Engineering Fibrous Tissues and Their Interfaces with Bone - Structural Interfaces and Attachments in Biology - page 317

Fig. 15.1 Tendon-/ligament-
bone interface.
The fibrocartilaginous
enthesis (direct insertion) is
composed of four transitional
zones: fibrous tissue region,
uncalcified fibrocartilage
region, calcified fibrocartilage
region, calcified bone region.
(Reproduced, with
permission, from Yang
and Temenoff [ 7 ])
can strengthen the bone insertion connection by reducing stress concentrations at the
bone interface [ 10 ]. The following zone, calcified fibrocartilage, contains hypertro-
phic chondrocytes and collagen X. This region is characterized as similar to
mineralized tissue. The fourth zone is characterized as calcified bone and provides
a secure attachment of the tissue to the bone interface. This region contains
osteoblasts, osteoclasts, osteocytes, and mineralized collagen I fibers [ 43 ]. Fibrous
interfaces are typically found on the shafts of long bones and fibrocartilaginous
interfaces are typically found at joint surfaces, such as the knee joint, or at short
bones, such as the wrist or ankle [ 16 , 44 ].
Because the two components of this interface have opposing mechanical
properties (tendons and ligaments are strong in tension and bone is optimized for
compression) [ 10 , 21 ], there is a need to gradually transition the mechanical
properties from one tissue to another. The uncalcified and calcified regions in a
fibrocartilaginous enthesis (direct insertion) are able to effectively transmit loads
and have been shown to increase Young's modulus across the different zones
[ 45 , 46 ]. When using tissue engineering methods to reconstruct the interface, results
must ensure that this mechanical transition is recreated to reduce stress
concentrations and prevent failure at the insertion site.