What Is the Shoulder? Shoulder Anatomy and Basic Structures

The shoulder is the anatomical region where the upper arm joins the body and permits movement of the arm in different directions. Shoulder anatomy comprises joints formed by the scapula, clavicle, and humerus, along with muscles, tendons, ligaments, bursae, blood vessels, and nerves. These structures work in coordination as the arm moves (PMID 30059442).

Summary: The shoulder is an anatomical region where the scapula, clavicle, and humerus move together with muscles, ligaments, and the rotator cuff. It encompasses not only the glenohumeral joint but the entire movement system between the body and the arm. The location of shoulder pain may provide a clue about the affected structure, but does not establish a diagnosis on its own. On examination, scapular movement, muscle strength, the nervous system, and circulation are assessed alongside shoulder movements. Sudden trauma, deformity, changes in circulation, marked loss of strength, chest pain, or shortness of breath require urgent evaluation.

Raising your arm overhead seems simple, yet during this movement the head of the humerus rotates on the glenoid, the scapula changes direction across the ribcage, and the rotator cuff muscles stabilise the joint. The clavicle also follows the scapula's positional changes. This coordination underpins the shoulder's extensive range of motion.

Wide range of motion facilitates daily life, yet exposes the tendons, joint capsule, and muscles around the shoulder to strain. Pain felt at the front of the shoulder, over the top, on the outer side, around the scapula, or radiating down the arm does not necessarily indicate the same problem for this reason. The location of pain should be interpreted alongside its onset pattern, relationship to movement, and associated findings.

Which Region Does the Shoulder Comprise and What Boundaries Does It Have?

The shoulder is an anatomical region extending from the lower neck to the beginning of the upper arm, and from the clavicle region anteriorly to the upper and outer portions of the scapula posteriorly. Besides the joint point where the arm attaches to the body, it includes the muscles, tendons, ligaments, bursae, blood vessels, and nerve tissues that move and protect this connection.

In everyday language, "shoulder" typically refers to the rounded region on the outer side of the arm. Anatomically, however, the shoulder is a broader area. The movement system between the upper arm and the body depends on three bones and the connections between them working together. Although complaints felt at the front, side, or around the scapula lie in the same general region, they may originate from different structures.

The boundaries of the shoulder region can be practically described as follows:

• Superiorly: The lower lateral neck region and the upper aspect of the clavicle
• Anteriorly: The clavicle, the upper portion of the pectoral muscle, and the anterior aspect of the glenohumeral joint
• Laterally: The muscle tissue covering the humeral head and the outer contour of the shoulder
• Posteriorly: The scapula, the muscles surrounding it, and the posterior aspect of the joint
• Inferiorly: The axillary fold and the beginning of the upper arm

The outward shape of the shoulder is not formed by bone alone. The deltoid muscle makes a considerable contribution to the rounded external contour of the shoulder. The posture of the scapula, the position of the clavicle, and the function of the rotator cuff tendons also influence the appearance and movement pattern of the shoulder girdle.

When the arm is raised, movement does not occur only at the glenohumeral joint. The scapula rotates and translates across the ribcage, and the clavicle accompanies this movement. For this reason, movements such as lifting the arm overhead, reaching backwards, or abducting the arm from the body involve assessment of the entire shoulder girdle.

Pain around the shoulder does not always originate from shoulder structures. Referred pain from nerve roots in the neck, the ribcage, and certain internal organs can also be felt in this region. In particular, if pain does not change markedly with movement and is accompanied by chest, abdominal, respiratory, or circulatory symptoms, evaluation should not be limited to the shoulder.

Which Bones and Joints Form the Anatomy of the Shoulder?

The shoulder anatomy is formed by three bones and four fundamental articulations between them. The humerus, scapula, and clavicle work together in the glenohumeral, acromioclavicular, and sternoclavicular joints, as well as in the functional scapulothoracic articulation. This arrangement contributes to the generation of arm movements and the transfer of loads to the body.

Three Bones Forming the Shoulder

• Humerus: The head of the humerus articulates with the glenoid, a shallow joint surface on the scapula. The relationship between the rounded humeral head and the relatively shallow glenoid permits the arm to move in different directions.

