THE REPRODUCIBILITY OF ADAM’S GRADING SYSTEM FOR ASSESSING DISCOGRAM MORPHOLOGY

Abstract

Routine use of Computed Tomography (CT) to evaluate discogram morphology is time consuming, costly and incurs additional radiation hazards. In our spinal unit, discography is routinely performed without the aid of CT. Discogram morphology for different stages of disc degeneration is evaluated using the modified Adam’s grading system on images obtained on fluoroscopy. Our aims were to assess the validity of the modified Adam’s grading system of discogram morphology, by assessing its inter- and intra-observer agreement.

We reviewed the discographic images (133 intervertebral levels) of 71 patients with chronic low back pain undergoing discography as part of a preoperative assessment between 1995 and 1997. Using the modified Adam’s grading system, three independent surgeon observers of three levels of experience (Senior Fellow, Senior and Junior residents) retrospectively evaluated the morphological appearance of each disc level in a randomized and blinded manner. Each observer was supplied with descriptions and illustrations of the 5 grades1, and each level was classified accordingly. The exercise was repeated three weeks later. The respective inter- and intra-observer agreements were calculated using the kappa statistic (Fleiss 1971) and generalized kappa statistic (Landis and Koch 1977).

The inter-observer agreement was excellent (kappa = 0.77; standard error = 0.054). The intra-observer agreement for each of the three observers was also excellent (kappa = 0.8, 0.8, and 0.85 with respective standard errors = 0.046, 0.049 and 0.042).

Significance and conclusions: The inter- and intra-observer agreement and therefore the reliability of the modified Adam’s grading system is excellent. This classification is easy to apply and has a high degree of reproducibility amongst observers with different levels of spinal experience. In view of the high reproducibility, we recommend the Adam’s classification for the grading of discogram morphology. The routine use of computed tomography with the concomitant radiation exposure and additional cost would seem not to be justified.