title: Decreased muscle loading delays maturation of the tendon enthesis during postnatal development.
abstract: Physical environment influences the development and maintenance of musculoskeletal tissues. The current study uses an animal model to explore the role of the physical environment on the postnatal development of the supraspinatus tendon enthesis. A supraspinatus intramuscular injection of botulinum toxin A was used to paralyze the left shoulders of mice at birth. The supraspinatus muscles of right shoulders were injected with saline to serve as contralateral controls. The supraspinatus enthesis was examined after 14, 21, 28, and 56 days of postnatal development. Histologic assays were used to examine fibrocartilage morphology and percentage osteoclast surface. Micro-computed tomography was used to examine muscle geometry and bone architecture. At 14 days there were no differences between groups in fibrocartilage formation, muscle geometry, bone architecture, or osteoclast surface. When comparing groups at 21, 28, and 56 days, muscle volume was decreased, fibrocartilage development was delayed, mineralized bone was decreased, and osteoclast surface was higher at each timepoint in the botulinum group compared to the contralateral saline control group. Our results indicate that the development of the tendon enthesis is sensitive to its mechanical environment. A reduction in muscle loading delayed the development of the tendon-to-bone insertion site by impeding the accumulation of mineralized bone. Physical factors did not play a significant role in enthesis maturation in the first 14 days postnatally, implying that biologic factors may drive early postnatal development.
authors.affiliation: Department of Orthopaedic Surgery, Washington University, St. Louis, Missouri 63110, USA. ThomopoulosS@wustl.edu
authors.forename: Stavros
authors.initials: S
authors.lastname: Thomopoulos
authors.forename: Hyun-Min
authors.initials: HM
authors.lastname: Kim
authors.forename: Stefan Y
authors.initials: SY
authors.lastname: Rothermich
authors.forename: Carrie
authors.initials: C
authors.lastname: Biederstadt
authors.forename: Rosalina
authors.initials: R
authors.lastname: Das
authors.forename: Leesa M
authors.initials: LM
authors.lastname: Galatz
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001862:Bone Resorption; D019274:Botulinum Toxins, Type A / Q000494:pharmacology; D004195:Disease Models, Animal; D007273:Injections, Intramuscular; D051379:Mice; D008815:Mice, Inbred Strains; D009133:Muscular Atrophy / Q000139:chemically induced / Q000473:pathology* / Q000503:physiopathology; D010010:Osteoclasts / Q000187:drug effects / Q000473:pathology; D010291:Paresis / Q000209:etiology / Q000473:pathology / Q000503:physiopathology; D017006:Rotator Cuff / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology; D012785:Shoulder Joint / Q000187:drug effects / Q000473:pathology* / Q000503:physiopathology; D013710:Tendons / Q000254:growth & development / Q000473:pathology*; D014057:Tomography, X-Ray Computed / Q000379:methods; D016474:Weight-Bearing
chemical_list: D019274:Botulinum Toxins, Type A