The Relationship Between Age and 30-day Outcomes Following Unicompartmental versus Total Knee Arthroplasty.

Background: An enhanced understanding of the short-term complication profile following unicompartmental knee arthroplasty (UKA) versus total knee arthroplasty (TKA) can improve surgical decision-making and subsequent patient outcomes. This study aimed to determine if the difference in risk of 30-day morbidity and mortality between UKA and TKA varied as a function of patient age.

Methods: This retrospective study of a national quality improvement database using data from 2014 to 2020 included 403,342 patients undergoing UKA (n = 12,324) or TKA (n = 391,018). A generalized additive model (GAM) evaluated non-linear relationships between primary outcome and predictors (age, procedure type, and procedure type x age interaction) using a 1:5 UKA to TKA matched sample. Probabilities and odds ratios (95% CI [confidence interval]) estimated the relative risk of complications across the age spectrum.

Results: In the GAM, TKA patients relative to UKA had 1.30 higher odds (95% CI 1.19 to 1.43, P < 0.001) of 30-day morbidity and mortality. There was a significant, non-linear relationship between age and the primary outcome (P = 0.02), such that the odds were lowest at younger ages. They increased slowly until about age 65 years, at which point the slope became steeper. The interaction terms for age and procedure type were not significant (P = 0.30). The 30-day probability for short-term complications of a 65-, 75-, and 85-year-old undergoing UKA was 2.1% (95% CI, 1.8 to 2.3), 2.4% (95% CI, 2.0 to 2.8), and 3.2% (95% CI, 2.3 to 4.1), respectively. Conversely, the probability of a 65-, 75-, and 85-year-old undergoing TKA was 2.9% (95% CI, 2.7 to 3.0), 3.6% (95% CI, 3.3 to 3.8), and 5.5% (95% CI, 4.7 to 6.3).

Conclusions: Patients undergoing UKA had a quantifiable lower likelihood of morbidity or mortality than TKA at all ages. These data can provide individualized risk for UKA and TKA across the age spectrum and could be helpful in counseling patients regarding their risk for perioperative complications.