The Case for Neuropathic Pathogenesis;
Mechanical Tension and its Consequences

Barrett L. Dorko, P.T.


          The following is a very brief and limited overview of some recent literature pertaining to the subject of nervous irritation and, at times, its clinical presentation. It is meant to clarify and support specifically my contention that in many cases of discomfort the appropriate essential diagnoses is that of adverse neural tension.

          Even mild, brief retraction of the nerve root during discectomy reduces blood flow significantly (more so in symptomatic roots) and can result in postoperative pain.
          (Matsui)

          Positive sensory symptoms correlate in intensity and time to ectopically generated and antidromically conducted nerve impulses as detected by microneurography. Mechanical stimulation of the peripheral nerves altered these findings. It follows that repositioning by whatever means can reduce pain due to nervous irritation.
          (Nordin)

          There are indications that antidromic activation of peripheral nociceptors may follow nerve root irritation. Treatment of the distal portion of the nerve relieves distal pain.
          (Xavier)

          Pain and neurologic dysfunction are seen to resolve despite no evidence that previously described compression had been relieved.
          (Garfin)

          The sheaths of the nerve trunks themselves are innervated (the nervi nervorum) and when distended will typically produce a report of deep, aching pain.
          (Asbury)

          Simple, manual compression of the brachial plexus is typically positive for radiating pain when the cervical cord is deformed as seen on MRI.
          (Uchihara)

          Irritated nerve roots always produce pain with further distention (Kuslich) and the pain from nervous irritation produces a rise in sympathetic tone: whereas muscular nociception enhances parasympathetic tone.
          (Gellhorn)

          Trigger points, although commonly present in both active and inactive states, have never been consistently identified as anything other than an area within the muscle that displays spontaneous needle EMG activity. No abnormality in the muscle is seen by light microscopy, histochemical study or electron microscopy. It is evident that the muscular activity has its origins in sympathetically activated intrafusal contractions.
          (Hubbard)

          Distorted nervous tissue changes chemically first and foremost. Fibrosis occurs only in the last stages of mechanical deformation or immobilization and its presence has been shown to be unrelated to pain.
          (Cornefjord)

          Studies indicate that mobilization of nervous tissue increases peripheral blood flow, implying a physiologic shift toward parasympathetic dominance.
          (Kornberg) REFERENCES

Annertz, M., Jonnson, Stromquist, Holtas No relationship between epidural fibrosis and sciatica in the lumbar postdisectomy syndrome. Spine Vol. 20, Number 4, pp. 449-453.

Asbury, Fields Pain due to peripheral nerve damage: An Hypotheses. Neurology 1984; 34: 1587-90.

Cornefjord, M., Olmarker, Farley, Weinstein, Rydevik Neuropeptide changes in compressed spinal nerve roots. Spine Vol. 20, Number 6, 1995.

Garfin, S., Brown Compressive neuropathy of spinal nerve roots. A mechanical or biological problem? Spine Vol. 16, Number 2, 1991.

Gellhorn Autonomic-somatic integrations. University of Minnesota Press, 1967.

Hubbard, D., Berkoff Myofascial trigger points show spontaneous needle EMG activity. Spine Vol 18, Number 13, pp. 1803-1807, 1993.

Kornberg, C., McCarthy, T. The effects of neural stretching techniques on sympathetic outflow to the lower limbs. JOSPT Vol. 16, Number 6, Dec. 1992.

Kuslich, S.D., Ulstrom, R.N., Michael, C.J. The tissue origin of low back pain in sciatica. Orth. Clin. North Amer. 1991:22 No. 2, 181-187.

Matsju, H., Kitagawa, Kawaguchi, Tsujo Physiologic changes of nerve root during posterior lumbar discectomy. Spine Vol. 20, Number 6, 654-659, 1995.

Nordin, M., Nystrom, B., Wallin, V., Hagbarth, K.E. Ectopic sensory discharges and paresthesiae in patients with disorders of peripheral nerves dorsal roots and dorsal columns. Pain 1984:20; 231-245.

Uchihara, T., Furukawa, Taukagoshi Compression of brachial plexus as a diagnostic test of cervical cord lesion. Spine Vol. 19, Number 19, pp. 2170-2173, 1994.

Xavier, A.V., Farrell, C.E., McDanal, J., Kissin, I. Does antidromic activation of nociceptors play a role in sciatic radicular pain? Pain. 1990:40:77-79.

Yoshizawa, H., Kobayashki, Morita Chronic nerve root compression. Spine Vol. 19, Number 19, pp. 2170-2173, 1994.

Consider this passage from page 125 of Moving In On Pain (Butterworth-Heinemann Australia 1995) edited by Michael O. Shacklock:

Intraneural Blood Flow

When nerves are elongated within physiologic (normal) limits, adequate neural blood flow is maintained, but only up to the point where the normal vascular protective mechanisms are preserved. Maintenance of intraneural blood flow during neural elongation is accomplished by the blood vessels in nerves containing undulations and coils. When nerves are loose, these vascular convolutions are accentuated. However, if the nerve is lengthened, the vascular coils follow the nerve elongation and are pulled taut. Furthermore, the lumen of the vessels is reduced and occlusion can occur, particularly when the nerve is stretched beyond the limit of protection (Lundborg & Rydevik 1973). The blood vessels are then strangled, intraneural blood flow is compromised and nerve function deteriorates (Ogata & Ngaito 1986). If the stretch is taken only slightly beyond the protective limits, and for a brief period, nerve function is likely to return rapidly to normal (Lundborg et at 1982). However, if the strain in the nerve is particularly severe or sustained, the alterations in nerve function will be permanent. The relevance of intraneural blood flow is that excessive mechanical stress may cause anoxia and nerve damage, leading to heightened mechanosensitivity and pain. In these circumstances, movements that mechanically stress the neural tissues may evoke symptoms.

REFERENCES

Lundborg G, Rydevik B 1973 Effects of stretching the tibial nerve of the rabbit. Journal of Bone and Joint Surgery 55B: 390-401

Ogata K, Ngaito M 1986 Blood flow of peripheral nerve effects of dissection, stretching and compression. Journal of Hand Surgery 11B: 10-14

Lundborg G, Gelbermann R, Minteer-Convery M et al 1982 Median nerve compression in the carpal tunnel - functional response to experimentally induced controlled pressure. Journal of Hand Surgery 7: 252-259