Ligament and Tendon Enthesis: Anatomy and Mechanics - Structural Interfaces and Attachments in Biology - page 74

is now limited to the superficial attachment where the collagen fibers become
confluent with the periosteum [ 16 ].
Mechanical and biochemical changes also occur in these soft tissues following
immobilization. There are significant increases in joint stiffness with alterations of
articular cartilage. With longer periods of immobilization, areas of necrosis in
cartilage are seen in underlying contacting areas. Ulcerations could also occur
even in non-contact areas. The significance of these findings is escalated when one
considers the dependency of the insertion site on maintaining structural integrity.
This is especially important for the collateral ligaments of the knee, where the
collagen fibrils of the distal attachments become confluent with the periosteum,
with some fibrils passing directly into the bone. There are also profound changes
in the substance of the ligament, as fibrils morphologically alter their normal
arrangement and cellular organization. Concomitant biochemical changes include
reduction of glycosaminoglycans and water as well as significant changes in the
mass, rate of turnover, and cross-linking of collagen. It was noted that, after
immobilization, disruption of the MCL-tibia junction was great, with a time-
dependent decrease in ultimate load and an increase in tibial avulsions, indicating
that a longer period of immobilization resulted in greater resorption of bone [ 1 ]. In
the ACL insertion, however, the effects of immobilization were more modest, with
no appreciable change observed in either attachment under light microscopy and no
incidence of increased avulsion failure [ 17 ].
4.4.2 Remobilization
Despite the deleterious effects of immobilization on ligaments and tendons and
their insertion sites, a reversal of these effects has been demonstrated, although
it takes much more time. In our research center, we found that the mechanical
properties of the MCL returned to control values relatively quickly following
remobilization. However, the structural properties of the FMTC remained inferior
because of incomplete recovery at the insertion site, as shown by areas of resorbed
bone and the presence of osteoclasts, as well as regions where disorganized tissue
was undergoing reossification. Failures therefore continued to occur at bone inser-
tion sites.
Thus, there is an asynchronous recovery rate between the insertion site and the
ligament substance following immobilization and remobilization. The recovery of
the MCL substance is much faster than that of the insertion, and 52 weeks of
remobilization after immobilization may be required in order to restore the MCL
insertion [ 1 ].
Based on these findings, we proposed a set of hypothetical curves to represent
the biomechanical properties in response to immobilization, remobilization, and
exercise. These curves illustrate the reduction in biomechanical performance
with immobilization, improvement with remobilization, and the asynchronous
recovery rate between the ligament substance and insertion site (Fig. 4.7 ).