Cigarette Smoking Was Not Associated With Lower Odds of Radiographic Fusion After Combined TLIF and Posterolateral Lumbar (270°) Arthrodesis: A CT-based Retrospective Cohort Evaluation.

backgroundSmoking is widely regarded as a risk factor for impaired spinal fusion, particularly in posterolateral fusion, and prior studies have generally relied on plain radiographs for assessment. However, data evaluating the association of smoking on transforaminal lumbar interbody fusion (TLIF) with adjunctive posterolateral arthrodesis using modern CT-based evaluation remain limited. QUESTIONS/PURPOSES: (1) Is cigarette smoking associated with a reduced likelihood of achieving radiographic spinal fusion, as assessed by thin-slice CT, after TLIF with adjunctive posterolateral arthrodesis? (2) Does the quality of TLIF (interbody) and posterolateral (intertransverse) fusion differ between patients who smoked and those who did not? (3) Does smoking intensity, measured in pack-years, correlate with reduced fusion quality or increased odds of cage subsidence? (4) Are patient-related factors such as gender, age, and BMI associated with differences in fusion quality or cage subsidence?

methodsBetween 2013 and 2017, one surgeon at a single private hospital performed 360 TLIF procedures with adjunctive posterolateral fusion for degenerative lumbar disease. During this period, surgery was offered to patients who smoked after individual assessment of overall surgical risk, including medical stability and ability to adhere to follow-up recommendations. Of these 360 patients, 18% (63) smoked cigarettes and 82% (297) did not. Smoking exposure was summarized in pack-years and was analyzed both categorically, using a threshold of 25 pack-years, and as a continuous variable in the adjusted models. Among patients who smoked cigarettes, 65% (41 of 63) had thin-slice CT scans obtained at least 6 months after surgery (which is sufficient for assessing early fusion maturation); among patients who did not smoke, 95% (281 of 297) met the imaging requirement, resulting in a final cohort of 322 patients. Patients who smoked cigarettes and those who did not did not differ in age, BMI, and diagnosis, and these variables were included in the adjusted analysis. Fusion was assessed on thin-slice CT and evaluated separately for the TLIF and posterolateral beds. We compared fusion percentages and grades between patients who smoked cigarettes and those who did not, assessed the association of smoking intensity with fusion measures, and examined associations with age, gender, and BMI. To address our first question, we compared the likelihood of achieving fusion between patients who smoked cigarettes and those who did not using thin-slice CT as the reference standard and applying a strict definition of fusion for both the TLIF and intertransverse beds. To address our second question, we compared the distribution of TLIF and intertransverse fusion grades between patients who smoked and those who did not, treating the grading scales as ordinal outcomes. For our third question, smoking exposure was quantified in pack-years. For our fourth question, we examined whether age, gender, and BMI were associated with fusion grades or cage subsidence, and we included these variables in the adjusted models to evaluate their independent associations. The available sample included 63 patients who smoked cigarettes and 259 who did not. With alpha set at 0.05 and beta at 0.20, this sample provided 80% power to detect an absolute difference of approximately 17 percentage points in the likelihood of achieving fusion; smaller differences may not have been detected.

resultsCigarette smoking was not associated with a lower likelihood of achieving CT-defined fusion after TLIF with posterolateral arthrodesis (patients who smoked cigarettes 65% [41 of 63] versus those who did not 66% [170 of 259], OR 0.98 [95% confidence interval 0.55 to 1.74]; p = 0.52). TLIF (interbody) and posterolateral (intertransverse) fusion grade distributions did not differ between patients who smoked cigarettes and those who did not. Smoking exposure measured by pack-years was not associated with fusion quality (TLIF or intertransverse) or with cage subsidence. Women were more likely to achieve TLIF Grade 3 fusion (87% [132 of 151] versus 64% [110 of 171]; p < 0.001) and more frequent intertransverse Grade 3 fusion (69% [104 of 151] versus 44% [75 of 171]; p < 0.001) and had a higher proportion of Grade 1 subsidence (83% [125 of 151] versus 70% [120 of 171]; observed p = 0.08; model p = 0.03). Age and BMI showed no associations with fusion or subsidence.

conclusionWe found that cigarette smoking was not associated with impaired radiographic fusion after TLIF with adjunctive posterolateral arthrodesis performed using a standardized technique. Under these conditions, factors such as biologic healing capacity, bone quality, and construct-related variables may be more influential determinants of CT-defined fusion. These findings address radiographic outcomes only and do not speak to perioperative complications; generalizability may be limited in settings that mandate preoperative cessation or use different perioperative protocols. Within the limits of a retrospective study, these findings suggest that if TLIF with adjunctive posterolateral fusion is otherwise indicated, ongoing smoking alone should not require delaying or denying surgery, when other perioperative risks are acceptable. Smoking cessation counseling remains important for general health and for reducing nonfusion-related complications, but concerns about impaired fusion alone should not be the primary reason to withhold this procedure. LEVEL OF EVIDENCE: Level III, therapeutic study.