Study design: A 5-year follow-up study of exposure of discordant monozygotic twin pairs with repeated interviews and spine imaging.
Objective: The primary goals were to record changes in the degenerative signs over a 5-year interval and to estimate the effects of familial influences and suspected environmental risk factors on the speed of lumbar degeneration.
Summary of background data: Traditionally, disc degeneration has been attributed to aging and environmental exposures; recently, a dominant effect of genetics has been revealed. Yet the etiopathogenesis of disc degeneration remains poorly understood and controversial despite being a primary target of diagnostic and therapeutic interventions.
Methods: Among 116 monozygotic twin pairs, which had been examined 5 years earlier, 75 pairs (150 men) were reexamined. They were imaged using the same MRI scanner and examination protocol as at baseline. The data were analyzed using statistical methods for longitudinal studies.
Results: Progression in disc height narrowing, disc bulging, osteophytosis, and fatty degeneration in the lumbar spine was seen in about 7% to 13% of the discs in 7% to 46% of subjects during 5-year follow-up. Few degenerative findings appear to reverse; few disc height measures increased, some anular tears were no longer visible, and bulging/herniation diminished. New anular tears (in axial view) were detected in 1.5%, disappeared in 2%, and were unchanged in 5.3% of discs; in the sagittal view, new high intensity zones findings were identified in 0.5%, were no longer apparent in 1.6%, and were unchanged in 7.1% of discs. There were no clear changes in upper endplates: in 2.1% of discs, the irregularity score increased and in 1.8% it decreased. Familial aggregation, reflecting genetic, and shared environmental influences, explained 47% to 66% of the variance in progression of degenerative signs on lumbar MRI, and resistance training and occupational physical loading together explained 2% to 10% of the progression in the degenerative signs in lumbar MRIs.
Conclusions: Progression of disc height narrowing, bulging, osteophytes, and fatty degeneration was detected in about 10% or less of the T12-S1 discs. Development and disappearance of anular lesions were rarer. No clear changes were seen in endplate irregularities. The results also confirm that hereditary effects have a dominant role in the progression of disc degeneration and suggest that occupational lifting and leisure time resistance training have modest additional effects.