• Scapula: A flat, triangular bone located in the upper back. In addition to the glenoid cavity, the acromion and coracoid processes are parts of the scapula. The acromion contributes to the bone contour of the upper shoulder; the coracoid serves as an attachment site for various muscles and ligaments.

• Clavicle: Extends between the breastbone and the scapula. It acts as a bony strut, holding the shoulder girdle at a defined distance from the body. It contributes to the transfer of loads from the upper limb to the skeletal framework of the body and to the positioning of the scapula.

Four Articulations in the Shoulder Complex

Structure	Regions joined	Primary function
Glenohumeral joint	Humeral head with glenoid	Permits multidirectional movement of the arm
Acromioclavicular joint	Acromion and clavicle	Accompanies small changes in the position of the scapula
Sternoclavicular joint	Clavicle and sternum	Provides a bony connection between the shoulder girdle and the axial skeleton
Scapulothoracic articulation	Scapula and rib cage	Allows the scapula to glide and rotate over the chest wall

Unlike the other three structures, the scapulothoracic articulation is not a true anatomical joint lined with cartilage; it is a functional gliding surface. Nevertheless, it is considered a separate articulation when assessing shoulder anatomy. The position of the scapula on the rib cage influences the orientation of the glenoid surface and the pattern of movement as the arm is raised.

The mobility of the glenohumeral joint is related to the shallowness of the glenoid surface relative to the humeral head. Shoulder stability therefore depends on more than the fit between the bones. The joint capsule, ligaments, labrum and rotator cuff tendons contribute to this stability passively or dynamically (PMID 34509200).

The labrum is a fibrocartilaginous structure surrounding the glenoid rim. It forms a ring around the articular surface, contributing to the functional depth of the socket. Labral injuries may be associated with pain, catching, a feeling of instability or a sensation that the shoulder may dislocate; however, these symptoms are not specific to labral problems.

The joint capsule and ligaments surround the joint and limit excessive movement in certain directions. Excessive capsular laxity may contribute to instability, while capsular stiffening may be associated with restricted movement. The shoulder is therefore assessed as a coordinated shoulder girdle system, rather than a collection of independent parts.

What Do the Shoulder Muscles and Rotator Cuff Do?

The shoulder muscles raise and rotate the arm, bring it towards the body and move it backwards. The rotator cuff consists of four muscles and their tendons, originating from the scapula and extending around the humeral head. It helps keep the humeral head controlled on the glenoid during movement and contributes to dynamic joint stability.

The rotator cuff is not the name of a single muscle; it is a structure formed by four muscles with complementary functions and their tendons. In the anatomical and physical assessment of the shoulder, each muscle is evaluated separately, but the findings are interpreted in the context of the whole joint (PMID 30059442).

• Supraspinatus: Contributes to the initial phase of raising the arm sideways. Its tendon runs close to structures at the top of the shoulder.
• Infraspinatus: Participates in external rotation of the upper arm and helps control the humeral head.
• Teres minor: Supports external rotation and helps stabilise the joint, particularly in certain arm positions.
• Subscapularis: Originates on the anterior surface of the scapula and contributes to internal rotation of the upper arm.

The tendons of these muscles form a cuff-like layer around the humeral head. As well as producing movement, the rotator cuff helps maintain the relationship between the joint surfaces. As the arm is raised, the deltoid pulls on the humerus; the rotator cuff helps control movement of the humeral head on the glenoid.

The shoulder's muscular system is not limited to the rotator cuff:

Muscle or muscle group	Main function
Deltoid	Helps raise the arm forwards, sideways and backwards
Rotator cuff	Produces rotation and supports dynamic control of the glenohumeral joint
Trapezius and serratus anterior	Regulate the position and rotation of the scapula on the rib cage
Rhomboid muscles	Help draw the scapula towards the spine
Pectoralis major	Helps bring the arm towards the body and rotate it inwards
Latissimus dorsi	Helps move the arm backwards, downwards and towards the body

The scapula does not remain still while the arm moves. The trapezius, serratus anterior and other surrounding muscles rotate it in the appropriate direction. The glenoid surface thus changes orientation as the arm rises. Coordination of the rotator cuff, deltoid and muscles controlling the scapula is important for everyday tasks such as combing hair, dressing, reaching and lifting.

