title: The deltoid, a forgotten muscle of the shoulder.
abstract: The deltoid is a fascinating muscle with a significant role in shoulder function. It is comprised of three distinct portions (anterior or clavicular, middle or acromial, and posterior or spinal) and acts mainly as an abductor of the shoulder and stabilizer of the humeral head. Deltoid tears are not infrequently associated with large or massive rotator cuff tears and may further jeopardize shoulder function. A variety of other pathologies may affect the deltoid muscle including enthesitis, calcific tendinitis, myositis, infection, tumors, and chronic avulsion injury. Contracture of the deltoid following repeated intramuscular injections could present with progressive abduction deformity and winging of the scapula. The deltoid muscle and its innervating axillary nerve may be injured during shoulder surgery, which may have disastrous functional consequences. Axillary neuropathies leading to deltoid muscle dysfunction include traumatic injuries, quadrilateral space and Parsonage-Turner syndromes, and cause denervation of the deltoid muscle. Finally, abnormalities of the deltoid may originate from nearby pathologies of subdeltoid bursa, acromion, and distal clavicle.
authors.affiliation: Department of Radiology, Centre Hospitalier de l'Université de Montréal, Hôpital Notre-Dame, 1560 rue Sherbrooke Est, Montréal, QC H2L 4M1, Canada. thomas.moser@umontreal.ca
authors.forename: Thomas
authors.initials: T
authors.lastname: Moser
authors.forename: Junie
authors.initials: J
authors.lastname: Lecours
authors.forename: Johan
authors.initials: J
authors.lastname: Michaud
authors.forename: Nathalie J
authors.initials: NJ
authors.lastname: Bureau
authors.forename: Raphaël
authors.initials: R
authors.lastname: Guillin
authors.forename: Étienne
authors.initials: É
authors.lastname: Cardinal
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000000981:diagnostic imaging / Q000293:injuries / Q000473:pathology; D009135:Muscular Diseases / Q000175:diagnosis*; D000070599:Shoulder Injuries; D012785:Shoulder Joint / Q000473:pathology / Q000528:radiation effects; D014057:Tomography, X-Ray Computed / Q000379:methods*