it passes through the quadrilateral space, a small opening in the posterior aspect of the shoulder, to reach the deltoid muscle.

The axillary nerve supplies both motor and sensory innervation to the deltoid muscle. It provides the motor innervation that allows the deltoid muscle to contract and produce movement at the shoulder joint, including abduction (lifting the arm away from the body), flexion (raising the arm in front of the body), and extension (moving the arm backward). The axillary nerve also provides sensory innervation to the skin overlying the deltoid muscle, as well as the joint capsule of the shoulder joint.

Injury or damage to the axillary nerve can result in weakness or paralysis of the deltoid muscle, which can lead to difficulty with shoulder movement and stability.

Blood supply

The deltoid muscle receives its blood supply from several arteries, including the posterior circumflex humeral artery, the deltoid branch of the thoracoacromial artery, and the suprascapular artery.

The posterior circumflex humeral artery is the main arterial supply to the deltoid muscle, and it arises from the third part of the axillary artery. It runs around the surgical neck of the humerus, along with the axillary nerve, and then divides into several branches that supply the deltoid muscle.

The deltoid branch of the thoracoacromial artery is a small branch that arises from the thoracoacromial artery, which is a branch of the axillary artery. It supplies the anterior part of the deltoid muscle.

The suprascapular artery is another small branch of the subclavian artery that supplies the shoulder joint and the muscles around it, including the deltoid muscle.

These arteries provide a rich blood supply to the deltoid muscle, which is important for the muscle's function and recovery after injury.

Function of Deltoid muscle

The deltoid muscle is responsible for several movements of the shoulder joint and provides stability to the joint during arm movements. Its functions include:

• Shoulder abduction: The deltoid muscle is the primary muscle that lifts the arm away from the body in the plane of the scapula. When the deltoid contracts, it pulls the humerus bone upward and away from the body, allowing the arm to move outward and upward.
• Shoulder flexion: The anterior fibers of the deltoid muscle assist in flexing the arm at the shoulder joint, allowing the arm to move forward and upward in front of the body.
• Shoulder extension: The posterior fibers of the deltoid muscle assist in extending the arm at the shoulder joint, allowing the arm to move backward behind the body.
• Shoulder horizontal abduction: The middle fibers of the deltoid muscle are responsible for moving the arm outward away from the midline of the body.
• Shoulder horizontal adduction: The anterior fibers of the deltoid muscle are involved in moving the arm inward towards the midline of the body.
• Medial and lateral rotation: The deltoid muscle also assists in rotating the arm medially (inward) and laterally (outward).

Overall, the deltoid muscle is a critical muscle for shoulder joint mobility and stability, and it is essential for many activities that involve arm movement, such as throwing, reaching, lifting, and pushing.

Clinical significance

The deltoid muscle can be affected by various injuries and conditions that can result in pain, weakness, or limited range of motion. Some of the clinical significance of the deltoid muscle include:

• Rotator cuff injuries: The rotator cuff muscles and tendons, which surround the shoulder joint, are often injured in sports or from overuse. These injuries can result in pain, weakness, and limited mobility of the shoulder joint, which can affect the function of the deltoid muscle.
• Shoulder impingement syndrome: This condition occurs when the tendons of the rotator cuff and the bursa (a fluid-filled sac) become compressed between the bones of the shoulder joint, causing pain, inflammation, and reduced mobility. Shoulder impingement syndrome can affect the function of the deltoid muscle and limit its ability to lift the arm.
• Shoulder dislocation: When the humerus bone is forced out of the shoulder joint, it can damage the deltoid muscle, as well as other muscles and tissues around the shoulder. Shoulder dislocations can cause pain, swelling, weakness, and limited range of motion in the shoulder joint.
• Nerve injuries: The axillary nerve, which innervates the deltoid muscle, can be injured or compressed due to trauma or overuse, resulting in weakness or paralysis of the deltoid muscle.
• Muscle strains or tears: The deltoid muscle can be strained or torn due to overuse or trauma, resulting in pain, swelling, weakness, and limited range of motion of the shoulder joint.

