title: The role of subscapularis muscle denervation in the pathogenesis of shoulder internal rotation contracture after neonatal brachial plexus palsy: a study in a rat model.
abstract: We assessed the role of subscapularis muscle denervation in the development of shoulder internal rotation contracture in neonatal brachial plexus injury. Seventeen newborn rats underwent selective denervation of the subscapular muscle. The rats were evaluated at weekly intervals to measure passive shoulder external rotation. After 4 weeks, the animals were euthanized. The subscapularis thickness was measured using 7.2T MRI axial images. The subscapularis muscle was then studied grossly, and its mass was registered. The fiber area and the area of fibrosis were measured using collagen-I inmunostained muscle sections. Significant progressive decrease in passive shoulder external rotation was noted with a mean loss of 58° at four weeks. A significant decrease in thickness and mass of the subscapularis muscles in the involved shoulders was also found with a mean loss of 69%. Subscapularis muscle fiber size decreased significantly, while the area of fibrosis remained unchanged. Our study shows that subscapularis denervation, per se, could explain shoulder contracture after neonatal brachial plexus injury, though its relevance compared to other pathogenic factors needs further investigation.
authors.affiliation: Hospital da Luz Lisboa, UIME, Centro de Imagiologia, Portugal.
authors.forename: Vasco V
authors.initials: VV
authors.lastname: Mascarenhas
authors.forename: Marcelo
authors.initials: M
authors.lastname: Casaccia
authors.forename: Alejandra
authors.initials: A
authors.lastname: Fernandez-Martin
authors.forename: Mario
authors.initials: M
authors.lastname: Marotta
authors.forename: Cesar G
authors.initials: CG
authors.lastname: Fontecha
authors.forename: Sleiman
authors.initials: S
authors.lastname: Haddad
authors.forename: Jorge
authors.initials: J
authors.lastname: Knörr
authors.forename: Francisco
authors.initials: F
authors.lastname: Soldado
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001720:Birth Injuries / Q000150:complications*; D020516:Brachial Plexus Neuropathies / Q000150:complications*; D003286:Contracture / Q000209:etiology*; D004195:Disease Models, Animal; D009121:Muscle Denervation; D018482:Muscle, Skeletal / Q000601:surgery*; D017207:Rats, Sprague-Dawley; D012399:Rotation; D012785:Shoulder Joint / Q000473:pathology*
keywords: glenohumeral dysplasia; muscle growth; neonatal brachial plexus palsy; shoulder internal rotation contracture; subscapularis muscle