Plenty of studies had investigated risk factors of SSI after spinal surgery.[2, 5, 6] However, when a patient with several factors needs spine surgery, the exact SSI incidence possibility is ambiguous and the treatment decision still depended on clinicians’ experience. While intelligent algorithms based on previous complicated patient data will provided a wealth of information. A paper had applied a Deep Neural Network model using 35 unique variables to predict SSIs after posterior spinal fusions.[12] They mainly pay attention on demographics, combined disease and operation type.[12] We hold that more specific variables are necessary to improve ML predictive models. To our best knowledge, no study had yet explored ML models to predict SSI after posterior cervical surgery.
Our models shown reliably predive performance based on patient data from this institution. Xgboost, random forest, ANN and decision tree got predictive accuracy more than 90% in test set. The ability to predict SSI may assist surgeons in identifying potential risk patients, better selecting candidates for posterior cervical surgery, managing patient expectations and timely intervene to improve outcomes. These lends to precision-based spine care and more bespoke management to optimize patient outcomes and improve daily function, with decreasing healthcare-related costs.[11]
We established sex different models to find the most robust one, which contain one deep learning and two model ensembles. Deep learning has superior fitting ability than traditional models, suitable to big data. Model ensembles, like xgboost and random forest, combines plenty weak classifiers to increase accuracy on ML tasks. However, in this study xgboost and random forest got slightly better predictive ability than ANN, the deep learning algorithm, which may explain by the low order of magnitude data. Interestingly, the decision tree also achieved satisfactory result after grid searching for best parameters. This may due to our fine-tuning work and well feature selection.
We input more individual features like, nutritional status and operation data, differing from national level database taking into account plenty demographic and general management variables. We thought these may better providing personalized preoperative status and provide more individual information. However, these variables were all manual inputted and laborious.
A main challenge of ML needed to overcome is Black box, that limits application of ML in medicine. It is that most AI technologies operate based on opaque logic and hardly understandable to users. Interpretation of xgboost based on SHAP is a solution of Black box. Beyond get an unexplainable prediction, we could examine contribution of each valuable on the individual prediction. Two examples are shown in Fig 3 and Fig 4.
Drainage volume and drainage duration were identified as predictors in the present study. Prolonged drainage duration has frequently been cited as independent risk factors for SSI.[4, 13, 14] Liu et al used multivariable analysis to confirm that prolonged drainage duration was a risk factor for SSI after lumbar spinal surgery.4 Moreover, Rao et al suggested to remove the drain as early as possible for reducing infection rate following spinal fusion.17 Drains may induce local tissue inflammation and become direct access for bacteria by ascending the drain tube, thus increasing the risk of infection.18 Also, a study demonstrated two-fold reduction of SSI with implementation of prolonged prophylactic systemic antibiotics regimen for the duration of drain.[15]
Previous researches had suggested a positive relationship between BMI and SSI. Pesenti et al confirmed that obesity is a significant risk factor for SSI after spinal arthrodesis and BMI > 30 kg m−2 as a significant risk factor in most of studies.[6] Another meta-analysis found 21 % increase in risk of spinal SSI for every 5-unit increase in BMI, after adjusting for diabetes and other confounders.[16] It has been reported that increasing subcutaneous adipose tissue raises the likelihood of fat necrosis and thus increases infection risk.[17]
A multivariate analysis found that perioperative blood loss≥500 mL was a risk factor for SSI in spine surgery.[18] Zhou et al indicated that the SSI incidence of blood loss>500 mL was twice those blood loss<500 mL.[19] Meanwhile, they found surgical time≥3 hours have higher incidence of spinal SSI, which may be explained by that prolonging operative duration increases the chance of contamination in surgical wounds.[19] However, some studies found no relation between the surgical time and SSI.[20] Besides “operative time”, total anesthetic time is also an independent predictor of SSI, when patient remains in the operative room environment.[21]
Our model identifies cholesterin, PNI and albumin as risk factors, while the total cholesterol had no signature between SSI and non-SSI in previous researchs.[22, 23] Lower preoperative PNI and lower serum albumin were found be risk factor for SSI after spine surgery.[4, 5, 24] However, PNI and albumin are higher in SSI(51.95±3.82 and 42.13±3.80 g/dL) than non-SSI(48.26±5.66 and 39.48±4.45) among this cohort, which opposite to previous studies. And the relationship between sex and SSI is controversial in some studies. Ogihara et al found male sex were risk factors for deep SSI after thoracolumbar instrumented fusion.[25] While sex was not significantly associated with SSI in a cohort of over 1000 consecutive spinal fusions.[21] Next, hypertension had been found as risk factors for SSI in spine surgery by a few studies.[23]
Although performance of ML models on SSI after posterior cervical surgery are robust, this study has noteworthy limitations. First, the sample of this study is small, and further larger sample inputting may improve prediction results. Also, the data retrieved from a single institution, and further external validation is necessary to elevate models’ expansibility.