Study design:

Retrospective cohort study.

Objective:

To evaluate whether the intraoperatively estimated parameters, as calculated on a cross-table lateral radiograph, are maintained in an upright position at discharge and at two years postoperatively and to identify the appropriate disc height (DH) to achieve substantial clinical benefit.

Summary of background data:

The amount of correction retained following LLIF surgery had not been reported.

Methods:

A single-center, consecutive series of patients who underwent single-level LLIF with at least two years of follow-up were retrospectively reviewed. Upright standardized preoperative, 1-week, and 2-year postoperative radiographs, as well as intraoperative lateral radiographs, were analyzed for disc height (DH), foraminal height (FH), and segmental lumbar lordosis (SLL) at the index level. Clinical outcomes were compared between preoperatively and one week and two years postoperatively.

Results:

In total, 89 patients were evaluated (mean follow-up, 42.8 months [range, 24-83 months]). DH decreased from 12.5 ± 2.7 mm intraoperatively to 11.7 ± 3.1 mm at one week postoperatively, FH decreased from 15.9 ± 3.6 mm to 15.1 ± 3.6 mm, and SLL decreased from 13.6° ± 1.7° to 12.4° ± 1.7°. A linear correlation between intraoperative and two-year postoperative parameters was found (R2 = 0.552, 0.518, and 0.616, respectively). Clinical outcomes, including back pain, leg pain, and ODI, significantly improved two years postoperatively. The optimal cut-off point for substantial clinical benefit thresholds for the ODI was a 4.18 mm increase in DH (sensitivity, 64.3%; specificity, 80.3%; area under the curve, 0.793; 95% confidence interval, 0.642-0.855).

Conclusions:

Some of the improvements in DH, FH, and SLL achieved intraoperatively during LLIF surgery were lost by the postoperative one-week follow-up. An intraoperative radiograph can predict radiographic and clinical outcomes of the two-year follow-up. The difference between preoperative DH and intraoperative DH should be more than 4.18 mm.Level of Evidence: 4.