The Influence of Psychologic Factors on Diskography in Patients With Chronic Axial Low Back Pain

Patient Recruitment 

The institutional review board of Quorum Review approved the study. All patients were informed of the nature of the study and the risks of diskography before consenting to the procedure. None of the participants received any remuneration for partaking in this study. The exclusion criteria were as follows: subjects and patients with allergies to contrast media, iodine, or cephalosporin antibiotics; inability to undergo MRI scanning because of ferromagnetic implants or severe claustrophobia; and inability to tolerate positioning for MRI or diskography.

Eighty-one patients with CLBP were recruited (54 men, 27 women; age range, 20–65y; mean age, 43±12y). Before the study, subjects and patients were instructed in the use of the 0-point to 10-point NRS for pain intensity responses. Those completing the NRS were instructed that 0 indicated no pain, 6 indicated bad pain, and 10 indicated the worst pain imaginable. The patients agreeing to continue in the study underwent pressure-controlled manometric diskography.8 All patients were required to obtain or to provide an MRI scan of their lumbar spine that had been taken within the last 6 months.

Psychometric Test 

Before diskography was performed, subjects and patients completed a back pain history and psychometric screening questionnaire, which included a standard pain diagram. The psychometric screening consisted of a modified ZSDS score9, 10 and an MSPQ score.9, 11, 12 Patients were divided into 4 groups according to the psychometric test findings, using the DRAM scores: normal was defined as a ZSDS score less than 17; at-risk was defined as a ZSDS score between 17 and 33 and an MSPQ score of less than 12; distressed depressive was defined as a ZSDS scored greater than 33; and distressed somatic was defined as a ZSDS score between 17 and 33 and an MSPQ score greater than 12. These modified ZSDS and MSPQ scores were then combined, and the correlation between the psychometric scores and the diskography parameters was examined.

The Pressure and Injection Speed–Controlled Manometric Diskography Technique 

Diskography was performed by 1 of 3 diskographers, who had between 5 and 25 years experience with the procedure, in a surgical suite under aseptic conditions. Intravenous antibiotics (2g of cephalosporin) were administered 20 minutes before the procedure. All patients were premedicated with .025mg/kg of midazolam before the procedure. Throughout the procedure, the patients were monitored with pulse oximetry and a blood pressure cuff. Supplemental oxygen was administered through a nasal cannula.

Nonionic contrast medium mixed with 6mg/mL of cephalosporin was injected into each disk at a rate of .05mL/s using a controlled injection syringe with digital pressure readout.a

At the time of the disk injection, each patient was awake, alert, and able to respond to instructions or questions. They were asked to report the nature and location of any pain that had been evoked during the procedure, and to rate its intensity on a 0 to 10 NRS for pain.

The pressures were monitored throughout each injection. The opening pressure was recorded when the contrast medium was first observed to enter the disk. At each subsequent injection of 0.5mL contrast medium, the pressure of the injection, the location of the contrast medium, and any pain response were recorded. The injection was continued until one of the following endpoints had been reached: an intradiskal pressure of 80 to 100psi above the opening pressure, or a total of 3.5mL contrast medium had been injected. In some cases, the final pressure of the injection exceeded 100psi because of a rapid increase in pressure during the final few seconds of the injection.

When each injection was terminated, anteroposterior and lateral spot films were obtained to record the distribution of the contrast medium. When all the levels in each patient had been tested, CT was performed on all those levels. The participants tolerated the procedure well, and there were no complications.

Diskography Parameters 

Subjects were scored using a standard 0-point to 10-point NRS. The diskography parameters were compared with the psychometric scores after excluding the nonpainful disks. The pressure (in psi) associated with a given pain response was noted. The pressure and injected volume at which the pain was first evoked and the NRS values at 15, 30, and 50psi above the opening pressure and the maximal NRS during more than 50psi of intradiskal stimulation were recorded.

Pain Behaviors 

All patients were videotaped throughout the procedure to corroborate the pain response or its absence. Three examiners subsequently reviewed the videotape of each procedure and scored it for the pain behavior using the modified Wong-Baker Faces Pain Rating Scale.13 The agreed score was entered when all 3 examiners agreed on their rating. When the examiners disagreed, the videotape was viewed again until a consensus score had been achieved. Each of these instruments rated the pain behavior on a 0 to 4 scale, on which 0 indicated no pain behavior and 4 indicated maximum pain behavior. The facial expressions were evaluated as follows: 0 was does not hurt, 1 was hurts slightly (grimace observed), 2 was hurts even more (intensity mild and intermittent), 3 was hurts quite a lot (intensity moderate), and 4 was hurts the worst (tearing). According to the 0 to 4 rating scale of the facial expression, the vocal expression was also rated on a 5-point scale: 0 was does not hurt, calm, no vocal sound; 1 was hurts slightly, groans briefly; 2 was hurts even more, intensity mild and intermittent, moan; 3 was hurts quite a lot, intensity moderate, long-lasting moaning; and 4 was hurts the worst, intensity quite pronounced, screaming or shouting.

