The inflamed biceps tendon as a pain generator in the shoulder: A histological and biomolecular analysis

Abstract

Introduction: The long head of the biceps (LHB) is often resected in shoulder surgery. However, its contribution to inflammatory processes in the shoulder remains unclear. In the present study, inflamed and noninflamed human LHBs were comparatively characterized for features of inflammation. Materials and methods: Twenty-two resected LHB tendons were classified into inflamed (n ¼ 11) and noninflamed (n ¼ 11) samples. For histological examination, samples were stained with hematoxylin eosin, Azan, van Gieson, and Masson Goldner trichrome. Neuronal tissue was immunohistochemically visualized. In addition, specific inflammatory marker gene expression of primary LHB-derived cell cultures were analyzed. Results: Features of tendinopathy, such as collagen disorganization, infiltration by inflammatory cells, neovascularization, and extensive neuronal innervation were found in the tendinitis group. Compared to noninflamed samples, inflamed LHBs showed a significantly increased inflammatory marker gene expression Conclusion: Structural and biomolecular differences of both groups suggest that the LHB tendon acts as an important pain generator in the shoulder joint. These findings can, on the one hand, contribute to the understanding of the biomolecular genesis of LHB tendinitis and, on the other hand, provide possibilities for new therapeutic approaches.

Structural and molecular characteristics of axons in the long head of the biceps tendon

“…Scale bar, 10 μm specimen suggesting that they are a regular constituent of LHBT. Meyelinated nerve fibers have been observed in the Achilles tendon of cat (Andres et al, 1985) but so far not in human tendons including the LHBT (Alpantaki et al, 2005, Boesmueller et al, 2017, Schmalzl et al, 2019, Achilles tendon (Ackermann et al, 2003, Alfredson et al, 2003, plantaris tendon (Spang et al, 2015), and proximal tendon of the flexors and extensors of the forearm (Ljung et al, 2004, Ljung et al, 1999a. Thus, our novel findings would prompt for further analyses to clarify whether myelination is a specific feature of the LHBT or is repeated in other human tendons.…”

The Fascial Breath

“…A decline in the sliding of fascial tissues causes a picture of local inflammation, as shown for some types of cervicalgia [18]. An altered position of the collagen fibres, for example in a tendon, could change its mechanical function, creating pain but not inflammation [19]. If the layers and fascial orientations of an anatomical area lose the ability to move between them, the vectors of collagen fibrils will change, there will be an implementation of collagen deposition, creating a metabolic environment of inflammation and anomalous mechanical tension of the scaffold cell and extracellular matrix.…”

“…Maintaining an optimal position of the collagen fibres, adapted to a specific anatomical structure (muscle, joint, visceral capsule, meninges, etc. ), means maintaining health [5,[19][20].…”

Association of high sensitivity C-reactive protein with tearing of the long head of the biceps tendon

“…However, few studies have verified whether inflammation is associated with LHBT tear. Recently, Schmalzl et al [21] reported that the gene expression of the proinflammatory cytokines of IL-1A, IL-1B, and TNF-α and of the catabolic enzymes MMP-1, − 3, − 9, and − 13 was upregulated, whereas the expression of the anti-inflammatory gene TIMP1 was downregulated in biceps tendinitis patients. The difference between this study and those previous studies is that this study newly focused on the inflammatory biomarker, hs-CRP, as an independent risk factor.…”