Anterior Lumbar Interbody Fusion Versus Total Disc Replacement with a Viscoelastic Prosthesis for Single-Level Lumbar Degenerative Disc Disease in Young Adults: A Comparative Retrospective Cohort Study

Background/Objectives: The optimal surgical approach for patients with lumbar degenerative disc disease (DDD) remains a subject of ongoing debate, particularly when comparing anterior lumbar interbody fusion (ALIF) and total disc replacement (TDR). The primary objective of this study was to compare short-term outcomes between these two surgical approaches in terms of clinical efficacy, patient satisfaction, and safety profile. The secondary objective was to evaluate patient-specific variables associated with postoperative improvement in order to identify potential factors that may guide a personalized surgical strategy. Methods: This retrospective, single-center observational study included 87 patients who underwent single-level lumbar surgery using either an ALIF (n = 38) or TDR (n = 49) approach between January 2021 and May 2025. Eligible patients were younger than 45 years and had complete preoperative, intraoperative, and 1-year follow-up data. Demographic, clinical, preoperative, and intraoperative variables, as well as patient satisfaction and quality-of-life improvement, were collected, analyzed, and compared between groups. The primary between-group analysis used analysis of covariance (ANCOVA) with adjustment for baseline outcome values and prespecified confounders (age, sex, body mass index, smoking status, ASA class). Longitudinal effects were assessed using a linear model with treatment × time interaction and cluster-robust standard errors. A formal smoking × surgical-strategy interaction was tested in a multivariable regression on 12-month Oswestry Disability Index (ODI) change. Reporting followed the STROBE guidelines for observational studies. Results: Both groups showed substantial within-group improvement at all follow-up time points (all p < 0.05 except ALIF leg pain at 6 months; paired Wilcoxon test). Baseline-adjusted between-group comparisons (ANCOVA) showed a numerically modest early difference favoring TDR for Visual Analogue Score (VAS) low-back pain at 3 and 6 months (adjusted Δ = −1.46, 95% CI −2.63 to −0.30, p = 0.016 at 3 months; −1.35, 95% CI −2.63 to −0.07, p = 0.043 at 6 months), below the minimum clinically important difference of 2 points though neither survived Holm–Bonferroni correction for multiple comparisons. The formal treatment × time interaction test was not significant for any outcome (ODI p = 0.39; VAS back p = 0.29; VAS leg p = 0.06. Overall, 92% of patients in the ALIF group and 86% of patients in the TDR group reported being satisfied or very satisfied, and 60–72% of patients returned to work. Radiographic analysis in the TDR group showed maintained segmental mobility, with median range of motion of 4.0° (IQR 2.0–8.0°) overall (median 6.0°, IQR 4.0–8.5° at L4–L5; 3.0°, IQR 2.0–6.0° at L5–S1). A multivariable regression model on 12-month ODI change, adjusted for age, sex, BMI, ASA class, and baseline ODI, showed a highly significant smoking-burden × surgical-strategy interaction (dose–response smoker code × TDR coefficient = −9.47, 95% CI −15.6 to −3.3, p = 0.004): higher preoperative smoking burden was associated with reduced ODI improvement specifically in the TDR group (Spearman r = −0.41, p = 0.004) but not the ALIF group (Spearman r = +0.17, p = 0.32). Conclusions: This cohort study suggests that both ALIF and TDR were associated with substantial clinical improvement and high patient satisfaction at 1 year postoperatively; because treatment selection was not randomized, these findings should not be interpreted as evidence of comparative effectiveness. A modest early difference favoring TDR was observed for VAS low-back pain (below the minimum clinically important difference); no statistically significant between-group differences were demonstrated for any outcome after correction for multiple comparisons. The observed associations between 1-year ODI improvement and patient-specific variables require confirmation in larger independent cohorts. The finding of a significant smoking-burden × surgical-strategy interaction is an exploratory and hypothesis-generating and, if confirmed in prospective cohorts, may inform preoperative optimization strategies for TDR candidates.