Background: The transition to the new ICD-10 (International Classification of Diseases, Tenth Revision) coding system in the U.S. poses challenges to the ability to consistently and accurately measure trends in comorbidities and complications. We examined the prevalence of comorbidities and postoperative medical complications before and after the transition from ICD-9 to ICD-10 among patients who underwent primary total hip or knee arthroplasty (THA or TKA). We hypothesized that the transition to ICD-10 codes was associated with discontinuity and slope change in comorbidities and medical complications.

Methods: The Elixhauser comorbidities and medical complications were identified using the Premier Healthcare database from fiscal year (FY)2011 to FY2018. Using multivariable segmented regression models, we examined the changes in the levels and slopes after the transition from ICD-9 to ICD-10 coding. Odds ratios (ORs) of <1 and >1 indicate decreases and increases, respectively, in levels and slopes.

Results: Overall, 2,006,581 patients who underwent primary THA or TKA were identified. The mean age was 65.9 ± 10.5 years, and the median length of the hospital stay was 2 days (interquartile range [IQR], 2 to 3 days). Of the comorbidities studied, congestive heart failure, hypertension, and obesity had a statistically significant but clinically small discontinuity after the transition from ICD-9 to ICD-10 coding. Of the complications, pneumonia (OR = 0.66, 95% confidence interval [CI] = 0.48 to 0.90), acute respiratory failure (OR = 1.88, 95% CI = 1.52 to 2.33), sepsis (OR = 2.54, 95% CI = 1.45 to 4.44), and urinary tract infection (OR = 1.79, 95% CI = 1.32 to 2.42) demonstrated statistically significant discontinuity. Alcohol abuse and paralysis had an increasing prevalence before the ICD transition, followed by a decreasing prevalence after the transition. In contrast, metastatic cancer, weight loss, and acquired immunodeficiency syndrome (AIDS) showed a decreasing prevalence before the ICD transition followed by an increasing prevalence after the transition. Generally, complications showed a decreasing prevalence over time.

Conclusions: The discontinuities after the transition from ICD-9 to ICD-10 coding were relatively small for most comorbidities. Medical complications generally showed a decreasing trend over the quarters studied. These findings support caution when conducting joint replacement studies that rely on ICD coding and include the ICD coding transition period.