Partial-Width Injuries of the Rat Rotator Cuff Heal with Fibrosis

Abstract

PurposeThe purpose of this study was to identify the healing outcomes following a partial-width, full-thickness injury to the rotator cuff tendon-bone attachment and establish if the adult attachment can regenerate the morphology of the healthy attachment.\n\nHypothesisWe hypothesized that a partial-width injury to the attachment would heal via fibrosis and bone remodeling, resulting in increased cellularity and extracellular matrix deposition, reduced bone volume, osteoclast presence and decreased collagen organization compared to shams.\n\nMaterials and MethodsA biopsy punch was used to create a partial-width injury at the center one-third of the rat infraspinatus attachment, and the contralateral limb underwent a sham operation. Rats were sacrificed at 3- and 8-weeks after injury for analyses. Analyses performed at each time-point included cellularity (Hematoxylin & Eosin), ECM deposition (Massons Trichrome), bone volume (micro-computed tomography; microCT), osteoclast activity (Tartrate Resistant Acid Phosphatase; TRAP), and collagen fibril organization (Picrosirius Red). Injured and sham shoulders were compared at both 3- and 8-weeks using paired, two-way ANOVAs with repeated measures and Sidaks correction for multiple comparisons.\n\nResultsCellularity and ECM deposition increased at both 3- and 8-weeks compared to sham contralateral attachments. Bone volume decreased and osteoclast presence increased at both 3- and 8-weeks compared to sham contralateral limbs. Collagen fibril organization was reduced at 3-weeks after injury compared to 3-week sham attachments.\n\nConclusionsThese findings suggest that a partial-width injury to the rotator cuff attachment does not fully regenerate the native structure of the healthy attachment. The injury model healed via scar-like fibrosis and did not propagate into a full-width tear after 8-weeks of healing.