INTRODUCTION: This study describes prevalence and risk factors associated with an unusual pattern of disc degeneration of the lumbar spine which we term “skipped” level disc degeneration (SLDD), in which levels of degenerated discs have intervening non‐degenerated level(s).
METHODS: As part of a large population‐based genetic study in Southern Chinese (N=1,989), subjects had MRI assessments of the whole lumbar spine. Disc degeneration of more than two levels (n=838) were grouped into SLDD (n=174) and non‐SLDD (contiguous, multilevel; n=664). Additional radiographic abnormalities and subject demographics were also assessed.
RESULTS: SLDD was present in 8.7% of the population, and 20.8% of subjects with multilevel disc degeneration (n=838). SLDD was more prevalent in males (adjusted OR: 1.48; 95% CI: 1.04 to 2.10; p=0.028), and was significantly associated with the presence of Schmorl's nodes (adjusted OR: 2.72; 95% CI: 1.78 to 4.15; p<0.001). A number of patterns of “skipped” can be identified in which there could be more than one level of intervening non‐degenerated discs, or multiple levels of degeneration above and below the non‐degenerated level. Disc bulge/extrusion and back injury history were significantly associated with non‐SLDD (p<0.05), as was back pain. A greater degree of overall disc degeneration severity was associated with non‐SLDD. Other demographics and MRI findings did not significantly differ between groups (p>0.05).
CONCLUSIONS: To our knowledge, this is the first study to describe the prevalence and factors associated with SLDD. Our study challenges the “traditional” paradigm for the development of disc degeneration. Although age and biomechanical factors may play a role, the presence of skipped levels would suggest non‐mechanical factors or altered mechanics of the lumbar spine plays a role in the development of disc degeneration. Such factors warrant further investigation and may shed light into the cause and mechanism of disc degeneration.