Positive Diskogram Criteria 

The magnetic resonance images of each disk tested were graded for their signal intensity using a I to V scale for disk degeneration.14 The CT diskograms were graded for the presence and extent of radial fissures as 0, 1, 2, 3, 4, and 5 according to the Dallas Discogram Scale.15 Four criteria have been previously used to determine the presence of positive disk on diskography: (1) an abnormal disk (Dallas scale grade ≥3), (2) NRS pain response of 6 or more out of 10, (3) at a pressure level 50psi or less, pain described by the patient as familiar, and (4) a negative control disk.16 In contrast with the criteria of Walsh et al,17 we did not require 2 or more pain behaviors documented by videotape to establish a positive level.

The prediskography and postdiskography pain scores were used to compare and confirm the concordant assessments made during the injection.

Data Analysis 

All statistical analyses were performed with SPSS/PC+ software.b When comparing positive diskography rates with psychometric groups, the chi-square test was used. Partial correlation coefficients were analyzed for relation parameters of diskography with summation of psychometric scores.

Sample Characteristics 

Two hundred sixty-three disks were recruited from 81 patients with CLBP. Thirty-seven disks in 12 patients not at risk (normal) and 139 disks in 42 at-risk patients were evaluated with a psychometric test. In 27 patients who showed abnormal psychometric findings, 22 for distressed depressive and 5 for distressed somatic findings were analyzed. The duration of pain was 47.21±64.61 months.

Comparison of Psychometric and Diskographic Findings 

Pain severity and positive rates with pressure during diskography 

The mean NRS scores at 50psi above opening pressure were 3.99±3.87 for the normal group, 4.40±3.92 for the at-risk group, and 4.34±3.87 for the abnormal psychometric groups. There were no significant NRS score or positive rate differences among psychometric groups at 15, 30, and 50psi above opening pressure (table 1, fig 1).

Table 1. The Rate of Positive Disks of Each Psychometric Subgroup at Various Pressures

	Pressures	Normal (%)	At Risk (%)	Abnormal (%), (DD/DS), n
	NRS at 15psi	19	14	20(21/14)
	NRS at 30psi	27	23	31(34/14)
	NRS at 50psi	41	31	33(37/14)

Abbreviations: DD, distressed-depressive; DS, distressed-somatic.

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Fig 1. Mean NRS curves of psychometric subgroups according to pressure level during diskography.

Pressure of initial pain response 

The mean pressures initially evoking any pain were 51.38±24.20psi for the normal group, 53.65±7.12psi for the at-risk group, and 48.74±11.45psi for the abnormal psychometric groups (fig 2). There were no significant differences in the pressures that evoked pain among psychometric groups.

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Fig 2. Pressure of initial pain response (Evo-Pre) in each psychometric subgroup during diskography.

Volume of initial pain response 

The mean injected contrast media volume at which pain was initially evoked was 2.21±1.46mL in the normal group, 2.41±1.41mL in the at-risk group, and 2.19±0.56mL in the abnormal psychometric groups (fig 3). There were no significant differences in the volumes that evoked pain among psychometric groups.

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Fig 3. Volume of initial pain response (Evo-Vol) in each psychometric subgroup during diskography.

Pain behaviors during diskography 

The facial and verbal behaviors were scaled during diskography and with video analysis after procedure. The mean pain behavior scores did not differ among psychometric groups (fig 4).

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Fig 4. Mean pain behavior score in each psychometric subgroup during diskography.

Correlation between diskographic findings and psychometric scores 

The correlation between MSPQ and facial scores was .139; between MSPQ and verbal scores, it was .148 (table 2). However, these correlations were negligible. Mean pain scores or pressure and volume of initial pain response did not show a significant correlation with psychometric scores.

Table 2. Correlation Coefficients Between Diskographic Findings and Psychometric Scores

	Measures	MSPQ	ZSDS
	NRS at 15psi	.077	.042
	NRS at 50psi	.021	−.012
	Maximal NRS	.060	.045
	Evo-Pre	−.049	−.051
	Evo-Vol	−.023	−.010
	Facial expression	.139⁎	.053
	Vocal expression	.148⁎	.053

Abbreviations: Evo-Pre, pressure at which pain was first evoked; Evo-Vol, injected volume at which pain was first evoked; maximal NRS, maximal pain response during the diskography.

⁎ Significant at the 0.1 level.

Study Limitations 

The primary limitation of our study was that only the MSPQ and modified ZSDS were used to evaluate the psychometric profiles. Because pain sensitivity can vary depending on other psychiatric states not measured by the MSPQ and modified ZSDS, it is possible that a more extensive or different set of instruments might have detected or modified a correlation. Nevertheless, our study indicates that the use of a more precise method of provoking a stimulus may limit the confounding influences of psychometric factors.