Open Access Open Badges Study protocol

The SNAP trial: a double blind multi-center randomized controlled trial of a silicon nitride versus a PEEK cage in transforaminal lumbar interbody fusion in patients with symptomatic degenerative lumbar disc disorders: study protocol

Roel FMR Kersten1*, Steven M van Gaalen1, Mark P Arts2, Kit CB Roes3, Arthur de Gast1, Terry P Corbin4 and F Cumhur Öner5

Author Affiliations

1 Clinical Orthopaedic Research Center–midden Nederland (CORC-mN), Department of Orthopaedics, Diakonessenhuis, Utrecht/Zeist, The Netherlands

2 Department of Neurosurgery, Medical Center Haaglanden, the Hague, The Netherlands

3 Julius Centre for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands

4 Corbin & Company, Maple Grove, MN, USA

5 Department of Orthopaedics, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands

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BMC Musculoskeletal Disorders 2014, 15:57  doi:10.1186/1471-2474-15-57

Published: 25 February 2014



Polyetheretherketone (PEEK) cages have been widely used in the treatment of lumbar degenerative disc disorders, and show good clinical results. Still, complications such as subsidence and migration of the cage are frequently seen. A lack of osteointegration and fibrous tissues surrounding PEEK cages are held responsible. Ceramic implants made of silicon nitride show better biocompatible and osteoconductive qualities, and therefore are expected to lower complication rates and allow for better fusion.

Purpose of this study is to show that fusion with the silicon nitride cage produces non-inferior results in outcome of the Roland Morris Disability Questionnaire at all follow-up time points as compared to the same procedure with PEEK cages.


This study is designed as a double blind multi-center randomized controlled trial with repeated measures analysis. 100 patients (18–75 years) presenting with symptomatic lumbar degenerative disorders unresponsive to at least 6 months of conservative treatment are included. Patients will be randomly assigned to a PEEK cage or a silicon nitride cage, and will undergo a transforaminal lumbar interbody fusion with pedicle screw fixation. Primary outcome measure is the functional improvement measured by the Roland Morris Disability Questionnaire. Secondary outcome parameters are the VAS leg, VAS back, SF-36, Likert scale, neurological outcome and radiographic assessment of fusion. After 1 year the fusion rate will be measured by radiograms and CT. Follow-up will be continued for 2 years. Patients and clinical observers who will perform the follow-up visits will be blinded for type of cage used during follow-up. Analyses of radiograms and CT will be performed independently by two experienced radiologists.


In this study a PEEK cage will be compared with a silicon nitride cage in the treatment of symptomatic degenerative lumbar disc disorders. To our knowledge, this is the first randomized controlled trial in which the silicon nitride cage is compared with the PEEK cage in patients with symptomatic degenerative lumbar disc disorders.

Trial registration


Disc degeneration; Spondylolisthesis; Lumbar interbody fusion; PEEK; Silicon nitride; Ceramic implant; Randomized controlled trial