Peripheral nerve trunks are viscoelastic tissues with unique mechanica
l characteristics. Tensile strength, which includes elastic limit and
mechanical failure, concerns surgeons. This study shows that measureme
nts of the load necessary to achieve certain elongations on specimens
outside the body do not correspond with in situ measurements. The nece
ssary load is influenced by the presence or absence of branches and by
the amount of fibrosis. Because of transverse contraction, elongation
beyond a certain limit substantially decreases intrafascicular volume
, leading to increased intrafascicular pressure. Stress relaxation is
effective only if the nerve repair site is maintained under constant t
ension. Its beneficial effect disappears after 10 minutes if the repai
red nerve is returned to a relaxed state. Therefore, tension at the re
pair site should be minimized.