The deltoid is the main muscle of the shoulder. It consists of three parts, also known as the head: the anterior deltoid, the lateral deltoid, and the posterior deltoid. All three contribute to arm elevation and play an important role in moving and stabilizing the shoulder joint and upper arm.
The entire deltoid extends from the ridge of the shoulder blade (scapula) to the end of the clavicle (clavicular).
This article discusses the anatomy of the deltoid muscle. It covers its function, health conditions that affect it, and recovery after injury or surgery.
Each head of the deltoid has a slightly different attachment point, also known as the insertion point. This allows for more control and full range of motion at the shoulder joint.
The anterior head of the deltoid works closely with the pectoralis major (chest muscle). This allows complete stabilization near its higher attachment point on the clavicle.
When each of the three heads of the deltoid is contracted together, it allows the arm to be raised to the side, up to 15 degrees from the body. This then triggers the rest of the shoulder (glenohumeral) joint to help stabilize the shoulder. Additional muscles contract to provide the rest of the arc of motion.
The anterior (front) deltoid rotates the shoulder joint by pulling the arm inward. By flexing (lifting the arm) and rotating inward (inside), it lifts the arm toward the front of the body. This is called forward bending.
This action can be seen in a variety of functional tasks and is important for arm movement. The forward bending motion moves the arm toward the insertion point of the anterior deltoid muscle.
The lateral (lateral) deltoid muscle rotates the shoulder joint laterally (to one side), bringing the arm out or away from the body. This is also called kidnapping. This movement is important when walking, reaching, and doing any task that moves the arms away from the center of the body.
This abduction moves the shoulder joint down to accommodate the outward movement of the entire arm. Contraction of the lateral deltoid muscle pushes the arm towards the insertion point of the lateral deltoid muscle on the proximal humerus (upper arm).
The posterior deltoid rotates the joint laterally, which in turn moves the arm back and out. This moves the entire arm toward the spine, which is where this part of the muscle attaches. This movement often occurs when dressing, reaching back, or throwing.
The deltoid is made up of three parts or heads: the anterior deltoid, the lateral deltoid, and the posterior deltoid. Everyone has a role to help move the arm, whether it’s forward, sideways, or backwards.
During pregnancy, the embryo develops a portion of the deltoid muscle from mesoderm cells. This is the middle layer in the earliest stages of development and becomes the structures that include bone and muscle.
Myoblasts are early muscle cells that evolve into muscle fibers. They usually develop into upper extremities (arms and hands) and lower extremities (legs and feet) during early development. The deltoid develops from dorsal muscle cells, which face the back of the body.
The anterior deltoid is composed of clavicle fibers because its insertion point is on the clavicle.
The outside of the deltoid has acromial fibers because it connects to the acromion, part of the scapula.
The posterior deltoid has spinal fibers due to its connection to the spinal protrusions or bony protrusions of the vertebrae.
The deltoid muscle develops from mesoderm cells in early pregnancy. This layer grows into muscle, bone, and other tissues.
Anatomical variations are possible differences in the structure of people’s bodies.
A common variation of the deltoid consists of a separate fascial sheath (connective tissue) and muscle fibers in the back of the deltoid. This can lead medical professionals to mistake a separate muscle fiber in the back of the deltoid for another muscle in the shoulder called the teres minor.
In some cases, the lateral deltoid bundle is associated with medial epicondyle The humerus (upper arm) is visible. This differs from its typical insertion point for the acromion of the humerus (in the scapula).
Such changes can complicate blood supply and nerve distribution. This makes it important for medical professionals to be vigilant during internal procedures such as surgery.
There may be other changes involving the blood supply.This thoracic shoulder Arteries play an important role in providing blood supply and oxygen to each deltoid head. This artery usually passes through the groove between the deltoid and pectoralis major muscles.
However, changes may be noticed in some individuals where this artery passes through the deltoid muscle rather than around it. If any of the deltoid muscles are injured, it may cause pain, cramping, changes in sensation, or a lack of blood supply.
There may be anatomical variations or differences in the deltoid structure of some people. This may include changes in where the muscle is attached. Also, the thoracoacromial artery may pass through the deltoid rather than surrounding it.
As mentioned earlier, the deltoid muscle plays an important role in arm movement. Each head of the deltoid also acts to stabilize the shoulder joint. This helps improve the fluidity and overall quality of arm movement.
The shoulder or glenohumeral joint consists of the scapula (scapula) and the humerus (upper arm). It relies on the upper arm muscles for stability and overall joint integrity.
Motor function is the only and main job of the deltoid.
