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Introduction | Other Sciatica Pain Mechanisms | The Study | Results | MRI Results | Points of Interest | Downfalls | Good Quotes | Acknowledgments |

Karppinen J. et al. “Severity of Symptoms and Signs in Relation to Magnetic Resonance Imaging Findings Among Sciatic Patients.” Spine 2001 ;26(7):E149-E154


Traditionally it had been thought that the size of the disc herniation and amount of nerve root compression are directly related to the magnitude of patient pain and disability (26-28); however, there is now conclusive evidence that this may not be the case (1,18).

In 2001, Karppinen et al. published an investigation that demonstrated neither the size of a patient's disc herniation nor the degree of nerve root compression correlated with the magnitude of the patients subjective pain or level of functional disability. Or in plain english, bigger and more compressive disc herniations do not create proportionally stronger pain and disability when compared to smaller non-compressive disc bulges--there is no correlation between size, compression, and patient pain.

In that same investigation, was discovered that 20% of the sciatica-suffering patients had no compressive disc disc herniation of any kind on MRI, despite the fact that they were suffering moderate to severe sciatic pain and disability. Amazingly, more than one-half of those non-herniation patients suffered classic radicular pain (62%), in the absents of nerve root compression!

That information begs the question, "if nothing was compressing the nerve roots, then how could these patients be suffering real nerve-root related radicular pain? In response the author stated, "pain mechanisms other than the extent of disc herniation ... generate the subjective symptoms among sciatic patients."

Other Possible Pain Mechanisms which may Generate Sciatica:

One possible explanation for this bizarre finding was put forth by both Ohnmeiss et al. (19,20) and Milette et al. (21) These investigators experimentally demonstrated that disruptions within the substance of the disc (annular tears) not only caused low back pain, but it also caused ‘referred pain’ into the lower limb; we may call this referred lower limb pain ‘discogenic sciatica’.   [Ohnmeiss Paper & Milette Paper]

Another explanation is based upon the investigations of Olmarker et al.   This group has repeatedly demonstrated that the application of nucleus pulposus upon the spinal nerve root can create marked morphological change (axon damage) and functional change (decreased conduction speed) to the micro-anatomy of that nerve root, as well as cause ‘pain-related behaviors’ to occur within the test animals (90-95).  

Therefore, if this nucleus pulposus get ‘loose’ in the epidural space (most likely from a grade 5 posterior annular disc tear), it may well cause the pathological spinal nerve root changes described by Olmarker (90-95) and result in a painful sciatica syndrome without nerve root compression.   Researchers have termed this phenomenon “Chemical Radiculopathy” (257,285).

The final theory on non-compression induced sciatica implicates the activation of the patient's own immune system against the nucleus pulposus-soaked nerve root (30, 31). This ‘auto-immune’ type reaction may help perpetuate the syndrome of chronic sciatic pain.

Whatever the cause, it is clear that non-compressive disc defects (bulges and contained herniations) are just as painful and disabling as the classic large compressive disc herniation.   Therefore the symptoms of sciatic pain without disc herniation on MRI should not be simply dismissed by the doctor.  

The Study:

In year two-thousand, 160 consecutive acute sciatica patients were gathered for an investigation.   The objective of this study was to determine whether or not the patient’s perceived-pain and level of disability were related to the degree of disc displacement on MRI, i.e., the size of their disc herniation.

All of the patients suffered a major complaint of unilateral sciatica that traveled downward from the low back, past the knee, and into the leg. The average patient age was 43.7 years, and the average duration of the sciatica was 2 months.   There were no outcomes reported as part of the study.

All patients underwent a contrast-enhanced MRI, EMG testing, and a thorough Physical examination.   The physical examination included range-of-motion testing, the straight leg raise test, dermatome testing, and “root-specific testing,” which was defined as follows: L4 = diminished Patellar Reflex, L5 = diminished great toe dorsiflexion power and S1 = diminished Achilles’ Reflex.

The patients were next put through some standard self-assessment testing.   These tests included the Visual Analogue Scale (VAS), the Oswestry Low Back Disability Questionnaire (6), and patient-completed pain drawings.  

MRI interpretations were done by two radiologists who were blinded to the study.   Any disagreements on the classification of disc displacement were settled between then.   Over-all, their agreement were excellent and the only disagreements concerned the difference between contained versus noncontained herniations (this did not affect the results of the study).

The following classification system was used to differentiate the degree of disc displacement:


Type of Disc Defect:

Description of Disc Defect:




Grade 1

Normal disc:

Disc material did not extend beyond the margins of the vertebral end-plate.

Grade 2

Disc Bulge:

Symmetrical extension of the peripheral anulus beyond the margins of the vertebral endplates.

Grade 3

Contained Herniation:

Focal extrusion of disc material through the annulus but not through the posterior longitudinal ligament (PLL).

Grade 4

Non-Contained Herniation:

Extrusion of disc material through the PLL.

Grade 5


Disc fragment not in contact with the parent disc.

The radiologists also categorized the amount of ‘nerve root compression’.   The categories were none (no compression of the root at all), minor (dislocation of the nerve root by disc herniation), or major (compression of the nerve root by the disc herniation against the bony structures of the vertebrae).


