This main finding of this study was that there were no significant differences in outcomes between cannabis users and nonuser controls. Combined cannabis and tobacco use was found to be associated with worse outcomes compared with tobacco alone. Specifically, combined use was associated with higher rates of ED visits within 90 days, and nonunion within 2 years of the index procedure compared with tobacco use alone. These findings suggest that although cannabis use alone does not significantly affect postoperative outcomes following ankle and hindfoot arthrodesis, the combined use of cannabis and tobacco is associated with a greater risk of complications. Based on the observed associations, surgeons should be mindful of the associated risks of combined cannabis and tobacco use when evaluating patient risk factors and developing postoperative care plans.

Previous studies investigating the effect of cannabis use on orthopaedic procedures have yielded mixed results. For instance, in patients undergoing total shoulder arthroplasty, cannabis use alone was not associated with adverse postoperative outcomes. ⁶ However, contrasting findings were observed in studies examining total knee arthroplasty, where cannabis use was associated with increased rates of infection, venous thromboembolism, and revision surgery.^17,31,32,36 Additionally, in patients undergoing spinal fusion, cannabis was associated with higher rates of nonunion compared with controls. ² These disparate results highlight the complexity and variability in how cannabis use may affect different types of orthopaedic procedures. For foot and ankle procedures, cannabis-only users undergoing open reduction and internal fixation for ankle fractures had no significant differences in outcomes compared with nonuser controls, but combined cannabis and tobacco users had worse outcomes. ⁹ We found similar results in patients undergoing ankle and hindfoot arthrodesis. These findings, combined with prior literature on foot and ankle procedures, suggest that tobacco is associated with worse outcomes whereas cannabis use does not appear to be associated with increased complication rates.

Cannabis use has previously been suggested to affect surgical outcomes through several mechanisms. For example, cannabis use has been shown to negatively affect bone healing, increasing bone turnover and reducing bone mineral density. ¹⁹ When broken down, metabolites of cannabis bind to cannabinoid receptors that are also present in the skeletal system and may regulate osteoblast and osteoclast activity.^22,28 Additionally, cannabis use has been associated with immunosuppressive properties, potentially increasing the risk of postoperative infection.^8,25 Our findings suggest that cannabis use alone does not appear to be associated with adverse postoperative outcomes following ankle and hindfoot arthrodesis, although further research is needed to clarify these results in the context of previous literature. The reason for this is ultimately unclear but may be due to several factors. First, much of the literature regarding the effects of cannabis use is limited to animal studies. It is possible the dosage and frequency of cannabis use among humans is insufficient to exert a measurable impact on surgical outcomes. Second, the duration and timing of cannabis use relative to the surgery were unable to be accounted for and may affect complication rates. Chronic, long-term use may have different effects compared with occasional or short-term use. Prior literature has found that tobacco cessation in the weeks leading up to surgery significantly reduces the overall complication rate. ²⁹ Although our study lacks data on the timing of cannabis use relative to surgery, it is worth considering that the cessation of cannabis use in the days or weeks prior to surgery could have potentially influenced outcomes. Future studies are warranted to determine how the dosage, frequency, and timing of cannabis use in relation to surgery affect outcomes.

Tobacco use, on the other hand, is a well-documented modifiable risk factor for adverse outcomes after a variety of orthopaedic procedures, including ankle and hindfoot arthrodesis.^4,7,26,37 Tobacco use has been shown to have immunosuppressive effects, impair wound and bone healing, and increase inflammation throughout the body, increasing the risk for adverse outcomes.^1,14,16,27 The results in the present study support this, in that tobacco use was associated with increased risk of all 2-year surgery-specific complications including nonunion, hardware removal, infection, and wound dehiscence. Interestingly, this effect was increased among combined tobacco and cannabis users, as combined use was associated with an increased risk of nonunion compared with tobacco alone. This may be due to an enhanced negative effect on bone healing. It is also possible that people who use both tobacco and cannabis tend to consume higher quantities of tobacco or cannabis, as they may have different substance use behaviors. This increased consumption could further exacerbate the negative effects on postoperative outcomes. Further research is needed to better understand the interplay between these substances and their impact on surgical outcomes.