Age-related changes, strain or tears in the rotator cuff tendons do not cause the same symptoms in everyone. Symptoms and imaging findings may not correspond directly. Assessment considers the duration of pain, loss of strength, history of trauma, everyday function and examination findings together. In suitable patients, non-surgical management may include activity modification, exercise and physiotherapy (PMID 37003656).

How Does the Shoulder Joint Move?

The shoulder joint allows the arm to move forwards, backwards, sideways and towards the body, as well as to rotate inwards and outwards. These movements do not arise solely from the glenohumeral joint. The scapula, clavicle, deltoid and rotator cuff work together to support range of motion and control the humeral head on the glenoid.

What are the main shoulder movements?

Shoulder anatomy forms a system that allows the arm to move in different planes:

• Flexion: Raising the arm forwards and upwards.
• Extension: Moving the arm behind the body.
• Abduction: Moving the arm out to the side.
• Adduction: Bringing an outstretched arm towards the body.
• Internal rotation: Inward rotation of the humerus, used when bringing the hand to the waist or back.
• External rotation: Outward rotation of the humerus, evident in movements such as combing the hair or reaching the back of the neck.
• Circumduction: Circular movement of the arm produced by a sequence of flexion, abduction, extension and adduction.

When the arm is raised overhead, not all of the movement is produced by the glenohumeral joint. Rotation of the scapula on the rib cage and changes in clavicle position also contribute. Range of motion may vary with age, pain, muscle strength, joint stiffness, posture and the measurement method.

Why does the scapula participate in movement?

As the arm rises, the scapula rotates upwards and outwards, with the clavicle accompanying this change in position. Coordinated movement of the glenohumeral joint and scapula is called scapulohumeral rhythm. This describes functional coordination that can vary throughout movement, rather than a fixed ratio.

Movement component	Main contribution
Glenohumeral joint	Allows the humerus to move on the glenoid
Scapular movement	Changes the orientation of the glenoid surface as the arm rises
Clavicular movement	Accompanies coordinated positioning of the scapula relative to the trunk
Rotator cuff muscles	Help control the humeral head throughout movement
Deltoid muscle	Generates force to raise the arm
Trunk and spine	Influence the direction and overall extent of reaching when needed

When the balance between the rotator cuff and deltoid is disrupted, the arm may still move, but movement may feel painful, restricted or unstable. Early elevation of the scapula or sideways leaning of the trunk may compensate for restricted shoulder movement. Examination therefore assesses not only the final position the arm reaches, but also how it moves.

Active movement is movement of the arm using the person's own muscle strength. In passive movement, the examiner moves the arm while minimising the person's muscular contribution. Differences between active and passive movement can provide clues about pain, muscle and tendon function, and joint stiffness, but do not establish a diagnosis on their own.

Which Nerves Pass Through the Shoulder Region?

The nerves of the shoulder region arise largely from the brachial plexus, which extends from the neck into the arm. The axillary and suprascapular nerves contribute directly to shoulder muscle movement and regional sensation. The long thoracic, musculocutaneous and radial nerves also participate in the functional movement chain of the scapula and upper limb.

The brachial plexus is a nerve network usually formed by the anterior rami of the C5, C6, C7, C8 and T1 spinal nerves. Fibres from the roots pass through trunks, divisions and cords before branching into peripheral nerves. As anatomical variations can occur, neurological assessment does not rely solely on a schematic distribution (PMID 19412559).

The main nerves have the following functions:

• Axillary nerve: Runs close to the lower part of the shoulder joint. It supplies the deltoid and teres minor muscles and contributes to sensation in a specific area of skin on the outer side of the shoulder.
• Suprascapular nerve: Passes through anatomical openings in the scapula to reach the supraspinatus and infraspinatus muscles.
• Long thoracic nerve: Supplies the serratus anterior. This muscle helps keep the scapula aligned with the chest wall and controls its rotation as the arm rises.
• Musculocutaneous nerve: Travels into the front of the upper arm and supplies the muscles involved in bending the elbow.
• Radial nerve: Passes through the back of the upper arm and connects with muscles that help extend the elbow, wrist and fingers.

