Determination of Risk Factors for Pseudoarthrosis in Minimally Invasive Spine Surgery in Transforaminal Lumbar Interbody Fusion Procedure

Introduction: We aim to identify and combine risk factors for development of pseudoarthrosis in MIS TLIF procedures into a risk index.

Methods: Operative patients undergoing minimally invasive surgery with 2 year data were isolated. Patients were stratified as undergoing TLIF (T) or not (NT). Descriptive analyses and means comparison tests identified differences in baseline parameters, surgical characteristics, radiographic and deformity measurements, rates of complications, and patient-reported outcome measures. Multivariate logistic regression analyses determined significant predictors for development of pseudoarthrosis. Backstep logistic regression helped derive predictors of development of pseudoarthrosis. Risk score was then validated via Receiver Operating Characteristic curve method analysis. Categories via conditional inference tree (CIT) analysis-derived thresholds were tested for thresholds correlating to high risk.

Results: 465 spine patients included (59.9±14.7yrs, 27.3±5.3kg/m2, CCI: 1.63±1.6, FI: 3.12±1.65), with 34.4% (n=160) underwent TLIF. Cohort mean baseline SVA was 15.45±34.40mm, PI-LL 1.41±12.17°, and PT 16.24±8.80°. There were no differences in baseline age, gender, BMI, or baseline deformity between groups. A predictive risk score for pseudoarthrosis was developed with the following preoperative variables: age, frailty, history of diabetes, osteoporosis, depression, ASA grade, baseline L4-S1, and baseline T1PA. This predictive risk score generated an AUC of 0.87. Following CIT machine learning, thresholds for the Risk Score were derived: >5 No Risk (NoR), 3-5 Low Risk (LowR), 2-3 Moderate Risk (ModR), and < 2 High Risk (HighR). The rates of pseudoarthrosis for each category were: NoR – 0%; LowR - 1.6%; ModR – 9.3%; HighR – 24.3%. TLIF patients had overall the following pseudoarthrosis rates according to Risk Score: 5.9% NoR, 9% LowR, 2.7% ModR, 1.9% HighR. TLIF patients in HighR had 2.3 times lower risk with surgical prophylaxis (OR: -2.27 [1.79, 2.31] p=.004). Additionally, the use of BMP-2 lowered the risk significantly in those in HighR (p=.032).

Conclusion : Our study developed a risk score for those undergoing TLIF procedure for development of pseudoarthrosis. In those with high risk, surgical prophylaxis and BMP-2 demonstrated positive effects on patient outcomes.