Prospective match cohort study of disc degeneration progression over ten years with and without baseline discography

To compare progression of common degenerative findings between lumbar discs injected ten years earlier with those same disc levels in matched subjects not exposed to discography

Seventy-five subjects without serious low back pain illness underwent a protocol MRI and a L3/4, L4/5 and L5 S1 discography in 1997. A match group was enrolled at the same time and underwent the same protocol MRI examination. Subjects were followed for ten years. At 7 to 10 years after baseline assessment, eligible discography in controlled subjects underwent another protocol MRI. MRI graders, blind to group designation, scored both groups for qualitative findings.

Well matched cohorts, including 50 discography subjects and 52 control subjects met eligibility criteria for follow up evaluation. In all graded or measured parameters, discs that had been exposed to puncture and injection had greater progression of degenerative findings compared to control (non-injected) discs: progression of disc degeneration, 54 discs (35%) in the discography group compared to 21 (14%) in the control group (p=0.03); 55 new disc herniations in the discography group compared to 22 in the control group (p=0.0003). New disc herniations were disproportionately found on the side of the annular puncture (p=0.0006). The quantitative measures of disc height and disc signal also showed significantly greater loss of disc height (p=0.05) and signal intensity (p=0.001) in the discography disc compared to the control disc.

This study demonstrates that the dimensions of the LSP change with age. Increases in LSP height occur with age. More impressive increases in LSP width occur with advancing age. This study suggests that loss of lumbar lordosis is correlated with changing LSP morphology. The increased width of the LSP with age influences access to the spinal canal, particularly if midline-preserving approaches are attempted in the ageing population. There is increased bone volume for bone grafting procedures with increasing age. The reduced distance between LSPs with age may influence design of implants that stabilize this region of the spine, and occur not only as a result of disk space narrowing, but also as a consequence of increased LSP dimensions.

Introduction Spondylolysis and isthmic spondylolisthesis (IS) have both a familial and mechanical aetiology, yet the phenotypic expression of the familial aetiology is unknown except for the observation of spinal bifida occulta. Other posterior element abnormalities are unrecognised, and any facet joint orientation (FJO) abnormality at the effected level has been ignored because of presumed previous mechanical defunctioning by the pars defect. The recognition of multilevel sagittal FJO in L4/5 degenerative spondylolisthesis (DS), begs the question whether more proximal segment examination may reveal FJ variations in IS.

Methods MRI scans were used to measure orientation of the FJ at L3/4, L4/5, and L5/S1 in 30 individuals with normal scans, and 30 patients with IS. The angular measurement recorded is in relation to the coronal plane. Repeated measures assessment confirmed method validity.

Results Mean measurement of axial FJO at L3/4 and L4/5 was 51.1 and 42.5deg in normal subjects, and 45.2 and 35.0deg in IS. The more coronal angulation at the levels above a pars defect in IS was highly statistically significant (p=0.0006 & p=0.00002). At L5/S1 orientations were the same (39deg).

Discussion Relative coronal FJO in the lumbar spine may be the phenotypic expression of the congenital aetiology of IS. The mechanism of effect may be increased stress concentration at the pars between or below coronally oriented FJs. These more coronal FJOs in IS also explain:- the common observation of retrolisthesis at L4/5 above IS when the L4/5 disc degenerates, lateral overhang of the L4/5 FJ to the L5 pedicle entry-point above an IS, and the exceptionally uncommon combination of DS at L4/5 and IS at L5/S1 when both disorders are independently common. This latter observation can be further explained by the generalization that DS occurs in those individual with sagittal lumbar facets, and that IS occurs in those with more coronal FJs.