Killian ML, Cavinatto LM, Ward SR, Havlioglu N, Thomopoulos S, Galatz LM.
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.
The purpose of this study was to evaluate healing outcomes of
muscle, tendon, and bone after tendon repair in a model of chronic rotator cuff
disease and to compare these outcomes to those of acute rotator cuff injuries 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 injuries and repair.
Controlled laboratory study.
Chronic rotator cuff injuries, 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 rats.
After 8 weeks of injury, tendons were surgically reattached to the humeral head,
and an acute, dual-tendon injury 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.
All repairs were intact at the time of dissection, with no evidence of
gapping or ruptures. 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 injuries and repair. SS and IS muscles were atrophic at
8 weeks after repair of chronic injuries, indicating incomplete recovery after
repair, whereas SS and IS muscles exhibited less atrophy and degeneration in the
acute injury group at 8 weeks after repair. After chronic injuries 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.
Chronic degenerative changes in rotator cuff muscles, tendons, and
bone led to inferior healing characteristics after repair compared with acute
injuries and repair. The changes were not reversible after repair in the time
course studied, consistent with clinical impressions.
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.
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