Quantitative discometry: Low-dose concordant pain onset identifies sensitized annular nociceptors under pressure–volume–controlled provocation

Background Provocative discography is controversial because it couples mechanically induced disc stimulation to a subjective pain report and is often interpreted as a simple yes/no test of “discogenic pain.” Pressure–volume–controlled discography (“discometry”) allows disc provocation to be treated as a dose–response experiment using static pressure above opening (ΔP) and cumulative mechanical work (W), rather than pressure alone. Objective To determine whether discs that reproduce a patient's concordant pain under pressure–volume control exhibit a distinct low-dose onset phenotype compared with discs that never declare, and to interpret these patterns in the context of annular versus vertebrogenic pain mechanisms. Methods We retrospectively analyzed pressure–volume–controlled lumbar discography from a single outpatient spine practice. Discs were injected in fixed volume increments with static plateau pressures recorded at each step under protocol caps (ΔP ≤ 50 psi above opening; volume ≤3.5 mL). For each disc, we identified either the onset event (first 0.5 mL step with definite concordant pain ≥4/10, sustained ≥30 s) or a final-negative (censored) event if no onset occurred under the caps (i.e., the disc “never declared”). Static ΔP at the event (ΔP_event) and cumulative mechanical work (W_event = Σ ΔP × ΔV) were calculated, and an energy-equivalent stiffness (K_eq = 2W/V²) was derived. We compared onset versus censored doses across MRI morphologies (normal, fissured, disrupted), within encounters containing both positive and negative discs, and across apparatus conditions, and examined the volume step at which onset occurred. Results Structurally abnormal discs that reproduced the presenting pain almost always did so at relatively low ΔP_event and W_event, yet with moderate-to-severe pain intensity at onset. Discs that never declared under the same protocol caps tolerated substantially higher ΔP_event and W_event, and morphologically normal discs clustered at the extreme of high-dose tolerance with rare positive responses. This separation between low-dose onset and high-dose tolerance persisted within fissured and disrupted strata, within encounters (positive vs negative discs in the same patient), and after stiffness normalization using K_eq, arguing against generalized “softness” as the sole explanation. In a subset with complete step-index data, most onset-positive discs declared by approximately 1.7 mL of injected volume and nearly all by 1.7–2.2 mL under slow, staged injection. Conclusion These findings support a reproducible low-dose, high-intensity concordant pain phenotype in structurally abnormal discs, most consistent with chemically and mechanically sensitized nociceptors in the annulus and at the annulus–endplate junction. Other discs—whether morphologically normal or with more prominent vertebrogenic features—remain load-tolerant under bounded pressurization, suggesting different dominant generators. In this framework, pressure–controlled discography functions less as a binary test and more as a quantitative phenotyping tool that uses combined pressure and work thresholds to distinguish annular-/junctional-dominant low-dose responses from higher-dose, load-tolerant patterns, and may help refine patient selection for disc-directed versus vertebrogenic-targeted interventions in future prospective studies.