Editing Upper limb (section)

====Shoulder joint====
[[File:Gray326.png|thumb|Shoulder joint with ligaments]]
The [[glenohumeral joint]] (colloquially called the shoulder joint) is the highly mobile ball and socket joint between the [[glenoid cavity]] of the scapula and the head of the humerus.  Lacking the passive stabilisation offered by ligaments in other joints, the glenohumeral joint is actively stabilised by the [[rotator cuff]], a group of short muscles stretching from the scapula to the humerus.  Little inferior support is available to the joint and dislocation of the shoulder almost exclusively occurs in this direction.
<ref name="Sellers-3">{{harvnb|Sellers|2002| pp=3–5}}</ref>

The large muscles acting at this joint perform multiple actions and seemingly simple movements are often the result of composite antagonist and protagonist actions from several muscles.  For example,  [[pectoralis major]] is the most important arm flexor and [[latissimus dorsi]] the most important extensor at the glenohumeral joint, but, acting together, these two muscles cancel each other's action leaving only their combined medial rotation component.  On the other hand, to achieve pure flexion at the joint the [[Deltoid muscle|deltoid]] and [[supraspinatus]] must cancel the adduction component and the [[teres minor]] and [[infraspinatus]] the medial rotation component of pectoralis major.  Similarly, abduction (moving the arm away from the body) is performed by different muscles at different stages.  The first 10° is performed entirely by the supraspinatus, but beyond that fibres of the much stronger deltoid are in position to take over the work until 90°. To achieve the full 180° range of abduction the arm must be rotated medially and the scapula most be rotated about itself to direct the glenoid cavity upward.
<ref name="Sellers-3" />

; Muscles: of shoulder joint proper<ref name="Thieme-Atlas-256" />
:; Posterior: [[Supraspinatus]], [[infraspinatus]], [[teres minor]], [[subscapularis]], [[deltoideus]], [[latissimus dorsi]], [[teres major]]
:; Anterior: [[Pectoralis major]], [[coracobrachialis]]