There is a wealth of information available on smoking, drinking, and other substances, but not on marijuana use. Despite marijuana’s rising popularity, a recent study claims that it poses risks that we are not currently aware of.

According to a paper presented at the Scientific Forum of the American College of Surgeons (ACS) Clinical Congress 2022, patients who are marijuana dependent may have higher infection rates after knee and shoulder arthroscopy—a minimally invasive surgical procedure in which a small camera is inserted to diagnose and sometimes treat injury.

Researchers from the University of Chicago used PearlDiver, a national insurance claims database, to do a retrospective study of people who were dependent on marijuana and had knee or shoulder arthroscopy for complications like deep vein thrombosis (DVT), pulmonary embolism (PE), and infection after surgery.

Even though the effects of marijuana use on pain management and heart health have been studied, not many studies have looked at the effects of marijuana use by surgery patients.

Marijuana is becoming legal in more states, and by 2028, it’s expected that the cannabis business will be worth $91.5 billion.

Given this trend, a group of researchers from the University of Chicago set out to find out if people who are dependent on marijuana have a higher risk of complications after knee or shoulder arthroscopy.

“There’s so much information out there on smoking, alcohol, and other substances, but not on marijuana use,” adds study coauthor Jason Strelzow. “As providers and surgeons, we should be discussing marijuana use with our patients, something that we have traditionally shied away from.” 

Research

PearlDiver was used to retrospectively identify all patients undergoing knee or shoulder arthroscopy. Next, patients with a diagnostic code for marijuana dependence were identified within each surgery category; this is a strict definition requiring patients to meet three or more criteria, such as using marijuana longer than intended, difficulty quitting use, spending a great deal of time obtaining or recovering from marijuana, and high tolerance.

All of the patients were checked to see how often they got DVT, PE, and infections in the next 90 days. In order to compensate for known patient comorbidities, a multivariate logistic regression analysis was conducted after univariate studies of marijuana dependency on all outcomes (other medical conditions).

The Results

The researchers counted 747,938 shoulder and 1,113,944 knee arthroscopy patients. 21,823 of the 1,861,892 patients had a diagnosis of marijuana dependency.

The marijuana dependence cohort had higher rates of infection and DVT within both subgroups, although the PE rate remained constant. Infection rates rose from 0.7% to 1.7%, DVT rates from 0.2% to 0.4%, while PE rates remained at 0.2% for the shoulder arthroscopy group. The rates of infection increased from 1.1% to 2.6%, the rates of DVT increased from 0.2 to 0.3%, and the rates of PE remained at 0.3% in the group receiving knee arthroscopy.

Marijuana dependency was found to be an independent risk factor for infection in both cohorts in the multivariate analyses controlling for a number of patient risk variables, such as tobacco use or a history of diabetes. In this study, a statistical measure called a p-value (where p stands for probability) was used to figure out if the found relationship was just a coincidence (p-values of 0.001 or below) or if it really did exist (p-values above 0.001). The p-value for the knee group was 1.85, and the p-value for the shoulder group was 1.65.

Despite the fact that the study focused on minimally invasive surgery, Dr. Strelzow stated, “we would expect similar or larger effects with more open or invasive procedures”

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