Background: Although the tendon of the long head of the biceps is a
well-known source of shoulder pain, the pathophysiological basis of this pain
has yet to be explained. The aim of this study was to detect and characterize
any nervous element of the tendon and to determine a possible explanation for
pain originating from this structure.
Methods: The nature of the neuronal innervation of the tendon of the
long head of the biceps was studied immunohistochemically, in four tendons
from different human cadavers, with use of neurofilament antibody 2H3,
neurofilament-like antibody 3A10, calcitonin gene-related peptide, substance
P, and tyrosine hydroxylase.
Results: A large neuronal network, asymmetrically distributed along
the length of the tendon with a higher degree of innervation at the tendon
origin, was identified by the neurofilament and neurofilament-like antibodies
2H3 and 3A10. This innervation was found to be positive for calcitonin
gene-related peptide and substance P, suggesting the presence of thinly
myelinated or unmyelinated sensory neurons. It was also positive for tyrosine
hydroxylase, suggesting a post-ganglionic sympathetic origin.
Conclusions and Clinical Relevance: These findings demonstrate that
the tendon of the long head of the biceps is innervated by a network of
sensory sympathetic fibers, which may play a role in the pathogenesis of