Aims. Although there is increasing legalization of the use of cannabis in the USA, few well-powered studies have evaluated the association between cannabis use disorder and outcomes following primary total hip arthroplasty (THA). Thus, the aim of this study was to determine whether patients who use cannabis and undergo primary THA have higher rates of in-hospital length of stay (LOS), medical complications, implant-related complications, and costs. Methods. Using an administrative database, patients with cannabis use disorder undergoing primary THA were matched to a control group in a 1:5 ratio by age, sex, and various medical comorbidities. This yielded 23,030 patients (3,842 in the study group matched with 19,188 in the control group). The variables which were studied included LOS, 90-day medical complications, two-year implant-related complications, and 90-day costs of care. Mann-Whitney U tests were used to compare LOS and costs. Multivariate logistic regression analyses were used to calculate the odds ratios (ORs) of developing complications. Results. We found that patients in the study group had a significantly longer mean LOS compared with the controls (four days vs three days; p < 0.0001).The study group also had a significantly higher incidence and odds of developing medical (23.0 vs 9.8%, OR 1.6; p < 0.0001) and implant-related complications (16 vs 7.4%, OR 1.6; p < 0.0001) and incurred significantly higher mean 90-day costs ($16,938.00 vs $16,023.00; p < 0.0001). Conclusion. With the increasing rates of cannabis use, these findings allow orthopaedic surgeons and other healthcare professionals to counsel patients with cannabis use disorder about the possible outcomes following their THA, with increased hospital stays, complications, and costs. Cite this article: Bone Joint J 2021;103-B(7 Supple B):111–115

Introduction. With the widespread legalization of cannabis across the United States, well-powered studies evaluating the impact of cannabis use disorder on outcomes following primary total hip arthroplasty are warranted. Therefore, the aim of this study was to determine whether cannabis use disorder has an effect on patients who undergo primary hip arthroplasty in terms of: 1) hospital lengths of stay (LOS); 2) medical complications; 3) implant-related complications; and 4) costs of care. Methods. Using an administrative database, patients who underwent primary total hip arthroplasty and had cannabis use disorder were matched to a cohort who did not in a 1:5 ratio by age, sex, and various medical comorbidities. This yielded 44,154 patients; 7,361 who had cannabis use disorder and 36,793 who did not. Variables for analysis included postoperative LOS, 90-day medical complications, 2-year implant-related complications, and 90-day costs of care. Mann-Whitney-U tests were used to compare LOS and costs. Multivariate logistic regression analyses were used to calculate the odds ratios (ORs) of developing complications. A p-value less than 0.005 was considered statistically significant. Results. The study found that patients who had cannabis use disorder had significantly longer in-hospital LOS (4 vs. 3 days, p<0.0001) compared to the matched cohort. Additionally, study patients were found to have significantly higher incidences and odds of developing medical (11.23 vs. 4.82%; OR: 1.47, p<0.0001) and implant-related complications (18.14 vs. 8.60%; OR: 1.50, p<0.0001). Moreover, patients who had cannabis use disorder incurred significantly higher 90-day episode of care costs ($24,585.96 vs. $23,725.93, p<0.0001). Conclusions. With the growing rates of cannabis use, this study can allow orthopaedists and other healthcare professionals to educate cannabis use disorder on the possible outcomes following their total hip arthroplasty. It should be appreciated that cannabis use disorder is associated with longer hospital stays, increased complication rates, and higher costs following primary THA