Lumbar Discography

 

Introduction

MRI has been found to demonstrate an abnormal disk in approximately 28% of subjects without back pain or sciatica.  Provocative discography is the only method that directly relates a radiographic image to the patientķs pain.  A CT/discogram is considered as positive, only if significant pain and an abnormal image are present.  When these two portions of the test are taken into account, the study results in a 100% specificity.  Discography has been found to be more sensitive than MRI in detecting annular fissures. CT/discography has an overall accuracy of 87-94%.  Discography was not found to be sensitive to lesions in the middle or outer annulus that are not contiguous with the nucleus.  MRI, when compared to discography, is significantly better in demonstrating disk herniations (100% versus 86%). Discography was found to be more sensitive than myelography in detecting lateral disk herniations, especially at the L5-S1 level.  It is recommended that MRI be used initially in the diagnosis of low back pain. In terms of surgical outcome, it has been found that when a patient has both, a positive abnormal discographic image and a painful provocative injection, there is an 88% success rate in terms of a surgery while those patients that displayed a positive image but no symptomatic pain reproduction, the success rate is only 52%.  CT/discography can identify recurrent disk herniations not visualized by Gadolinium enhanced MRI.

Lumbar discogenic pain and internal disk disruption are defined as lumbar spine pain with or without referred pain, stemming from an intervertebral disk, caused by internal disruption of the normal structural and biochemical integrity of the symptomatic disk.  Discogenic pain occurs in 39% of patients with severe chronic low back pain in whom the etiology has not been well defined by less invasive diagnostic testing.

Internal disk disruption was described as being different from symptomatic disk herniation. In the syndrome of internal disk disruption, the primary symptom is back pain. Leg pain might be a significant part of the problem, but back pain is the dominant complaint. Provocative discography is required to establish this diagnosis. In symptomatic disk herniations, the mass effect of herniated disk material compresses neural elements causing a tissue reaction.  Leg pain is the dominant complaint and is always greater than back pain in the fully developed radicular syndrome. 

The most commonly abnormal levels are L4-5 and L5-S1 in combination, followed byL5-S1 alone, followed by the combined 3 level degeneration at L3-4, L4-5, andL5-S1.

 

Pain Provocation hypothesis:

1.       The injection may increase intradiscal pressure, which, in an abnormal disk, may stimulate nerve endings within the annular fibers of the disk, possible by stretching them.

2.       The injection may result in some biochemical or neuro chemical stimulation that causes pain.

3.       An injection may increase pressure at the end plates or pressure may be transferred to the vertebral body throughout the end plate resulting in an increase in intervertebral pressure and therefore pain. This hypothesis is supported by studies reporting disk injection resulting in end plate deflection and increased specimen height.

4.       Another hypothesis to explain the presence of pain from injection of a seemingly normal disk is that pressure from the injection is transferred to an abnormal, symptomatic adjacent disk and, thus, a positive pain response is elicited.

 

Indications

The three (3) main indications are: 

1.       To help assign the details of an operation.

2.       To help decided whether or not to perform the surgery.

3.       To determine if the patient is a candidate for IDET (Intradiscal Radiofrequency Annuloplasty / Nucleoplasty).

 

Discography should be performed only if the patient has failed adequate attempts of conservative therapy and noninvasive diagnostic tests, such as MRI.

 

Specific indications for discography include, but are not limited to, the following:

1.       Further evaluation of abnormal disks or recurrent pain from a previously operated disk and lateral disk herniation.

2.       Patients with persistent, severe symptoms in whom other diagnostic tests have failed to reveal clear confirmation of a suspected disk as a source of the pain. 

3.       Assessment of failed surgery patients to determine if there is painful pseudo arthrosis or a symptomatic disk in a posteriorly viewed segment.

4.       Assessment of disks, prior to fusion, to determine if the disks proposed fusion segment are symptomatic and to determine if disks adjacent to this segment can support a fusion.

5.       Assessment of minimally invasive surgical candidates confirmed a contained disk herniation or to investigate dye distribution pattern prior to chemonucleolysis.

6.       Patients with persistent, severe back pain in whom other diagnostic tests have failed to reveal the etiology.

 

Complications of discography

 Complications associated with discography include: spinal headache, meningitis, discitis, intrathecal hemorrhage, arachnoiditis, severe reaction to accidental intradural injection, damage to the disk itself, urticaria, retroperitoneal hemorrhage, nausea (2%), convulsions (4%), headache (10%), and increased pain (81%). Discography was found not to result in herniation of nucleus material or annular deterioration.  Eight (8) year follow-up has demonstrated no damage to normal discs after discography.

The incidence of discitis is 2-3% when using a single needle technique and 0.7%using a double needle technique. With regards to the incidence to discitis, when using a single needle technique, the incidence is 1.3%, when using a double needle technique, the incidence is 0.35%, and when prophylactic antibiotics are used, the incidence goes further than to 0.000%.

