The Role of Mechanobiology in the Attachment of Tendon to Bone - Structural Interfaces and Attachments in Biology - page 219

Chapter 11
The Role of Mechanobiology in the Attachment
of Tendon to Bone

Andrea Schwartz and Stavros Thomopoulos

11.1 Introduction

The attachment of dissimilar materials is a major engineering challenge. Stress
concentrations would arise at the interface of two disparate materials unless the
interface was tuned to the mechanical mismatch. An effective biologic solution to
this problem can be seen at the attachment of a relatively compliant tendon to a
relatively stiff and brittle bone. A functionally graded tissue develops between
tendon and bone to provide a robust attachment (the “enthesis”) that alleviates
potential stress concentrations. The development and maintenance of this tissue is
driven by mechanobiology; muscle loading is necessary for the formation of a
transitional tissue between tendon and bone and a loss of loading in the adult
enthesis leads to rapid loss of mechanical integrity. This unique transitional tissue
is not recreated during healing, so surgical reattachment of these two tissues often
fails. This chapter describes structure-function relationships at the tendon enthesis
and the role of mechanobiology for the development and healing of the enthesis.
Studies have demonstrated that the tendon-to-bone insertion is a functionally
graded material with regard to its extracellular matrix (ECM) composition, its
structural organization, its mineral content, and its mechanical properties. The
fetal and postnatal development of a functionally graded enthesis requires muscle
loading. The role of loading during tendon-to-bone healing is more nuanced; low
levels of load are beneficial to healing while high levels of load are detrimental to
healing. A better understanding of mechanobiology at the insertion may help guide
rehabilitation strategies (e.g., protective immobilization followed by active motion)
and tissue engineering protocols (e.g.,

tissue-specific bioreactor designs) for

enhancing tendon-to-bone healing.

A. Schwartz ￿ S. Thomopoulos ( * )
Department of Orthopaedic Surgery, Washington University, 660 South Euclid,
Box 8233, St. Louis, MO 63110, USA
e-mail: [e-mail] ; [e-mail]