In addition to these conditions, the deltoid muscle can also be affected by diseases such as muscular dystrophy or amyotrophic lateral sclerosis (ALS), which can result in muscle weakness and atrophy (wasting). Overall, understanding the anatomy and function of the deltoid muscle is important for the diagnosis and treatment of various shoulder-related injuries and conditions.

Stretching exercises of Deltoid muscle

Stretching the deltoid muscle can help improve shoulder mobility, reduce pain, and prevent injuries. Here are a few examples of stretching exercises for the deltoid muscle:

• Standing wall stretch: Stand facing a wall with your feet hip-width apart. Place one hand on the wall, with your arm straight and your fingers pointing upward. Slowly turn your body away from the wall, keeping your arm straight, until you feel a stretch in your shoulder. Hold for 15-30 seconds, then repeat on the other side.
• Cross-body stretch: Stand or sit with your back straight. Bring one arm across your chest and hold it with the opposite hand. Gently pull the arm toward your body until you feel a stretch in your shoulder. Hold for 15-30 seconds, then repeat on the other side.
• Doorway stretch: Stand in a doorway with your arms at your sides. Place your hands on the sides of the doorway at shoulder height. Step forward with one foot, keeping your arms straight and your hands on the doorway. Lean forward until you feel a stretch in your shoulders. Hold for 15-30 seconds, then step back and repeat on the other side.
• Shoulder circles: Stand with your feet hip-width apart and your arms at your sides. Slowly raise your shoulders up toward your ears, then roll them back and down in a circular motion. Repeat for 10-15 repetitions, then reverse the direction.

It's important to remember to stretch gently and gradually, without bouncing or jerking. If you have any shoulder pain or discomfort, consult a healthcare professional before starting any stretching or exercise program.

Strengthening exercises for Deltoid muscle

Strengthening the deltoid muscle can help improve shoulder stability and function, increase mobility, and prevent injuries. Here are a few examples of strengthening exercises for the deltoid muscle:

• Shoulder press: Stand or sit with your back straight and your feet hip-width apart. Hold a dumbbell or a barbell in each hand at shoulder height, with your palms facing forward. Raise the weights straight up above your head, then lower them back down to shoulder height. Repeat for 8-12 repetitions.
• Lateral raise: Stand or sit with your back straight and your feet hip-width apart. Hold a dumbbell or a weight plate in each hand at your sides, with your palms facing inward. Raise your arms straight out to the sides until they are parallel to the floor, then lower them back down to your sides. Repeat for 8-12 repetitions.
• Bent-over raise: Stand with your feet hip-width apart and your knees slightly bent. Hold a dumbbell in each hand, with your palms facing inward. Bend forward at the waist, keeping your back straight and your arms hanging down in front of you. Raise your arms straight out to the sides until they are parallel to the floor, then lower them back down. Repeat for 8-12 repetitions.
• Upright row: Stand with your feet hip-width apart and hold a barbell or a pair of dumbbells in front of your thighs, with your palms facing your body. Lift the weights straight up to your chin, keeping your elbows out to the sides. Lower the weights back down to your thighs. Repeat for 8-12 repetitions.

It's important to use proper form and technique when performing these exercises, and to start with a weight that is appropriate for your strength level. Gradually increase the weight and the number of repetitions as you get stronger. If you have any shoulder pain or discomfort, consult a healthcare professional before starting any strengthening or exercise program.

Conclusion

The deltoid muscle is a large, triangular muscle located in the shoulder region. It consists of three parts: the anterior, middle, and posterior deltoids, which have different origins, insertions, and functions. The deltoid muscle is responsible for a wide range of shoulder movements, including flexion, extension, abduction, adduction, and rotation.

Stretching and strengthening exercises for the deltoid muscle can help improve shoulder mobility, stability, and function, and prevent injuries. Examples of stretching exercises include standing wall stretch, cross-body stretch, doorway stretch, and shoulder circles. 

Examples of strengthening exercises include shoulder press, lateral raise, bent-over raise, and upright row. It's important to use proper form and technique when performing these exercises, and to start with a weight that is appropriate for your strength level. If you have any shoulder pain or discomfort, consult a healthcare professional before starting any stretching or exercise program.