|
Tendons are load-bearing collagenous tissues consisting mainly of type I collagen and various proteoglycans (PGs)
including decorin and versican. It is widely accepted that highly orientated collagen fibers in tendons a play critical role
for transferring tensile stress and demonstrate birefringent optical properties. However, the influence that proteoglycans
have on the optical properties of tendons is yet to be fully elucidated. Tendinopathy (defined as a syndrome of tendon pain,
tenderness and swelling that affects the normal function of the tissue) is a common disease associated with sporting
injuries or degeneration. PG's are the essential components of the tendon extracellular matrix; changes in their quantities
and compositions have been associated with tendinopathy. In this study, polarization sensitive optical coherence
tomography (PS-OCT) has been used to reveal the relationship between proteoglycan content/location and birefringent
properties of tendons. Tendons dissected from freshly slaughtered chickens were imaged at regular intervals by PS-OCT
and polarizing light microscope during the extraction of PGs or glycosaminoglycans using established protocols
(guanidine hydrochloride (GuHCl) or proteinase K solution). The macroscopic and microscopic time lapsed images are
complimentary; mutually demonstrating that there was a higher concentration of PG's in the outer sheath region than in
the fascicles; and the integrity of the sheath affected extraction process and the OCT birefringence bands. Extraction of
PGs using GuHCl disturbed the organization of local collagen bundles, which corresponded to a reduction in the
frequency of birefringence bands and the band width by PS-OCT. The feature of OCT penetration depth helped us to
define the heterogeneous distribution of PG's in tendon, which was complimented by polarizing light microscopy. The
results provide new insight of tendon structure and also demonstrate a great potential for using PS-OCT as a diagnostic
tool to examine tendon pathology.
|