Nerve involvement around the shoulder may cause more than shoulder pain. Numbness, tingling, burning, reduced sensation or changes in muscle strength may develop in the upper arm, forearm or hand. Symptoms that worsen with neck movement or extend to the hand make assessment of the nerve roots and brachial plexus important.

Traumatic nerve injuries may be associated with shoulder dislocation, injuries around the clavicle or strong traction applied to the neck and shoulder region. The mechanism of injury, distribution of weakness and location of sensory changes guide assessment (PMID 30707114).

Do not wait if new weakness, numbness, coldness, pallor or a bluish colour develops in the arm or hand. One or more of these signs may indicate vascular or nerve involvement and requires emergency assessment.

What Can the Location of Shoulder Pain Suggest About the Structure Involved?

The location of shoulder pain may guide assessment of the rotator cuff, acromioclavicular joint, biceps tendon, joint capsule, structures around the scapula or nerves arising from the neck. However, pain location does not identify the exact source. Its onset, changes with movement, night-time symptoms, trauma and neurological signs should be considered together.

Where the pain is felt	Structures that may be assessed	Possible accompanying clues
Top of the shoulder	Acromioclavicular joint	Pain when reaching towards the opposite shoulder or moving the arm across the chest
Front of the shoulder	Biceps tendon, subscapularis, glenohumeral joint	Tenderness during lifting, pulling or internal rotation
Outer side of the shoulder	Rotator cuff tendons, subacromial region	Pain when raising the arm sideways or difficulty lying on that shoulder
Back of the shoulder	Posterior rotator cuff, capsule, muscles around the scapula	Symptoms during external rotation or overhead movement
Around the scapula	Muscles controlling the scapula, structures originating in the neck	Burning or tension that increases after remaining in one position for a long time
An area extending below the elbow and into the hand	Nerve roots in the neck or peripheral nerves	Numbness, tingling, weakness or pain that changes with neck movement

Rotator cuff problems may cause pain on the outer side of the shoulder or towards the upper arm rather than directly over the tendon. Pain that increases during a particular part of sideways arm elevation and then eases may be described on examination as a ‘painful arc’. This finding alone does not establish a diagnosis; it is interpreted alongside other examination and imaging findings (PMID 30059442).

The following details help describe the distribution of pain:

• Whether the pain is felt at a small point or over a wider area
• Whether it changes when the arm is raised, moved backwards or rotated
• Whether it spreads from the shoulder towards the elbow, forearm or hand
• Whether neck movements alter the symptoms
• Whether numbness, tingling, weakness or restricted movement accompanies it
• Whether it started after a fall, impact, throwing action or sudden pull
• Whether the pain affects sleep or daily activities

Nerve root symptoms in the C5–C6 distribution may spread to the outer shoulder and upper arm. Not all pain felt in the shoulder therefore originates in the glenohumeral joint. Assessment also considers the neck, nervous system, acromioclavicular joint and scapular movement pattern.

If shoulder or upper torso pain begins with chest pain, sudden shortness of breath, fainting, coughing up blood or a rapid heartbeat, call 112 or go to an emergency department. One or more of these signs may be associated with serious cardiovascular or lung problems.

After trauma, one or more signs such as severe pain, deformity, inability to move or inability to bear weight require emergency assessment for dislocation or fracture. Trying to force the shoulder back into place can damage blood vessels, nerves and soft tissues.

How Are Shoulder Symptoms Assessed?

Shoulder symptoms are assessed through the history, a physical examination comparing both sides and imaging when needed. Questions cover the onset of pain, its relationship to trauma, changes with movement and effects on sleep. Active and passive range of motion, muscle strength, joint stability, scapular movement, sensation and circulation are then assessed together.

What is checked during examination?

The location of pain matters, but does not identify the affected structure on its own. Problems arising in the neck, elbow, nerves or certain internal organs may cause shoulder-region pain. Assessment therefore does not focus solely on the painful point.

The examination may include the following steps:

• The position of the shoulders, muscle bulk, swelling, redness and deformity are observed.
• The clavicle, scapula, acromioclavicular joint and surrounding soft tissues are assessed by palpation.
• Active movements performed using the person's own strength are compared with passive movements provided during examination.
• Rotator cuff muscle strength and the effect of specific movements on pain are assessed.
• The movement of the scapula over the rib cage as the arm rises is observed.
• Stability may be assessed if the joint feels unstable or as though it may dislocate.
• Sensation, reflexes, muscle strength, hand colour and circulation may be checked.
• Examination of the neck and elbow is included when necessary.

