Incidence of cervical spine instabilities and “severe” cervical spine instabilities at >5-year follow-up in 228 patients without “severe” cervical spine instability at baseline.

Patients were grouped by pre-existing cervical spine involvement: no instability, “moderate” atlantoaxial subluxation (AAS) alone (shown as AAS+), “moderate” vertical subluxation (VS) without subaxial subluxation (SAS) but with or without AAS (shown as VS+), and “moderate” SAS with and/or without either AAS and/or VS (shown as SAS+).*Including patients fulfilling multiple criteria.†p††p2 test or Fisher exact test with the Bonferroni adjustment to the threshold for significance.