Biomedical Engineering Reference
In-Depth Information
age-related changes in ligaments and tendons and their insertions. Finally, the
negative effects of immobilization on the insertion and its slow recovery following
remobilization, together with positive effects of exercise, will be presented with an
illustration of how activity level can be related to biomechanical properties by a
highly nonlinear curve.
One of the greatest challenges in studying ligament and tendon entheses is
accurate determination of their biomechanical properties, due to their complexity
and irregular geometry. With the development of the video dimensional analyzer
(VDA) system, the nonuniform elongation between the insertion site and along the
ligament could be measured. As a result, it has been shown that the percent
elongation at or near the insertion is always higher than that in the ligament or
tendon substance. We will also review other technologies, such as the use of a laser
micrometer, to determine the cross-sectional area of ligaments and tendons so that
their tensile stress could be properly determined. With the knowledge of a
stress-strain relationship, the mechanical properties of the ligament substance
could be determined and separated from the structural properties of the bone-
ligament-bone complex.
To conclude, we will discuss repair of the insertion sites of ligaments and
tendons after injury, including surgical reconstruction using a tissue autograft or
allograft. As graft-bone healing has not been able to replicate the normal soft tissue-
to-bone enthesis, new biomimetic technologies, including the use of bioscaffolds
aiming to reproduce the zones of transition across the insertion, are being explored.
Although the availability of new biomaterials that could assist the body in
recreating the complex insertion site indeed offers many exciting possibilities,
many challenges still remain, as in-depth knowledge of the composition and
properties of ligament and tendon insertion sites is still lacking. It is our belief
that fundamental studies to improve our understanding of enthesis structure, func-
tion, and their relationship are needed before one can be in a position to move
forward with regeneration of an enthesis on a scientific basis.
4.2 Anatomy
4.2.1 Morphology
The morphology of ligament and tendon insertions to bone is among the most
complex of all biological tissues. The transformation of soft to hard tissue requires a
gradual transition of collagen fibers to non-mineralized fibrocartilage, then to
mineralized fibrocartilage, and finally to bone. In addition, the structure of the
insertion site is different from ligament to ligament, as well as between the two ends
of the same ligament. Nevertheless, researchers have been able to categorize
ligament and tendon insertions into two general types: direct insertions and indirect
insertions.
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