Motion Characteristics of the Functional Spinal Unit During Lumbar Disc Injection (Discography) Including Comparison Between Normal and Degenerative Levels.

OBJECTIVE: While provocation lumbar discography has been used to identify discs responsible for low back pain, the biomechanical effects of disc injection have received little attention. The purpose of this study was to assess the motion of the functional spinal unit including the endplate and facet/pedicle region during disc injection including comparison between normal and degenerative discs.

SUBJECTS: Subjects represent 91 consecutive patients referred for discography with chronic low back pain.

METHODS: Lateral projection vertebral motion was retrospectively analyzed at 232 levels (normal: 76 [32.8%], degenerative: 156 [67.2%]). Pre- and postinjection fluoroscopic images were size scaled, and lower endplates were superimposed on separate PowerPoint images. Upper endplate and facet/pedicle motion was separately and independently analyzed on toggled PowerPoint images, subjectively graded as prominent, intermediate, questionable/uncertain, or no motion. Disc morphology was graded using the anteroposterior/lateral postinjection disc appearance (Adams criteria).

RESULTS: Prominent or intermediate endplate and facet/pedicle motion was identified at most lumbar levels with substantial overall agreement (degenerative: κ = 0.93, 95% confidence intervals [CI] = 0.87-1.00; normal: κ = 0.80, 95% CI = 0.61-1.00). Degenerative levels were strongly associated with a lower degree of endplate and facet/pedicle motion compared with normal: ("prominent" motion grade: endplate: 61% [95/156] vs 89% [68/76], P < 0.001; facet/pedicle: 60% [93/156] vs 88% [67/76], P < 0.001).

CONCLUSION: Disc injection expands the disc space inducing endplate motion, pedicle motion, and facet translation in almost all normal and most degenerate levels. Disc injection therefore biomechanically "provokes" the entire functional spinal unit. When provoked pain is encountered during lumbar discography, contribution from the associated facet joint and myotendinous insertions should be considered.