Propensity score matching (PSM) is a commonly used statistical method in orthopedic surgery research that accomplishes the removal of confounding bias from observational cohorts where the benefit of randomization is not possible. An alternative to multiple regression analysis, PSM attempts to reduce the effects of confounders by matching already treated subjects with control subjects who exhibit a similar propensity for treatment based on preexisting covariates that influence treatment selection. It, therefore, establishes a new control group by discarding outlier control subjects. This new control group reduces the unwanted influences of covariates, allowing for proper measurement of the intended variable. An example from orthopedic spine literature is discussed to illustrate how PSM may be applied in practice. PSM is uniquely valuable in its utility and simplicity, but it is limited in that it requires the removal of data and works primarily on binary treatments. In addition to matching, the propensity score can be used for stratification, covariate adjustments, and inverse probability of treatment weighting, but these topics are outside the scope of this paper. Personnel in the orthopedic field would benefit from learning about the function and application of this method given its common use in the orthopedic literature.

Study Design. Retrospective comparative study. Objective. The purpose of this study was to investigate whether preoperative depressive symptoms, measured by mental component score of the Short Form-12 survey (MCS-12), influence patient-reported outcome measurements (PROMs) following an anterior cervical discectomy and fusion (ACDF) surgery for cervical degeneration. Summary of Background Data. There is a paucity of literature regarding preoperative depression and PROMs following ACDF surgery for cervical degenerative disease. Methods. Patients who underwent an ACDF for degenerative cervical pathology were identified. A score of 45.6 on the MCS-12 was used as the threshold for depression symptoms, and patients were divided into two groups based on this value: depression (MCS-12 ≤45.6) and nondepression (MCS-12 >45.6) groups. Outcomes including Neck Disability Index (NDI), physical component score of the Short Form-12 survey (PCS-12), and Visual Analogue Scale Neck (VAS Neck), and Arm (VAS Arm) pain scores were evaluated using independent sample t test, recovery ratios, percentage of patients reaching the minimum clinically important difference, and multiple linear regression – controlling for factors such as age, sex, and BMI. Results. The depression group was found to have significantly worse baseline pain and disability than the nondepression group in NDI (P < 0.001), VAS Neck pain (P < 0.001), and VAS Arm pain (P < 0.001) scores. Postoperatively, both groups improved to a similar amount with surgery based on the recovery ratio analysis. The depression group continued to have worse scores than the nondepression group in NDI (P = 0.010), PCS-12 (P = 0.026), and VAS Arm pain (P = 0.001) scores. Depression was not a significant predictor of change in any PROMs based on regression analysis. Conclusion. Patients who presented with preoperative depression reported more pain and disability symptoms preoperatively and postoperatively; however, both groups achieved similar degrees of improvement. Level of Evidence: 3