The motor functions of the deltoid include:
- Shoulder Abduction: Raise the arm to the side or away from the midline of the body
- Shoulder Flexion: Raise your arms above your head
- Shoulder extension: Keeps the shoulders in their resting position while also offering the option to move backwards
The deltoid allows movement that is important for using the arm in everyday tasks.
The deltoid muscle has no sensory function, but the nerves and arteries that run through it provide oxygen and allow movement. Severe damage to the deltoid may indirectly result in injury to the underlying nerves and arteries that pass through or near the deltoid.
Associated conditions are often associated with damage to the deltoid or nearby muscles with similar functions.
Muscles in the upper arm region include the supraspinatus, infraspinatus, teres minor, and subscapularis (collectively known as the rotator cuff). The most common injury to this group of muscles is a rotator cuff tear, which tears the tendon where the arm joins the shoulder.
While the deltoid is not one of the rotator cuff muscles, it can be affected due to poor motor function or surgery on this group of muscles. This may place undue mechanical stress on the deltoid. If it goes on for a long time, it can lead to muscle sprains.
The abnormal muscle movement that causes this stress can be addressed by rehabilitating the entire upper arm after an injury or surgery.
The deltoid may also be a consideration when surgeons consider surgery on other parts of the arm.
The anterior head of the deltoid is located on the front of the arm. Therefore, this muscle is an important consideration when surgeons need to operate in this area.
Some procedures, such as rotator cuff repair surgery, may use a deltoid approach. This uses deltoid and pectoralis major fibers and anatomical landmarks to guide the incision.
Both the frontal and lateral methods of surgery involve splitting the deltoid fibers and then suturing them together.
Any method of splitting the deltoid fibers will damage the deltoid. This may require restoration of the deltoid as well as typical rehabilitation specific to surgery.
The axillary nerve, located just below the deltoid, controls the deltoid and other upper arm muscles. This nerve can also be affected by surgery or trauma. This will require broader rehabilitation efforts, as well as more procedures to attempt nerve regeneration and repair.
This nerve loss causes the deltoid and other muscles supplied by the axillary nerve to lose motion. There may also be a lack of sensation in your deltoid, depending on the severity.
The cephalic vein is adjacent to the deltoid muscle and aids in circulation and fluid management. Any type of cephalic vein injury can lead to fluid buildup in the upper arm.
If not resolved immediately, fluid buildup can lead to other complications. These include skin changes, decreased blood flow, nerve damage, and loss of muscle strength.
The deltoid may be affected by injury or surgery to the surrounding muscles and ligaments. For example, a rotator cuff tear can cause abnormal muscle movement that can put pressure on the deltoid. Some arm surgeries involve splitting the muscle fibers in the deltoid muscle and may require muscle rehabilitation.
Rehabilitation of the deltoid looks very similar to rehab for most of the large muscles of the arm.
If someone has had surgery on the deltoid or has an injury that requires extensive rehabilitation, treatment will follow a specific protocol. The protocol will vary slightly depending on the injury that occurred and whether surgery was performed.
Most protocols require the individual to wear a brace to keep the arm still for two to three weeks. This stability gives the muscle enough time to recover from repair without further or repetitive damage.
Physical Therapy After Shoulder Surgery
When the arm is immobilized, an occupational or physical therapist will help move the joint under the upper arm. This includes elbows, wrists and fingers. If these joints don’t move, it can lead to muscle weakness, which can prolong the recovery period.
More advanced exercises and range of motion activities begin about six weeks after surgery or injury. Later, your practice may develop into functional tasks including dressing, writing, driving, and throwing. This progression depends on how well you endured the previous steps and whether you have pain or complications.
This protocol may vary if nerve loss is caused by injury or surgery. In this case, pure reinforcement is not the focus of rehabilitation professionals. Retraining the nerves along with the muscles increases the chances of restoring the nerve connections between the brain and the injured muscle.
Whether it’s an injury or surgery, it’s important to exercise caution and strictly follow the instructions of an occupational or physical therapist. They are in close contact with your healthcare provider and will update each relevant professional.
Early treatment will help give you the best chance of restoring movement and nerve function in your shoulder.
The deltoid is the main muscle of the shoulder. It consists of three parts: the anterior deltoid, the lateral deltoid, and the posterior deltoid. All three parts help move the arm and stabilize the shoulder joint.
Each part of the deltoid has insertion (attachment) points in different structures of the body. The anterior deltoid muscle has an insertion point in the clavicle. There is one on the outside of the deltoid on the scapula. The posterior deltoid has an insertion point on the vertebrae.
Surgery to other muscles in the shoulder may damage or affect the deltoid. Rehabilitation can help restore movement and reduce pain. You may need to put the brace on first to give the muscles time to heal. Rehabilitation may then include specific exercises to build strength without reinjuring the shoulder.