- 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
- Thorax (including sternum, ribs, spinal vertebrae, etc.)
- Acromioclavicular joint
- Glenohumeral joint
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.
- 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
|Trapezius||Spinal accessory nerve||Helps move/stabilize the scapula to allow normal shoulder motion especially shoulder abduction beyond 90º.|
|Serratus anterior||Long thoracic nerve||Abduction (protraction) of the scapula. Responsible for assisting with shoulder flexion especially beyond 90º of flexion.|
|Rhomboid Major and Minor||Dorsal scapular nerve||Scapular adduction or retraction, elevation, and downward rotation.|
|Subclavius||Subclavius nerve||Depresses and stabilizes the clavicle.|
|Pectoralis Major||Lateral and medial pectoral nerve||Adducts and medially rotates the humerus.|
|Pectoralis minor||Medial pectoral nerve||Thrusts shoulder forward; tilts scapula anteriorly; aids respiration.|
|Levator Scapulae||Cervical (C3, C4) nerve, dorsal scapular nerve||Elevates the scapula.|
|Teres Major||Subscapular nerve||Medially rotates, adducts, and extends the shoulder joint.|
|Latissimus Dorsi||Thoracodorsal nerve||Abducts, extends and internally rotates the shoulder.|
|Deltoid (Anterior Fibers, Middle Fibers, Posterior Fibers)||Axillary nerve||Shoulder joint abduction, flexion (anterior fibers), extension (posterior fibers), and (depending on patient position) internal (patient supine) and external rotation (patient prone).|
|Coracobrachialis||Musculocutaneous nerve||Flexes and adducts the shoulder joint.|
|Rotator Cuff Muscles|
|Supraspinatus||Suprascapular nerve||Abduction of the shoulder.|
|Infraspinatus||Suprascapular nerve||Externally rotates the shoulder.|
|Teres Minor||Axillary Nerve||Externally rotates the shoulder.|
|Subscapularis||Upper subscapular nerve, lower subscapular nerve||Medially rotates the shoulder joint; stabilizes the head of the humerus.|