Purpose: To examine associations between lumbar intervertebral disc degeneration (LDD) and type II Modic changes (MC) when retaining information at each interspace ('interspace-level analysis'), as compared to aggregating information across interspaces as is typically done in spine research ('person-level analysis') . The study compared results from (1) interspace-level analyses assuming a common relationship across interspaces (the 'interspace-level, common-relationship' approach), (2) interspace-level analyses allowing for interspace-specific associations (an 'interspace-level, interspace-specific' approach), and (3) a conventional person-level analytic approach. Methods: Adults in primary care (n=147) received lumbar spine magnetic resonance imaging (MRI) and neuroradiologist-evaluated assessments of prevalent disc height narrowing (DHN), type II MC, and other LDD parameters. Analyses examined associations between DHN and type II MC in interspace-level, common-relationship analyses, interspace-level, interspace-specific analyses, and conventional person-level analyses. Results: Cross-sectional, interspace-level, common-relationship analyses found large-magnitude DHN-type II MC associations (adjusted OR [aOR]=6.5, 95% confidence intervals (CIs) 3.3-13; p<0.001). The magnitude of this association was larger and more precise than that yielded by person-level analyses (aOR=2.9 [95% CI 1.2-7]), and substantially more precise than interspace-level, interspace-specific analyses which allowed the association between DHN and type II MC to vary across levels. Across exploratory analyses of disc signal intensity and other MC types, interspace-level, common-relationship analyses produced larger-magnitude and more precise associations than person-level analyses in most situations, and were more precise than interspace-level, interspace-specific analyses. Conclusions: Interspace-level analytic approaches offer some advantages to person-level analyses that may be useful in understanding relationships between spinal degeneration findings.

The authors have declared no competing interest.

https://osf.io/5arpy/.

This work was supported by the University of Washington (UW) Clinical Learning, Evidence and Research (CLEAR) Center Administrative, Methodologic, and Resource Cores and NIAMS/NIH grant P30AR072572. Drs. Suri, Jarvik, Rundell, and Heagerty have leadership roles at the CLEAR Center. Drs. Suri is employed by the VA Puget Sound Health Care System. The contents of this work do not represent the views of the US Department of Veterans Affairs, the National Institutes of Health, or the US Government. Ms. Elgaeva was supported by the Russian Science Foundation (grant #22-15-20037) and Government of the Novosibirsk region. Dr. Tsepilov was supported by the budget project of the Institute of Cytology and Genetics № FWNR-2022-0020.

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