The Journal of Bone and Joint Surgery (American). 2009;91:1172-1180.
doi:10.2106/JBJS.H.00191
© 2009 The Journal of Bone and Joint Surgery, Inc.
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Effect of Corticosteroids on the Biomechanical Strength of Rat Rotator Cuff Tendon

David K. Mikolyzk, MD1, Anthony S. Wei, MD1, Pietro Tonino, MD1, Guido Marra, MD1, Denis A. Williams, MD1, Ryan D. Himes, BS1, Frederick H. Wezeman, PhD1 and John J. Callaci, PhD1

1 Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, 2160 South First Avenue, Maguire Building, Suite 1700, Maywood, IL 60153. E-mail address for D.K. Mikolyzk: dmikoly{at}lumc.edu

Investigation performed at the Department of Orthopaedic Surgery and Rehabilitation, Loyola University Medical Center, Maywood, Illinois

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants of less than $10,000 from the Walgreen Foundation. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

Background: The effect of corticosteroids on tendon properties is poorly understood, and current data are contradictory and diverse. The biomechanical effect of steroids on rotator cuff tendon has not been studied, to our knowledge. The current study was undertaken to characterize the biomechanical effects of corticosteroid exposure on both uninjured and injured rat rotator cuff tendon.

Methods: One hundred and twenty-three male Sprague-Dawley rats were randomly assigned to four groups: control (C), tendon injury (I), steroid exposure (S), and tendon injury plus steroid exposure (I+S). Unilateral tendon injuries consisting of a full-thickness defect across 50% of the total width of the infraspinatus tendon were created. Steroid treatment consisted of a single dose of methylprednisolone placed into the subacromial space. At one, three, and five weeks postoperatively, the shoulders were harvested and the infraspinatus tendon was subjected to biomechanical testing. Two specimens from each group were used for histological analysis.

Results: At one week, maximum load, maximum stress, and stiffness were all significantly decreased in Group S compared with the values in Group C. Mean maximum load decreased from 37.9 N in Group C to 27.5 N in Group S (p < 0.0005). Mean maximum stress decreased from 18.1 MPa in Group C to 13.6 MPa in Group S (p < 0.0005). Mean stiffness decreased from 26.3 N/mm in Group C to 17.8 N/mm in Group S (p < 0.0005). At one week, mean maximum stress in Group I+S (17.0 MPa) was significantly decreased compared with the value in Group I (19.5 MPa) (p < 0.0005). At both the three-week and the five-week time point, there were no significant differences between Group C and Group S or between Group I and Group I+S with regard to mean maximum load, maximum stress, or stiffness. Histological analysis showed fat cells and collagen attenuation in Groups S and I+S. These changes appeared to be transient.

Conclusions: A single dose of corticosteroids significantly weakens both intact and injured rat rotator cuff tendons at one week. This effect is transient as the biomechanical properties of the steroid-exposed groups returned to control levels by three weeks.

Clinical Relevance: Our findings in this rat model suggest that a single corticosteroid dose has significant short-term effects on the biomechanical properties of both injured and uninjured rotator cuff tendon. These effects should be weighed against any potential benefit prior to administering a subacromial corticosteroid injection.


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