Abstract
The innervation of the long head of the biceps tendon (LHBT) is not sufficiently documented. This is a drawback since pathologies of the LHBT are a major source of shoulder pain. Thus, the study aimed to characterize structurally and molecularly nervous elements of the LHBT. The proximal part of 11 LHBTs was harvested intraoperatively. There were 8 female and 3 male specimens. Age ranged from 66 to 86 years. For structural analyses, nervous elements were viewed in the transmission electron microscope. For molecular characterization, we used general neuronal markers including antibodies against neurofilament and protein gene product 9.5 (PGP9.5) as well as specific neuronal markers including antibodies against myelin basic protein (MBP), calcitonin gene-related product (CGRP), substance P (SP), tyrosine hydroxylase (TH), and growth-associated protein 43 (GAP43). Anti-neurofilament and anti-PGP9.5 visualized the overall innervation. Anti-MBP visualized myelination, anti-CGRP and anti-SP nociceptive fibers, anti-TH sympathetic nerve fibers, and anti-GAP43 nerve fibers during development and regeneration. Immunolabeled sections were analyzed in the confocal laser scanning microscope. We show that the LHBT contains unmyelinated as well as myelinated nerve fibers which group in nerve fascicles and follow blood vessels. Manny myelinated and unmyelinated axons exhibit molecular features of nociceptive nerve fibers. Another subpopulation of unmyelinated axons exhibits molecular characteristics of sympathetic nerve fibers. Unmyelinated sympathetic fibers and unmyelinated nociceptive fibers express proteins that are found during development and regeneration. Present findings support the hypothesis that ingrowth of nociceptive fibers are the source of chronic tendon pain.
Highlights
Roland Blumer and Sandra Boesmueller contributed to this work.Surgery, Medical University Vienna, A-1090 Vienna, Austria 4 Departamento de Fisiología, Facultad de Biología, Universidad de Sevilla, 41012 Sevilla, Spain 5 Department of Anatomy and Biomechanics, Division of Anatomy and Developmental Biology, Karl Landsteiner University of Health Science, A-3500 Krems an der Donau, AustriaA tendon is a though fibrous band that connects the muscle to the bone or muscle to muscle and is designed to transmit muscle force
Chronic overuse of tendons leads to tendon disorders which is associated with pain, swelling, and impaired mobility
Human spinal cord was used as reference tissue to test the specificity of the antibodies (MBP, calcitonin gene-related product (CGRP), substance P (SP), tyrosine hydroxylase (TH), and growth-associated protein 43 (GAP43))
Summary
Chronic overuse of tendons leads to tendon disorders (tendinopathy) which is associated with pain, swelling, and impaired mobility. The etiology of chronic tendon pain often remains idiopathic. Several studies have focused on nervous elements in tendons as the cause of chronic pain. Neuroanatomical studies have been performed in the Achilles tendon due to frequency of tendinopathy in running and jumping sportsmen and in sedentary and elderly persons (Alfredson and Lorentzon, 2000).
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