Sato EJ, Killian ML, Choi AJ, Lin E, Choo AD, Rodríguez-Soto AE, Lim CT, Thomopoulos S, Galatz LM, Ward SR.
Injury to the rotator cuff can cause irreversible changes to the
structure and function of the associated muscles and bones. The temporal
progression and pathomechanisms associated with these adaptations are unclear.
The purpose of this study was to investigate the time course of structural muscle
and osseous changes in a rat model of a massive rotator cuff tear.
Supraspinatus and infraspinatus muscle architecture and biochemistry and
humeral and scapular morphological parameters were measured three days, eight
weeks, and sixteen weeks after dual tenotomy with and without chemical paralysis
via botulinum toxin A (BTX).
Muscle mass and physiological cross-sectional area increased over time
in the age-matched control animals, decreased over time in the tenotomy+BTX
group, and remained nearly the same in the tenotomy-alone group. Tenotomy+BTX led
to increased extracellular collagen in the muscle. Changes in scapular bone
morphology were observed in both experimental groups, consistent with reductions
in load transmission across the joint.
These data suggest that tenotomy alone interferes with normal
age-related muscle growth. The addition of chemical paralysis yielded profound
structural changes to the muscle and bone, potentially leading to impaired muscle
function, increased muscle stiffness, and decreased bone strength.
Structural musculoskeletal changes occur after tendon injury,
and these changes are severely exacerbated with the addition of neuromuscular
Full text (pdf)