Spine. Volume 34(23), 1 November 2009, pp 2545-2550

Dynamic Bulging of Intervertebral Discs in the Degenerative Lumbar Spine

Zou, Jun MD, MS*; Yang, Huilin MD, PhD*; Miyazaki, Masashi MD, PhD†; Morishita, Yuichiro MD, PhD†; Wei, Feng MD, PhD†; McGovern, Scott MD†; Wang, Jeffrey C. MD†. From the *Department of Orthopaedic Surgery, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China; and †Department of Orthopaedic Surgery, University of California at Los Angeles, Los Angeles, CA. © 2009 Lippincott Williams & Wilkins, Inc.

Study Design. The effect of postural change on degenerative lumbar discs was quantified using novel kinematic magnetic resonance imaging (kMRI).

Objective. The purpose is to describe the bulging of degenerative intervertebral lumbar discs in vivo subjected to different postural loads using a novel kMRI.

Summary of Background Data. Symptomatic lumbar disc degeneration is a leading cause of pain and disability throughout the world. Over 70% of US citizens will experience a debilitating episode of low back pain. Earlier reports of degenerative disc changes are cadaver studies or are performed with recumbent MRI that eliminates the functional effects of gravity and muscle power. Little data are available on the behavior of degenerative intervertebral discs in vivo under physiologic loads.

Methods. A total of 513 patients obtained kMRI. Disc bulging beyond the intervertebral space was quantified during upright neutral, flexion, and extension imaging. The degree of intervertebral disc degeneration was correlated using the Pfirrmann Classification.

Results. Moderately degenerated intervertebral discs (grade III and IV) demonstrated greater bulging than mildly degenerated discs (grade II). Severely degenerated discs (grade V) also showed a trend toward greater bulging, but this was not significant. Grade I discs at all levels moved posteriorly in flexion and anteriorly in extension when compared to neutral posture. However, mild to severe (grade II–V) degenerative discs behaved differently in response to postural loads. Extension resulted in significant posterior bulging, while flexion did not demonstrate obvious anterior derangement.

Conclusion. Disc bulging increases with the severity of disc degeneration. Grade I discs demonstrate the expected sagittal migration in response to postural load. However, more degenerative discs behave less predictably, and spine extension may result in significant posterior disc bulging. Degenerative changes in the intervertebral disc significantly affect the kinematic patterns under postural load in vivo. kMRI is a useful tool to quantify the kinematic behavior of degenerative intervertertebral discs.

kMRI, disc degeneration, disc bulging, load-bearing, lumbar