Cannabis Use Does Not Affect Outcomes After Total Knee Arthroplasty.

Background: The self-reported use of cannabis has increased since its recent legalization in several states. The primary purpose of this study is to report total knee arthroplasty (TKA) outcomes in patients using cannabis.

Methods: Seventy-one patients who underwent a primary unilateral TKA with minimum 1-year follow-up, who self-reported cannabis use, were retrospectively reviewed. The study period was from January 2014 to February 2018 at a single institution. Patients with a history of opioid consumption, alcohol abuse, tobacco, or illicit drug use were excluded. A matched control was conducted based on age, body mass index, gender, smoking status, and insurance type (surrogate of socioeconomic status) in patients with a unilateral TKA who did not report cannabis use. Outcome measures included Knee Society Scores (KSS), range of motion, Veterans RAND-12 mental and physical component scores. No preoperative differences were noted with these measures. Postoperative complications were recorded and reported.

Results: No difference in length of stay was noted between the users (46.9 hours ± 15.7) and nonusers (49.3 hours ± 20.4) (P = .464). In-hospital total morphine equivalents did not differ between the 2 groups (user = 137 ± 104 mg, nonuser = 146 ± 117 mg, P = .634). Postoperative range of motion did not differ between users (128.4° ± 10.4°) and nonusers (126.9° ± 7.5°) (P = .346). No mean differences in follow-up KSS (user = 180.1 ± 24.9, nonuser = 172.0 ± 33.9, P = .106) or total change (user = 61.7 ± 32.8, nonuser = 62.7 ± 30.7, P = .852) in KSS were noted. Likewise, no significant mean differences in Veterans RAND-12 (mental component scores: user = 54.8 ± 9.3, nonuser = 55.9 ± 8.79, P = .472; physical component scores: user = 48.3 ± 9.9, nonuser = 45.8 ± 10.1, P = .145) scores were demonstrated. There were no differences in readmissions (user = 5, nonuser = 4, P = .730) or reoperations (user = 5, nonuser = 2, P = .238).

Conclusion: Cannabis use does not appear to influence (adverse or beneficial) short-term outcomes in patients undergoing a primary TKA. Further studies are warranted to determine the efficacy and safety of cannabis as a constituent of multimodal pain management following TKA before endorsements can be made by orthopedic surgeons.