Can preoperative radiographic parameters be used to predict fusion in non-instrumented posterolateral fusion for degenerative spondylolisthesis?

Study Design: Prospective cohort.
Objective: To determine whether preoperative radiographic parameters (translation, angular motion, and lateral disc height) can predict fusion status in patients with degenerative spondylolisthesis who underwent a single-level decompression and non-instrumented posterolateral fusion using autogenous iliac crest bone graft.
Summary of Background Data: Non-instrumented posterolateral fusion is sometimes considered in patients with degenerative spondylolisthesis who do not have radiographic evidence of instability. No previous study has attempted to determine whether preoperative radiographic parameters can be used to predict successful fusion.
Methods: A prospective, randomized, controlled, multicenter clinical study was previously conducted to compare the outcomes of osteogenic protein 1 (BMP-7) putty to autogenous iliac crest bone graft for single-level non-instrumented posterolateral fusion for the treatment of symptomatic degenerative spondylolisthesis with spinal stenosis. A total of 90 patients who were randomized to the autograft group formed the basis of this study, 67 of whom had data on the 3 radiographic parameters. Preoperative and postoperative radiographs were evaluated by 2 independent observers. The spine was determined to be fused if there was presence of continuous bone bridging between the transverse processes, an angulation of ≤5°, and a translational movement of ≤3 mm on flexion/extension radiographs of the affected level.
Results: Forty-two (63%) of the 67 patients had a radiographic fusion. The mean preoperative translation in this group was 1.87 mm (range, 0.3-7.35 mm), the angular motion was 4.44° (range, 0.1°-12.1°), and the lateral disc height was 8.74 mm (range, 0.2-15.34 mm). Twenty-five (37%) of the 67 patients had a radiographic pseudarthrosis. The mean preoperative translation in the pseudarthrosis group was 1.20 mm (range, 0-3.55 mm), the angular motion was 4.66° (range, 1.1°-12.95°), and the lateral disc space height was 8.10 mm (range, 1.98-13.315 mm). There was no significant difference in these 3 parameters between the fusion and the pseudarthrosis group.
Conclusion: These results indicate that preoperative radiographic parameters that may indicate the absence of gross instability in degenerative spondylolisthesis are not reliable in predicting radiographic fusion in a single-level non-instrumented fusion.