Shoulder Joint

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Introduction

The shoulder, or glenohumeral joint, connects the upper arm to the chest. It provides articulation between the glenoid fossa of the scapula and the head of the humerus. These articulating surfaces are separated by a narrow cavity filled with synovial fluid, making it a synovial joint.

The shoulder joint is an example of a ball and socket joint, which is highly mobile due to the minimal contact between its two articulation points, allowing for a wide range of movement. This extra mobility does, however, come at the expense of joint stability.

The shoulder joint is made up of several structures including:

  • Bones: scapula, humerus and clavicle
  • Muscles: rotator cuff muscles (supraspinatus, infraspinatus, teres minor, subscapularis), deltoid, pectoralis major, teres major
  • Ligaments: glenohumeral, coracohumeral, coracoacromial

Bony structure

The shoulder joint is comprised of three bones, the humerus, scapula, and clavicle.

Humerus

Proximal articulation: with the glenoid fossa of the scapula

Distal articulations:

  • Laterally, the capitulum articulates with the head of the radius
  • Medially, the trochlea articulates with the trochlear notch of the ulna

The humerus has both an anatomical neck and a surgical neck:

  • The anatomical neck is the site of attachment of the joint capsule
  • The surgical neck is found inferior to the head of the humerus
Humerus
Figure 1. The left humerus from an anterior view.6

Scapula

The scapula acts as the point of attachment for the rotator cuff muscles.

Proximal articulation: the clavicle

Distal articulation: the head of the humerus

 

Scapula bone of the shoulder joint
Figure 2. The right scapula is shown from an anterior view (left) and posterior view (right).7

Clavicle

The clavicle is an S-shaped bone which is contoured by the many muscles which attach to it. It is also the most commonly fractured bone in the body.

Proximal articulation: the manubrium

Distal articulation: the acromion of the scapula

Clinical relevance: Shoulder dislocation

Dislocation, or subluxation, of the shoulder joint, is a relatively common injury. Anterior dislocation of the shoulder joint (95% of cases) is caused by excessive extension and lateral rotation of the humerus. It most commonly occurs in males aged 16-20 years old.

A serious complication of shoulder dislocation is axillary nerve injury. The axillary nerve runs along the surgical neck of the humerus. Injury to this nerve causes paralysis of the deltoid muscle and loss of sensation over the ‘regimental badge’ area.

Anterior shoulder dislocation
Figure 3. X-ray of an anterior shoulder dislocation, demonstrating the head of the humerus resting beneath the coracoid process.8

Ligaments

The shoulder joint includes the following ligaments:

  • Glenohumeral ligaments (x3)
  • Coracohumeral ligament
  • Coracoacromial ligament

Glenohumeral ligament

There are three glenohumeral ligaments that run between the glenoid fossa of the scapula and the head of the humerus – the superior, medial, and inferior ligaments. Their job is to stabilise the shoulder joint.

Medial glenohumeral ligament

Origin: the medial edge of the glenoid fossa

Insertion: the lesser tubercle of the humerus

Superior glenohumeral ligament

Origin: the apex of the glenoid fossa

Insertion: the lesser tubercle of the humerus

Inferior glenohumeral ligament

Origin: the lower edge of the glenoid fossa

Insertion: the anatomical neck of the humerus

Coracohumeral ligament

The coracohumeral ligament is divided into a superior and inferior band. Both of these bands function to strengthen the upper joint capsule.

Superior band

Origin: the coracoid process

Insertion: the superior band forms a common insertion with the tendon of supraspinatus on the greater tubercle

Inferior band

Origin: the coracoid process

Insertion: the lesser tubercle of the humerus

Coracoacromial ligament

The coracoacromial ligament is clinically important as it prevents superior dislocation of the humeral head of the shoulder joint.

Origin: the coracoid process of the scapula

Insertion: the acromion

Glenohumeral (shoulder) joint
Figure 4. Diagram of the glenohumeral joint. It is a synovial ball-and-socket joint supported by a series of ligaments and muscles.9

Bursae

The shoulder joint contains a few fluid-filled sacs called synovial bursae. The function of these is to minimise friction between the articulating surfaces. The bursae located in the shoulder joint include:

  • Subacromial-subdeltoid bursa: located between the joint capsule and the deltoid muscle
  • Subacromial bursa: located between the joint capsule and the acromion
  • Subcoracoid burse: located between the joint capsule and the coracoid process
Clinical relevance: Subacromial bursitis

The subacromial bursa lies between the joint capsule and the acromion of the scapula. It functions to reduce friction between these two structures.

Subacromial bursitis refers to inflammation of this bursa, often developing as a result of repetitive overhead abduction of the shoulder. It commonly presents as a form of impingement syndrome, with associated pain, weakness and stiffness of the shoulder joint. See our shoulder examination guide for more details.


Rotator cuff muscles

There are a number of muscles that act to move the shoulder joint. The most notable and clinically important are the rotator cuff muscles. Their main function is to stabilise the shoulder joint and allow its excessive range of motion.

