Factors Affecting the Fusion Process and Comparison of PLIF and TLIF Techniques in Lumbar Interbody Fusion

Study Design: Retrospective cohort study. Objective: To evaluate factors affecting the fusion process and to compare radiological and clinical outcomes among different surgical techniques in patients undergoing posterior lumbar interbody fusion (PLIF). Summary of Background Data: PLIF is widely performed to restore spinal stability in degenerative lumbar conditions. The rate and timing of solid fusion are influenced by multiple patient- and surgery-related factors, including age, sex, graft type, cage usage, smoking, and diabetes status. Understanding these factors is essential for optimizing surgical planning and postoperative outcomes. Methods: Seventy-three patients who underwent PLIF for degenerative lumbar pathologies with a minimum of 24 months of follow-up were retrospectively analyzed. Patients were stratified according to age, sex, smoking status, diabetes, graft type, cage usage, and surgical technique (PLIF, PLIF+facetectomy, TLIF). Fusion status was evaluated using the Bridwell fusion criteria. Radiological parameters (lumbar lordosis, sacral inclination, four-to-floor angle, disc height) and clinical outcomes (Odom’s criteria) were compared. Statistical analyses were performed using SPSS v27.0; a P value<0.05 was considered significant. Results: Female patients demonstrated significantly higher 12-month fusion rates compared to males ( P <0.001). Autograft usage was associated with higher—but not statistically significant—fusion rates at 12 months ( P =0.232). Cage placement resulted in significantly better preservation of disc height ( P =0.019) and a significant postoperative improvement in lumbar lordosis ( P =0.028). No statistically significant differences were found between surgical techniques in terms of Odom’s criteria or sagittal balance parameters, although all groups showed clinical and radiological improvement. Conclusions: Female sex and autograft use appear to favor earlier fusion, while cage placement provides significant benefits in preserving disc height and improving lumbar lordosis. Surgical technique (PLIF, PLIF+facetectomy, TLIF) did not significantly affect long-term fusion rates or clinical outcomes, emphasizing the importance of patient-specific surgical planning and optimization of modifiable risk factors. These findings highlight that personalized surgical decision-making, rather than the choice of fusion technique alone, plays a key role in optimizing outcomes following PLIF.