Dynamic Slip Comparing Upright and Supine Positions Predicts Reoperation After Lumbar Decompression Surgery for Degenerative Lumbar Disease.

Abstract

Background context: Lumbar segmental instability is an important factor in determining surgical strategies for degenerative lumbar spine disorders. Although dynamic slip comparing extension and flexion radiographs (DSEF) is commonly used, dynamic slip comparing upright and supine positions (DSUS) has been proposed as an alternative measure.

Purpose: To examine the association between DSUS and postoperative outcomes after lumbar decompression surgery without fusion and to identify a DSUS threshold predictive of reoperation.

Study design: Multicenter retrospective cohort study.

Patient sample: A total of 188 patients who underwent initial single-level lumbar decompression surgery and were followed for at least three years.

Outcome measures: Symptomatic reoperation, Oswestry Disability Index (ODI), visual analogue scale (VAS) scores, and radiographic parameters.

Methods: DSUS and DSEF were measured using standing-supine imaging and flexion-extension radiographs. Patients were classified as DSUS-positive (≥3 mm) or DSUS-negative (<3 mm). Clinical and radiographic outcomes were compared longitudinally. Time-to-event outcomes were assessed using Kaplan-Meier and Cox proportional hazards models. Receiver operating characteristic (ROC) analyses were performed.

Results: DSUS and DSEF showed moderate correlation (r = 0.37) with frequent discordance. Thirty-three patients (17.6%) were DSUS-positive. DSUS-positive patients had significantly higher reoperation rates, worse postoperative ODI and VAS scores, and greater postoperative slip progression. In Cox models, DSUS independently predicted reoperation after adjustment for key covariates. ROC analysis identified 3.0 mm as the optimal cutoff (area under the curve 0.90).

Conclusions: DSUS is associated with poorer postoperative outcomes and increased reoperation risk after lumbar decompression surgery.