Supraspinatus

Origin: the supraspinous fossa

Insertion: the superior facet of the greater tubercle of the humerus

Function: abduction of the humerus

Innervation: suprascapular nerve (C5)

Vascular supply: suprascapular artery

Figure 5. Supraspinatus muscle 11

Infraspinatus

Origin: the infraspinous fossa

Insertion: the middle facet of the greater tubercle of the humerus

Function: external rotation of the humerus

Innervation: suprascapular nerve (C5)

Vascular supply: suprascapular artery, circumflex scapular artery

Infraspinatus
Figure 6. Infraspinatus muscle 11

Subscapularis

Origin: the subscapular fossa

Insertion: the lesser tubercle of the humerus

Function: internal rotation of the humerus

Innervation: upper and lower subscapular nerve (C5/6)

Vascular supply: subscapular artery

 

Subscapularis
Figure 7. Subscapularis muscle 12

Teres minor

Origin: the lateral border of the scapula

Insertion: the inferior facet of the greater tubercle of the humerus

Function: external rotation of the humerus

Innervation: axillary nerve (C5)

Vascular supply: posterior circumflex humeral artery, circumflex scapular artery

 

Teres minor
Figure 8. Teres minor muscle 12
Clinical relevance: Impingement syndrome

Impingement syndrome is caused by rotator cuff tendonitis as the tendons pass beneath the acromion. The supraspinatus muscle’s tendon is most commonly affected.

Impingement syndrome typically presents with pain, weakness and restricted shoulder movement. Patients with impingement syndrome often complain of pain when their arms are raised (this is particularly common in mechanics and manual labourers who work with their arms overhead). When the arm is raised, the subacromial space narrows, which can result in impingement of the supraspinatus muscle tendon leading to an inflammatory response.

Clinical examination

Typical findings on clinical examination in supraspinatus impingement syndrome include:

  • Pain experienced between 60-120° of shoulder abduction (known as a ‘painful arc’).
  • Weakness and pain experienced when the supraspinatus muscle is isolated using the ‘Empty can/Jobe’s test
  • See our shoulder examination guide for more details.

Other muscles of the shoulder

Deltoid

The deltoid is a large and triangular-shaped muscle. The deltoid muscle plays a significant role in both the range of shoulder joint movement and in preventing joint dislocation when carrying heavy objects.

Origin: the anterior border of the clavicle, acromion and spine of the scapula

Insertion: the deltoid tuberosity of the humerus

Function: abduction, flexion and extension of the shoulder

Innervation: axillary nerve

Vascular supply: posterior circumflex humeral artery

Deltoid muscle
Figure 9. Deltoid muscle 13

Teres major

Origin: the posterior aspect of the inferior angle of the scapula

Insertion: the intertubercular sulcus of the humerus

Function: internal rotation and adduction of the shoulder

Innervation: lower subscapular nerve

Vascular supply: subscapular and circumflex scapular artery

Teres major
Figure 10. Teres major muscle 11

Pectoralis major

Pectoralis major is a large muscle located on the anterior chest wall that has several shoulder joint related functions. This muscle works in combination with pectoralis minor which lies underneath it.

Origin: the clavicular head

Insertion: the bicipital groove of the humerus

Function: flexion, adduction and internal rotation of the humerus

Innervation: lateral and medial pectoral nerve

Vascular supply: pectoral branch of the thoracoacromial trunk

Pectoralis major
Figure 11. Pectoralis major muscle

 

Latissimus dorsi

Origin: lower thoracic vertebrae (T8-12), lumbar vertebrae, ribs 9-12, iliac crest

Insertion: the intertubercular sulcus of humerus

Function: extension, adduction and internal rotation of the humerus

Innervation: thoracodorsal nerve

Vascular supply: thoracodorsal branch of the subscapular artery

Table 1. Table showing muscles of the shoulder joint and the movements that they produce.

Latissimus dorsi
Figure 12. Latissimus dorsi muscle

Movements of the shoulder

Below is a brief overview of which muscles are involved in specific shoulder movements.

Movement

Muscles involved
Abduction

Supraspinatus

Deltoid

Adduction

Pectoralis major

Teres major

Latissimus dorsi

Subscapularis

Internal rotation

Subscapularis

Teres major

Deltoid

Pectoralis major

Latissimus dorsi

External rotation

Deltoid

Infraspinatus

Teres minor

Flexion

Pectoralis major

Deltoid

Extension

Deltoid

Latissimus dorsi


References

  1. Richard Drake, A. Wayne Vogl, Adam Mitchell. Gray’s Anatomy for Students (4th Edition). Published in 2019. Available from: [LINK]
  2. Athwal, G. OrthoInfo. Rotator Cuff Tears. Published in 2017. Available from: [LINK]
  3. Bogart, Bruce. Elselvier’s Integrated Anatomy and Embryology. Published in 2007. Available from: [LINK]
  4. Mayo Clinic. Dislocated Shoulder. Published in 2018. Available from: [LINK]
  5. Openstax. Anatomy and Physiology. Published in 2013. Available from: [LINK]
  6. Bduttabaruah, Wikipedia. Anterior View of the Left Humerus. Licence: CC BY-SA. Available from: [LINK]
  7. OpenStax Anatomy and Physiology. The Scapula. License: CC BY-SA. Available from: [LINK]
  8. Hellerhoff. Anterior Dislocation of the Shoulder. License: CC BY-SA. Available from: [LINK]
  9. OpenStax Anatomy and Physiology. Coronal view of the Shoulder Joint. License: CC BY-SA. Available from: [LINK]
  10. OpenStax Anatomy and Physiology. Muscles of the Pectoral Girdle. License: CC BY-SA. Available from: [LINK]
  11. Mikael Häggström, used with permission. Available from: [LINK].
  12. Anatomography. Subscapularis and teres minor muscles. License [CC BY-SA 2.1 JP]. Available from [LINK].
  13. OpenStax College. Deltoid muscle. Licence: CC BY. Available from: [LINK].

Reviewer

Ishani Sinha

Junior Doctor


Editor

Arunachalam Soma


 

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