Effects of Preoperative HbA1c on Postoperative Outcomes Following Transforaminal and Posterior Lumbar Interbody...

Introduction Uncontrolled diabetes mellitus (DM) is associated with higher rates of postoperative complications and poor outcomes following spinal surgery. The purpose of this study was to compare postoperative patient-reported outcome measures (PROMs) between non-diabetic (non-DM) and diabetic (DM) patients undergoing posterior lumbar interbody fusion (PLIF) or transforaminal lumbar interbody fusion (TLIF), characterize the clinical trajectory and rate of improvement between non-DM and DM cohorts, and determine if a clinically relevant HbA1c cutoff exists. Materials and methods Retrospective analysis was performed, identifying non-DM and DM patients who underwent elective single or multilevel PLIFs or TLIFs for degenerative pathology between 2019 and 2023. Diabetes was defined as having a preoperative HbA1c ≥ 6.5%. Patient demographics, Oswestry disability index (ODI), and patient-reported outcomes measurement information system (PROMIS) scores were collected longitudinally. Maximum medical improvement (MMI) was defined as the time point where more than 90% of the cohort achieves minimal clinically important difference (MCID) for both ODI and PROMIS score reports. Descriptive and inferential statistics were performed. Results A total of 114 non-DM and 14 DM patients were included. The DM cohort was observed to have higher average BMI (non-DM: 30.7, DM: 35.0, p = 0.029, t = 2.210) and decreased availability of a care partner (non-DM: 80 (85%), DM: 6 (60%), p = 0.046, x² = 3.981). No difference was noted for cohort age (non-DM: 55.3 years, DM: 61.3 years, p = 0.097, t = 1.671), complications (non-DM: nine (8%), DM: zero (0%), p = 0.276, x² = 1.189), approach (non-DM minimally invasive surgery (MIS): nine (8%), non-DM open: 105 (92%), DM MIS: one (7%), DM open: 13 (93%), p = 0.921, x² = 0.010), procedure (non-DM TLIF: 29 (26%), non-DM PLIF: 84 (74%), DM TLIF: five (36%), DM PLIF: nine (64%), p = 0.423, x² = 0.624), or number of levels fused (non-DM: 1.3, DM: 1.1, p = 0.399, t = 0.845). The DM cohort reported poorer preoperative PROMIS overall (non-DM: 28.6, DM: 23.7, p = 0.003, t = 3.071), PROMIS physical (non-DM: 37.5, DM: 33.1, p = 0.004, t = 2.904), and PROMIS mental (non-DM: 43.7, DM: 38.9, p = 0.023, t = 2.304) scores but were found to have similar preoperative ODI scores (non-DM: 45.2, DM: 53.1, p = 0.058, t = 1.912). Clinical improvement was comparable between the two groups, exceeding MCID at one-year follow-up. Both cohorts achieved MMI at similar rates. Multivariate analysis showed that preoperative HbA1c was not correlated with the rate of MCID achievement, MMI, or outcome scores when controlling for age, BMI, sex, care partner presence, number of levels fused, procedure type, approach type, and complications. There was no difference in outcomes between MIS and open surgery patients. Conclusion Elevated preoperative HbA1c was correlated with worse preoperative outcome measures. Despite this, both diabetic and non-diabetic patients achieved similar postoperative recoveries following elective PLIF and TLIF, with no difference in long-term outcomes, complications, and rate of improvement. Our results highlight the importance of continued research on preoperative optimization, risk management, patient counseling, and the development of individualized treatment plans.