The following patients-conditions were excluded from this investigation:

1) Stenosis.

2) Non-degenerative spondylolisthesis.

3) Pending applications for early-retirement. (I like this one!)

4) Clinical depression.

5) Prior back surgery.

6) Complaints of Low Back Pain being greater than Leg Pain.

7) Rare causes of sciatica. (Synovial cysts, tumors, etc.)



160 Sciatica Patients:

Positive Valsalva’s Test (pain on coughing):

87 (54%)

Average degree of + SLR:

58 degrees (45 – 70)

Average reported Back Pain (VAS):

6.1 (3.8 – 7.6)

Average reported Leg Pain (VAS):

7.7 (6.3 – 8.8)

Average reported Disability (Oswestry):

42% (32% - 52%)


Positive for a disc herniation relating to the patient's symptoms:

131 (82%)


90 (56%)


130 (81%)

MOTOR DEFICITS: (as test by Achilles’ Reflex (S1), Patellar Reflex (L4), and Extensor Hallucis Power (L5 ).

35 (22%)


8 or 70 (11%)








Total #

Number of Patients:

5 (3%)

24 (15%)

50 (31%)

68 (43%)

13 (8%)


Radicular Pain: (confined to dermatome)

2 (1.5%)

16 (12%)

38 (29%)

62 (48%)

12 (9%)


Nerve root enhancement:







Major root compression:



25 (31%)

44 (55%)

11 (14%)


Motor deficit: (lost reflex etc.)



8 (23%)

19 (54%)

5 (14%)


Straight Leg Raising (deg.)






58 deg.


Back pain intensity: (VAS)







Leg pain intensity: (VAS)







Days of Sick Leave:







Patient disability: (Oswestry)









18% of the patients had no disc herniation, a negative Straight Leg Raise and no “major nerve root compression”, despite having moderate to severe sciatica and back pain (VAS) and  moderate disability (40% via Oswestry). In fact their pain and disability were basically the same as the disc herniation / nerve-root compression group.


Gadolinium enhancement of the symptomatic nerve root was only found in 44% of the patients.   Gadolinium was not useful in predicting which nerve root related to the sciatica.


Positive Straight leg raising (< 55 degrees) is greatly associated with disc herniation and nerve root compression, but it did NOT seem to be associated with patient symptoms (despite what the author says on page E153), although other investigations have demonstrated a relationship between SLR and disability (15,25)

#4. There was very some correlation between positive Motor Findings (a serious finding) and the type of disc displacement. For example, here are the percentages of 'motor findings' found within each of the subgroups: Normal Contour Disc = 0%, Bulge = 13%, Contained HNP = 16%, Non-Contained = 28%, Sequestration = 38%. I would have thought that the extrusion and sequestrated group would have had a much higher rate of positive motor finds?


Neither the degree of disc displacement (degree of herniation) nor the degree of nerve root compression were associated with the subjective pain and disability level on VAS and Oswestry.


As pointed out by Dr. Jon D. Lurie, MD, the degree of disc displacement did, however, strongly correlate with the finding of ‘true radicular pain’ as defined as pain confined to a dermatome below the knee.



“The results (of this investigation) suggest that pain mechanisms other than the extent of disc herniation on MRI generate the subjective symptoms among sciatic patients.”


“Symptoms of sciatic patients without HNP (disc herniation) in MRI are often underestimated…there is general agreement that factors besides compression…also play a crucial role in the pathogenesis of sciatica.” (12,22)


“Not all leg pain is sciatica and not all sciatic pain is radicular; careful synthesis of clinical symptoms, signs, psychosocial factors, and imaging is necessary for accurate diagnosis.” (2) [3]


Print error: I was horrified to learn that Spine had published this paper despite it containing a rather large error. I spotted it immediately and contacted the author: Thankfully I receive an e-mail from the author who stated that not all patients had positive EMGs for radiculopathy, as was stated on page E151 under the heading “Characteristics of the Study Population”. More explicitly, in the sentence, “Five patients had L4, 89 had L5, and 66 had S1 radiculopathy.” the word “radiculopathy” should have been “radicular pain”.   Which cleared up that issue but creates another, for now it appears all of the patients had “radicular pain”, but the results-table states that only 140/160 had radicular pain?  Is anyone proofing these investigations for content over at Spine???


I would like to thank Dr. Karppinen MD for taking the time out of his busy schedule to answer my barrage of e-mail questions about his investigation. He graciously answered everything that was asked which certainly added to the quality of my review.

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1) Karppinen J. et al. “Severity of Symptoms and Signs in Relation to Magnetic Resonance Imaging Findings Among Sciatic Patients.” Spine 2001 ;26(7):E149-E154

2) Errico TJ, et al. “Open discectomy as treatment for herniated nucleus pulposus of the lumbar spine” Spine 1995 ;20:1829-33.

[3] Lurie, JK.   ‘Point of View’:E154 IN: Karppinen J. et al. “Severity of Symptoms and Signs in Relation to Magnetic Resonance Imaging Findings Among Sciatic Patients.” Spine 2001 ;26(7):E149-E154

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