2002 - University of Washington Bone and Joint Sources

Figure 2: Loaded- 36 Newtons. Partial un-crimping- 12X.
(Figure 2 and 3). The 67, 100, and 220
N loaded specimens displayed no
evidence of crimping in any region
(Figure 4). The blinded observer
correctly identified the loading history
in 14/16 specimens. Two of the 9N
loaded specimens were incorrectly
identified as un-loaded specimens.
Collagen Fiber Interaction
Loading the uncut ligaments at
150N resulted in complete un-crimping
of the ligament. “Deep” section through
the anterior 1/3 of the patellar ligament
resulted in a crimping of the cut fibers
which was visible to the full depth of
the incision, and which was visible from
insertion to insertion (Figure 5). The
uncut fibers immediately deep to the
incision were loaded and completely
un-crimped (Figure 5). The cut fibers
at the deepest point of the incision were
retracted to approximately the same
distance as the superficial fibers.
Superficial section, partially through
the superficial band of the patellar
ligament, resulted in a localized
retraction and crimping of fibers near
the cut site (Figure 6). However, the cut
fibers remained uncrimped along the
majority of the length of the ligament.
A triangular shaped lesion was visible
on SEM, as the cut fibers adjacent to
the loaded fibers were not as retracted,
nor as crimped as the superficial cut
fibers (Figure 7).
Figure 3: Loaded- 36 Newtons. Partial un-crimping- 60X.
Figure 4: Loaded- 67 Newtons. No Crimp 12X.
DISCUSSION
This study shows that freezefixation
can preserve ligament collagen
in an un-crimped state, and thus loaded
fibers can be distinguished from nonloaded
fibers in which a crimp remains.
Using this technique, the rabbit patellar
ligament showed a consistent pattern
of strain dispersion with increasing
load. Under these loading conditions,
the central 1/3 of the ligament uncrimped
at lower applied loads than the
deep and superficial regions. The crimp
in the entire specimen was extinguished
at approximately 67N which, based
upon ligament cross-sectional
estimates, correlates closely with the
previously reported toe-region of the
stress strain curve of the rabbit patellar
ligament (approx 4.5 MPa) (Woo et al,
1993). The strength of this technique
is that it enables investigators to
examine entire ligaments or tendons
preserved in a functionally loaded state
using various forms of microscopy,
including the potential use of high
2002 ORTHOPAEDIC RESEARCH REPORT 33