Quadrangular space syndrome (QSS) is an uncommon diagnosis mainly because of lack of literature on the subject and possible misdiagnosis.
QSS is present on ~1% of shoulder MRIs 6.
Patients present with posterior shoulder pain and paresthesia over the lateral arm 5.
QSS most commonly occurs when the neurovascular bundle is compressed by fibrotic bands within the QS and/or by hypertrophy of the muscle boundaries.
Fibrotic bands form as the result of trauma, with resultant scarring and adhesions. Cases reported in throwing athletes, tennis players, and in the dominant arm of volleyball players support the fibrosis and hypertrophy based hypotheses.
Variation in axillary nerve division and a genetically smaller QS have been hypothesised to predispose to QSS. This may account for the limited number of reported cases.
Other reported cases of QSS include:
- acute trauma, e.g. crush or traction injury 5
- ganglion cyst
- paralabral cyst arising from a detached inferior glenoid labral tear
- aneurysms and traumatic pseudoaneurysms of posterior circumflex artery
- tumours, e.g. humeral osteochondroma
MRI is the investigation of choice, demonstrating atrophy +/- fatty infiltration in the teres minor and/or deltoid muscle. Literature review has shown varying proportions of deltoid and teres minor involvement.
Direct MR imaging of the QS is not always possible, unless there is a lesion in QS.
Angiography - DSA
Before the advent of MR conventional angiography was the primary diagnostic modality. Angiography would show occlusion or compression of the posterior circumflex artery in the QS region.
Treatment and prognosis
Treatment is initially conservative if no cause is found. Refractory cases require surgery. If a definitive lesion in the QS is demonstrated on MR then primary surgery can be undertaken.
The identification of MRI findings of QSS and the exclusion of other treatable abnormalities in the shoulder may allow institution of appropriate nonsurgical therapy for QSS to be followed potentially by surgical treatment in some refractory cases. Even if other shoulder abnormalities are present, findings of QSS may provide an explanation for some of the patients who have persistent discomfort after treatment of the primary shoulder abnormality.
On imaging consider
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- 4. Vlychou M, Spanomichos G, Chatziioannou A et-al. Embolisation of a traumatic aneurysm of the posterior circumflex humeral artery in a volleyball player. Br J Sports Med. 2001;35 (2): 136-7. doi:10.1136/bjsm.35.2.136 - Free text at pubmed - Pubmed citation
- 5. Cirpar M, Gudemez E, Cetik O et-al. Quadrilateral space syndrome caused by a humeral osteochondroma: a case report and review of literature. HSS J. 2006;2 (2): 154-6. doi:10.1007/s11420-006-9019-y - Free text at pubmed - Pubmed citation
- 6. Brant WE, Helms C. Fundamentals of Diagnostic Radiology. Lippincott Williams & Wilkins. (2012) ISBN:1608319113. Read it at Google Books - Find it at Amazon