Muscle strength is often recorded clinically using the Medical Research Council scale from 0 to 5. Zero means no observable contraction; five indicates strength considered normal under examination conditions. Pain, fear and the person's participation may affect the result, so the score is interpreted in context.

Which imaging method is used and when?

Method	Contribution to assessment
X-ray	Provides information about fractures, dislocations, bone structure, joint congruity and joint space
Ultrasound	Can examine the rotator cuff tendons, biceps tendon and fluid collections during movement
Magnetic resonance imaging	Assesses soft tissues such as tendons, muscles, ligaments, labrum, capsule and cartilage in detail
Computed tomography	Helps examine complex bony structures, certain fractures and articular surfaces

Not every case of shoulder pain requires imaging. The method is chosen according to the presence of trauma, examination findings, symptom duration and the structure being assessed. In traumatic shoulder girdle injuries, the extent of bone and soft-tissue assessment may vary with the mechanism of injury (PMID 31076034). For persistent non-traumatic pain, imaging decisions also depend on the clinical question (PMID 28537759).

The initial approach varies with the diagnosis and the person's circumstances. Activity modification, controlled exercise and physiotherapy may be considered in suitable patients. Exercise type, frequency and load should be planned according to pain, movement capacity and diagnosis; exercise therapy does not mean using the same programme for every shoulder problem (PMID 38848304).

Which symptoms require prompt attention?

If one or more of the following signs are present, call 112 or go to an emergency department:

• Sudden shortness of breath, chest pain, fainting, coughing up blood, or rapid heartbeat
• Severe pain that is disproportionate to the injury, persistent or rapidly worsening
• Pain that markedly worsens with passive movement
• Tense swelling, new numbness or weakness
• Coldness, pallor, a bluish colour, new numbness or new weakness in the limb
• New confusion or incoherent speech; fever is not required
• Severe pain, deformity, inability to move or inability to bear weight
• Uncontrolled bleeding

Rapidly increasing pain out of proportion to the injury, accompanied by tense swelling, a marked increase in pain with passive movement, numbness or weakness, may suggest compartment syndrome. This is a surgical emergency; if one or more of these symptoms develops, do not delay to try painkillers.

If one or more of the following occurs, medical assessment is needed the same day:

• One-sided leg swelling, pain, or calf tightness
• Increasing redness, warmth, swelling or discharge at the wound; fever need not be present
• Wound edges opening
• A temperature of 38°C or above, persistent fever, chills or deterioration in general condition; if discharge instructions specify a lower threshold, that threshold applies
• New severe pain or inability to bear weight after a fall or impact

How Can Shoulder Health Be Protected During Everyday Movements?

To reduce unnecessary shoulder load, keep carried objects close to the body, take breaks during repetitive overhead tasks and arrange the workspace within comfortable reach. Regular movement matched to capacity may support muscular endurance. Do not force a movement to continue if sharp pain, catching or new weakness develops.

In everyday life, the shoulder may become fatigued less from a single major strain than from repeatedly making the same movement in an unsuitable position for a long time. Computer work, reaching for a high shelf or carrying a bag may seem ordinary, but the distance of the arm from the body, the weight carried and the number of repetitions alter how the shoulder muscles work.

• Bring the workspace closer: Keep the keyboard, mouse and frequently used items within a distance that does not require repeated reaching. Holding the elbow away from the body for long periods can make the shoulder muscles work continuously.
• Take breaks during overhead tasks: Do not perform tasks such as hanging curtains, organising high shelves or painting without interruption. Work on a secure surface; do not use unstable chairs or platforms.
• Distribute the load evenly: Instead of carrying a bag on the same shoulder for long periods, consider options that spread the load across both sides. The bag's weight should match the person's capacity.
• Keep objects close to the body: As a load moves further from the body, the leverage that the shoulder muscles must counter increases. Asking for help with heavy or bulky objects may be safer.
• Prepare for activity gradually: Before sport or strenuous physical work, begin with gentle general movements. The duration and content of a warm-up may vary with the activity, age and current health status.
• Do not force the range of motion: If sharp pain, catching, a sensation of impending dislocation or marked weakness occurs, do not insist on completing the movement.
• Increase the load gradually: When starting new exercises, do not increase weight, repetitions and time spent working overhead all at once. Progress according to the person's response and the guidance of the physiotherapist or doctor.
• Adjust your sleeping position to your symptoms: If lying on the painful shoulder worsens symptoms, turning onto the other side or your back may help. How a pillow is placed under the arm varies from person to person; an uncomfortable position should not be imposed.

