The Effects of Smoking on Extensor Mechanism Injury and Post Surgical Complications: A National Database Study
Authors: Yang Daniel , Curtis Kyle , Daniels Alan , Owens Brett , DeFroda Steven 
Published: July 2020

Objectives: The extensor mechanism of the knee is composed of the quadriceps tendon, the patellar tendon, and the patella. These injuries are associated with several comorbidities including diabetes mellitus, rheumatoid arthritis, gout, hyperparathyroidism, chronic renal failure and corticosteroid or anabolic steroid use. Cigarette smoking is also a known risk factor for extensor mechanism rupture, with increased number of pack years associated with decreased tendon thickness and increased incidence of rupture. Smoking has also been shown to have deleterious effects on tendon repair, with a higher frequency of post-surgical complications involving soft-tissue infection, failure of wound healing, and worse functional outcomes in smokers relative to non-smokers. Using a large national data set of extensor mechanism repair patients, risk factors for extensor tendon injury, and the effects of smoking on the risk of postoperative complication were analyzed. We hypothesized that patients who smoke would have higher rates of post-surgical complications relative to non-smokers. Methods: This retrospective study utilized the Humana insurance data set within the PearlDiver Patient Records Database (PearlDiver Inc, Fort Wayne, Indiana), a large private/commercial and Medicare medical record database. Patients who underwent extensor mechanism repair using Current Procedural Terminology (CPT) codes CPT-27380, CPT-27524, and CPT-27385 were identified. These patients were partitioned into two cohorts, one coding for tobacco use or nicotine dependence before their repair and another who did not. Gender, age, obesity, morbid obesity, diabetes, hypertension, chronic obstructive pulmonary disease (COPD), steroid use, renal dialysis, thyroid disease, end stage renal disease, hyperlipidemia, and systemic inflammation rates were assessed in each population. Postoperative complications, including 30-day readmission rate, 1-year revision rate (defined as a repeat procedure within 1 year post-index surgery), urinary tract infection (UTI), surgical site complication, deep vein thrombosis (DVT), sepsis, pneumonia, myocardial complications, respiratory complications, cardiac complications, cardiac arrest, coagulation, and death were investigated for the two groups. Multivariate logistic regression was used to calculate odds ratios, controlling for age, gender, race, Charlson Comorbidity Index (CCI), and all risk factors that were found to have significantly different risks between smoking and non-smoking patients. Statistical analysis was performed using the PearlDiver software, which runs R, Version 1.1.442. An α value of .05 was set as the level of significance. Results: Among extensor mechanism repair patients, 1559 (22.5%) smoking patients and 5376 (77.5%) non-smoking patients were included in the analysis. The age distribution of both cohorts of patients was similar, with most patients being between 65 and 74 years of age (Table 1). Pre-operative comorbidities associated with extensor mechanism injury were found to be significantly different between the smoking and non-smoking cohorts, specifically with regards to smokers 11.2% vs. 5.9% (p<0.0001) were obese, 51.4% vs. 37.1% had diabetes (p<0.0001), 82.5% vs. 34.1% were hypertensive (p<0.0001) and 10.3% vs. 1.9% had COPD (p<0.0001) at the time of initial injury. Smoking extensor mechanism repair patients had higher rates of 1-year revision, total 30-day complications, UTI, surgical site complications, sepsis, pneumonia, myocardial complications, and respiratory complications (Table 2). Conclusions: Patients who are smokers at the time of extensor mechanism injury are more likely to have a higher number of medical comorbidities including obesity, diabetes mellitus, hypertension, and COPD. Recognizing that smokers with extensor mechanism injuries have more medical comorbidities at baseline, placing them at higher risk for anesthesia, should influence the surgeons’ decision making with regards to location of the surgery (hospital versus ambulatory surgery center), as well as the possible need for post operative admission Additionally smoking portends a much higher complication rate following extensor mechanism repair, most notably in our study, a 65.7% incidence of need for 1-year revision, and a 21.4% incidence of a 30-day complication. It is important for surgeons to recognize the increased risk of complications in these patients and counsel them regarding these risks and encourage smoking cessation. [Table: see text][Table: see text]