Comparison of discographic findings in asymptomatic subject discs and the negative discs of chronic LBP patients: can discography distinguish asymptomatic discs among morphologically abnormal discs?

BACKGROUND CONTEXT: Lumbar discography has been widely used for evaluating discogenic low back pain (LBP). Comparison of pain responses from suspected symptomatic discs with pain responses from asymptomatic negative discs is routine. However, the ability of discography to distinguish asymptomatic morphologically abnormal discs from those that are symptomatic has been understudied. In addition, the discographic characteristics of negative discs in patients with chronic discogenic LBP have not been reported. Criteria for negative morphologically abnormal discs may be valuable for excluding discs from further treatment and examination.

PURPOSE: To determine if discography can distinguish asymptomatic discs among morphologically abnormal discs in patients with suspected chronic discogenic LBP and establish the standard characteristics of negative discs.

STUDY DESIGN/SETTING: Prospective, experimental with control group.

PATIENT SAMPLE: Fifty-five discs from a control group of 16 healthy volunteers without current back pain (11 men, 5 women, 32-61 years of age, mean age: 47 years) and 282 discs from a patient group of 90 LBP patients (59 men, 31 women, 20-70 years of age, mean age: 44.7 years) were recruited.

METHODS: Discography was performed using a pressure-controlled manometric technique with an injection rate of 0.05 mL/s and a 3.5 mL restricted total volume. Concordance was rated as none/unfamiliar, or familiar. Pain was rated via a 0-10 numerical rating scale (NRS). The pressure and volume at which pain was evoked and NRS pain responses at 15, 30, and 50 psi were recorded. Annular disruption grade was rated during the procedure by computed tomography discography and fluoroscopic imaging. Negative discogram required no pain described by the participant as "familiar," with no pain responses >or=6/10 NRS at pressures <or=50 psi above opening pressure and <or=3.5 mL total injected volume. Patient discs were partitioned into two subgroups based on discographic findings: Neg-D (negative discs) and Pos-D (positive discs). Only discs with Grade 3 annular tears (Dallas Discogram Scale) were included in the study.

RESULTS: Among 55 asymptomatic control group discs, 32 (58.2%) exhibited Grade 3 annular tear. All discs in the asymptomatic control group satisfied negative response criteria. Among 282 patient group discs, 199 (70.6%) exhibited Grade 3 annular tear. Of 199 discs with Grade 3 annular tears, 104 (52.3%) satisfied negative response criteria and were categorized as the Neg-D group. The other 95 discs were categorized as a Pos-D group. Patients showed significantly lower pain tolerance relative to control subjects (p<.05). The control and Neg-D groups showed similar pressures and volumes at which pain was initially evoked. Mean control group pain scores were 0.47 NRS at 15 psi and 1.58 NRS at 50 psi. Mean Neg-D group pain scores were 0.11 NRS at 15 psi and 1.1 NRS at 50 psi. Discographic findings for the Pos-D group were significantly different from those of the control and Neg-D groups (p<.001).

CONCLUSIONS: Pain tolerance was significantly lower in patients relative to asymptomatic subjects. Negative patient discs and asymptomatic subject discs showed similar characteristics. Pressure-controlled manometric discography using strict criteria may distinguish asymptomatic discs among morphologically abnormal discs with Grade 3 annular tears in patients with suspected chronic discogenic LBP.