Substance P Containing Intraosseous Nerves Within the Human Vertebral Body

Baylor College of Medicine, Houston, TX, USA

The innervation of the spinal column is complex, and incompletely understood. Recently in our laboratory, abundant intraosseous nerves were identified within human vertebral bodies by histologic techniques. The nerves were noted to consistently accompany the basivertebral vessels that enter the vertebrae through the large posterior neurovascular foramen. Because of their proximity to these vessels, the nerves were termed the "basivertebral nerves".

In the present study, thirty-five vertebrae from five adult human cadaveric thoracic spines were used to evaluate the basivertebral nerve. Fifteen specimens were discarded due to tissue degradation and "freezer burn". In the remaining specimens, the nerve was identified by microscopically-aided dissection, harvested by dissecting the nerve free of bony tissue at the point of entry into the bone, and evaluated histologically and immunohistochemically. Nerve segments from 5mm to 8mm in length, with diameters from 0.25mm to 0.5mm were consistently harvested. In all 26 of these vertebrae, the harvested tissue was confirmed by microscopic evaluation to be myelinated nerve.

This tissue was then evaluated with immunohistochemical strains for S-100 and substance P. All 26 specimens were strongly positive for both S-100 (an immunohistochemical marker for nerve tissue) and for substance P (a neurotransmitter for nocioception). The presence of substance P within these nerves was consistent; no nerves were seen that were non-reactive with substance P antibody.

The microscopically-aided dissection revealed that the anatomic origin of the basivertebral nerve could be traced to a small plexus of nervous tissue overlying the central vascular foramen, lying immediately ventral to the posterior longitudinal ligament.

These results confirm the consistent presence of the basivertebral nerve within the human vertebral body, demonstrate that the basivertebral nerve can be reliably harvested by manual dissection, illustrate the immunohistochemical characteristics of the harvested nerve; and suggest a probable anatomic origin for the nerve. The possible function of this nerve is under investigation, however, with the demonstration of substance P within the nerve, the role of this nerve in some forms of clinical back pain is strongly suspected.