Innervation of the thoracolumbar fascia

Abstract

The aim of the study was to obtain information on the sensory functions of the thoracolumbar fascia (TLF). The types of nerve fibres present in the TLF were visualized with specific antibodies to neuropeptides and sympathetic fibres. Most data were obtained from the TLF in rats, but some findings from the human fascia are also included. The only receptive nerve ending found was the free nerve ending, i.e. no corpuscular receptors existed in our specimen. An exclusive innervation with free nerve endings speaks for a nociceptive function, but the TLF may also fulfill proprioceptive functions, since many of the free nerve endings have a low mechanical threshold. Most of the fibres could be visualized with antibodies to CGRP [calcitonin gene- related peptide (CGRP)] and SP [substance P (SP)]. The latter ones most likely were nociceptors. The TLF contained a great proportion of postganglionic sympathetic fibres, which may be vasoconstrictors. A comparison between an inflamed and intact fascia showed an increase of the CGRP- and SP-positive fibres in the inflamed TLF. This finding could be one explanation for the low back pain of many patients, since practically all lesions of the fascia are accompanied by a sterile inflammation.

Keywords: Thoracolumbar fascia; fasciitis; free nerve endings; innervation; nociception; proprioception.

Figures

Fig 1.

Schematic drawing of a free nerve ending innervating an arteriole. The ending exhibits several axonal widenings (varicosities) in which neuropeptides and neurotrophins are stored. When the ending is stimulated by chemical or mechanical stimuli, the contents of the varicosities are released and influence the nearby blood vessels leading to vasodilation and increase in capillary permeability. ATP and protons are particularly effective stimuli for endings in deep soft tissues. Please note that many free nerve endings have a low mechanical threshold and might function as proprioceptors.

Fig 2.

Cross-section through the rat thoracolumbar fascia with its three layers plus subcutaneous tissue (A). The section was stained with antibodies to PGP 9.5 to show all neuronal structures, irrespective of their function. B, free nerve ending with chains of varicosities. C, D, fibres of passage that terminate somewhere outside the section.

Fig 3.

Cross-section of a human TLF stained with antibodies to PGP 9.5. A, dorsal view of a scheme of the TLF showing the site close to vertebra L5 (red quadrangle) where the biopsy specimen were taken. B, nerve ending with many varicosities in the adventitia of a small artery. C, free nerve ending with several chains of varicosities in the inner layer.

Fig 4.

Whole mount preparation of the rat TLF stained with antibodies to CGRP. A network of small nerve fibres is visible that accompany blood vessels that are barely visible (in the right lower corner). Some fibres to the left exhibit varicosities.

Fig 5.

Longitudinal section through the outer layer of a rat TLF. A SP-ir free nerve ending with many varicosities courses through the section. To the left some collagen fibre bundles are visible.

Fig 6.

Sympathetic fibres and endings surrounding a blood vessel in the subcutaneous tissue of a rat TLF. The units were stained with antibodies to tyrosin hydroxylase (TH). The efferent fibres have many varicosities and thus look similar to the afferent ones.

Fig 7.

Computer-assisted quantitative evaluation of the length of fibres and endings in the rat TLF of three fibre types: PGP 9.5-ir, CGRP-ir, and SP-ir. The y-axis shows the mean length of fibres and endings per 1.000 μm2. Open bars indicate numbers in intact (non-inflamed) fascia, black bars those in inflamed fascia. The numbers underneath the bars give the number of cross-sections from which the bars were constructed. The mean length of fibres and endings is assumed to be a means of innervation density.