Collagen fibrils in human tendons, is everything already said? A qualitative ultrastructural assessment

Improving structural knowledge of human tendons
is fundamental for a better understanding of pathological
and regenerative processes occurring in these key
structures. Recent advances in tendon biology indicate
cellular heterogeneity between tendons of different muscles.
In contrast, very little is known about potential differences
in extracellular matrix in tendons across anatomy.
In the present work, we aimed to assess collagen
fibril organisation ultrastructurally in human supraspinatus,
semitendinosus, and quadriceps tendons, as well
as in the anterior cruciate and patellar ligaments. Samples
were obtained with appropriate permissions from
seven different donors belonging to the Anatomy Gift
Programme of the Royal College of Surgeons in Ireland
in Dublin, that had been previously embalmed for routine
anatomical examination.
Samples from the tendon mid-body were harvested
and processed for Transmission Electron Microscopy
(TEM).
We examined a total of 34 tendons (n=2 samples of
each). Collagen fibrils were well recognisable in 32 tendons.
O
verall, marked heterogeneity between samples
from the same tendon type of different donors, or
between the various tendons of the same donor, was
observed in terms of collagen fibril shape (rounded
vs more irregular-polygonal), size distribution, and
width. The greatest similarity in fibril organisation was
observed between patellar ligament and quadriceps tendon.
The anterior cruciate ligament showed smaller,
less rounded fibrils, which were more consistent in size.
Supraspinatus also showed bundles perpendicular to the
longitudinal tendon axis. Consistency in fibril organisation
between both samples of the same individual tendon
was observed in 26 cases.
This study demonstrates that ultrastructural analysis
of collagen fibril is feasible in tissue from anatomical
donors despite the embalming process not being
a standard procedure of fixation for TEM examination.
This first description also offers a basis for a more
detailed and quantitative assessment of the collagen
fibrils in human tendons.
References
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