Evaluation of the degenerative lumbar spondylolisthesis instability classification (DSIC) system as a guide to surgical technique selection.

Purpose: Degenerative spondylolisthesis (DS) is addressed with a wide range of surgical techniques, though controversy exists regarding surgical technique selection. Given the lack of high-quality evidence to guide surgical technique selection in DS, appropriateness criteria and classification systems have been developed based on expert opinion. The DSIC System uses imaging and patient characteristics to predict stability. The purpose of this study was to evaluate the DSIC system as a guide for technique selection by determining if patients within each DSIC Type have different outcomes when treated with various surgical techniques.

Methods: Patients undergoing surgery for symptomatic DS were prospectively enrolled at two centers. All patients were classified by DSIC Type and surgical technique. Due to small numbers in some subgroups, decompression alone and decompression with uninstrumented fusion were combined as uninstrumented group and decompression with instrumented and circumferential fusion were combined as instrumented group. The primary outcome was the 12-month change on the Core Outcome Measures Index (COMI).

Results: Of the 508 patients enrolled, 459 patients could be classified according to DSIC criteria. 10 patients were classified as DSIC Type I (stable), 366 as DSIC Type II (potentially unstable), and 83 as DSIC Type III (unstable). Surgical technique varied significantly across DSIC Type, with decompression alone performed most commonly in DSIC I and decompression and fusion performed more commonly in DSIC II and III. There were no significant differences in COMI scores between the DSIC groups at baseline, 3 or 12 months post-operatively. At 12 months, the DSIC I uninstrumented group improved by 3.48 points on the COMI compared to 1.75 points in the DSIC I instrumented group (p > 0.05). The DSIC III uninstrumented group improved by 2.94 points at 12 months compared to the DSIC III instrumented group that improved by 4.06 points (p > 0.05). DSIC II patients showed similar COMI score improvement between the surgical technique groups. All DSIC groups improved significantly from baseline with greater than 75% of patients meeting minimal clinically important difference. Patients in DSIC I trended toward greater improvement with decompression alone, and patients in DSIC III trended toward greater improvement with decompression and instrumented fusion. There were no significant differences in reoperation rates between surgical technique cohorts.

Conclusion: This study found no significant differences in COMI scores between the surgical technique cohorts within each DSIC Type. There were non-significant trends suggesting that DSIC III patients with unstable slips may benefit from instrumented fusion, whereas DSIC I patients with stable slips may improve more with decompression alone or with an uninstrumented fusion. This study does not support the use of the DSIC for surgical technique selection and suggests that more work is needed to develop an evidence-based classification system that can guide surgical technique selection.