In primary impingement, there is a structural narrowing of the subacromial space. Internal impingement is most commonly associated with the supraspinatus and infraspinatus tendons. Conversely, internal impingement results when the tendons of the rotator cuff encroach between the humeral head and glenoid rim. External, or subacromial impingement, results from a mechanical or physical encroachment of the soft tissue located within the subacromial space.
Shoulder impingement syndrome can be described according to either the location of the impingement, characterized as external or internal, and/or the underlying cause of the impingement, referred to as primary or secondary impingement. Repetitive pathologic compression, degeneration, and fraying of the rotator cuff tendons are known to contribute to the narrowing of the subacromial space, but it is unknown whether or not the inflamed and damaged tendons cause impingement, or if the narrowed subacromial space causes the tendon inflammation. The symptom of pain associated with shoulder impingement results with this movement due to the humeral head applying a compressive force to either the rotator cuff, the subacromial bursa, or both structures. This subacromial space, which is normally 1.0 to 1.5 cm in width, narrows with the superior migration of the humeral head, allowing it to approach the anteroinferior edge of the acromion. Bigliani and Morrison classified the shape of the acromion by its three most common morphologies: ĭuring the actions of shoulder abduction, forward flexion, and internal rotation, normal shoulder girdle movement results in narrowing of the subacromial space. The acromion shape is thought to play a role in the development of external, or "outlet-based" impingement syndrome. The acromion and coracoacromial ligament provide the anterior border, the acromioclavicular (AC) joint acts as the superior border, and the humeral head serves as the inferior border. Its anatomic borders define the subacromial space. Previously, shoulder impingement syndrome was thought to be a sole diagnosis itself but is now considered to be a cluster of symptoms and anatomic characteristics. Įxternal impingement, often commonly referred to by clinicians and providers as shoulder impingement, is best described as a painful condition of the shoulder that results from the inflammation, irritation, and degradation of the anatomic structures within the subacromial space.
#Abduction of shoulder manual#
Shoulder external impingement should be recognized as a clinical entity that is separate from internal impingement. The most basic clinical differentiation between the former and the latter is defined by the rotator cuff as the anatomic boundary of the external and internal forms. The latter occurs secondary to a repetitive impingement in overhead throwers or manual laborers and constitutes articular-sided rotator cuff pathology, glenohumeral internal rotation deficit (GIRD), and superior labrum anterior posterior (SLAP) tears.
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