Introduction

The role of fusion in degenerative spondylolisthesis (DS) is controversial. The CARDS and DSIC systems were developed to assist surgeons in surgical technique selection based on individual patient characteristics. These systems have not been clinically validated. The goal of this study was to determine if outcomes vary with different surgical techniques across the CARDS and DSIC categories.

Methods

DS patients undergoing surgery were enrolled at 2 institutions in Switzerland and the United States and classified according to the CARDS and DSIC systems. The Core Outcomes Measure Index (COMI) was completed at baseline, 3 months, and 12 months post-operatively. Due to small numbers in some subgroup analyses, patients treated with decompression alone or decompression with uninstrumented fusion were combined for analysis (uninstrumented group) as were patients treated with decompression and posterolateral instrumented fusion or decompression with posterolateral and interbody instrumented fusion (instrumented group). Unadjusted analyses and mixed effect models compared COMI scores between the two surgery technique groups (uninstrumented vs. instrumented), stratified by CARDS and DSIC category over time. Re-operation rates were also compared between the surgery technique groups stratified by CARDS and DSIC category.

Results

508 patients were enrolled in the study, 460 had sufficient data to be classified according to CARDS, and 459 could be classified according to DSIC. Seven percent were classified as CARDS A, 28% as CARDS B, 48% as CARDS C, and 17% as CARDS D (CARDS A most “stable”, CARDS D least “stable”). 2% were classified as DSIC 1, 80% as DSIC 2, and 17% as DSIC 3 (DSIC 1 most “stable, DSIC 3 least “stable”). 133 patients (26%) underwent decompression alone, 30 (6%) underwent decompression and uninstrumented fusion, 42 (8%) underwent decompression and posterolateral instrumented fusion, and 303 (60%) underwent decompression with posterolateral and interbody instrumented fusion. Patients in the least “stable” categories tended to be less likely to be treated with an uninstrumented technique (CARDS D 19% and DSIC 3 21% vs. 32% for the other categories, p=0.10 for CARDS, p=0.02 for DSIC). There were no significant differences in 3 or 12 month COMI scores between surgical technique groups stratified by CARDS or DSIC category in the unadjusted or adjusted analyses. In the unadjusted analyses, there was a trend towards less improvement in 12 month COMI change score in the CARDS D patients in the uninstrumented group compared to the instrumented group (-3.01 vs. -3.88, p=0.10). Reoperation rates were not significantly different between the surgical technique groups stratified by CARDS and DSIC category.

Discussion

In general, outcomes for uninstrumented and instrumented surgical techniques were similar across the DSIC and CARDS categories. There was a trend towards less improvement in the CARDS D patients treated with uninstrumented techniques, suggesting that in patients with kyphosis (the defining feature of the CARDS D category) better outcomes may be associated with instrumentation. The major limitation of this study was the low numbers in the CARDS D (n=15) and DSIC 3 (n=17) uninstrumented groups, likely due to surgeons choosing to avoid uninstrumented techniques in these patients.