Revision Risk After Primary Adult Spinal Deformity Surgery: A Nationwide Study With Two-Year Follow-up

Study Design Cohort study. Objectives To report the two-year revision risk following primary adult spinal deformity (ASD) surgery, describe reasons for revisions, and assess risk factors for revision surgery. Summary of Background Data Revision risk following primary ASD surgery has been reported to vary between 7% and 26%, but with loss to follow-up as a considerable challenge. Methods Patients ≥18 years of age undergoing primary instrumented surgery for ASD in Denmark during 2006–2014 were identified by procedure and diagnosis codes in the Danish National Patient Registry (DNPR). Complete two-year follow-up on revision surgery for each patient was achieved. Medical records were reviewed to determine reasons for revisions. Overall comorbidity was summarized using the Charlson Comorbidity Index (CCI) based on DNPR data; low comorbidity (CCI 0); medium comorbidity (CCI 1–2); and high comorbidity (CCI ≥3). Risk factors for revision were assessed in a Cox regression model. Results A total of 553 patients were identified. Of these, 19.9% were revised within the two-year follow-up and 7.2% of patients were revised more than once. Median time to revision was 308 days (interquartile range 105–508). The most common reason for revision was implant failure (38.2%) followed by infection (11.8%). Increased age (hazard ratio [HR] = 1.13, 95% confidence interval [CI] 1.01–1.26, per 10 years increment) and high comorbidity burden (HR = 2.10, 95% CI 1.16–3.79) were associated with increased revision risk. Risk of revision increased from 2006 to 2014; hence, year of primary surgery (with 2006 as reference) was associated with increased revision risk (HR = 1.09, 95% CI 1.01–1.18). Conclusions The revision risk within 2 years after primary ASD surgery was 19.9% nationwide in Denmark, and implant failure was the most common reason for revision. Increased comorbidity and age were separately associated with increased risk of revision. Level of Evidence Level II.