Randomized double blind clinical trial of ABM/P-15 versus allograft in non-instrumented lumbar fusion surgery.

BACKGROUND CONTEXT: Due to poor bone stock in the elderly, a non-instrumented fusion is commonly performed in Scandinavia when instability is present. Allograft bone is often used as graft extender with consequent low fusion rates. The use of 15 amino acid residue (ABM/P-15) has shown superior fusion rates in dental and cervical spinal surgery but no clinical studies have been conducted in non-instrumented lumbar fusion surgery.

PURPOSE: To evaluate patient reported outcomes (PROs) and the intertransverse fusion rate in non-instrumented posterolateral fusion with either ABM/P-15 or allograft.

STUDY DESIGN: Double-blind randomized clinical trial PATIENT SAMPLE: Patients 60 years or older with degenerative spondylolisthesis (DS) undergoing decompression and non-instrumented posterolateral fusion.

OUTCOME MEASURES: Visual analog scales (VAS) for back (BP) and leg pain (LP), Oswestry Disability Index and EuroQoL-5D.

METHODS: One hundred one patients were enrolled in the study and randomized 1:1 to either ABM/P-15 (mixed 50/50, 5cc/level) or allograft bone (30g/level), both mixed with local bone graft. PROs were collected at baseline and at 12 and 24 months after surgery. The patients underwent one-year postoperative fine cut CT-scans (0.9 mm) with reconstructions, independently evaluated by 3 reviewers. Fusion status was concluded by consensus of 2 of the 3 as "fusion" or "no fusion."

RESULTS: There were 49 patients available for analysis in both cohorts. The two groups were similar in terms of sex distribution, age and number of levels fused. The fusion rate was significantly higher in the ABM/P-15 group with 50% fused compared with 20% in the allograft group. PROs at baseline and at all follow-up time points were similar between the two groups.

CONCLUSIONS: Patients undergoing non-instrumented posterolateral fusion augmented with ABM/P-15 had a statistically significantly higher fusion rate compared to allograft when evaluated with postoperative fine cut CT-scans (0.9 mm) with reconstructions. However, this did not translate to better clinical outcomes.