Deltoid Muscle: Anatomy, Function, and Treatment

The deltoid muscle is the main muscle of the shoulder. A triangle-shaped muscle, it helps move your upper arm and stabilizes the shoulder joint.

The deltoid connects to the clavicle (collarbone), spine of the scapula (shoulder blade), and humerus (upper arm bone). Braces Manufacturers

Deltoid Muscle: Anatomy, Function, and Treatment

Conditions that affect the deltoid muscle include rotator cuff injuries, nerve and blood vessel injuries, as well as strains, tendonitis, and shoulder infringement syndrome.

This article describes the anatomy of the deltoid muscle, as well as symptoms, treatment, and healing time for conditions affecting the deltoid muscle.

Deltoid muscles are a type of skeletal muscle involved in body movements. Unlike smooth muscles, which are involuntary, skeletal muscles are voluntary (meaning you control them).

Each deltoid muscle is located where the ball-and-socket joint of your shoulder connects your humerus (upper arm bone) to your trunk.

The main functions of the deltoid muscles are to stabilize the shoulder joint and move the humerus at or through the shoulder. These muscle movements are referred to as:

The deltoid muscles have three heads that attach to bone and other tissue. Their origins—where the muscle attaches to a fixed point that does not move when the muscle contracts—are the clavicle and scapula. Their insertion—the point that attaches to a bone that moves—is the humerus.

Together, these points help stabilize the shoulder joint and allow for a full range of motion of the upper arm.

The deltoid muscle is a common place to give drug and vaccine injections because it's easy to access.

Each of the three deltoid heads—anterior, lateral, posterior—enables different movements either on their own or together.

The anterior deltoid, located at the front of the shoulder, internally rotates the shoulder joint and moves the arm forward. It does so with a combination of flexion and medial rotation (rotating of a joint inward).

The origin point of the anterior deltoid is on the clavicle alongside the pectoralis major muscle of the chest. The adjacent points help stabilize the shoulder.

The lateral deltoid, located in the middle of the shoulder, lifts the humerus to the side (laterally) away from the body. During abduction, the lateral deltoid moves downward to accommodate the arm's outward movement.

The origin point of the lateral deltoid is at the outer tip of the scapula, which is known as the acromion process .

The posterior deltoid, located at the back of the shoulder, also rotates the joint laterally to move the arm outward and backward. During extension, the posterior deltoid allows the humeral head to rotate downward and inward in the socket of the joint.

The origin point of the posterior deltoid is on the part of the scapula known as the spine. This prominent ridge also serves as an origin point for several other muscles. This attachment both stabilizes and prevents the overextension of the shoulder joint.

The deltoid muscles are vulnerable to injuries that can affect not only the muscle but also connective tissues called tendons that connect muscles to bones. Underlying nerves or blood vessels can also be injured.

The rotator cuff is a group of muscles and tendons that surround the shoulder joint, keeping the head of the humerus firmly situated within the socket of the shoulder.

A rotator cuff tear is a common injury in which tendons are torn either partially or completely. Although the deltoid muscle isn't one of the rotator cuff muscles, the destabilizing effect of a tear can place mechanical stress on the deltoid muscle, leading to a deltoid strain.

Symptoms of a rotator cuff injury may include:

In some cases, treating a rotator cuff tear involves cutting through the deltoid muscle and then stitching it back together. This means you will need to rehabilitate the deltoid muscle along with the repaired rotator cuff.

The healing time for a rotator cuff injury varies depending on the size of the tear. If surgery is required, it takes six to nine months before it's completely healed.

The axillary nerve lies immediately below the deltoid muscle and controls both the deltoid muscle and other muscles of the upper arm. The nerve can be damaged by surgery or traumatic injuries, leading to symptoms such as:

Depending on the cause of the nerve injury, some people won't need treatment. The injury may get better on its own. But surgery may be needed to repair the damage along with extensive rehabilitation to regain shoulder, arm, and hand strength.

The rate of recovery is different for everyone, but it can take many months to heal.

The cephalic vein is a blood vessel that runs beside the deltoid muscle down the arm to the hand. It assists with circulation and fluid management within the muscle tissues.

An injury to the cephalic vein can result in fluid buildup in the upper arm, known as peripheral edema. This can cause pain and weakness and limit your range of motion.

The thoracoacromial  artery is another blood vessel that directly services all three deltoid heads. The artery typically runs through a groove between the deltoid and pectoralis muscles, but, in some people, the vessel tunnels through the deltoid muscle itself.

In such cases, any injury to the deltoid muscle can also damage the thoracoacromial artery, causing nerve injury, pain, spasms, and muscle atrophy (wasting) if not promptly treated.

Other conditions that affect the deltoid muscle include:

Strains and overuse injuries: When muscle fibers get overstretched, it causes muscle strain, which can happen suddenly or develop gradually over time from overuse or repetitive movements. Symptoms may include pain and difficulty moving and lifting your arm. Depending on how severe the strain is, it can take a few weeks to several months to heal.

Tendonitis: When the tendons in the shoulder get inflamed, it results in shoulder tendonitis. Symptoms may include pain and tenderness in the shoulder and the inability to hold your arm in certain positions. Mild tendonitis may take just a few weeks to heal, while chronic tendonitis can take months to heal.

Shoulder impingement syndrome: This occurs when the shoulder muscles or tendons rub against bones. Symptoms include joint pain and inflammation. Depending on the extent of the injury, it can take three to six months or up to a year for this injury to heal.

Treatment for these injuries may include:

You should call your healthcare provider if you have:

Although anyone can have problems with their deltoid muscles, your risk for shoulder problems increases if you:

If you have surgery or a severe injury involving the deltoid muscle, rehabilitation would typically involve an immobilizing shoulder brace to keep the arm still for at least two to three weeks. This gives the muscle ample time to heal and also prevents re-injury.

While the arm is immobilized, you would be encouraged to keep the elbow, wrist, and finger joints moving. Not doing so can lead to muscle stiffness in other areas and result in longer rehabilitation times.

You will likely start doing strength and range-of-motion exercises six weeks after surgery or injury under the guidance of your orthopedic surgeon or a physical therapist. An occupational therapist may be recruited to help you manage or regain abilities such as dressing, writing, driving, or throwing.

This rehabilitation timeline varies by your age, general health, the seriousness of your injury or surgery, the absence or presence of vascular or nerve damage, and how adherent you are to the rehabilitation plan.

Not surprisingly, exercise is the best way to keep deltoid muscles healthy and reduce the risk of injury. This may involve resistance and weight training or, in older people or those with physical limitations, stretching and rotational exercises to keep joints and tendons flexible.

Exercises beneficial to the shoulders and deltoid muscles include:

In addition, there are certain habits that can prevent repetitive stress injuries to the shoulder (including tendinitis and bursitis). This includes improving your general posture and not overdoing it with heavy weights at the gym or work.

The deltoid is the main muscle in the shoulder. It is made up of three heads called the anterior, lateral, and posterior deltoids. All three heads help move the arm and stabilize the shoulder joint. Each head also has different insertion points and enables different movements known as abduction, flexion, extension, and rotation.

The deltoid muscle can be injured or impacted by surgery either directly or indirectly. In such cases, rehabilitation may be needed to restore flexibility, range of motion, and strength.

Contact a healthcare provider if you have shoulder pain that has lasted for weeks; trouble sleeping due to shoulder pain; or decreased range of motion in your arm.

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By Brittany Ferri Brittany Ferri, MS, OTR-L, CCTP, is an occupational therapist, consultant, and author specializing in psychosocial rehab.

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Deltoid Muscle: Anatomy, Function, and Treatment

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