Background/Purpose: Spine osteoarthritis (SOA) has been defined by the presence of: 1) disc space narrowing (DSN) and vertebral osteophytes (OST), or 2) facet joint OA (FOA). Anatomical differences between these structures suggest they may have different etiologies. Furthermore, a current clinical paradigm is that SOA leads to lumbar spine instability and subsequent FOA, suggesting a transition pathway. The purpose of this study was to 1) describe the participants with SOA and FOA over time 2) describe the proportion that transitioned from neither SOA nor FOA at baseline to either FOA only or SOA only at follow-up and 3) describe the proportion that transitioned from FOA only or SOA only at baseline to both SOA and FOA at follow-up. Elucidating these transitions would improve our understanding of the underlying pathophysiological processes and may indicate the potential for separate clinical phenotypes.

Methods: These analyses used baseline (2006-2010) and follow-up (2013-2015) data from the Johnston County Osteoarthritis Project. Paired (baseline and follow-up) lumbar spine radiographs were graded using the Burnett Atlas for OST (0-3), DSN (grade 0-3), and FOA (present or absent). SOA was defined as the presence of at least ≥ 1 DSN and the presence of at least a ≥1 OST at the same lumbar level. Participants were categorized into those with 1) FOA only 2) SOA only 3) neither FOA nor SOA and 4) both FOA and SOA (excluded at baseline). Starting with neither FOA nor SOA at baseline, we describe the transition to SOA only and to FOA only at follow-up. Starting with prevalent FOA only or SOA only at baseline, we describe the transition to both SOA and FOA. Counts and percentages with 95% confidence intervals (CI) were used to describe the prevalence at baseline and incidence of transitions occurring at follow-up. The mean follow-up time was 5.5 years.

Results: A total of n=762 participants had complete data for these analyses. The mean age and body mass index (BMI) were 66.2 (SD 10.2) years and 30.9 (SD 6.5) kg/m2, respectively; 65.7% were women, and 32.6% were African American (AA).

The figure illustrates the counts and proportions of those with prevalent SOA only or FOA only at baseline and those that transition from either SOA (blue) or FOA (green) to both SOA and FOA (orange) at follow-up. At baseline, 13% of participants had neither SOA nor FOA, 32.3% had FOA only, 8% had SOA only, and 47% had both. At follow-up, a large proportion of participants remained within the same subgroup as baseline and did not transition: 69.1% neither SOA nor FOA (N1), 64% of those with FOA only (N2) and 87% of those with SOA only (N3). Among those with neither SOA nor FOA at baseline, 7% (95% CI 3% to 16%) transitioned to FOA only (A) and 24% (95% CI 16% to 36%) transitioned to SOA only (B). Among those with baseline SOA or FOA only, 36% (95% CI 30% to 42%) transitioned from FOA only to both (D) compared to 13% (95% CI 5% to 21%) that transitioned from SOA to both (E).

Conclusion: Participants in this study tended to remain within these subgroups over time. The most common transitions were from neither SOA nor FOA to SOA only and prevalent FOA only to both SOA and FOA. These findings suggest a different etiological process may exist between SOA and FOA and supports the potential for separate clinical phenotypes.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/transitions-in-lumbar-spine-osteoarthritis-the-johnston-county-osteoarthritis-project/