This week, some thoughts on a recent favorite of mine: the Costal Neurofascia. The contemporary ribcage, twisted as it is from messenger bags and gall bladder removals, seems to assert itself as a frequent problem area. If you look at a single segment of the thoracic nervous system, it’ll look something like this:
Thoracic nerves — with a few exceptions — most follow this pattern: Starting inside the vertebra at the spinal cord, they send out dorsal and ventral roots, which join into one while exiting the intervertebral foramen. Immediately upon exiting the foramen the nerve root splits in three very different directions.
The dorsal ramus exits dorsally (duh), right between the ribs, and sends two major branches (medial and lateral) toward the surface. This dorsal ramus innervates everything dorsal to the transverse processes, including the facet joints, spinal ligaments, paraspinal muscles, lumbodorsal fascia, and skin. As it emerges toward the surface, the dorsal ramus usually follows a gentle downslope (postero-inferiorly) at a similar angle as the adjacent spinous process. The medial branch eventually makes it to the areolar fascia just underneath the skin, but to do so it has to perforate several thick fascial sheets and traverse big changes in surrounding fluid pressure. Fascial pathology in the back often leads to chronic inflammatory pain — and sometimes motor and sensory changes — in these dorsal rami.
The thickest nerve branch — the ventral ramus — exits laterally from the spine and follows a tunnel just beneath its corresponding rib. The rib’s periosteum hangs downward to make a long fascial “hammock” for the nerve as it rounds the curvature of the ribcage, and this sheet is then thickly invested with intercostal muscles. When it reaches the lateral ribs, it sends a branch perforating to the surface that emerges right between the tapered ends of serratus anterior, and innervates the skin on the side of the torso. Then it continues anteriorly, innervating the abdominal muscles and sending a last branch to the surface at the sternal notch or rectus sheath. Just like the dorsal ramus, these lateral and anterior branches are common culprits for pain, inflammation, and movement dysfunction.
Oft-forgotten are the rami communicantes (white and grey) — a pair of thin filaments extending anteriorly along the vertebral body and connecting to a sympathetic ganglion. These filaments provide a two-way communication between the somatic and sympathetic nervous systems, allowing both to respond synergistically on a local level. (For example a muscle may contract around an injured organ.) Both ganglion and rami communicantes are embedded in a nested cylinder of prevertebral fascia, and from there the ganglion sends branches into various visceral compartments. The prevertebral fascia must, like a well-fitting sock, be able to twist and torque along with the spine, or local forces can alter (or injure) the function of the sympathetic chain.
Deep to the ribs, the visceral chamber has two major neurofascial players — the vagus and phrenic nerves — each of which descends from above and enters the ribcage at the thoracic inlet. The vagus spreads out like angelhair pasta around the heart, major blood vessels, trachea and esophagus. The phrenic nerve traverses and innervates the pericardium/diaphragm unit. While these nerves don’t emerge segmentally like the others, their fascial envelope certainly exchanges force with the rest of the nervous system. The visceral cylinder’s role in producing movement dysfunction and chronic pain/inflammation should not be ignored.
Try to build this map in your mind just as an embryo would — first the compartments, then the organs/muscles/bones. Doing so will lead to a much easier time palpating and working on these nerve structures, and inform your model of how the whole neurofascial organ moves together.