Prospective, randomized, controlled trial of silicate-substituted calcium phosphate versus rhBMP-2 in a minimally invasive transforaminal lumbar interbody fusion

Abstract

Study design: Prospective, randomized, controlled trial.

Objective: To compare arthrodesis rates between patients undergoing a primary single-level minimally invasive transforaminal lumbar interbody fusion (MIS TLIF) with either Actifuse or recombinant human bone morphogenetic protein-2 (rhBMP-2).

Summary of background data: Preclinical animal studies suggest that silicate-substituted calcium phosphate (Actifuse) bone graft substitute offers equivalent or an increased fusion rate compared with other graft enhancers/extenders and rhBMP-2.

Methods: Fifty-two patients undergoing a single-level unilateral MIS TLIF were evenly randomized into 2 cohorts as follows: the Actifuse cohort received Actifuse combined with 5 mL of bone marrow aspirate (n = 26; 50%), whereas the rhBMP cohort received 4.2 mg of rhBMP-2 (n = 26; 50%). A pre hoc G*Power analysis yielded a sample size of n = 26 that was determined through a 2-tailed distribution calculation. Computed tomographic analysis was performed at 6 months and 1 year postoperatively. Pre- and postoperative visual analogue scale scores were obtained to assess the clinical outcomes. Arthrodesis was determined by 2 separate, blinded orthopedic surgeons and a board certified radiologist.

Results: At 1-year follow-up, 65% (17/26) of the Actifuse cohort and 92% (24/26) of the rhBMP-2 cohort demonstrated a radiographical arthrodesis (P = 0.01). In both study cohorts, the 1-year postoperative visual analogue scale scores significantly improved (P < 0.001). Pseudarthrosis rates at 1 year were 35.0% (9/26) and 7.7% (2/26) for the Actifuse and rhBMP-2 groups, respectively (P = 0.01, OR = 6.35, 95% CI = 1.22-33.1). A greater reoperation rate was noted in the Actifuse cohort (35.0%, 9/26) compared with the BMP-2 cohort (7.7%, 2/26; P = 0.01). One patient with BMP-2 also experienced symptomatic neuroforaminal bone growth (3.8%, n = 1/26).

Conclusion: Silicate-substituted calcium phosphate was associated with a significantly lower rate of arthrodesis than rhBMP-2 in a MIS TLIF. The patients with pseudarthrosis in both cohorts were all clinically symptomatic with an unimproved visual analogue scale score. Additional analysis of Actifuse and other graft enhancers/extenders are needed prior to the utilization for an MIS TLIF.

Level of evidence: 2.