Unmyelinated nerve fibers distributed in the human crural fascia of Thiel-embalmed cadavers.

Muscle fascia is implicated to play a role in musculoskeletal pain; however, the distribution of unmyelinated nerve fibers within human fascia remains to be characterized. Conventional formalin fixation of biological tissues for long periods degrades the antigenicity of protein markers, often resulting in loss of nerve fiber immunoreactivity, limiting immunohistochemical analysis. This study aimed to examine the intrafascial distribution of immunohistochemically labeled unmyelinated nerve fibers in the muscle fascia of cadavers embalmed for 4-21 months using the Thiel-embalming method, which employs a low concentration of formaldehyde. Immunohistochemical staining of peripherin-immunoreactive (-ir) nerve fibers, representing unmyelinated C-fibers, was performed in the proximal, middle, and distal third regions of the crural fascia (CF) from 16 lower legs of eight Thiel-embalmed cadavers. The area occupied by peripherin-ir nerve fibers was quantified for each region. Peripherin-ir nerve fibers were identified in the CF of all specimens. The areas of peripherin-ir fibers were significantly greater in the middle and distal regions compared with the proximal region. Overall immunoreactivity, defined as the total area of peripherin-ir nerve fibers, was not affected by post-embalming storage duration of up to 21 months. These findings demonstrate the presence of unmyelinated nerve fibers in the human CF of Thiel-embalmed cadavers and reveal region-specific differences in their intrafascial distribution. The results provide neuroanatomical evidence supporting the potential involvement of fascia in human myofascial pain.