BACKGROUND: Chronic rotator cuff tears present a clinical challenge, often with poor outcomes after surgical repair. Degenerative changes to the muscle, tendon, and bone are thought to hinder healing after surgical repair; additionally, the ability to overcome degenerative changes after surgical repair remains unclear. PURPOSE/HYPOTHESIS: The purpose of this study was to evaluate healing outcomes of muscle, tendon, and bone after tendon repair in a model of @entity717 and to compare these outcomes to those of @entity131 and repair. The hypothesis was that degenerative rotator cuff changes associated with chronic multitendon tears and muscle unloading would lead to poor structural and mechanical outcomes after repair compared with acute @entity130 and repair. STUDY DESIGN: Controlled laboratory study. METHODS: Chronic rotator cuff @entity130 , induced via detachment of the supraspinatus (SS) and infraspinatus (IS) tendons and injection of botulinum toxin A into the SS and IS muscle bellies, were created in the shoulders of @entity35 . After 8 weeks of @entity1796 were surgically reattached to the humeral head, and an acute, @entity1796 and repair was performed on the contralateral side. After 8 weeks of healing, muscles were examined histologically, and tendon-to-bone samples were examined microscopically, histologically, and biomechanically and via micro-computed tomography. RESULTS: All repairs were intact at the time of dissection, with no evidence of gapping or @entity397 . Tendon-to-bone healing after repair in our chronic injury model led to reduced bone quality and morphological disorganization at the repair site compared with acute @entity130 and repair. SS and IS muscles were @entity3202 at 8 weeks after repair of chronic @entity130 , indicating incomplete recovery after repair, whereas SS and IS muscles exhibited less @entity194 and degeneration in the acute injury group at 8 weeks after repair. After chronic @entity130 and repair, humeral heads had decreased total mineral density and an altered trabecular structure, and the repair had decreased strength, stiffness, and toughness, compared with the acute injury and repair group. CONCLUSION: Chronic degenerative changes in rotator cuff muscles, tendons, and bone led to inferior healing characteristics after repair compared with acute @entity130 and repair. The changes were not reversible after repair in the time course studied, consistent with clinical impressions. CLINICAL RELEVANCE: High retear rates after rotator cuff repair are associated with tear size and chronicity. Understanding the mechanisms behind this association may allow for targeted tissue therapy for tissue degeneration that occurs in the setting of chronic tears.

Chronic Degeneration Leads to Poor Healing of Repaired Massive Rotator Cuff Tears in XXXX .

@entity131 :: ('MESH:D001930', 'Disease') :: ['acute rotator cuff injuries'] @entity3202 :: ('MESH:D016109', 'Disease') :: ['atrophic'] @entity397 :: ('MESH:D012421', 'Disease') :: ['ruptures'] @entity1796 :: ('MESH:D013708', 'Disease') :: ['dual-tendon injury', 'injury, tendons'] @entity194 :: ('MESH:D001284', 'Disease') :: ['atrophy'] @entity35 :: ('10116', 'Species') :: ['rats'] @entity717 :: ('MESH:D009069', 'Disease') :: ['chronic rotator cuff disease'] @entity130 :: ('MESH:D014947', 'Disease') :: ['injuries']
@entity35 :: (10116,Species) :: ['Rats']
