Minimally Effective Dose of Bone Morphogenetic Protein in Minimally Invasive Lumbar Interbody Fusions: Six Hundred Ninety Patients in a Dose-Finding Longitudinal Cohort Study.

ABSTRACT

STUDY DESIGN: Retrospective longitudinal cohort. OBJECTIVE: We sought to demonstrate the minimally effective bone morphogenetic protein (BMP) dose to achieve fusion in minimally invasive transforaminal lumbar interbody fusions. SUMMARY OF BACKGROUND DATA Multiple studies have been conducted, which used a wide range of BMP doses for lumbar fusions highlighting associated risks and benefits. There is, however, a paucity in the literature in determining the minimally effective dose. METHODS: Consecutive patients who underwent transforaminal lumbar interbody fusion from 2009 to 2014 were reviewed. Fusion was determined by a combination of computed tomography and dynamic x-ray by independent radiologists. We used backward stepwise multiple logistic regression with fusion as the dependent variable to determine whether BMP dose/level was a significant predictor for fusion. To determine the minimally effective dose of BMP/level, separate logistic regressions for different BMP dose ranges and sensitivity analyses were used. A P value ≤0.025 was considered significant. RESULTS: There were 1102 interspaces among 690 patients. Average BMP dose was 1.28 mg/level. Overall fusion was 95.2% with a mean follow-up of 19 months. BMP dose/level was a significant predictor for fusion. Odds of fusion increased by 2.02 when BMP dose range was increased from (0.16-1 mg/level) to (1.0-2 mg/level), but fusion odds did not increase when BMP dose increased to more than 2 mg/level. CONCLUSION: BMP dose/level was a significant predictor for fusion. There was a significant increase in odds of fusion when BMP dose increased from 0.16 to 1 mg/level to 1.0 to 2 mg/level. No benefit from increasing the dose more than 2 mg/level was found, suggesting 1.0 mg/level to be the minimally effective BMP dose. LEVEL OF EVIDENCE 3.