Complete removal of load is detrimental to rotator cuff healing.
OBJECTIVE
This study evaluated the effect of the mechanical environment on the healing rotator cuff by paralyzing the supraspinatus muscle in the operative shoulder of a rat model of rotator cuff injury and repair.


METHODS
Unilateral shoulders of rats underwent a supraspinatus injury and repair. Botulinum toxin A was used to paralyze the muscle after repair. Postoperatively, 1 group was immobilized and 1 group was allowed free range of motion. Saline-injected, casted rats were used as the control group. Repairs were evaluated histologically, geometrically, and biomechanically.


RESULTS
Specimens from the saline-injected rats had greater scar volume and cross-sectional area of the repair compared with the paralyzed groups. Structural properties were increased in the saline group compared with the paralyzed groups. Free range of motion (ie, uncasted group) resulted in modest improvements in biomechanical properties but did not obviate the effect of paralysis.


CONCLUSIONS
Complete removal of load was detrimental to rotator cuff healing, especially when combined with immobilization.
Department of Orthopaedic Surgery, Washington University at Barnes-Jewish Hospital, St. Louis, MO 63110, USA. galatzl@wustl.edu
Leesa M
LM
Galatz
Nichole
N
Charlton
Rosalina
R
Das
H Mike
HM
Kim
Necat
N
Havlioglu
Stavros
S
Thomopoulos
D000818:Animals; D001696:Biomechanical Phenomena; D001707:Biopsy, Needle; D019274:Botulinum Toxins, Type A / Q000494:pharmacology*; D004195:Disease Models, Animal; D007103:Immobilization / Q000379:methods; D007150:Immunohistochemistry; D008297:Male; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000294:innervation; D011336:Probability; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D020127:Recovery of Function; D012016:Reference Values; D017006:Rotator Cuff / Q000601:surgery*; D000070636:Rotator Cuff Injuries; D012680:Sensitivity and Specificity; D013708:Tendon Injuries / Q000473:pathology / Q000601:surgery*; D016474:Weight-Bearing; D014945:Wound Healing / Q000502:physiology*
D019274:Botulinum Toxins, Type A