Comparison of Radiographic and Clinical Outcomes Between Bone Morphogenetic Protein-2 and β-Tricalcium Phosphate Combined With Iliac Crest Bone Graft in Single-Level Extreme Lateral Interbody Fusion: An Ambidirectional Cohort Study

Background: Extreme lateral lumbar interbody fusion (XLIF) requires reliable graft material for arthrodesis.Bone morphogenetic protein-2 (BMP-2) is osteoinductive but costly and may cause complications.b-Tricalcium phosphate (b-TCP) combined with iliac crest bone graft (ICBG) may provide an alternative.This study compared the radiographic and clinical outcomes of BMP-2 versus b-TCP + ICBG in single-level XLIF.Material/Methods: This ambidirectional observational cohort included 79 consecutive patients who underwent single-level XLIF from 2014 to 2024 (BMP-2, 45; b-TCP + ICBG, 34).The Oswestry Disability Index (ODI), EuroQol 5-Dimension 5-Level (EQ-5D-5L), and EuroQol Visual Analog Scale (EQ-VAS) were assessed preoperatively and at 24 months.Radiographic alignment was evaluated preoperatively and at 24 months.Fusion was assessed at 12 and 24 months using computed tomography-supported criteria supplemented by dynamic radiographs. Results:Baseline characteristics and surgical indications were similar between groups.Fusion rates at 12 months were 75.6% with BMP-2 and 55.9% with b-TCP + ICBG (P = 0.065), increasing to 100% and 97.1%, respectively, at 24 months (P = 0.247).Both groups showed substantial improvements in ODI and EQ-5D-5L, without significant between-group differences at 24 months.Intervertebral disc height significantly increased in both groups, whereas foraminal height was maintained.Complication rates were comparable. Conclusions:Both grafting strategies produced favorable radiographic and clinical outcomes at 24 months.BMP-2 showed a numerically higher 12-month fusion rate, whereas b-TCP + ICBG achieved a similar final fusion rate.Given the observational design and limited sample size, these findings support b-TCP + ICBG as a potential alternative but do not establish equivalence.