Quadrilateral Space Syndrome

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Quadrilateral Space Syndrome (QSS) is a relatively uncommon disorder, initially described by Cahill and Palmer in 1983, which involves the compression of the axillary nerve and the posterior humeral circumflex artery (PHCA) within the quadrilateral space. Four distinct features of QSS were originally identified by Cahill:

  1. Generalized pain in the shoulder area,
  2. Nondermatomal paraesthesia,
  3. Point tenderness above the quadrilateral space, and
  4. Angiogram results indicating positive findings when in a provocative position.

Compression can occur either at rest or during movement, and thus, QSS should be considered in patients presenting with the main symptoms of neck pain, shoulder pain, lateral arm paraesthesia, and/or quadrilateral space tenderness.

Anatomy Pathophysiology

The axillary nerve supplies the teres minor and deltoid muscles, which play vital roles in abduction and external rotation. Characteristic fibrous bands can be found within the quadrilateral space, and these bands may intensify symptoms, particularly pain, triggered by movements involving the deltoid and teres minor muscles. Anatomical variations in glenohumeral joint innervation patterns among patients can complicate the process of distinguishing whether pain arises from suprascapular nerve palsy or axillary nerve compression. The PHCA wraps around the neck of the humerus, rendering it susceptible to repetitive tension and mechanical stress. This stress can lead to thrombosis and aneurysmal degeneration within the PHCA wall.

Although neurovascular compression is responsible for the acute manifestations of QSS, such as pain, paraesthesia, and muscle atrophy, there is ongoing debate as to whether the primary issue stems from neural entrapment or vascular compression.

Clinical Features

QSS typically affects younger patients, who are under forty years of age and generally healthy. These individuals often have a history of engaging in repeated overhead activities, such as playing volleyball, baseball, or swimming. The presentation of symptoms in QSS can be non-specific and involve either neurogenic or vascular features. Neurogenic QSS is characterized by nonspecific patterns of paraesthesia, fasciculations, weakness, or neurogenic pain. Vascular QSS symptoms may indicate acute ischemia (pain, pallor, absent pulses), thrombosis, or embolism (coolness or cyanosis of the hand or digits). In addition to vascular and neurogenic symptoms, QSS patients can also exhibit muscular atrophy and associated weakness, which is believed to result from denervation. Tenderness over the quadrilateral space may also be present in patients.

In severe cases of QSS, thrombosis of the PHCA can obstruct blood flow from the axillary artery, leading to embolization and subsequent cyanosis, digital ischemia, and cold intolerance.



Literature Review