What is the pathophysiology of the flaccid stage of hemiplegic shoulder pain?

Updated: Feb 08, 2019
  • Author: Robert Gould, DO; Chief Editor: Stephen Kishner, MD, MHA  more...
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Answer

Answer

Once the inciting injury to the brain occurs, the flaccid stage evolves with a state of areflexia. This stage of areflexia includes loss of muscle tone and volitional motor activity, variable sensory loss, and loss of muscle stretch reflexes.

Muscular support of the humeral head in the glenoid fossa by the supraspinatus and deltoid muscles is lost. This leads to downward and outward subluxation of the humeral head, with the only support coming from the joint capsule.

The shoulder capsule is thin and is composed of 2 tissue layers. The inner synovial layer, the stratum synovium, is highly vascular but poorly innervated, making it insensitive to pain but highly reactive to heat and cold. The outer layer, the stratum fibrosum, is poorly vascularized but richly innervated, predisposing it to pain from stretch. For this reason, Faghri and coauthors suggest that added capsular stretch in a flaccid shoulder may predispose the capsule to irreversible damage and the shoulder to pain. [12]

Flaccidity of the trapezius, rhomboids, and serratus anterior muscles leads to depression, protraction, and downward rotation of the scapula, which Cailliet believes leads to significant angular changes of the glenoid fossa, subsequently contributing to subluxation. [10] Also, the spine begins to flex laterally toward the hemiparetic side because of the elimination of the righting reflex, further altering the scapulothoracic relationship.

However, Prevost and colleagues compared the affected and unaffected shoulders by using a 3-dimensional (3-D) radiographic technique that determines the true position of the humeral head in relation to the scapula. This technique revealed less downward rotation of the glenoid fossa than originally expected, and no significant relationship was found between the extent of scapular orientation and the severity of subluxation. [13, 14, 15]

Subsequently, it was concluded that scapular position does not contribute as much to inferior subluxation as was originally thought. Teasell points out that this now appears to be the most widely accepted viewpoint. [4]


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