gms | German Medical Science

Objective: Over the last years there is an ongoing debate if patients with degenerative spondylolisthesis and stenosis should receive decompression alone or additional fusion. Instability criteria from functional X-rays is a diagnostic tool mainly used to decide if additional fusion is needed. However it has been shown that this static imaging underestimates instability and does not take into account the dynamically complex behavior of the spine [1]. Dynamic assessment methods could improve the understanding of individual spinal movement patterns and patient outcome.

Methods: A biomechanical computer simulation model able to be adapted to the spine of individual patients was created. Vertebra geometry from CT data and ligaments with parameters from literature were included. Next the model was fitted to neutral and inclination poses derived from X-ray functional images. The intermediate steps then were interpolated by simulation. The model was tested to retrospectively assess 9 patients that underwent lumbar decompression (+/- fusion) in our institution from January 1st 2017 to July 30 2018. Inclusion criteria were single level spinal stenosis with additional ventral displacement of the vertebral bodies. Exclusion criteria were instability, previous surgery, fractures or multilevel stenosis. The mean patient age was 69.7 years. For each patient an individual model was created followed by simulation of an inclination movement that was used as a baseline. Next interlaminar fenestration (ILF) and laminectomy (LAM) were performed for each model and the same inclination movement was simulated again to compare the destabilizing effects.

Results: Ventral sliding after LAM compared to ILF changed significantly. It increased from 2%, to 6.5% (ILF vs. LAM). The rotation angles showed a significant increase in the LAM group compared to ILF indicating this technique to be more destabilizing.

Conclusion: The simulation model showed that decompression surgery increased the instability of a spinal segment. The effect was stronger in more invasive decompression techniques (LAM vs. ILF). This fact, already well known, could now also be quantified. In future applications a preoperative simulation may help to better predict the destabilizing effect and to decide if e.g. additional fusion is needed.