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1. Identify the major joints and associated ligaments in the shoulder region. Explain what kind of movements occur at the joints and other pertinent information.

Movement Videos

The acromioclavicular (AC) joint is located at the articulation of the acromial end of the clavicle and acromion of the scapula. It is an example of a plane joint (gliding/sliding of scapula on clavicle).

• Accessory structures:

  • Ligaments

    • Acromioclavicular ligaments are intrinsic ligaments and help to strengthen the joint capsule. There are superior and inferior divisions.

    • Coracoclavicular ligaments are extrinsic ligaments and are vital to the organization and support of the AC joint [often considered the strongest ligament of the AC joint].

  • Articular disc

    • Fibrocartilaginous disc that becomes progressively less complete (particularly in the inferior and center portions) with progressive age.

• Clinical significance: The term shoulder separation is synonymous with acromioclavicular joint injuries. 

The glenohumeral (shoulder) joint is the most mobile [ball and socket] joint in the body, and with this high level of mobility, there is decreased stability. Accessory structures play a dominant role in structural stability. The glenohumeral joint is formed by the head of the humerus and glenoid cavity of the scapula. The glenoid cavity is very shallow and accepts only ~1/3rd of the humeral head.

• Accessory structures:

  • Tendons

    • Rotator cuff tendons are the main source of stability for the glenohumeral joint. These tendons almost completely surround the joint with a notable and clinically important inferior deficiency.

    • Long head of biceps brachii tendon attaches to the supraglenoid tubercle of the scapula, which is within the articular capsule, making this tendon intracapsular.

  • Ligaments

    • Glenohumeral ligaments: 3 anterior sets (superior, middle, & inferior); observed on internal portion of articular capsule

    • Coracohumeral ligament: extends from coracoid process of scapula to the greater & lesser tubercles of the humerus

    • Transverse humeral ligament: connects the greater & lesser tubercles of humerus; the long head of biceps brachii tendon runs between the tubercles [intertubercular sulcus/bicipital groove] and deep to this ligament

    • Coraco-acromial ligament: part of the coraco-acromial arch [between coracoid process and acromion of scapula] over the shoulder region and helps prevent superior dislocations of glenohumeral joint

  • [Glenoid] labrum

    • Fibrocartilaginous lip circumscribing the glenoid cavity, which helps to provide a better fit of the humeral head.

• Bursae

  • Subacromial (subdeltoid) bursa: Located deep to the coraco-acromial arch and deltoid m., and superficial to the supraspinatus tendon and joint capsule. It facilitates movement of the supraspinatus tendon deep to the coraco-acromial arch. It does not typically communicate with the joint capsule.

  • Subtendinous bursa of subscapularis muscle: Located between the tendon of subscapularis m. and articular capsule. It protects the tendon of subscapularis as it passes across the neck of the scapula. This bursa is unique in that it typically communicates with the articular cavity via an opening of the articular capsule typically located between the superior and middle glenohumeral ligaments.

• Clinical significance: 

  • Shoulder dislocations occur at the glenohumeral joint. Most dislocations occur inferiorly (due to a weak point in the musculotendinous rotator cuff). Clinically, dislocations are described as anterior (most frequent) or posterior dislocations.

  • Rotator cuff injuries are frequent causes of shoulder pain, particularly in cases over repetitive actions of rotator cuff muscles. The supraspinatus tendon (tendonitis) is the most commonly affected area.

  • Adhesive capsulitis [frozen shoulder] involves scarring/fibrosis between the articular capsule and surrounding structures, and often associated with other pathologies/injuries of the glenohumeral joint.

2. Describe the blood supply to the shoulder region, and give an example of collateral blood supply.

The blood supply to the shoulder is comprised of several anastomosing arteries. High mobility joints typically have an extensive collateral supply. The arteries that supply the shoulder come from the subclavian a. and its continuation, the axillary a. 

The axillary a. begins as a continuation of the subclavian a. at the distal end of the first rib. The axillary a. consists of three parts, defined by their relationship to the pectoralis minor m. The 1st part is medial to pectoralis minor, the 2nd part is posterior (deep) to pectoralis minor, and the 3rd part is lateral to pectoralis minor.

The axillary a., its parts, and their branches are as follows:

• • Axillary a.

    • 1st part

      • Superior thoracic a.

    • 2nd part

      • Thoraco-acromial a. (supplies pectoralis major & minor mm., deltoid m., shoulder joint)

      • Lateral thoracic a. (supplies serratus anterior m.)

    • 3rd part

      • Subscapular a. (supplies infraspinatus m., teres minor & major mm., subscapularis m.)

        • Thoracodorsal a. (supplies latissimus dorsi m.)

        • Circumflex scapular a. (supplies infraspinatus m., teres minor & major mm.)

