Background context:

Allograft and polyether-ether-ketone (PEEK) radiographic, biomechanical, histological properties have been extensively studied and both spacers have their advantages and shortcomings. There are no comparative randomized or double-blinded spinal fusion clinical trials reported to date.

Purpose:

The study’s primary objective was to prospectively investigate clinical and radiological outcomes in patients undergoing lumbar interbody fusions and randomized to receive either PEEK or structural bone allografts.

Study design/ setting:

A prospective, randomized, double-blinded clinical trial was initiated at a single center.

Patient sample:

A total of 138 patients were enrolled, randomized and 121 patients completed the study.

Outcome measures:

The primary clinical outcome parameters were scored from standardized patient-reported questionnaires. The severity of lower back and leg pain was evaluated using the 11-point Visual Analog Scale (VAS). The Oswestry Disability Questionnaire was used to evaluate chronic disability and activities of daily living. Health-related quality of life and functional outcomes were assessed using Health-related Quality of Life Questionnaire (SF-36 v2). Two scores within the scoring algorithm were analyzed: Physical Component (PCS) and Mental Component Summary (MCS). The primary radiological outcomes included restoration and maintenance of vertebral body height, lumbar sagittal and segmental alignment, and fusion status.

Methods:

All patients were followed for 2 years ± 2 months; radiographic and clinical outcomes were assessed at 3, 6, 12 and 24 months with an additional follow-up at 3 weeks for radiographic assessment.

Results:

A total of 138 patients undergoing transforaminal lumbar interbody fusions (TLIF) were randomized (1:1) to receive either cortical allograft or PEEK interbody lordotic spacers. Although no differences were detected between the allograft and PEEK patient groups at any of the follow-up time points, there was a highly significant (p<0.0001) improvement in all clinical outcome measures. Overall, evidence of radiographic fusion was achieved in 118 (97.5%) patients at the 24 months follow-up. Three patients, all in the allograft group, had pseudoarthrosis and underwent revision surgeries. Postoperative improvement of sagittal alignment, anterior (ABH) or posterior body height (PBH) was initially achieved, but it was mainly lost or reduced at the final follow-up and there were no statistically significant differences between the groups. At the end of the study, improvement and maintenance of lumbar lordosis were achieved in 43.3% and 49.2% patients and segmental alignment in 38.3% and 36.1% for the allograft and PEEK patient groups, respectively. Similarly, ABH was improved and maintained in 28.3% and 36.1% patients and PBH in 28.3% and 44.3% for the allograft and PEEK groups, respectively.

Conclusions:

Although allograft-assisted surgeries may have reduced fusion rates, the study findings demonstrated that TLIF surgery with two different types of cages and in conjunction with rhBMP-2 resulted in similar radiological or clinical outcomes and a highly statistically significant improvement in all clinical outcome measures at the end of the study regardless of the randomization group.