• The shoulder serves to connect the upper extremity to the trunk.
  • The muscles acting here are often denervated in brachial plexus and proximal peripheral nerve injury patterns.
  • With dysfunction at the shoulder, the upper extremity cannot be properly positioned in space to perform normal functions even if normal hand or other distal function is preserved.
  • Restoration of shoulder movement must be a priority in peripheral nerve injury patients.

Structures of the Shoulder

  • Bones:
    • Thorax (including sternum, ribs, spinal vertebrae, etc.)
    • Clavicle
    • Scapula
    • Humerus
  • Joints:
    • Scapulothoracic
    • Acromioclavicular joint
    • Glenohumeral joint
    • Sternoclavicular

Movements of the Shoulder

Movement at the shoulder is complex:

  • The shoulder glenohumeral joint where the key motion occurs is dependent on normal movement at the shoulder girdle (which is made up of the scapula/clavicle and their connection to the thoracic). 
  • Dysfunction of scapular motion (which can be seen in various patterns of brachial plexus and peripheral nerve injury) can greatly impede shoulder, and thereby upper extremity, movement.

Key movements:

  • Flexion and extension are movements about a coronal axis.
  • Abduction and adduction are movements about a sagittal axis.
  • Horizontal abduction and horizontal adduction are movements in a transverse plane about a longitudinal axis.
  • Internal/Medial rotation and external/lateral rotation are movements about a longitudinal axis through the humerus.

Scapular Movement (in turn allows normal glenohumeral joint movement):

  • Abduction and adduction
  • Upward (lateral) rotation and downward (medial) rotation
  • Anterior tilt and posterior tilt
  • Elevation and depression

Glenohumeral Joint Movement:

  • Anterior flexion and posterior extension
  • Abduction and adduction
  • Horizontal abduction and horizontal adduction
  • Lateral/external and medial/internal rotation
  • Circumduction
Muscle NameInnervationAction
Major Muscles
TrapeziusSpinal accessory nerveHelps move/stabilize the scapula to allow normal shoulder motion especially shoulder abduction beyond 90º. 
Serratus anteriorLong thoracic nerveAbduction (protraction) of the scapula. Responsible for assisting with shoulder flexion especially beyond 90º of flexion.
Rhomboid Major and MinorDorsal scapular nerveScapular adduction or retraction, elevation, and downward rotation.
SubclaviusSubclavius nerveDepresses and stabilizes the clavicle.
Pectoralis MajorLateral and medial pectoral nerveAdducts and medially rotates the humerus.
Pectoralis minorMedial pectoral nerveThrusts shoulder forward; tilts scapula anteriorly; aids respiration.
Levator ScapulaeCervical (C3, C4) nerve, dorsal scapular nerveElevates the scapula.
Teres MajorSubscapular nerveMedially rotates, adducts, and extends the shoulder joint.
Latissimus DorsiThoracodorsal nerveAbducts, extends and internally rotates the shoulder.
Deltoid (Anterior Fibers, Middle Fibers, Posterior Fibers)Axillary nerveShoulder joint abduction, flexion (anterior fibers), extension (posterior fibers), and  (depending on patient position) internal (patient supine) and external rotation (patient prone).
CoracobrachialisMusculocutaneous nerveFlexes and adducts the shoulder joint.
Rotator Cuff Muscles
SupraspinatusSuprascapular nerveAbduction of the shoulder.
InfraspinatusSuprascapular nerveExternally rotates the shoulder. 
Teres MinorAxillary NerveExternally rotates the shoulder. 
SubscapularisUpper subscapular nerve, lower subscapular nerveMedially rotates the shoulder joint; stabilizes the head of the humerus.