Shoulder exercises are not the same for everyone. Do not start exercises found online if there is acute trauma, suspected dislocation, a fracture, new weakness or marked restriction of movement. Follow the direction, resistance and repetition pattern demonstrated by the physiotherapist or doctor.

If pain persists, treatment is chosen according to the diagnosis. Activity modification, exercise and physiotherapy may be considered for many shoulder problems. Injections are not all alike: their contents, potential benefits and risks vary with the diagnosis. Surgery may be considered when suitable non-surgical options are insufficient or inappropriate; it does not guarantee a particular outcome.

An orthopaedic assessment is appropriate if pain progressively worsens, repeatedly interrupts sleep, limits daily activities or is accompanied by new weakness. After trauma, a change in shoulder shape, inability to move the arm, or numbness, coldness, colour change or weakness in the hand requires assessment without delay.

Frequently asked questions

This section answers basic questions about the location of the shoulder, the spread of pain and symptoms that may require emergency assessment. The answers provide general guidance; a diagnosis cannot be based solely on the area of pain. The history of trauma, restricted movement, muscle strength, neurological and circulatory findings and, when needed, imaging results should be assessed together.

What causes pain in the shoulder region?

Shoulder pain may arise from muscle or tendon strains, rotator cuff problems, osteoarthritis, capsular stiffness, instability, dislocation, fracture or nerve involvement. Neck problems and certain internal organ conditions may also cause referred shoulder pain. To identify the cause, the onset, trauma, location of pain and changes with movement are assessed together.

Can the gallbladder cause shoulder pain?

Gallbladder problems can cause referred pain, particularly around the right shoulder or right scapula. Medical assessment is needed the same day if there is also right upper abdominal pain, tenderness, nausea, vomiting, fever, chills or jaundice. Such symptoms should not be interpreted solely as a shoulder muscle or joint problem.

Can shoulder pain cause nausea?

Severe pain can trigger nausea in some people, but the source of nausea is not always the muscles, bones or joint of the shoulder. Call 112 if there is chest pain, sudden shortness of breath, cold sweating, fainting or a rapid heartbeat. Right shoulder pain occurring with abdominal pain should also be assessed for possible internal organ causes.

Where can shoulder pain spread?

Shoulder pain can spread to the upper arm, neck, area around the scapula and elbow. Rotator cuff-related pain is often felt on the outer side of the shoulder and may increase when the arm is raised. If pain extending to the hand is accompanied by numbness, tingling or weakness, the neck, nerve roots and peripheral nerves are also assessed.

Which structures can cause pain at the front of the shoulder?

Pain at the front of the shoulder may be related to the biceps tendon, subscapularis tendon, glenohumeral joint, joint capsule or surrounding soft tissues. It may increase with forward arm elevation, carrying, pulling or rotation. As location alone does not establish a diagnosis, pain is assessed alongside examination and, when necessary, appropriate imaging.

Are the humeral head and acromion the same region?

The humeral head and acromion are not the same anatomical structure. In everyday language, the ‘top of the shoulder’ often means its prominent outer area. The acromion is the bony projection of the scapula extending over the shoulder. The humeral head articulates with the glenoid surface, forming the upper-arm side of the glenohumeral joint.

When does shoulder pain require emergency assessment?

Emergency help is needed for sudden shortness of breath, chest pain, fainting, coughing up blood, a rapid heartbeat, uncontrollable bleeding, new confusion or coldness and colour change in a limb. After trauma, severe pain, deformity, inability to move or bear weight, new numbness or weakness is also a reason for emergency assessment, even if only one is present.

This section provides general information and does not replace examination or a medical diagnosis.

This information is for educational purposes and does not replace diagnosis and treatment. Please consult your doctor about your symptoms.