E. Yamamoto et al., Mechanical properties of collagen fascicles from in situ frozen and stress-shielded rabbit patellar tendons, CLIN BIOMEC, 15(4), 2000, pp. 284-291
Objective. To know the effects of stress shielding on the biomechanical pro
perties of collagen fascicles obtained from in situ frozen patellar tendons
(an autograft model).
Design. Collagen fascicles of approximately 300 mu m in diameter tt ere obt
ained from in situ frozen rabbit patellar tendons and also from in situ fro
zen and stress-shielded ones, and their mechanical properties and fibroblas
t density were determined.
Background Stress shielding changes the mechanical properties of in situ fr
ozen patellar tendons in which there exist no fibroblasts, The mechanisms o
f this phenomenon have not been studied well.
Method. Patellar tendon of both in situ frozen group and in situ frozen and
stress-shielded group were frozen in situ by liquid nitrogen to kill fibro
blasts. Then, in the in situ frozen and stress-shielded group, no tension w
as applied to the tendons for 2, 3, and 6 weeks, while normal tension was a
pplied to the tendons of the in situ frozen group. Tensile properties of th
e collagen fascicles obtained from these tendons were determined using a mi
crotensile tester, and were compared to the collagen fascicles from nonfroz
en, stress-shielded patellar tendons.
Results. Tangent modulus and tensile strength of collagen fascicles from th
e in situ frozen and stress-shielded group progressively decreased with the
time of stress shielding; however, these decreases were much smaller than
those of the fascicles obtained from non-frozen, stress-shielded tendons. A
lthough there were few fibroblasts in the patellar tendon of the in situ fr
ozen and stress-shielded group at 2 weeks, the modulus and strength of the
fascicles from the posterior portion were significantly lower than those in
the in situ frozen group. In addition, the reduction of strength caused by
stress shielding was much smaller in collagen fascicles than in bulk patel
lar tendons.
Conclusion. The mechanical properties of collagen fascicles in in situ froz
en tendons (an autograft model) are affected by stress shielding even under
acellular condition.