 

Anesthesia

It is recommended that short acting medications (Propofol, Remifentanil, etc.) be used, since it is absolutely necessary to have an awake and responsive patient for questioning about reproduction of pain. If possible, avoid Bezodiazepines or long acting narcotics that can confuse the interpretation of the results. We use intravenous Norflex (orphenedrine) 60 mg + Toradol (ketorolac) 60 mg before the start of any pain procedures.

 

Contrast Material

You should always use a water-soluble, nonirritating, non-ionic, preservative-free, hypoallergenic contrast. We currently use Isovue 300M.  An abnormal disk will usually accept two (2) or more ml of fluid

 

Clinical Symptoms

Interestingly, there are some studies to clinically evaluate discogenic pain by using a ģbony vibration stimulation".  An attempt should be made to determine whether or not the patient can feel pain by placing a tuning fork over the spinous processes. The main symptoms are:

1.       Internal disk disruption - The primary symptom is back pain.

2.       Symptomatic disk herniations - Leg pain is the dominant complaint and is always greater than back pain in the fully developed radicular syndrome.

 

Procedure

 Prophylactic antibiotics and/or antihistamines should be considered.  A double needle technique should always be used.  The injection should be performed with contrast as previously described.  (Water-soluble, etc.). Accurate needle placement is required to avoid annular injections, which could produce false positive results. Injection against the vertebral end plate can also cause false positive response.

Pressure from the discography injection could be transferred to an adjacent abnormal, symptomatic disk and thus, a positive pain response could be elicited. Due to this, it is always a good idea to monitor the pressure of the adjacent disks as contrast material is being injected and the end point pressure tested.

 

The information recorded should include: 

1.       The resistance to the injection. (End-point)

2.       The amount of contrast injected. (Maximum Volume)

3.       The volume at which the patient experienced pain. (Pain Volume)

4.       The pattern of dye distribution. (Diffuse, location of fissure, extravasation, herniations, Schmorl's node, etc.).

5.       Pressure at which patient experienced a "pressure sensation".

6.       Pressure at which the patient experienced "Pain".

7.       The pain response. (Location, character, distribution, intensity, and concordance or discordance with the patientķs typical pain and pain pattern)

 

Pain intensity is recorded on a 0-10 scale

 

Interpretation

 Very careful attention should be paid to interpretation the pain response during the injection of each disk, including if the pain is similar to or exactly like the symptoms for which the patient seeks relief.  The location of the pain, and its intensity.  Discography should then be followed by actual CT scanning.

Pain at low pressures is most likely due to chemical irritation. .  Low resistance is generally associated with a tear throughout the outer annulus Pain at high-pressures is possibly due to mechanical irritation, end-plate deflection, or stimulation of pressure receptors.

An intradiscal pressure of 60-70 pounds per square inch (400-500 kilopascals) is the maximum pressure that can be sustained by manual injection technique (thumb pressure on a 3.0 cc luer-lock syringe).  The normal intradiscal pressure of a supine patient is approximately 15-25 PSI.  Sitting or standing increases this normal pressure to approximately 80 PSI.

Generally, if a large volume of contrast can be injected, the disc is degenerated or there is a fissure extending through the outer annular wall.  Injection pressure or resistance to injection should be noted

 

CT classification of Discography:

 

 

 

Type 1 the discogram is normal manometrically, volume metrically, radiographically, and produced no pain.  The CT discogram showed contrast to be centrally located in the axial and sagittal projections. 

 

 

 

 

Type 2 is identical to type 1 except that it is positive for reproduction of pain. 

 

 

 

 

Type 3 the annular tears lead to a radial fissure.  This group is further subdivided into Type 3a when the radial fissure is posterior,3b when it radiates posterolateral, and 3c when the fissure extends lateral to a line drawn from the center of the disk tangential to the lateral border of the superior articulating process.

 

 

 

 

Type 4 once the radial fissure reaches the periphery of the annulus fibrosus, nuclear material may protrude causing the outer annulus to bulg

 

 

 

 

Type 5 when the outer annular fibers rupture, nuclear material may extrude beneath the posterior longitudinal ligament and come in direct contact with either the dura or a nerve root. 

 

 

 

 

Type 6 when the extruded fragment is no longer in continuity with the interspace it is said to be sequestrated.  Manometrically, volumetrically, and radiographically, the discograms are always abnormal. Familiar pain may only be reproduced if enough pressure is generated against the free fragment to cause stimulation of the pain sensitive structures. 

 

 

 

 

Type 7 the end stage of this degeneration is internal disk disruption, in which multiple annular tears occur.  The discograms are abnormal manometrically, volumetrically, and familiar pain may or may not be reproduced.   Radiographically, the contrast usually fills the entire interspace in a chaotic fashion.  The CT discograms show contrast extravasation throughout multiple annular tears. 

