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Effects of Stress Deprivation on Lubricin Synthesis and Gliding of Flexor Tendons in a Canine Model in Vivo
Yu-Long Sun, PhD1; Chunfeng Zhao, MD1; Gregory D. Jay, MD, PhD2; Thomas M. Schmid, PhD3; Kai-Nan An, PhD1; Peter C. Amadio, MD1
1 Orthopedic Biomechanics Laboratory, Division of Orthopedic Research, Mayo Clinic College of Medicine, Mayo Clinic, 200 First Street S.W., Rochester, MN 55905. E-mail address for Y.-L. Sun: sunyulong@yahoo.com
2 Department of Emergency Medicine, Rhode Island Hospital, The CORO Building, Suite 106, One Hoppin Street, Providence, RI 02903
3 Department of Biochemistry, Rush University, 1735 West Harrison Street, Cohn Research Building, Suite 556, Chicago, IL 60612
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Investigation performed at the Mayo Clinic, Rochester, Minnesota

Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Copyright © 2013 by The Journal of Bone and Joint Surgery, Inc.
J Bone Joint Surg Am, 2013 Feb 06;95(3):273-278. doi: 10.2106/JBJS.K.01522
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Lubricin facilitates boundary lubrication of cartilage. The synthesis of lubricin in cartilage is regulated by mechanical stimuli, especially shear force. Lubricin is also found in flexor tendons. However, little is known about the effect of mechanical loading on lubricin synthesis in tendons or about the function of lubricin in flexor tendons. The purpose of this study was to investigate the relationship of mechanical loading to lubricin expression and gliding resistance of flexor tendons.


Flexor tendons were harvested from canine forepaws that had been suspended without weight-bearing for twenty-one days and from the contralateral forepaws that had been allowed free motion. Lubricin expression in each flexor tendon was investigated with real-time RT-PCR (reverse transcription polymerase chain reaction) and immunohistochemistry. Lubricin in the flexor tendon was extracted and quantified with ELISA (enzyme-linked immunosorbent assay). The friction between the flexor tendon and the proximal pulley was measured.


The non-weight-bearing flexor tendons had a 40% reduction of lubricin expression (p < 0.01) and content (p < 0.01) compared with the flexor tendons in the contralateral limb. However, the gliding resistance of the tendons in the non-weight-bearing limb was the same as that of the tendons on the contralateral, weight-bearing side.


Mechanical loading affected lubricin expression in flexor tendons, resulting in a 40% reduction of lubricin content, but these changes did not affect the gliding resistance of the flexor tendons.

Clinical Relevance: 

The gliding resistance of flexor tendons was not affected after a period of limited motion. This suggests that physical activity after a short period of limited motion does not lead to wear of intact tendons and their surrounding tissue.

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    These activities have been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of the American Academy of Orthopaedic Surgeons and The Journal of Bone and Joint Surgery, Inc. The American Academy of Orthopaedic Surgeons is accredited by the ACCME to provide continuing medical education for physicians.
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