The innervation pattern of the human Achilles tendon: studies of the normal and tendinosis tendon with markers for general and sensory innervation

Abstract

Pain-free normal Achilles tendons and chronic painful Achilles tendons were examined by the use of antibodies against a general nerve marker (protein gene-product 9.5, PGP9.5), sensory markers (substance P, SP; calcitonin gene-related peptide, CGRP), and immunohistochemistry. In the normal tendons, immunoreactions against PGP9.5 and against SP/CGRP were encountered in the paratendinous loose connective tissue, being confined to nerve fascicles and to nerve fibers located in the vicinity of blood vessels. To some extent, these immunoreactions also occurred in the tendon tissue proper. Immunoreaction against PGP9.5 and against SP/CGRP was also observed in the tendinosis samples and included immunoreactive nerve fibers that were intimately associated with small blood vessels. In conclusion, Mechanoreceptors (sensory corpuscles) were occasionally observed, nerve-related components are present in association with blood vessels in both the normal and the tendinosis tendon.

Expression profiling of metalloproteinases and tissue inhibitors of metalloproteinases in normal and degenerate human achilles tendon

“…In conjunction with reductions in antiangiogenic factors (such as TIMP-3), proteolytic activities are also likely to play an important role in the infiltration of vessels and nerves commonly seen in painful Achilles tendinopathy (1,2,29). A mechanism such as this is consistent with the hypothesis that increased innervation and the local release of neurotransmitters, such as glutamate, substance P, and calcitonin gene-related peptide, are implicated in the perception of pain and the chronicity of the disease process (29,59,60).…”

Achilles Pain, Stiffness, and Muscle Power Deficits: Achilles Tendinitis

“…17,63 Nerve supply to the Achilles tendon is primarily from branches of the sural nerve. 13 Nerve fibers have also been detected in the ventral portion of the paratenon. Further, afferent mechanoreceptors have been sparsely detected at the Achilles tendon proper and surrounding areolar tissue.…”

“…The Achilles tendon is the largest 112 and strongest 13,95 tendon in the body. The Achilles serves as the conjoined tendon for the gastrocnemius and soleus muscles.…”

“…Further, afferent mechanoreceptors have been sparsely detected at the Achilles tendon proper and surrounding areolar tissue. 13 The Achilles tendon, similar to other tendons and dense connective tissue alike, undergoes morphologic and biomechanical changes with increasing age. Morphologic changes include, but are not limited to, decreased collagen diameter 28 and density, 128 decreased glycosaminoglycans and water content, 44 and increased nonreducible cross-links.…”

“…10 Further, the abnormal neovascularization is accompanied by increases in varicose nerve fibers. 13 Increased tendon thickness has been observed in subjects with symptomatic Achilles tendi-nopathy. 57 However, a recent study linked abnormal tendon structure and symptoms but not tendon thickness, emphasizing the association of internal tendon structure with pain.…”