Tissue Origin of Sciatica & LBP?

The Study | Result Table | Detailed Results | My Conclusions

Kuslich SD, et al. "The Tissue Origin of Low Back Pain and Sciatica: A report of pain response to tissue stimulation during operations on the lumbar spine using local anesthesia." Orthop Clinics North Am 1991 ;22 (2):181-187

Although there have been other published studies into the relationship between the stimulation of human in vivo spinal structures, and the patients perception of pain, [3,13,17] Kuslich's work in this area is unprecedented and is still frequently quoted in the literature today.  

During the 1980s, Dr. Stephen Kuslich of Minneapolis, Minnesota performed over 700 lumbar spinal surgeries using only a local anesthesia to deaden the pain. In other words, this method left the patients awake and able to answer questions. During many of these surgeries, Kuslich would gently compress different neural structures intra-operatively and then ask the patient to describe the location and degree of pain experienced.

The "bottom line" of these reproducible findings was this: if you irritate a nerve root (via pressing upon it with the surgical instrument or shocking it) that is visibly inflamed (such as the one that had the herniation pressing on it), the patient will suffer the identical lower extremity pain that he was being operated on for. However, if you stimulate the actual posterior annulus (the one with all those pain-carrying nerve fibers), then all you get is minor low back pain— there is no radiation into the lower extremity or even buttock. Also noteworthy is the fact that they could only reproduce the patient's complaints of sciatica by stimulating the structures: the caudal dura, the nerve root sleeves (on the affected side I assume), on the dorsal root ganglion, or distal to the dorsal root ganglion.*They noted the dorsal root ganglia was more sensitive than the other structures.  

The Study:

Between 1987 and 1990, 193 consecutive patients were prospectively studied.   All of these patients were operated upon for complaints of intractable lower back and/or lower limb pain (sciatica) secondary to either disc herniation or spinal stenosis.   In stead of the use of general anesthesia, only a "progressive" local anesthesia was used, leaving the patients fully awake and responsive.

During the operation the surgeon randomly "stimulated" various tissues in and around the exposed disc and spinal nerve/nerves by means of 'mechanical force' (they used forceps, blunt surgical instruments or the electric shocking of the tissue with low volt electricity0.  

The patients were then asked to describe and rate any associated sensations of pain, numbness, or burning on an analog scale of 0 to 5, where 5 was severe pain that was exactly like their usual and customary pain (concordant pain).

Results:

Detailed Results :

Normal (non-compressed or irritated) nerve root:   The normal, uncompressed, or unstretched nerve root was completely insensitive to painful stimulation.   It could be handled and retracted (pulled and held with a metal retracted) without and anesthetic. "Forceful retraction over an extended period of time resulted in mild paresthesias but never any significant pain."

Compressed nerve root : Stimulation of a compressed or stretched nerve root (via exposure to a pre-surgical disc herniation or stenosis) consistently produced the same sciatic distribution of pain as the patient had experienced before the surgery.   "In spite of all that has been written about other tissues in the spine causing leg pain, we were never able to reproduce the patient's sciatica except by finding and stimulating a stretched, compressed, or swollen nerve root.   Sciatica could be produced by either pressure or stretch on the caudal dura, on the nerve root sleeve, on the ganglion, or on the nerve distal to the ganglion, depending on the site of compression.   In general, the closer one stimulated to the site of compression or tension, the greater the pain suffered by the patient.   This pain could always be eliminated by the injection of Xylocaine beneath the nerve sleeve proximal to the site of compression."  

Scar tissue : (Post laminectomy syndrome) "Another interesting finding involved operations on patients who had undergone prior laminectomies.   In those cases, there was always some degree of perineural fibrosis (I think he means epidural fibrosis or scar tissue).   The scar tissue itself was never tender; however, the nerve root was frequently very sensitive.   In addition, we concluded that the presence of scar tissue compounded the nerve pain by fixing the nerve in one position and thus increasing the susceptibility of the nerve root to tension or compression."

Anulus Fibrosus of the posterior disc:   (The authors confessed that the PLL and central anulus are so tightly interwoven that it was almost impossible to stimulate the two separately.)   The authors report that about 66% of the patients had pain in this structure.   "Referral of depended upon the exact site of the anulus being stimulated.   The central anulus and PLL produced central back pain.   Stimulation to the right or left of the PLL directed pain to the side being stimulate.   In other words, if the right side of the anulus was stimulated, the patient suffered right sided lower back pain, if the middle of the anulus was stimulated the patient perceived pain in the center of the lower back.    Some patients always reported highly concordant lower BACK pain (usual pain) with stimulation of the posterior anulus but there was never any reproduction of sciatica in any of the patients tested !   If they directly stimulated a disc herniation (toward the side of the IVF) they could sometimes get some pain into the buttock but still no sciatica.   The anulus was exquisitely tender in about 33% of the patients, moderately tender in another 33% of the patients, and completely insensitive in the remaining 33%.   Kuslich theorized, " perhaps certain individuals are more richly innervated than others.   Or, alternatively, perhaps there exists some chemical or mechanical irritant that sensitizes certain discs to become painful. " [ ah men]  

Facet Joints:   If took great 'experimenter force' to elicit pain from this structure and when the pain came, it was localized an did not cause their typical deep lower back pain.   Sometimes the facet capsule was painful but it referred pain into the back and "very rarely" into the butt, and "never" down the lower limb.   Upon piercing the facet capsule they found that the facet synovium and articular cartilage was "never" tender.   (Comment: maybe, like the nerve root, it takes 'something' to sensitive the tissue of the facet to pain.   If so, we wouldn't expect any of these disc patients to have a sensitive facet.)

Geek's Conclusions:

This is an absolutely amazing study. One that would never be allowed today under the strict rule of the institutional review board! This study demonstrated that 90% of all inflamed, stretched (tented over a disc herniation) or compressed nerve roots reproduced the patients concordant (same) sciatica when stimulated during surgery!

There is some conflict between these results and those of the Ohnmeiss' study which clearly indicated that full thickness anular tears, with or without disc bulging/herniation, may also reproduce concordant lower limb pains (referred sciatica) in about 60% of properly screened patients with chronic lower back pain.

Another interesting finding was the fact only stimulation of the compressed, inflamed, or stretched nerve root produced foot pain. This confirms my own suspicions that a patient with sciatica which runs completely into the foot (like me) is suffering root injury and not discogenic pain.

In all fairness to Ohnmeiss, Kuslich was not able to stimulate the disc from the 'inside-out', the way Ohnmeiss's discography procedure did; therefore, the fact that his probing of the outer anulus/PLL combo did not trigger sciatica (or even butt pain) does not necessarily mean that the anulus can't refer pain into the lower limbs.

References:

3) Hirsch C. "An attempt to diagnose the level of disc lesion clinically by disc puncture." Acta Orthop Scand 18:132-140, 1948

13) Smyth MJ, Wright V, "Sciatica and the intervertebrl disc. An experimental study." J Bone Joint Surg [Am] 40:1401-1418, 1958

17) Wiberg G. "Back pain in relation to the nerve supply of the intervertebral disc." Acta Orthop Scand 19:211-221 1950