The renewed role of interspinous devices: the InSpan system-a narrative review on surgical indications

Interspinous devices have evolved from simple distraction spacers to interlaminar fixation systems capable of promoting fusion and stability. Early distraction-only implants were associated with high failure and reoperation rates, leading surgeons to abandon this technology. The InSpan system represents a new generation of posterior, interlaminar fixation devices designed to provide indirect decompression and interlaminar fusion. The goal of this review is to define practical, evidence-based indications and contraindications for the InSpan system within the context of interlaminar fixation, and to position this strategy among decompression alone and pedicle-based fusions.

This narrative review synthesizes evidence on interspinous and interlaminar fixation devices, with focus on the InSpan system. A search of PubMed/MEDLINE, Embase, and Cochrane Library databases up to November 2025 using the MeSH terms "interspinous device", "interlaminar fixation", "InSpan", "lumbar spinal stenosis", "spondylolisthesis", and "disc herniation" identified studies evaluating device design, kinematic behavior, clinical outcomes, and complications. Emphasis was placed on data informing practical surgical indications, contraindications, and patient selection criteria for InSpan.

Available biomechanical studies suggest that InSpan provides meaningful flexion-extension control and serves as an effective scaffold for interlaminar fusion, while avoiding pedicle violation and preserving the posterior structures. Clinical series report sustained improvements in pain and disability scores, low revision and complication rates, and radiographic evidence of fusion in selected patients. The most promising indications include: (I) recurrent lumbar disc herniation after microdiscectomy with segmental micromotion or disc height loss; (II) single-level lumbar spinal stenosis with low-grade spondylolisthesis or mild instability in patients at elevated risk for pedicle-screw fusion; and (III) foraminal or far-lateral stenosis where preservation of foraminal height is critical. Severe instability, high-grade spondylolisthesis, deformity, and multilevel disease remain better suited to conventional fusion constructs.

Interlaminar fixation devices appear to occupy a valuable niche between decompression alone and pedicle-based fusion, particularly in single-level degenerative pathology and fragile patients. When combined with decompression, InSpan can provide indirect decompression and interlaminar fusion with reduced surgical morbidity. Nevertheless, current evidence is largely limited, and high-quality randomized and long-term studies are needed to refine indications, durability, and cost-effectiveness.