Interspinous spacers and disc herniation. Geomorphometric and clinical study of 71 cases treated by L4-L5 microdiscectomy associated to spacer placement

Objective: A controversial indication of interspinous spacers is their use as a complement to discectomy. At the present time, there is no solid clinical evidence of effectiveness of that association, which might result from variability in spacer positioning, restricting its correct biomechanical actions. In this study our goal was to identify and analyse the variability in the placement of an interspinous spacer, and to investigate its relationship with the clinical results. Materials and methods: We performed a retrospective study on X-ray films from 71 patients suffering from disc herniation in L4-L5 who underwent surgery in our hospital, consisting of: microdiscectomy and biomed interspinous spacer implantation. The geomorphometric techniques used to analyse the data were procrustes superimposition and principal components analysis. We compared the clinical results (using the Herron and Tamer scale), segmental lordosis and surgical distraction with the geomorphometric parameters. Results: Significant morphological variability was found in the implant position showing cephalo-caudal translation and clockwise-counterclockwise rotations. This variability did not correlate with clinical results. A relationship with anatomical features (lordosis) and additional surgical distraction was identified. A different morphology of implant-segment configuration was identified in cases with recurrence of disc herniation. Conclusions: Geometric morphometrics allowed identifying high variability in the final placement of interspinous spacers. Nevertheless, it seems not to be related to the clinical outcome, depending rather on the degree of lordosis and distraction. Some differences in segment-implant morphology were identified in cases with recurrences. To assess the effectiveness of spacers, larger studies including morphological and clinical variables are required. (C) 2013 Sociedad Espanola de Neurocirugia. Published by Elsevier Espana, S.L.U. All rights reserved.