Understanding the causes of junctional failure in lumbar spine surgery through retrospective clinical analyses and ex-vivo tests

Spine diseases and failure have a significant effect on the patient’s quality of life. The aim of this PhD project was to improve the understanding the mechanisms leading to the spine instability and junctional pathology in the lumbar spine after posterior fixation. A combination of ex-vivo experiments and retrospective clinical analyses were performed. In the first part, cadaver spine segments were sequentially tested in the intact condition, after two-level hemilaminectomy, after a full laminectomy and after posterior fixation. Hemilaminectomy did not significantly affect the biomechanics of the lumbar spine. Conversely, after laminectomy, the range of motion significantly increased in flexion. Lateral bending was the most critical configuration for the strain in the intervertebral discs. Posterior fixation significantly reduced the range of motion and increased the strain in the disc adjacent the fixation both in flexion and in lateral bending. Two retrospective studies focused on patients with posterior fixation on the lumbar spine who required a revision surgery due to a failure in the caudal region. The junctional pathology onset was assessed on the pre-operative and post-operative spinopelvic parameters both in the sagittal and coronal planes, on the correction performed, on the patients’ clinical data, and addressing the different mechanisms of failure. In the sagittal plane (1690 patients included), the likelihood of mechanical failure was higher in patients older than 40 years with a thoraco-lumbar fixation, where some spinopelvic parameters were not properly restored. In the coronal plane (105 scoliotic patients included), the main parameters and their post-operative variations leading to failure were identified. In conclusion, the findings of these ex-vivo and clinical analyses could support the surgeons in being aware of possible outcomes when a treatment is needed, and when possible, to personalize spine surgeries, aiming to the long term to decrease the mechanical failure and revision surgeries.