      • Anterior circumflex humeral a. (supplies deltoid m. & proximal portions of arm mm.)

        • Near surgical neck of humerus

      • Posterior circumflex humeral a. (supplies deltoid m. & proximal portions of arm mm.)

        • Near surgical neck of humerus

There are several arterial anastomoses in the shoulder region, two that are of particular importance at the shoulder:

• • Anastomosis between the dorsal scapular a., the suprascapular a., and the circumflex scapular a. on the posterior scapula.

  • Anastomosis between the anterior & posterior circumflex humeral aa. and often acromial branches from the thoracoacromial a.

3. Understand details (actions, attachments, innervation, blood supply, etc.) regarding muscles in the shoulder region.

Click here for a downloadable PDF version of the individual muscle charts.

Click here for a downloadable PDF of a comprehensive muscle chart. 

*Students are only responsible for muscles discussed in the main text of the learning objectives and/or list of structure

The muscles of the shoulder region include:

• Deltoid m.

• Rotator cuff muscles

  • Supraspinatus m.

  • Infraspinatus m.

  • Teres minor m.

  • Subscapularis m.

• Teres major m.

• Latissimus dorsi m. 

4. Diagram the brachial plexus beginning with nerve roots and ending with terminal branches. Label the nerve roots, trunks, divisions, cords, and the 5 main terminal nerves of the upper limb. Identify the major muscle groups innervated by these terminal nerves.

Most nerves of the upper limb arise from the brachial plexus, which is made up of the ventral primary rami of C5-T1 spinal nerves. These are the roots of the plexus. The roots unite to form three trunks (superior, middle, inferior), which divide into anterior and posterior divisions. The anterior divisions ultimately innervate anterior compartment muscles (flexors) and the posterior divisions ultimately innervate posterior compartment muscles (extensors). These divisions unite to form cords, which are named based on their location relative to the axillary artery: lateral, medial, and posterior cords. These cords give rise to branches or terminal nerves that innervate the upper limb.

Brachial plexus components (proximal-distal):

• • ROOTS

    • Ventral primary rami of C5-T1

  • TRUNKS

    • Superior (C5-C6)

    • Middle (C7)

    • Inferior (C8-T1)

  • DIVISIONS

    • Anterior (innervate anterior/flexor compartment muscles)

    • Posterior (innervate posterior/extensor compartment muscles)

  • CORDS (name based on location relative to axillary a.)

    • Medial (anterior division of inferior trunk; sometimes a branch of anterior division of middle trunk)

    • Posterior (all three posterior divisions)

    • Lateral (anterior divisions of superior & middle trunks)

  • BRANCHES

    • Musculocutaneous n.

      • A terminal branch of lateral cord (C5-C7)

        • Some sources describe as C5-C6

    • Axillary n.

      • Posterior cord (C5-C6)

    • Radial n.

      • Terminal branch of posterior cord (C5-T1)

    • Median n.

      • Contributions from lateral & medial cords (C6-T1)

    • Ulnar n.

      • Continuation of medial cord (C7*; C8-T1)

        • *C7 contribution based on most recent research and Gray's Anatomy; some sources describe as C8-T1

There are various, supraclavicular branches directly off the certain roots and trunks that should be noted, specifically:

• • Dorsal scapular n. (C5)

  • Long thoracic n. (C5-C7)

  • Suprascapular n. (Superior trunk)

You can follow the formation, distribution, and paths of nerve fibers as terminal nerves are formed from the brachial plexus in the images below. You should be able to draw a diagram of the brachial plexus and know the spinal cord levels of the terminal nerve branches: musculocutaneous, axillary, radial, median, & ulnar. Note that there are some differences between sources.

5. Predict the functional loss that may result from injury to upper or lower roots, cords, and/or terminal nerves.

Injuries to the brachial plexus affect sensation and movement of the upper limb, ie, anesthesia and paralysis. Signs and symptoms depend on what part of the plexus is injured. What would be affected if the upper part of the plexus was injured (C5 & C6) – Erb-Duchenne palsy? Remember, the upper parts of the plexus supply the more proximal upper limb. Or if the lower part was injured (C8 & T1) – Klumpke paralysis? Remember, lower part of the plexus supplies the more distal portion.

Erb-Duchenne palsy - injuries to the superior parts (C5 & C6) of the brachial plexus. The upper limb typically presents with an adducted shoulder (deltoid affected), medially rotated arm (rotator cuff mm. affected), pronated forearm (biceps brachii m. affected), and extended elbow (anterior compartment of arm affected).

Klumpke’s palsy - injuries to the inferior parts (C8 & T1) of the brachial plexus. These types of injuries are less frequent than those of the superior parts of the brachial plexus. Muscles of the hands are commonly affected (claw hand).