Outcomes of risk prediction for secondary lumbar instability (SLI) after lumbar decompression surgery: Validation of a new scoring system in 107 patients

Surgical management of lumbar spinal stenosis remains controversial, as factors qualifying patients for fusion procedures may not be met and decompression alone may carry the risk for the development of secondary lumbar instability (SLI). The aim of this study was to validate a novel scoring system for SLI risk prediction including a 14-point scale, created using the most relevant risk factors selected by the authors’ spine surgery research group with the help of a peer-review process. Patients treated with lumbar “over-the-top” decompression due to spinal stenosis at the author’s department from January until December 2018 were included. BMI, gender, smoking history, age, previous lumbar surgery, presence of low back pain, presence of spondylolisthesis (> 5 mm), dynamic olisthesis (> 3 mm), segmental kyphosis (> 10°), disc height > 6.5 mm, facet joint angle (> 50°) and fluid-filled facet joints were retrospectively assessed. Clinical deterioration, presented as SLI with requirement for spondylodesis of the previously operated segment during a postoperative 2-year follow-up was defined as the primary outcome value. 107 patients (45 female, 62 male) with a median age of 69 years (inter-quartile range [IQR] 61, 76) were included in this study. Twenty-eight patients (26.2%) had mechanical low back pain with VAS > 4, and 24 patients (22.4%) were already previously operated at the respective segment. The median SLI score was 6/14 (IQR 5, 8). Patients who subsequently required spondylodesis (9/107, 8,4%) had a significantly higher SLI score compared to patients who did not subsequently develop SLI (9 vs. 6, p = 0.013). The most relevant risk factors for development of SLI were disc height > 6.5 mm, BMI as well as the presence of a lumbar olisthesis with a relative risk (RR) of 2.8, 2.3 and 2.8, respectively. Using the novel SLI score, we were able to show a clear difference regarding pre-defined risk factors for patient with and without subsequent fusion surgery after lumbar decompression. Further studies are needed in order to define clear cut-off values for a more efficient distinction and easer decision-making during the preoperative evaluation of patient scheduled for decompression or fusion surgery.