 

 

 

 

Clinical classification:

1.       No pain or pressure. (NP)

2.       Pressure (P)

3.       Pain dissimilar to clinical symptoms. (D)

4.       Pain similar to clinical symptoms. (S)(Inconsistent)

5.       Exact reproduction of symptoms. (ER)(Concordant)

6.       Pain intensity is recorded on a 0-10scale

ģCotton Ballī

ģLobularī

ģIrregularī

ģFissuredī

ģRupturedī

 

 

Contrast distribution: (as evaluated by Fluoroscopy)

 

Discogram Type

 Stage of Disk Degeneration

ģCotton Ballī (CB)

No signs of degeneration, Soft white amorphous nucleus

ģLobularī (L)

Mature disk with nucleus starting to degenerate into fibrous lumps.

ģIrregularī (I)

Degenerated disk with fissures and clefts in the nucleus and inner annulus.

ģFissuredī (F)

Degenerated disk with radio fissure leading to the outer edge of the annulus.

ģRupturedī (R)

Disk has a complete radio fissure that allows injected fluid to escape.  Can be in any stage of degeneration.

Reference: ģThe Stages of disc degeneration as revealed by discograms.ī M.A. Adams, P. Dolan, W.C. Hutton. The Journal of Bone and Joint Surgery ń British Edition. Vol. 68-B No.1, January1986.

 

Interpretation:

1.       Low resistance is generally associated with a tear throughout the outer annulus.

2.       Pain at high pressures is possibly due to mechanical irritation, end-plate deflection, or stimulation of pressure receptors.

3.       Intradiscal pressure of 60-70 pounds per square inch (PSI) is the maximum pressure that can be sustained by manual injection technique (thumb pressure on a 3.0 cc luer-lock syringe.)

4.       Generally, if a large volume of contrast can be injected, the disc is degenerated or there is a fissure extending through the outer annular wall.

5.       In general, degeneration of the intervertebral disc will cause a decrease in the mean intradiscal pressures.

6.       Opening or intrinsic pressure is defined as the pressure at which the contrast starts to enter a disc.

7.       Leakage pressure is defined as the pressure on the P-V curve, where a sudden change occurs in the curve inclination, whereby the volume increased substantially, while the pressure either stopped increasing, or changed minimally.

8.       Chemical irritation is defined as pain at or below 15 PSI above opening pressure.

9.       Mechanical irritation is defined as pain between 15 and 50 PSI above opening pressure.

10.    Indeterminate discs are defined as having pain between 51 and 90 PSI above opening pressure.

11.    Normal disc have no pain.

12.    Annular disruption ń leaking / protrusion / annular fissuring

13.    Kpa x0.14504 = PSI

 

 

Intradiscal Pressure Values for Different Positions and Exercises

Position

Pressure (PSI)

Lying supine

15

Lying on the side

17

Lying prone

16

Lying prone, extended back, supporting on elbows

36

Laughing heartily, lying laterally

22

Sneezing, lying laterally

55

Peaks by turning around

102-116

Standing, relaxed

73

Standing, performing valsalva maneuver

133

Standing, bent forward

160

Sitting relaxed, without backrest

67

Sitting actively straightening the back

80

Sitting with maximum flexion

120

Sitting bent forward with tight supporting the elbows

62

Sitting slouched into the chair

39

Standing up from a chair

160

Walking barefoot

77-94

Walking with tennis shoes

77-94

Jogging with hard street shoes

51-138

Jogging with tennis shoes

51-123

Climbing stairs, one at a time

73-102

Climbing stairs, two at a time

44-174

Walking down stairs, one stair at a time

55-87

Walking down stairs, two stairs at a time

44-131

Lifting 20Kg, bent over with round back

334

Lifting 20Kg, as taught in back school

247

Holding 20Kg close to the body

160

Holding 20Kg, 60cm away from the chest

261

Pressure increase during night (over a period of 7 hr.)

15-36

Reference: ģ New In Vivo Measurements of Pressures in the Intervertebral Disc in Daily Lifeī Wilke et al. Spine Vol.24, No 8, pp755-762,1999.

 

 

Level

Average Volume (ml)

Volume Range (ml)

L2-3

0.58

0.4 - 0.7

L3-4

1.06

0.4 - 2.6

L4-5

1.09

0.22 - 2.4

L5-S1

0.99

0.42 - 2.0

Transition

0.40

NA

 

Discogram Type

Mean Injection Pressure (PSI)

Mean Injection Volume (mL)

1

34

0.62

2

28

0.71

3

26

1.20

4

17

1.54

5

19

More than 2.0

 

Disk Classification

Intradiscal Pressure

Pain Response Intensity

Pain Response Category

0-normal

>80 PSI

0

NA

1-asymptomatic

>50 PSI

Pressure, discomfort only

NA

1-asymptomatic

>50 PSI

Definite pain (>5/10)

Discordant

2-indeterminate

<50 PSI

Definite pain (>5/10)

Discordant

3-mechanical (strain)

30-50 PSI

Definite pain (>5/10)

Discordant

4-chemical (sensitized)

<30 PSI

>5/10

Concordant