To determine, for patients with degenerative disc disease, which method of single-level anterior cervical interbody fusion using the anterior approach gives the best clinical and radiological outcome.

The Cochrane Controlled Trials Register (issue 1998-4), Current Contents from 1996 to April 1999, and MEDLINE from 1966 to 1998, were all searched. An extensive list of search terms is presented in the paper. References from retrieved articles were also checked.

Study designs of evaluations included in the review

Randomised controlled trials (RCTs) with a minimum 6-month follow-up.

Specific interventions included in the review

Compared discectomy alone to discectomy with polymethylmethacrylate to promote fusion, the Cloward fusion procedure using an iliac graft, Smith-Robinson fusion, and Caspar plating fusion.

Participants included in the review

To be operated on, the patients had to be suffering from degenerative disc disease at a single level. Trials containing patients with fractures, tumours or multi-level disorders were excluded.

Outcomes assessed in the review

Two types of outcome were assessed: radiological (plain X-ray to determine bony union, alignment, fusion and kyphosis) and clinical (pain scores from patient and observer, self-reported symptoms measure, and benefit and complaints questionnaire).

How were decisions on the relevance of primary studies made?

Two reviewers made decisions regarding the selection of studies. When no consensus was reached, a third reviewer was consulted.

Methodological quality was assessed using criteria developed by Chalmers et al. (see Other Publications of Related Interest). Two independent reviewers evaluated the articles.

The authors do not state how data were extracted for the review, or how many of the reviewers performed the data extraction.

How were the studies combined?

The trials were discussed narratively.

How were differences between studies investigated?

Some differences between the trials were briefly noted, e.g. reporting of methods and outcome measures. No formal test of heterogeneity was conducted.

Three RCTs were included in the review's analysis (n=197). Five other trials met the inclusion criteria but did not meet the methodological requirements; these were not analysed further (n not reported).

The fusion rates varied between 28% for an allograft method and 63% for a discectomy-alone method. In one study, kyphosis varied from 40 to 62% between treatments. Good clinical outcome ratings (disability, pain and symptoms) varied from 66 to 82%.

From this systematic literature review, no 'gold' standard for the treatment of degenerative disc disease could be identified. The wide variety of treatments, the small group sizes and the variety in outcome measurements make it difficult to draw detailed conclusions about which technique is best for anterior interbody fusions. The need for more and better-designed RCTs in the field of the evaluation of degenerative cervical spine treatments is apparent.

This is, on the whole, a methodologically-sound review that is well-reported. The review question was stated clearly and supported by study inclusion criteria. The literature search was fairly comprehensive, though attempts to identify unpublished literature were weak. Validity assessment was performed using a validated set of criteria, and results of that assessment were presented adequately. Study details were poorly reported, e.g. participant characteristics were missing. Aspects of the review process were also reported poorly, e.g. it was unclear whether validity assessment and study selection were conducted independently, and details of the data extraction process were missing. No formal statistical test of heterogeneity was reported. The authors' conclusions do follow from the data presented.

Practice: The authors did not state any implications for practice.

Research: The authors state that there is a need for more and better designed RCTs in the field of the evaluation of degenerative cervical spine treatments.

Chalmers TC, Smith HJ, Blackburn B, Silverman B, Schroeder B, Reitman D, et al. A method for assessing the quality of a randomized control trial. Control Clin Trials 1981;2:31-49.

This is a critical abstract of a systematic review that meets the criteria for inclusion on DARE. Each critical abstract contains a brief summary of the review methods, results and conclusions followed by a detailed critical assessment on the reliability of the review and the conclusions drawn.